THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 


PRESENTED  BY 

PROF.  CHARLES  A.  KOFOID  AND 
MRS.  PRUDENCE  W.  KOFOID 


THE  PHYSIOLOGY^*- 


OF  THE 


DOMESTIC  ANIMALS 


A  TEXT-BOOK  FOR  VETERINARY  AND  MEDICAL  STUDENTS 
AND  PRACTITIONERS. 


BY 

ROBERT  MEADE  SMITH,  A.M.,  M.D., 

PROFESSOR  OF  COMPARATIVE  PHYSIOLOGY  IN  THE  UNIVERSITY  OF  PENNSYLVANIA 

FELLOW     OF     THE  -  COLLEGE     OF     PHYSICIANS      AND  .  ACADEMY     OF     THE 

NATURAL     SCIENCES,      PHILADELPHIA;      OF     THE      AMERICAN 

PHYSIOLOGICAL   SOCIETY;    OF   THE    AMERICAN    SOCIETY 

OF    NATURALISTS;     ASSOCIE    ETRANGER    DE    LA 

SOCIETE     FRANCAISE     D' HYGIENE,     ETC. 


WITH  OVER  400  ILLUSTRATIONS. 


PHILADELPHIA  AND  LONDON  : 

F.    A.   DAVIS,   PUBLISHER 

1890. 


Entered  according  to  Act  of  Congress,  in  the  year  1889,  by 

F.  A.  DAVIS, 

In  the  Office  of  the  Librarian  of  Congress,  at  Washington,  D.  C.,  U.  S. 
All  rights  reserved. 


Philadelphia: 

The  Medical  Bulletin  Printing  House, 
1231  Filbert  Street. 


TO  MY  FRIEND  AND  TEACHER, 

CARL   LUDWIG, 

IN 

HUMBLE  RECOGNITION  OF  THE  MANY   FAVORS 
CONFERRED  ON  THE  AUTHOR. 


M351840 


PREFACE. 


IN  lecturing  in  the  Veterinary  Department  of  the  Univer- 
sity of  Pennsylvania  the  author  has  found  it  a  serious  disad- 
vantage that  the  students  are  compelled  to  rely  solely  on 
the  notes  that  they  may  be  able  to  take  during  the  lectures. 
While  French  students  have  access  to  the  encyclopaedic  work 
of  Colin,  and  those  familiar  with  the  German  language  to  the 
admirable  works  of  Schmidt-Miilheim,  Bruckmiiller,  Munk, 
Ellenberger,  Ghirlt,  Thanhoffer,  Miiller,  and  others,  English- 
speaking  students  have  absolutely  no  work  to  which  they 
can  turn  to  obtain  any  application  of  the  laws  of  physiology 
to*  the  functions  of  the  domestic  animals.  Commenced 
originally  as  outline  notes  for  the  author's  own  use  in 
lecturing,  this  work  has  been  published  at  the  request  of  his 
students,  in  the  hope  that  it  may  supply  them  with  an 
exponent  of  the  laws  of  modern  physiology  applied,  as  far 
as  possible,  to  the  functions  of  the  domestic  animals,  and 
that  a  recognition  of  its  shortcomings  may  stimulate  inves- 
tigation of  this  much-neglected  branch  of  physiology. 

It  is  surprising,  in  view  of  the  ceaseless  activity  of 
physiological  students  throughout  all  the  world,  that  more 
attention  has  not  been  devoted  to  the  application  of  improved 
methods  of  research  to  the  study  of  the  functions  of  animals 
so  important  in  the  domestic  economy.  Unfortunately, 
investigators  in  this  domain  may  almost  be  counted  on  the 
fingers,  and  the  field  which  is  yet  untouched  is  almost 
unbounded.  The  author,  therefore,  has  been  compelled  to 
assume  that  in  many  cases  the  laws  of  the  physiology  of 
man,  which,  to  be  sure,  have  been  deduced  from  experiments 

(v) 


vi  PREFACE. 

on  animals,   are    applicable    to    the  vital   processes  of   the 
domestic  animals. 

Modern  physiology  rests  on  the  application  through 
experimental  research  of  the  laws  of  physics  and  chemistry. 
The  fundamental  principles  of  these  sciences  in  their  relation 
to  biology  have  been,  therefore,  discussed  somewhat  at 
length.  Experience  has  taught  that  a  comprehension  of  the 
laws  of  life  in  the  higher  mammals  is  best  attained  after  a 
familiarization  with  the  vital  operation  of  lower  forms.  The 
first  part  of  this  book,  therefore,  deals  with  the  general  laws 
of  life,  while  in  the  second  part  these  principles  are  applied 
to  the  study  of  the  vital  operations  in  the  domestic  animals, 
the  study  of  each  function  being  introduced  by  a  sketch  of 
the  mode  of  development  of  the  mechanism  by  which  that 
function,  in  passing  from  lower  to  higher  forms,  is  accom- 
plished. 

As  far  as  possible  the  author  has  acknowledged  in  the 
text  his  indebtedness  to  various  authorities  for  the  matter 
or  manner  of  his  subject,  though  references  to  publications, 
as  tending  to  confuse  the  student,  have  been  omitted. 

For  illustrations  the  author  is  indebted  to  the  liberality 
of  the  publisher,  Mr.  Davis,  and  to  Messrs.  Blakiston  and 
H.  C.  Lea  &  Co.,  of  Philadelphia ;  Appleton,  Win.  Wood  &  Co., 
and  Macmillan,  of  New  York;  Ferdinand  Enke,  Stuttgart; 
Engelmann  and  F.  C.  W.  Vogel,  Leipsic ;  Paul  Parey,  Berlin ; 
W.  Braumiiller,  Vienna;  Carl  Winter,  Heidelberg;  Hachette  & 
Cie,  Bailliere  &  Fils,  Asselin  &  Cie,  Paris;  Simpkin,  Marshall 
&  Co.,  London;  Moritz  Perles,  Vienna,  and  Hirschwald,  Berlin. 

ROBERT  MEADE  SMITH. 

PHILADELPHIA: 

332  SOUTH  TWENTY-FIRST  STREET, 
January  3,  1889. 


TABLE  OF  CONTENTS. 


PAGK 

INTRODUCTION, 1 

PART  I. 

GENERAL  PHYSIOLOGY. 
THE  PHYSIOLOGY  OF  ANIMAL  CELLS. 

SECTION  I. 

THE  STRUCTURE  OF  ORGANIZED  BODIES. 

I.  THE  GENERAL  PROPERTIES  OF  CELLS,        .        .        .        .        .12 

II.  THE  ORIGIN  OF  CELLS,      . .14 

III.  THE  MODIFICATION  IN  THE  FORM  OF  CELLS,      ....      26 
IT.  THE  DEVELOPMENT  OF  TISSUES  AND  ORGANS,    .        .  ,      31 

SECTION  II. 

CELLULAR  PHYSICS. 

I.  THE  PHYSICAL  PROCESSES  IN  CELLS,          .        .        .        ...      37 

1.  Cohesion,  38  ;  2.  Adhesion,  40 ;  3.  Capillarity,  40 ;  4.  Solution,  43 ; 
5.  Imbibition,  44 ;  6.  Filtration,  48  ;  7.  Diffusion  of  Liquids,  49  ; 
8.  Osmosis,  51;  9.  Diffusion  of  Gases,  56  ;  10.  Absorption  of  Gases, 
58. 

II.  THE  PHYSICAL  PROPERTIES  OF  THE  TISSUES,     .        .        .        .61 

1.  Cohesion,  62 ;  2.  Elasticity,  65 ;  3.  Optical  Characteristics,  68 ;  4. 
Electrical  Phenomena,  70. 

III.  MECHANICAL  MOVEMENTS  IN  CELLS, .70 

1.  Motion  Produced  by  Imbibition  in  Cells,  70  ;  2.  Protoplasmic  Move- 
ments, 72 ;  (1)  Movements  in  Protoplasmic  Contents  of  Cells, 
73 ;  (2)  Ciliary  Movement,  77 ;  (3)  Movement  in  Specialized 
Contractile  Tissues,  81. 

GENERAL  CONDITIONS  GOVERNING  PROTOPLASMIC  MOVEMENT,  .        »      82 
1.  Temperature,  82;  2.  Degree  of  Imbibition,  82;  3.  The  Supply  of 
Oxygen,  83;  4.  Various  Chemical  and  Physical  Agents,  84. 

(vii) 


Vlll  TABLE  OF  CONTENTS, 

SECTION  III. 

CELLULAK  CHEMISTRY. 

I-  PAGE 

THE  CHEMICAL  CONSTITUENTS  OF  ORGANIZED  BODIES,       ...       85 

A.  NITROGENOUS  ORGANIC  CEL£-CONSTITUENTS — PROTEIDS  AND  THEIR 

DERIVATIVES, 88 

Class  I.  Albumens,  92;  (1)  Serum-Albumen,  92;  (2)  Egg  Albumen, 
93;  (3)  Vegetable  Albumens,  93. 

Class  II.  Globulins,  96  ;  (1)  Vitellin,  97;  (2)  Myosin,  97  ;  (3)  Para- 
globulin,  97  ;  (4)  Fibrinogen,  97;  (5)  Globulin  or  Crystallin,  97. 

Class  III.  Fibrins,  98. 

Class  IV.  Derived  Albuminates,  98 ;  (1)  Acid  Albumen,  98;  (2) 
Alkali  Albumen,  101. 

Class  V.  Coagulated  Proteids,  102. 

Class  VI.  Amyloid  Substance  or  Lardacein,  102. 

Class  VII.  Peptones,  103. 

ALBUMINOIDS,      .        . .        .        .     104 

1.  Mucin,  104;  2.  Collagenous  Albuminoids,  105;  (a)  Collagen,  106; 
(b)  Gelatin,  106  ;  (c)  Chondrogen,  107  ;  (d)  Chondrin,  107  ;  3. 
Elastin,  108  ;  4.  Keratin,  109. 

DECOMPOSITION  OF  ALBUMINOUS  BODIES,    .        .        *"       .        .        .109 
FERMENTS, '-      V    '  •        •        •        •     HO 

B.  NON-NlTROGENOUS   ORGANIC    CELL-CONSTITUENTS,  .     .       .  .       112 

I.  CARBOHYDRATES, -    .        ..        .        .112 

(a)  Starches,  112;  (1)  Starch,  113;  (2)  Cellulose,  115;  (3)  Dextrin, 
116  ;  (4)  Glycogen,  116  ;  (5)  Inulin,  116. 

(5)  Glucoses,  117;  (1)  Grape-Sugar,  117;  (2)  Laevulose,  118;  (3) 
Inosite,  118. 

(c)  Saccharoses,  119  ;  (1)  Cane-Sugar,  119  ;  (2)  Maltose,  120;  (3)  Lac- 
tose, 120 ;  (4)  Arabin,  120. 

II.  HYDROCARBONS  OR  FATS, 120 

C.  INORGANIC  CELL-CONSTITUENTS, 123 

1.  Water,  124 ;  2.  Sodium  Chloride,  128 ;  3.  Potassium  Chloride,  129  ; 
4.  Sodium  and  Potassium  Carbonates,  129;  5.  Calcium  Carbonate, 
130;  6.  Magnesium  Carbonate,  130  ;  7.  Alkaline  Phosphates,  130 ; 
8.  Calcium  Phosphate,  133  ;  9.  Magnesium  Phosphate,  134 ;  10. 
Sodium  and  Potassium  Sulphates,  135  ;  11.  Hydrochloric  Acid, 
135. 

II. 

THE  CHEMICAL  PROCESSES  IN  CELLS, 136 

1.  The  Vegetable  Cell,  137  ;  2.  The  Animal  Cell,  142 ;  3.  Fermenta- 
tions, 145 ;  4.  The  Consumption  and  Development  of  Force  in 
Cells,  147. 


TABLE  OF  CONTENTS.  IX 


PART  II. 
SPECIAL  PHYSIOLOGY. 

BOOK  FIRST. 
THE  NUTRITIVE  FUNCTIONS. 

SECTION  I. 

FOODS.  PAGE 

I.  VEGETABLE  FOODS, 161 

1,  The  Cereals,  163 ;  2.  The  Leguminous  Plants,  173 ;  3.  Bulbs  and 
Roots,  174 ;  4.  Grasses,  175. 

II.  ANIMAL  FOODS, ...       V    188 

1.  Milk,  188  ;  2.  Meat,  188. 

III.  INORGANIC  FOODS, .        ..191 

1.  Water,  191 ;  2.  Nutritive  Salts,  192. 

IV.  THE  DIET  OF  ANIMALS, *-./-,     193 

SECTION  II. 

DIGESTION. 
I.  GENERAL  CHARACTERISTICS  OP  THE  DIGESTIVE  APPARATUS,  .    203 

IT.  PREHENSION  OF  FOOD, •     .  •        .226 

1.  Prehension  of  Solids,  226 ;  2.  Prehension  of  Liquids,  236. 

III.  MASTICATION, .    238 

1.  Movements  of  the  Jaws,  241  ;  2.  Action  of  the  Teeth  in  Mastica- 
tion, 245  ;  3.  Determination  of  Age  by  the  Teeth,  255  ;  4.  Action 
of  Tongue,  Lips,  and  Cheeks,  264. 

IV.  DIGESTION  IN  THE  MOUTH,     .        .        .        .."•..       .  ,      .    268 

The  Salivary  Secretion,  268  ;  1.  The  Parotid  Secretion,  274;  2.  The 
Submaxillary  Secretion,  279 ;  3.  The  Sublingual  Secretion,  283 ; 
4.  General  Characters  of  the  Salivary  Secretion,  284;  5.  The 
Quantity  of  Saliva,  286  ;  6.  The  Physiological  Role  of  the  Saliva, 
287  ;  7.  The  Mechanism  of  Salivary  Secretion,  293. 

!»•«••_»( 

V.  DEGLUTITION, 307 

VI.  RUMINATION,  .        .        . 316 

VII.  VOMITING, ^   331 


X  TABLE  OF  CONTENTS. 

PAGE 

VIII.  GASTRIC  DIGESTION, 337 

1.  Chemistry  of  the  Gastric  Juice,  342  ;  (a}  Pepsin,  346  ;  (5)  Milk- 
Curdling  Ferment,  347  ;  (c)  The  Acid  of  Gastric  Juice,  349 ;  2. 
The  Action  of  Gastric  Juice  on  the  Food,  351  ;  3.  The  Secretion  of 
Gastric  Juice,  356 ;  4.  Gastric  Digestion  in  Carnivora,  360  ;  5. 
Gastric  Digestion  in  Omnivora,  363  ;  6.  Gastric  Digestion  in  Soli- 
pecles,  368  ;  7.  Gastric  Digestion  in  Ruminants,  374 ;  8.  Gastric 
Digestion  in  Birds,  379, 

IX.  DIGESTION  IN  THE  SMALL  INTESTINE, 382 

I.  Bile,  382 ;  1.  The  Chemical  Characteristics  of  the  Bile,  383 ;  (a) 

Mucin,  384;  (6)  The  Bile  Acids,  384;  (c)  The  Coloring  Matters  of 
the  Bile,  387  ;  (d)  Cholesterin,  389 ;  O)  The  Inorganic  Constitu- 
ents of  the  Bile,  390 ;  2.  The  Secretion  of  the  Bile,  391 ;  3.  The 
Physiological  Action  of  the  Bile,  393. 

II.  The  Pancreatic  Secretion,  396  ;  1.  The  Chemical  Composition  of 

the  Pancreatic  Juice,  402;  The  Pancreatic  Ferments,  404  ;  2.  The 
Action  of  the  Pancreatic  Juice  on  Food-Stuffs,  405  ;  (a)  Action 
on  Carbohydrates,  406  ;  (&)  Action  on  Fats,  406 ;  (c)  Action  on 
Proteids,  408  ;  3.  The  Secretion  of  Pancreatic  Juice,  412. 

III.  The  Intestinal  Juice,  416. 

IV.  Fermentative  Processes  in  the  Small  Intestine,  418. 
V.  Intestinal  Digestion  in  Different  Animals,  419. 

X.  DIGESTION  IN  THE  LARGE  INTESTINE,     .        .        ,        i       ..    423 

1.    The  Functions  of  the  Caecum,  423 ;   2.  The  Functions  of  the 
Colon,  429. 

XI.  THE  COMPARATIVE  DIGESTIBILITY  OF  DIFFERENT  FOOD-STUFFS,    432 
XII.  THE  COMPOSITION  OF  FAECES,  .        .        ,        .        .        .        .    445 

XIII.  THE  MOVEMENTS  OF  THE  INTESTINES,     .....    448 

XIV.  DEFECATION,    .  .'451 

SECTION  III. 
ABSORPTION, .    453 

1.  Venous  Absorption,  453  ;  2.  Absorption  by  the  Lymphatics,  456. 

SECTION  IV. 
THE  CHYLE,       .  ' 459 


SECTION  V. 
THE  LYMPH,      .....;.  463 


TABLE  OF  CONTENTS.  JO. 

SECTION  VI.  PAGE 

THE  BLOOD, .•  469 

1.  The  Red  Blood-Corpuscles,  471 ;  2.  The  White  Blood-Corpuscles, 
479  ;  3.  Blood-Plasma  and  Blood  Coagulation,  483  ;  4.  The  Blood- 
Serum,  489. 

SECTION  VII. 

THE  CIRCULATION  OF  THE  BLOOD, 491 

1.  General  View  of  the  Organs  of  Circulation,  491  ;  2.  The  Action 
of  the  Heart,  499  ;  3.  The  Hydraulic  Principles  of  the  Circula- 
tion, 516  ;  4.  The  Circulation  in  the  Arteries,  523  ;  Blood  Pres- 
sure, 525  ;  Velocity  of  the  Blood,  530 ;  The  Pulse,  533  ;  5.  The 
Circulation  in  the  Capillaries,  536 ;  6.  The  Circulation  in  the 
Veins,  539  ;  7.  The  Influence  of  the  Nervous  System  on  the 
Heart,  540 ;  The  Inhibitory  Nerves  of  the  Heart,  549  ;  The  Ac- 
celerator Nerves  of  the  Heart,  551 ;  8.  The  Influence  of  the 
Nervous  System  on  the  Arteries,  552. 

SECTION  VIII. 

RESPIRATION, .  ...    561 

1.  General  View  of  the  Organs  of  Respiration,  562  ;.  2.  The  Mechani- 
cal Processes  of  Respiration,  574  ;  3.  The  Rhythm  of  Respiration, 
579;  4.  The  Chemical  Phenomena  of  Respiration,.  587  ;  5.  The 
Nervous  Mechanism  of  Respiration,  598  ;  6.  The  Influence  of 
Respiration  on  the  Circulation,  605. 

SECTION  IX. 
THE  MAMMARY  SECRETION, 609 

1.  The  Physical  and  Chemical  Properties  of  Milk,  610  ;  2.  Casein  and 
Milk  Coagulation,  614 ;  3.  Milk-Sugar,  616 ;  4.  Fat  and  Cream, 
617  ;  5.  The  Inorganic  Constituents  of  Milk,  619  ;  6.  Variations 
in  the  Quantity  and  Composition  of  Milk,  619  ;  7.  The  Secretion 
of  Milk,  624  ;  8.  Milk  Analysis  and  Inspection,  631. 

SECTION  X. 
THE  RENAL  SECRETION, x    635 

1.  The  Physical  and  Chemical  Properties  of  Urine,  635  ;  2.  The 
Mechanism  of  Renal  Secretion,  640 ;  3.  The  Mechanism  of  Mic- 
turition, 648. 

SECTION  XL 
THE  CUTANEOUS  FUNCTIONS, 651 

1.  The  Sweat  Secretion,  652 ;  2.  The  Sebaceous  Secretion  of  the  -Skin, 
655  ;  3.  Cutaneous  Absorption,  656 ;  4.  Cutaneous  Respiration, 
656 ;  5.  The  Lachrymal  Secretion,  658. 


Xll  TABLE  OF  CONTENTS. 

SECTION  XII,  PAGE 

NUTRITION, 659 

I.  THE  FATE  or  THE  ALBUMINOUS  FOOD-CONSTITUENTS,       .        .     660 
II.  THE  FATE  OF  THE  FATTY  FOOD-CONSTITUENTS,         .        .        .664 

III.  THE  FATE  OF  THE  CARBOHYDRATE  FOOD-CONSTITUENTS,   .        .     666 

IV.  THE  STATISTICS  OF  NUTRITION,          .     ;    .        .        .        .        .672 

1.  Tissue  Changes  in  Starvation,  674 ;  2.  The  Nutritive  Processes  in 
Feeding,  680;  (a)  Feeding  with  Meat,  680;  (6)  Feeding  with 
Fat,  682  ;  (c)  Feeding  with  Carbohydrates,  683. 

V.  THE  FOOD  REQUIRED  BY  THE  HERBIVORA  UNDER  DIFFERENT 

CONDITIONS,          .         .         .     .  ••;•        .        .-.•-.     .        ...     684 
VI.  HUNGER  AND  THIRST,         .        .        .        *        .  '      .        .        .     692 

SECTION  XIII. 
ANIMAL  HEAT,  .        .        .        .     ".       ^  -  -  ~ .-     ^        ^        ^        ^    693 

BOOK  SECOND. 
THE  ANIMAL  FUNCTIONS. 

SECTION  I. 
THE  PHYSIOLOGY  OF  MOVEMENT,       .        .        .        ..        .        .701 

1.  The  Contractile  Tissues,  701 ;  (a)  Chemical  Composition  of  Muscle, 
704 ;  (&)  Muscular  Irritability,  709  ;  (c)  The  Phenomena  of  Mus- 
cular Contraction,  710  ;  (d)  The  Electrical  Phenomena  in  Muscle, 
721  ;  2.  The  Applications  of  Muscular  Contractility,  722  ;  3.  Ani- 
mal Locomotion,  731;  4.  The  Gaits  of  the  Horse,  739  ;  (a)  The 
Walk,  744;  (5)  The  Amble,  746;  (c)  The  Trot,  748;  (d)  The 
Gallop,  749  ;  5.  Other  Movements  in  the  Horse,  750  ;  (a)  Rearing, 
750 ;  (&)  Kicking,  753 ;  (c)  Lying  Down  and  Rising  Up,  754 ; 
(d)  Walking  Backward,  754 ;  (e)  Swimming,  755  ;  6.  Special  Mus- 
cular Mechanisms — The  Voice,  757. 

SECTION  II. 

THE  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM,     .        .        .        .        .765 

I.  THE  CHEMICAL  AND  PHYSICAL  CHARACTERISTICS  OF  NERVOUS 

TISSUES,       .        . 774 

II.  NERVOUS  IRRITABILITY,  .        .        » 776 

III.  THE  ELECTRICAL  PHENOMENA  IN  NERVES,      .        .        .        .779 

IV.  GENERAL  PHYSIOLOGY  OF  THE  NERVE-CENTRES,     .        .        .     781 
1.  Reflex  Action,  782  ;•  2.  Automatism,  784 ;  3.  Inhibition,  785 ;   4. 

Augmentation,  785 ;  5.  Co-ordination,  785. 


TABLE  OF   CONTENTS.  xiii 

PAGE 

Y.  THE  FUNCTIONS  OF  THE  SPINAL  CORD, 786 

(a)  The  Spinal  Cord  as  a  Collection  of  Nerve-Centres,  789  ;  (&)  The 
Spinal  Cord  as  an  Organ  of  Conduction,  795. 

VI.  THE  FUNCTIONS  OF  THE  BRAIN, 803 

1.  The  Medulla  Oblongata,  810 ;  2.  The  Course  of  the  Fibres  of  the 
Medulla  Oblongata,  818  ;  3.  The  Pons  Yarolii,  821 ;  4.  The  Cere- 
bral Peduncles,  821 ;  5.  The  Corpora  Quadrigemina,  822  ;  6.  The 
Functions  of  the  Basal  Ganglia,  822;  7.  The  Functions  of  the 
Cerebral  Lobes,  823  ;  8.  The  Functions  of  the  Cerebellum,  825. 

VII.  THE  CRANIAL  NERVES, 832 

VIII.  THE  SYMPATHETIC  NERVOUS  SYSTEM,     .        .  .        .     835 

IX.  GENERAL  AND  SPECIAL  SENSIBILITY,       .        .        .        .        .837 

A.  THE  SENSE  OF  SMELL, 841 

B.  THE  SENSE  OF  SIGHT, .846 

1.  The  Dioptric  Mechanisms  of  the  Eye,  851;  2.  Visual  Sensations,  864. 

C.  THE  SENSE  OF  HEARING, 875 

D.  THE  SENSE  OF  TASTE, .893 

E.  THE  SENSE  OF  TOUCH,.        .        .        .        .        .        .        .        .     897 


PART  III. 

THE  REPRODUCTIVE  FUNCTIONS, .901 

SECTION  I. 
THE  REPRODUCTIVE  PROCESSES, 903 

1.  The  Reproductive  Tissues  of  the  Female,  908 ;  2.  The  Reproduc- 
tive Tissues  of  the  Male,  913. 


INTRODUCTION. 


PHYSIOLOGY  treats  of  the  functions  or  actions  of  living  beings. 

When  these  actions  or  functions  occur  in  a  disturbed  or  irregular 
manner,  they  constitute  disease,  or  abnormal  life,  and  become  the  subject 
of  abnormal  physiology  or  pathology.  Normal  physiology  is  the  basis  of 
pathology,  and  a  knowledge  of  the  one  must  precede  the  intelligent  study 
of  the  other:  just  as  an  acquaintance  with  the  functions  of  the  com- 
ponent parts  of  a  machine  must  precede  the  recognition  of  disordered 
movement  and  the  provision  of  means  of  repair. 

Since  the  functions  of  the  animal  body  are  resident  in  the  various 
tissues  and  organs  of  the  body,  an  acquaintance  with  the  forms  and 
structure  of  those  organs  and  tissues  must  precede  the  study  of  their 
functions.  The  study  of  anatomy  and  histology,  or  microscopic  anat- 
omy, must  therefore  precede  the  study  of  physiology. 

GENERAL  PHYSIOLOGY  treats  of  the  functions  of  organized  beings  in 
an  abstract  manner, — that  which  regards  the  general  laws  of  life,  whether 
seen  in  the  animal  or  vegetable  world.  Although  for  the  purposes  of 
practical  life  physiology  is  divided  into  several  provinces,  yet  the  knowl- 
edge of  general  physiology  is  essential  even  to  special  students,  since 
the  relation  between  the  different  forms  of  life  is  very  close. 

VEGETABLE  PHYSIOLOGY  is  concerned  solely  with  the  consideration 
of  the  vital  actions  or  functions  of  plants. 

COMPARATIVE  PHYSIOLOGY  treats  of  the  functions  of  animals  below 
man,  with  a  consideration  of  the  means  by  which  different  functions  are 
accomplished  by  different  animal  forms. 

SPECIAL  PHYSIOLOGY  is  confined  to  the  consideration  of  the  vital 
phenomena  of  a  single  species,  single  genus,  or  it  may  deal  with  the 
consideration  of  a  special  function.  In  this  book  special  physiology 
will  refer  mainly  to  the  study  of  the  vital  phenomena  of  the  domestic 
animals. 

HUMAN  PHYSIOLOGY  treats  exclusively  of  the  vital  phenomena  of 
man.  But,  while  this  branch  of  physiology  is  of  greater  importance  to 
the  physician  than  the  other  divisions,  in  consequence  of  its  relations 
to  human  pathology  and  therapeutics,  it  should  not  be  made  the  exclu- 
sive subject  of  study;  for  the  physiology  of  man  cannot  be  properly 
understood  without  a  previous  acquaintance  with  the  vital  phenomena  of 


2  INTRODUCTION. 

the  lower  animals  and  plants.  For  the  veterinary  physician  the  study 
of  life  in  the  domestic  animals  must  be  of  the  greatest  importance. 

Every  living  body  is  organized, — that  is.  composed  of  instruments 
or  organs  each  one  of  which  is  destined  to  fulfill  some  special  office  in 
the  organism  called  its  function,  the  sum  of  which  functions  constitute 
the  life  of  the  individual.  Other  bodies  met  with  in  nature,  and  not  so 
constituted,  are  called  unorganized,  or  inorganic,  e.g.,  the  mineral. 

DISTINCTIONS  BETWEEN  ORGANIZED  AND  UNORGANIZED  BODIES. — Organ- 
ized and  unorganized  bodies  have  few  or  no  correlative  points,  but  stand 
opposed  to  each  other  in  almost  every  characteristic  trait. 

Unorganized  matter  is  only  subject  to  the  forces  whose  generality 
of  action  constitutes  physical  and  chemical  laws.  Organized  matter  is 
also  controlled  to  a  certain  extent  by  the  same  laws,  and,  although  there 
are  a  great  many  actions  manifested  by  living  bodies  which  are  not 
readily  explicable  by  the  ordinary  physical  laws,  and  for  which  the  term 
"  vital  phenomena"  is  conveniently  employed,  it  does  not  by  any  means 
follow  that  we  have  here  to  deal  with  any  entirely  distinct  series  of  laws. 
The  attempt  to  reduce  the  so-called  vital  phenomena  to  physical  and 
chemical  laws  has  already  succeeded  in  demonstrating  the  dependence,  on 
physical  and  chemical  principles,  of  many  functions  previously  regarded 
as  purely  vital  in  nature,  and  the  hope  may  be  reasonably  held  for  con- 
tinued progress  in  this  direction.  The  sciences  of  physics  and  chemistry 
are  therefore  the  foundation-stones  of  modern  physiology. 

Nevertheless,  organized  and  unorganized  matter  differ  to  such  an 
extent  that  their  consideration  forms  entirely  distinct  branches  of  study. 
The  forms,  the  forces,  and  the  laws  of  unorganized  matter  are  the  sub- 
jects embraced  by  physics  and  chemistry.  The  forms  and  forces  of 
living  organized  matter  are  the  objects  of  physiological  science,  or 
biology. 

Organic  bodies  differ  from  inorganic — 

1.  In  their    Origin. — The  former  spring  from  a  parent,  or   from 
previously-existing  living  matter,  either  by  splitting,  budding,  seeds,  or 
eggs.     The  latter  have  no  such  origin,  but  ma}^  arise  from  the  combina- 
tion, under  the  influence  of  chemical  affinity,  of  the  elements  which  com- 
pose them.     Spontaneous  generation,  though  claimed  by  some,  has  not 
been  satisfactorily  established. 

2.  In  their  Form. — Organized  bodies  are  usually  determinate  in 
their  form,  rounded  in  their  outline,  and,  in  their  simplest  expression, 
either  spherical  or  spheroidal  in  shape.     Unorganized  bodies,  on  the 
other  hand,  are  irregular  in  their  outline  (amorphous),  or,  if  determinate 
in  form,  are  bounded  by  plane  surfaces  and  straight  lines. 

3.  Duration  of  Existence. — Organized  bodies  have  a  definite  time 
to  live,  pass  through  distinct  stages  of  development  and  growth,  and  ulti- 


INTEODUCTION.  6 

mately  die.  But  the  inorganic  body  may  continue  to  exist  until  some 
disrupting  force  separates  the  inorganic  elements  of  which  it  is  com- 
posed, and  enables  them  to  form  new  combinations ;  but  so  long  as 
uninfluenced  by  such  an  agency  it  may  remain  unchanged  for  an  indefi- 
nite period. 

4.  Size. — Organized  bodies  have  a  definite  limit  to  which  they  may 
attain,  varying,  however,  among  individuals  of  the  same  species.     And 
vhen  they  exceed  the  average  size  of  the  species  it   is  not   by  the 
increased  size  of  the  individual,  but  b}^  the  continued  production  of  new 
individuals  or  a  repletion  of  parts  already  existing.     The  unorganized 
body,  on  the  other  hand,  is  as  indeterminate  in  size  as  in  duration,  con- 
tinuing to  grow  so  long  as  fresh  particles  are  brought  together. 

5.  Chemical  Constitution. — Of  the  sixty-five  simple  elements  found 
in  nature  but  about  twenty  enter  into  the  composition  of  organized  bodies, 
and  of  these  but  four  are  to  be  regarded  as  essential,  viz.,  C.O.H.N., 
of  which  at  least  two  are  found  in  every  organic  compound.    The  remain- 
ing elements  are  called  incidental.    Unorganized  bodies  may  be  simple  in 
their  composition,  or  binary,  ternary,  quaternary,  or  higher ;  but  binary 
is  the  most  usual  combination. 

The  molecular  constitution  of  the  organic  body  is  also  different 
from  the  inorganic  in  being  much  more  complex,  both  in  the  number  of 
elements  which  it  contains  and  the  number  of  atoms,  or  combining 
equivalents  of  those  atoms,  which  exist  in  a  combining  equivalent  of 
the  compound.  Thus,  albumen,  which  forms  an  important  constituent 
of  nearly  all  organized  bodies,  may  be  represented  as  C^oHagaNggO.;,^ 
(Schutzenberger),  while  ammonium  carbonate,  an  inorganic  compound 
containing  the  same  elements,  with  the  exception  of  sulphur,  may  be 
written  as  follows:  (NH4)SCOS-J-H30. 

From  the  large  number  of  elements  which  enter  into  the  composition 
of  organic  bodies,  and  the  large  number  of  atoms  constituting  an  organic 
molecule,  arises  the  great  tendency  to  decomposition  by  which  they  are 
characterized ;  for,  "  the  greater  the  number  of  atoms  of  an  element 
which  enters  into  the  formation  of  a  molecule  of  a  compound,  the  less 
is  the  stability  of  that  compound." 

Inorganic  compounds  are  therefore  stable ;  organic  bodies,  unstable. 

It  was  formerly  supposed  that  organic  compounds  could  only  be 
formed  under  the  influence  of  vitality,  and  that  they  could  be  decom- 
posed by  the  chemist,  but  not  recomposed.  But  this  has  been  shown  to 
be  an  error,  some  of  the  organic  acids,  alcohols,  organic  coloring  matters, 
and  some  of  the  secondary  organic  components,  such  as  uric  acid  and 
urea,  having  been  synthetically  prepared  by  the  chemist.  It  is  thought, 
therefore,  not  to  be  impossible  that  some  of  the  higher  organic  com- 
pounds, such  as  albumen,  may  ultimately  be  also  made  in  the  same 


4:  INTRODUCTION. 

manner,  though  thus  far  all  attempts  in  this  direction  have  been  unavail- 
ing. All  those  compounds  which  have  as  yet  been  made  by  synthesis 
are  allied  to  those  which  result  from  a  long-continued  series  of  chemical 
changes  in  the  organism,  produced  by  the  action  of  oxygen  upon  prod- 
ucts of  disintegration. 

6.  In  their  Mode  of  Growth. — Organized  bodies  grow  by  assimila- 
tion,—the  internal  deposit  of  materials  by  which  the  unlike  become  the 
like.  Unorganized  bodies  grow,  or  increase  in  size,  by  external  deposit 
or  accretion.  The  organized  body  is  dying  from  the  moment  of  its  birth, 
and  requires  new  materials  to  repair  those  losses  and  for  the  increase  in 
size.  The  unorganized  body,  as  the  crystal  or  the  stalactite,  continues 
to  increase  in  size  so  long  as  fresh  particles  are  deposited  upon  it. 
Every  part  of  an  inorganic  body  is  therefore  alike  and  independent  of 
the  rest,  and  exhibits  the  same  properties  as  the  whole.  The  organized 
body,  on  the  contrary,  is  made  up  of  a  number  of  dissimilar  parts,  each 
of  which  is  more  or  less  dependent  upon  the  others,  and  each  of  which 
requires  different  materials  for  its  growth  and  reparation.  In  the  unor- 
ganized body  a  small  portion  serves  to  determine  by  anatysis  the  consti- 
tution of  the  whole ;  in  other  words,  it  is  homogeneous.  In  the  organ- 
ized body  each  part  is  more  or  less  dependent  on  the  remainder,  and 
differs  from  it  in  chemical  composition ;  in  other  words,  it  is  hetero- 
geneous. Organic  compounds,  moreover,  from  the  large  quantity  of 
fluid  they  contain,  are  usually  soft  and  ductile,  while  the  inorganic  body 
is  hard,  rigid,  and  inflexible,  and  when  once  the  affinities  of  its  chemical 
elements  are  satisfied  it  remains  an  inert  mass.  Within  the  organized 
living  body  all  is  change.  Death  and  repair  are  ever  taking  place.  From 
the  commencement  of  its  existence  its  growth,  its  progress  toward 
maturity,  its  decline,  decay,  and  death  are  all  made  up  of  an  incessant 
series  of  changes.  It  is  the  constant  round  of  these  actions  which  con- 
stitutes life ;  their  study  is  the  subject  of  physiology. 

It  is  thus  seen  that  organized  are  distinguished  from  unorganized 
bodies  by  three  cardinal  characteristics :  1.  Tlie  law  of  nutrition,  the 
most  fundamental  of  all  vital  laws ;  since  in  virtue  of  it  the  organism 
continues  to  exist  as  an  active  being,  and  increases  from  infancy  to 
maturity.  2.  The  law  of  development,  or  differentiation,  which  causes 
the  organism  to  pass  through  the  definite  cycles  of  change  constituting 
what  we  call  ages,  and  leading  inevitably  to  the  final  changes  which  we 
call  death.  3.  The  law  of  reproduction,  another  aspect  of  the  first  law, 
in  virtue  of  which  the  organism  gives  origin  to  similar  organisms  from 
one  generation  to  another. 

In  no  example  of  inorganic  matter  can  any  of  these  characteristics 
be  found.  When  inorganic  bodies  are  said  to  grow,  their  growth  is  a 
process  of  mere  aggregation,  one  part  adhering  to  another  similar  part. 


INTRODUCTION.  5 

The  growth  arises  from  no  internal  necessity,  as  in  organic  bodies.  The 
bulk  is  not  increased  by  a  process  of  assimilation  which  converts  the 
unlike  into  the  like.  Minerals  do  not  feed  ;  they  cohere.  Nor  have  they 
any  power  of  development.  They  pass  through  no  definite  cycles  of 
change ;  they  have  no  stages  of  growth,  no  ages,  no  power  of  repro- 
duction. 

The  constant  round  of  actions,  therefore,  in  the  organized  structure 
called  life,  in  them  is  wanting.  They  occupy  space,  but  have  neither 
birth  nor  death. 

DISTINCTION  BETWEEN  PLANTS  AND  ANIMALS. — Organized  bodies  are 
divided  into  two  classes, — animals  and  vegetables, — constituting  two  sep- 
arate kingdoms,  which,  though  capable  of  ready  recognition  when  studied 
in  their  higher  members,  seem  almost  to  overlap  in  their  lowest  expres- 
sion. Hence,  while  the  differences  between  the  higher  animals  and  higher 
plants  are  so  striking  as  not  to  need  mention,  when  we  examine  the  lowest 
forms  of  life  the  greatest  difficulty  will  sometimes  be  met  with  in  the 
attempt  to  decide  whether  the  organism  is  an  animal  or  a  vegetable.  For 
when  the  protozoa,  or  lowest  animals,  are  compared  with  the  protophyta, 
or  lowest  plants,  all  the  differences  which  are  so  striking  between  the 
higher  animals  and  plants  are  completely  wanting ;  yet  the  protozoa  are 
as  truly  animal  as  are  the  vertebrata,  and  the  protophyta  just  as  surely 
plants.  Consequently  the  definition  of  an  animal  or  a  plant,  to  be  of  any 
scientific  value,  must  include  the  lowest  as  well  as  the  highest  forms. 

We  found,  in  our  comparison  of  organic  and  inorganic  matter,  that 
differences  in  form  could  be  clearly  made  out.  The  external  charac- 
teristics of  plants  and  animals  are,  however,  inadequate  to  distinguish 
them.  Many  animal  forms,  such  as  the  hydrozoa,  are  essentially  plant- 
like  in  their  external  form,  growing  from  fixed  points  and  even  repro- 
ducing themselves  by  "  budding," — a  process  almost  universally  holding 
in  the  vegetable  kingdom.  So  also  the  well-known  coral  polyps  and  the 
sponge  closely  resemble  plants  in  external  configuration,  and,  though 
undoubtedly  animals,  were  long  placed  by  naturalists  in  the  vegetable 
kingdom. 

Then,  on  the  other  hand,  many  plants,  examined  in  respect  to  their 
external  form  alone,  would  often  be  confounded  with  animals.  Thus, 
the  germs  of  many  algae,  the  ciliated  zoospores,  are  scarcel}*  to  be  dis- 
tinguished from  infusorial  animalcules. 

It  was  at  one  time  thought  that  the  power  of  motion  was  a  proof 
of  animality ;  but  many  of  the  lowest  plants,  such  as  volvox  and  the 
diatoms,  possess  the  power  of  motion,  of  changing  their  location,  the 
instruments  being  the  same  as  in  many  animals,  viz.,  cilia.  Nor  is  the 
power  of  moving  in  response  to  an  irritant  peculiar  to  animal  life : 
witness  the  Mimosa  pudica,  the  sensitive  plant,  which  closes  its  leaflets 


6  INTRODUCTION. 

on  irritation ;  the  Dionsea  muscipula,  the  Venus'  Fly-Trap,  the  extremities 
of  whose  leaves  have  the  power  of  closing  on  insects  or  other  bodies 
brought  into  contact  with  them.  Plants  are  also  possessed  of  internal 
motion:  witness  the  circulation  of  the  sap  and  the  circulatory  motions 
in  the  interior  of  many  vegetable  cells.  They  also  turn  spontaneously 
to  the  light  and  extend  their  rootlets  to  the  most  nutritive  soil. 

Again,  all  animals  are  not  possessed  of  the  power  of  motion. 
Sponges,  coral  polyps,  hydroid  zoophytes,  sea-mats,  etc.,  are  entirely 
destitute  of  locomotive  power,  and  spend  their  entire  existence  rooted 
fast  to  some  immovable  object.  Hence,  the  possession  of  motor  power 
is  not  characteristic  of  animal  life,  and  its  absence  does  not  prove  the 
organism  to  be  a  vegetable. 

Chemical  analysis  helps  us  but  little  more  in  the  attempt  to  dis- 
tinguish animals  from  vegetables.  Carbon  and  nitrogen  compounds  form 
a  large  proportion  of  the  constituents  of  each,  and  a  large  number  of 
complex  combinations  found  in  animal  tissues  are  represented  by  entirely 
similar  compounds  in  vegetable  matter.  There  is  therefore  no  one  chemi- 
cal compound  whose  presence  is  characteristic  of  animality  or  vegetable 
nature;  for  u  cellulose,"  the  substance  out  of  which  wood-fibre  and  .the 
walls  of  plant-cells  are  formed,  has  been  ascertained  to  form  the  greater 
part  of  the  external  coverings  of  certain  molluscous  animals  (ascidians). 
So  also  chlorophyll,  the  green  coloring  matter  of  plants,  is  the  cause  of 
the  green  color  of  many  infusorial  animalcules  and  of  Hydra  viridis, 
while  starch  has  been  found  in  the  ventricles  of  the  brain  of  animals, 
and  is  represented  by  glycogen,  a  body  closely  analogous  to  starch  and 
manufactured  by  the  animal  economy.  Such  examples,  therefore,  show 
that  chemical  examination  can  give  us  no  definite  aid  in  separating  plants 
and  animals. 

The  microscope  is  also  powerless  to  give  us  an  infallible  rule  which 
will  enable  us  to  distinguish  animal  from  vegetable  tissue.  In  other 
words,  plants  and  animals  are  built  up  on  the  same  general  plan  ;  their 
intimate  structure  closely  coincides.  Both  originate  in  cells,  consisting, 
in  their  typical  form,  of  a  cell-wall,  cell-contents,  or  protoplasm, — nucleus 
and  nucleolus,— and  in  both  the  parent  cell  undergoes  subdivision  and 
results  in  the  birth,  growth,  and  development  of  myriads  of  other  cells, 
constituting  the  tissue  of  the  plant  or  animal,  and  differing  no  more  from 
each  other  than  almost  any  mature  animal  or  vegetable  cell  does  from 
the  germ  from  which  it  originated. 

Nor  is  the  possession  of  a  digestive  cavity,  mouth,  or  alimentary 
tube  characteristic  of  animals  ;  for  there  are  vegetables  which  possess  a 
stomach,  as  the  Nepenthes,  or  Pitcher-Plant,  which  has  a  cavity  cor- 
responding to  a  stomach,  in  which  digestive  fluids  are  poured  out,  and 
in  which  digestion  and  absorption  take  place.  On  the  other  hand,  many 


INTRODUCTION.  7 

animals  among  the  protozoa,  such  as  the  amoeba,  have  no  stomach,  the 
general  surface  serving  not  only  for  the  purpose  of  digestion,  but  also 
for  absorption,  an  extemporaneous  stomach  being  formed  by  wrapping  a 
part  of  the  external  general  body  surface  around  the  substance  to  be 
digested. 

So  also  in  the  tape-worms  and  other  parasitic  forms  of  animal  life, 
there  is  an  entire  absence  of  any  special  aperture  for  the  entrance  of 
nutritive  matter,  such  organisms  living  by  the  simple  imbibition  of 
nutritive  matter  in  solution. 

When,  however,  we  examine  into  the  nature  and  mode  of  assimila- 
tion of  food,  the  nutritive  processes  occurring  in  the  interior  of  the 
organism,  and  the  results  of  the  conversion  and  assimilation  of  food, 
then  only  have  we  any  reliable  scientific  data  for  distinguishing  animals 
from  plants.  In  the  first  place,  the  food  of  animals  differs  from  that  of 
plants  in  its  nature.  Animals  require  organic  food ;  plants  live  on  inor- 
ganic or  mineral  matter.  The  nutritive  processes  in  the  two  kingdoms 
are  also  diametrically  opposed :  the  plant  absorbs  water,  ammonia,  carbon 
dioxide  and  certain  salts,  and  out  of  these  manufactures  the  albuminoids, 
carbohydrates  and  hydrocarbons  found  in  vegetable  tissue.  The 
animal  feeds  on  these  complex  vegetable  compounds, — and  this  holds 
whether  the  animal  be  herbivorous  or  carnivorous, — and  returns  to  the 
soil  and  atmosphere  the  inorganic  matter  from  which  they  were  manu- 
factured by  the  plant;  and  in  the  same  form,  i.e.,  carbon  dioxide,  water, 
ammonia,  and  certain  salts.  The  plant  therefore  converts  simple  inor- 
ganic compounds  into  complex  organic  compounds,  while  the  animal 
reduces  complex  organic  matter  to  its  simple  inorganic  constituents. 

A  further  point  of  distinction  between  animals  and  vegetables,  and 
one  closely  connected  with  the  nutritive  processes,  is  their  behavior  to 
the  atmosphere.  The  animal  requires  for  the  processes  of  reduction 
already  mentioned  as  constituting  its  mode  of  nutrition  a  constant  supply 
of  ox}-gen,  which  is  withdrawn  from  the  atmosphere  and  returned  to  it 
in  the  form  of  CO,,  representing  one  of  the  end  products  of  oxidation 
of  the  carbon  of  its  tissues  and  food.  Plants,  on  the  other  hand,  absorb 
CO,,  and  under  the  influence  of  sunlight,  by  the  action  of  their  chloro- 
phyll, break  up  this  CO,,  fix  the  carbon  in  their  tissues,  and  set  free 
ox}-gen  into  the  air.  The  plant  thus  absorbs  what  the  animal  excretes, 
and  the  animal  absorbs  what  the  plant  excretes.  We  thus  see  that 
animals  and  plants  offer  striking  points  of  contrast  as  to  the  character 
of  their  food  and  the  nature  of  their  nutritive  processes,  and,  although 
there  are  several  apparent  exceptions  to  the  general  outline  here  given, 
their  consideration  may  be  deferred  to  the  chapters  on  the  Chemical 
Processes  in  Cells. 

We  have  found  now  that  all  objects  in  nature  must  be  either  organic 


8  INTRODUCTION. 

or  inorganic,  and  we  have  considered  the  means  by  which  these  bodies 
may  be  separated:  we,  therefore,  here  leave  the  inorganic  world  (the 
domain  of  physics,  chemistry,  mineralog}r,  etc.),  to  confine  our  studies 
to  the  animal  kingdom.  But  here,  from  the  fact  that  there  was  great 
difficulty  in  separating  the  lower  forms  of  animal  from  vegetable  life,  it 
must  be  recognized  that  animals  and  plants  possess  many  vital  functions 
in  common ;  and  as  the  simplest  expression  of  these  functions  must  be  in 
the  simplest  organisms,  the  study  of  those  functions  may  best  commence 
in  the  simple,  uncellular  organisms,  whether  animal  or  vegetable. 
General  physiology  will  thus  deal  with  the  Animal  Cell :  its  form,  origin, 
modifications,  constitution,  and  the  various  chemical  and  physical  proc- 
esses concerned  in  its  nutrition,  growth,  development  and  reproduction. 

It  will,  then,  be  shown  that  the  higher  animals  are  mere  associations 
of  such  simple  organisms,  in  which  the  modification  in  the  characters 
of  the  various  constituent  cells  leads  to  a  division  of  labor.  In  other 
words,  development  of  tissues  leads  to  a  specialization  of  function,  and 
Special  Physiology  will  deal  with  the  study  of  the  development  of  func- 
tion, especially  as  seen  in  our  domestic  animals.  The  functions  of  animals 
are  divided  into  the  Vegetative  Functions,  the  Animal  Functions, — or 
the  functions  of  relation, — and  the  Reproductive  Functions. 

The  Yegetative  Functions  include  everything  which  relates  to  the 
nutrition  of  the  animal  in  its  widest  sense.  As  the  blood  in  higher 
animals  is  the  organ  of  nutrition,  under  this  head  are  included  (1st) 
the  additions  to  the  blood, — therefore,  the  description  and  modes  of 
prehension  of  Food ;  Digestion,  or  the  preparation  of  food  for  absorption ; 
and  Absorption,  or  the  means  by  which  nutritive  and  other  matters  enter 
the  blood.  The  Blood  will,  then,  be  considered  as  a  tissue  of  nutrition 
<or  as  a  carrier  to  and  from  the  various  organs  of  the  body  by  means  of 
its  Circulation.  As  a  boundary  between  the  additions  and  (2d)  the  losses 
to  the  blood  Respiration  will  demand  attention,  while  under  the  latter 
head  come  the  functions  of  Secretion  and  Excretion.  The  means  by 
which  the  identit}^  of  the  individual  is  preserved  concludes  the  subject 
of  Nutrition  and  deals  with  the  nutritive  value  of  different  foods  and 
their  combinations,  the  adaptment  of  foods  to  the  different  demands  on 
the  animal  economy,  and  the  subject  of  Animal  Heat.  The  Animal  Func- 
tions, or  those  by  which  the  body  is  brought  into  relation  with  the 
external  world  by  means  of  sensation,  power  of  movement,  consciousness, 
and  volition,  include  the  study  of  the  Muscular  and  Nervous  Systems, 
while  finally  the  Reproductive  Functions  lead  to  the  preservation  of  the 
species,  and  include  the  subjects  of  Generation  and  Development,  or 
Embryology. 


PART  I. 


GENERAL  PHYSIOLOGY. 


THE  PHYSIOLOGY  OF  ANIMAL  CELLS. 


(9) 


SECTION   I. 
THE  STRUCTURE  OF  ORGANIZED  BODIES. 

CHEMICAL  ANALYSIS  has  shown  that  all  organized  bodies  are  capable 
of  resolution  into  simple  chemical  elements  which  in  themselves  do  not 
differ  from  the  elements  out  of  which  all  matter  is  composed :  in  other 
words,  that  the  simple  elements  of  which  organized  bodies  are  built  up 
are  universally  distributed  throughout  nature,  and  that  no  one  element 
is  peculiar  to  organized  matter.  The  characteristic  of  organized  bodies 
is,  therefore,  not  to  be  found  in  any  peculiarity  of  the  matter  of  which 
they  are  composed,  but  in  the  manner  in  which  the  atoms  composing 
that  matter  are  grouped.  In  an  inorganic  body  we  are  accustomed  to 
attribute  its  chemical  properties  to  the  nature,  number,  and  mode  of 
association  of  its  constituent  elements,  while  its  physical  properties  are 
attributable  to  the  mode  of  arrangement  of  its  molecules. 

Anatysis  of  organized  bodies  shows  that  in  them  we  have  certain 
elements  constantly  present  in  certain  definite  proportions:  it  is  there- 
fore warrantable  to  assume  that  the  chemical  properties  of  organized 
bodies  are,  as  in  the  case  of  inorganic  matter,  due  to  the  number,  nature, 
and  mode  of  association  of  their  elements.  Further,  we  find  in  all 
organized  living  bodies  a  certain  identity  of  physical  properties :  it  is 
therefore  warrantable  to  assume  that  the  physical  processes  seen  in 
organized  bodies  are  dependent  on  the  mode  of  arrangement  of  their 
constituent  molecules.  The  elements  constantly  associated  in  living 
matter  are  carbon,  nitrogen,  oxygen,  hydrogen,  and  sulphur,  forming  a 
complex  combination,  to  which  the  term  protoplasm  has  been  applied. 
This  matter,  protoplasm,  whether  found  in  the  tissues  of  the  highest 
animals  or  plants,  or  in  the  lowest  unicellular  members  of  either  kingdom, 
has  always  the  same  composition  and  is  always  possessed  of  nearly  the 
same  attributes ;  with  the  restriction  that  we  have  already  referred  to  as 
to  the  difference  in  functions  possessed  by  animals  and  plants, — differences 
which  will  probably  in  the  future  be  cleared  up,  and  found  not  to  be  in 
contradiction  to  the  statement  that  protoplasm  is  the  universal  basis  of 
organization. 

All  organized  bodies  are  built  up  of  associations  of  masses  of  proto- 
plasm, which  from  their  appearance  are  termed  cells,  or,  from  the  func- 
tions which  they  fulfill,  elementary  organisms:  and  as  the  physical 
properties  of  inorganic  matter  are  dependent  on  the  arrangement  of 


12  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

their  molecules,  so  the  physiological  peculiarities  of  organized  bodies 
are  dependent  on  their  cellular  structure. 

Physiology  is  therefore  the  study  of  the  properties  of  cells.  Cells 
possess  the  properties  of  Nutrition,  Reproduction,  Growth,  Develop- 
ment, and  in  many  cases  their  contents  are  capable  of  Motion  and  mani- 
festing Irritability. 

I.      THE   GENERAL   PROPERTIES   OF   CELLS. 

Microscopic  examination  teaches  that  every  living  object,  from  man 
down  to  the  smallest  animalcule  invisible  to  the  naked  eye,  —  from  the 
largest  tree  down  to  the  most  microscopic  plant,  —  is  built  up  on  the 
same  general  plan.  In  each  the  same  element  of  organization  is  found, 
and  every  living  form  is  built  up  of  associations  of  these  microscopic 
units,  each  of  which,  even  in  the  most  complex  forms  of  life,  may  be 
regarded  as  separate  individual  organisms.* 

For  even  in  complex  organisms  cells  to  a  certain  extent  carry  on  a 
separate  and  independent  existence.  We  see 
separate  cells  originate  separately,  grow,  repro- 
duce themselves,  become  diseased  and  die 
without  the  entire  organism  as  a  whole  taking 
any  part  in  these  different  stages  of  existence 
of  its  component  parts.  The  individual  life  of 
each  separate  cell  is  recognized  in  the  different 
activities  of  different  cells  :  the  activity  of  the 
FIG  i—  TYPICAL  ANIMAL  organism  is  the  result  of  the,  sum  of  these 
(m£nV)  °VUM  °F  separate  existences. 


In  tlieir   typical    form   both    animal    and 
vegetable  cells  consist  of  closed  vesicles,  with 

homogeneous  or  striated  walls,  a  viscid  albuminous  contents,  termed 
protoplasm,  containing  an  aggregation  of  granules  called  -a  nucleus, 
within  which  again  is  a  still  denser  formation  called  a  nucleolus.  The 
cell-contents  is  frequently  vacuolated,  i.e.,  contains  minute  cavities  filled 
with  a  clear  fluid. 

The  contents  of  the  cells,  which  we  shall  find  to  be  functionally  the 
most  important,  is  called  protoplasm.  It  is  a  transparent  mass  in  which 
numerous  granules  are  suspended,  and  which  possesses  in  all  young  cells 
(the  property  of  contractility.  It  is  often  seen  to  be  reticulated.  In 
older  cells  the  quantity  of  fluid  diminishes  and  the  cells  become  firmer 
and  drier,  while  vacuoles  often  form  and  contain  fluid.  This  change  in 
.the  physical  properties  of  cells  is  often  associated  with  a  visible  change 
in  their  chemical  nature,  —  thus,  with  a  deposit  of  coloring  matter,  starch 

*  Such  units  of  organization  are  termed  cells,  from  the  resemblance  which  micro- 
scopic sections  of  young  tissues,  whether  plant  or  animal,  bear  to  a  honey-comb. 


THE  GENERAL  PEOPEKTIES  OF  CELLS.  ;         13. 

granules,  fat  globules,  or  granular  matter.  All  substances  which  coagu- 
late proteids  have  the  same  effect  on  protoplasm.  The  vital  properties 
of  protoplasm  will  be  studied  later. 

A  membrane  is  usually  present  in  all  mature  cells,  though  always 
absent  in  embryonic  forms.  It  may  therefore  be  assumed  that  the  mem- 
brane results  from  a  condensation  of  the  outer  layers  of  the  cell-contents. 
The  membrane  is  apparently  homogeneous,  or  may  be  porous. 

The  nucleus,  the  size  of  which  is  generally  in  proportion  to  that  of 
the  cell,  and  which  is  usually  oval  or  spherical,  is  never  absent  in  early 
forms  of  active  cells,  though  it  may  disappear  when  the  cell  reaches 
maturity.  In  its  mature  stage  it  is  generally  reticulated, — that  is,  com- 
posed of  an  investing  cuticle  within  which  the  contents  are  arranged  in 
the  form  of  a  fibrillar  net-work.  The  presence  of  a  nucleus,  which  is 
often  difficult  of  recognition  on  account  of  its  minute  size,  may  be 
demonstrated  through  the  action  of  certain  reagents,  especially  dilute 
acids  and  staining  fluids.  Dilute  acids  render  the  protoplasm  of  cells 
transparent  without  affecting  the  nucleus,  which  consequently  becomes 
more  prominent;  while  staining  fluids,  such  as  carmine,  haematoxylin, 
and  the  anilin  dyes,  color  the  nucleus  deeper  in  tint  than  the  cell-contents. 
The  nucleus  appears  to  be  especially  important  in  the  reproductive  func- 
tions of  cells,  since  when  cells  multiply  by  division  the  division  always 
commences  in  the  nucleus. 

The  nucleolus  is  simpty  a  closer  aggregation  of  the  granules  which 
constitute  the  nucleus,  and  is  very  frequently  absent. 

Both  cell-wall  and  nucleus  may  be  absent  from  the  lowest  elementary 
organisms. 

As  our  conception  of  the  structure  of  the  higher  animals  and  plants 
is  an  association  of  elementary  organisms  invariably  taking  origin  from 
a  single  cell,  our  definition  of  such  a  simple  organism  or  cell  must  be 
modified  so  as  to  apply  to  the  description  of  the  simplest  conceivable 
organism  capable  of  carrying  on  an  independent  existence.  And  as  we 
have  seen  that  of  the  constituents  of  a  typical  cell  but  one,  the  cell-con- 
tents, or  protoplasm,  is  essential ;  and  as  we  know  that  there  are 
organisms  capable  of  carrying  on  an  independent  existence  in  whom 
neither  cell-wall,  nucleus,  or  nucleolus  is  to  be  detected,  a  cell  may  be 
defined  as  a  more  or  less  homogeneous  mass  of  organized  material, — 
protoplasm, — possessing  development,  growth,  reproduction,  nutrition, 
and  automatism. 

The  best  known  of  such  undifferentiated  forms  of  cell  life  is  the 
amoeba, — one  of  the  simplest  examples  of  an  animal  organism. 

In  its  lowest  form  the  amoeba  (Protamoeba  primitiva,  Haeckel)  con- 
sists of  a  mass  of  jelly-like,  structureless,  albuminoid  substance  (proto- 
plasm), which,  so  far  as  its  chemical  composition  and  general  attributes 


14  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

are  concerned,  cannot  be  distinguished  from  the  contents  of  all  active 
forms  of  cells  (Fig.  2). 

The  amoeba  is  capable  of  spontaneous  motion,  both  as  regards 
change  of  external  form  and  of  progressing  from  place  to  place. 
Motions  may  also  be  evoked  by  various  stimuli ;  hence,  free  protoplasm, 
in  common  with  muscular  fibre  and  ciliated  organisms,  is  contractile. 
The  peculiarity  of  protoplasmic  motion,  as  seen  in  the  amoeba,  is  that 
motion  does  not  occur  around  a  fixed  point,  but  rather  is  a  flowing 
motion,  such  as  might  occur  in  the  particles  of  a  fluid.  Thus,  in  an 
amoeba  the  changes  in  form  and  location  are  effected  through  the  thrust- 
ing out  of  lobe-like  prolongations  of  the  periphery  (pseudopodia),  and 
their  subsequent  withdrawal  or  the  flowing  into  these  extensions  of  the 
remainder  of  the  body. 

Occasionally  one  or  more  of  these  pseudopodia  become  gradually 
more  and  more  constricted,  until,  finally,  a  portion  becomes  entirely 

separated  from  the  original 
mass,  increases  in  size,  and 
itself  possesses  all  the  proper- 
ties of  the  parent  stock;  hence, 
protoplasm  is  reproductive, 
and  possesses  the  power  of 
growth.  Moreover,  the  move- 
ments of  an  amo3ba  are  not 

FIG.  2. -A  NON-NUCLEATED  CELL,  THE  PROT-    necessarily  the  consequences 
AMCEBAPRIMITIVA,  AFTER  HAECKEL.  (Wundt.)      of  externai  stimuli,  but  may 

A,  original  condition ;  B,  commencement  of  reproduction  by  fission :  ,  0        .     . 

C,  after  complete  separatum.  be       Self-Originating ;         llCHCC, 

protoplasm  is  also  automatic. 

If  watched  for  some  time,  an  amoeba  will  often  be  seen  to  take  into 
its  interior,  by  flowing  around  them,  small  vegetable  organisms,  of  which 
portions  are  dissolved  and  converted  into  the  substance  of  its  body, 
while  the  undigested  remainder  is  extruded  ;  therefore,  protoplasm,  even 
in  the  absence  of  all  digestive  organs,  possesses  the  power  of  nutrition. 

The  amoeba  requires  for  its  existence  an  atmosphere  of  ox3rgen, 
which  is  absorbed,  and  which  it  again  partly  exhales  as  carbon  dioxide. 
Protoplasm  is  therefore  respiratory. 

II.  ORIGIN  OF  CELLS. 

We  iiave  seen  that  in  the  amoeba  a  simple  mass  of  undifferentiated 
protoplasm  possesses  the  powers  of  reproduction,  contractility,  respira- 
tion, irritabilit}^  nutrition,  and  automatism.  Every  form  of  life  com- 
mences its  existence  in  the  form  of  just  such  a  simple  mass  of  proto- 
plasm. Starting  with  the  ovum,  and  ending  with  the  nucleated  elements 
found  in  the  organs  and  tissues  of  the  embryo  and  adult;  there  is  one 


OKIGIN   OF  CELLS.  15 

uninterrupted  series  of  generations  of  cells,  each  cell  becoming  so  modi- 
fied as  to  specialize  certain  functions  which  are  together  possessed  by  all 
forms  of  undifferentiated  protoplasm.  Thus,  in  the  higher  forms  certain 
cells  will  be  found  to  have  become  so  modified  as  to  have  the  function  of 
reproduction  especially  developed ;  they  will  therefore  constitute  the 
reproductive  tissues.  In  other  cells  the  nutritive  functions  will  become 
most  prominent ;  they  will  therefore  form  part  of  the  tissues  whose 
function  is  to  preserve  the  nutritive  balance  of  the  organism.  Specializa- 
tion of  function  is  therefore  the  explanation  of  the  development  of 
tissues;  the  result  is  a  plr^siological  division  of  labor.  We  will  have  to 
return  to  this  subject  again. 

The  germ  of  every  animal  and  vegetable  organism  is  a  cell  which 
owes  its  existence  to  some  similar,  previously-existing  cell.  Neglecting 
the  origin  and  development  of  cells  in  the  vegetable  kingdom,  every 
cell  which  forms  part  of  the  organs  or  tissues  of  all  forms  of  animal 
life  originated  in  and  developed  from  a  germ-cell  or  ovum. 

The  ovum  of  man  and  other  mammals  is 
a  minute  mass  of  protoplasm,  corresponding  in 
its  general  appearance  with  the  description  of  a 
typical  cell.  The  protoplasm,  or  cell-contents, 
is  surrounded  by  a  delicate,  striated  membrane, 
the  Zona  radiata,  or  vitelline  membrane.  Within 
the  cell-contents,  in  addition  to  numerous  minute 
particles, — the  so-called  yelk- globules, — is  a 
collection  of  denser  particles  of  protoplasm,  FIG.  3.— TYPICAL  ANIMAL 
—the  nucleus,  or  germinal  vesicle,  and  within  uS?"cx£jJ)  °VUM  OF 
that,  again,  one  or  more  still  more  solid  masses,  A» 
— the  nucleoli,  or  germinal  spots. 

The  cell-contents  is  identical  in  nature  and  properties  with  the  sub- 
stance of  the  amoaba,  and  before  and  immediately  after  fertilization  may 
even  be  the  seat  of  spontaneous  movements  of  contraction  and  expan- 
sion. When  mature,  its  diameter  in  the  domestic  animals  and  man  varies 
from  the  ^J^  to  the  T^  of  an  inch  (0.18-0.2  mm.). 

Fertilization  leads  to  a  cleavage  of  the  protoplasm  into  two  parts, 
the  nucleus  being  first  divided,  so  that  two  new  elements  originate  from 
the  ovum,  each  consisting  of  protoplasm  and  each  containing  a  nucleus. 
Each  of  the  two  new  cells  thus  formed  again  subdivide  into  four,  these 
into  eight,  and  so  on  through  many  generations,  until  a  large  number  of 
new  cells,  the  so-called  "mulberry  mass,"  results  from  the  subdivision  of 
the  original  parent  cell. 

According  to  Schleiden  and  Schwann,  the  founders  of  the  cell  doc- 
trine, organic  forms  of  life  may  originate  in  one  of  two  wa}rs, — either  by 
the  aggregation  of  granules  in  a  previously-existing  homogeneous  fluid 


16 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


FIG.  4.— BLOOD-CORPUSCLES 
IN  DIFFERENT  STAGES  OF 
DEVELOPMENT,  SHOWING 
REPRODUCTION  BY  FIS- 
SION. (Ranke.) 


(the  blastema),  forming  the  so-called  "free  cell-formation,"  or  by  the 
subdivision  of  a  previously-existing  cell, — the  "  endogenous  cell-forma- 
tion." 

According  to  the  first  of  these  views,  which  may  be  compared  to  the 
formation  of  crystals  in  a  saline  solution,  granules  first  develop  in  a  fluid 

which  contains  all  the.  chemical  constituents  of 
the  organism,  forming  the  nucleolus  of  the 
future  cell.  Around  this  other  granules  are 
gradually  deposited  until  the  nucleus  is  formed, 
and  the  cell-contents  and  membrane  gradually 
consolidate  around  this.  The  first  objection 
to  this  theory,  which,  it  is  seen,  implies  spon- 
taneous generation,  lies  in  the  fact  that  no  one- 
has  ever  been  able  to  demonstrate  such  a  cell- 
formation  or  to  discover  the  so-called  cyto- 
blasts.  It  was  then  shown  that  all  the  cells  of 
the  embryo  originate  in  the  segmentation 

spheres  of  the  ovum,  and  the  falsity  of  this  doctrine  of  free  cell- 
formation  is  further  proved  from  analogy  by  the  manner  in  which  the 
connective-tissue  cells  take  part  in  the  development  of  pathological  new 
formations.  There  is  now  no  more  firmly-established  dictum  in  plrysi- 
ology  than  the  statement  that  every  cell  originates  from  a  previously- 
existing  cell.  (Omnis  cellula  e  cellula.) 

The  other  view,  which  was  also  to  a  certain  extent  advocated  by 
Schwann,  as  to  the  origin  of  cells  by  sub- 
division of  a  parent  cell,  is  exemplified  in 
the  mode  of  reproduction  of  many  of  the 
lower  forms  of  life.  Cells  may  reproduce 
themselves  by  simple  division  of  the  parent 
cell  or  by  endogenous  division. 

Cell  reproduction  always  starts  in  the 
nucleus.  In  simple  division  the  nucleus  first 
becomes  marked  with  a  furrow,  which  gradt 
ually  deepens  until  the  nucleus  is  divided 
into  two.  The  protoplasm  of  the  cells  is 
then  modified  in  the  same  way,  until  two  new 
cells  are  formed  by  the  division  of  the 

parent  cell.  This  process  may  be  followed  in  the  reproduction  of 
the  nucleated  red  blood-corpuscles  of  the  embryo  of  the  chick  and 
even  in  mammals  (Fig.  4).  A  modification  of  this  form  of  cell 
reproduction  is  sometimes  described  as  "  budding."  This  process  also 
starts  with  the  nucleus.  A  number  of  nuclei  are  first  formed  by  the 
subdivision  of  the  nucleus ;  these  gradually  separate;  the  protoplasm 


FIG.  5.— GEMMATION.    A  BUD- 
DING  GERM-CELL   OF   GOR- 

DIUS,     AFTER    MEISSNER. 

(Wundt.) 


ORIGIN   OF   CELLS.  17 

collects  around  them  so  as  to  form  projections  from  the  periphery  of  the 
cell,  which  become  more  and  more  constricted  until  they  finally  separate 
(Fig.  5).  During  division  the  nuclear  membrane  disappears,  and  the 
nucleus  usually  divides  before  the  cell-protoplasm,  but  not  directly,  by 
simple  cleavage,  as  was  formerly  supposed,  but  indirectly,  by  karyo- 
kitiesis  (from  movement  of  nuclear  fibrils).  This  is  an  exceedingly  com- 
plicated process.  Its  different  stages  may  be  divided  about  as  follows  : — 

1.  The  nuclear  fibrils  become  very  distinct,  while  the  nuclear  mem- 
brane disappears  and  the  fibrils  of  the  nuclear  net-work  become  twisted 
and  bent  into  a  more  or  less  dense  convolution,  while  the  entire  nucleus 
•enlarges. 

2.  The  fibrils  unravel  into  loops  arranged  around  the  centre  as  a 
wreath  or  rosette. 

3.  The    peripheral  points  of  the  loops  become  broken  and  a  star- 
shaped  figure  of  single  loops  is  obtained.     This  is  termed  the  aster,  or 
star. 

4.  The  loops  separate  into  two  groups  or  new  centres.     This  is  the 
diaster,  or  double  star. 

5.  The  two  groups  of  threads  become  farther  apart,  as  if  attracted 
by  opposite  poles,  but  still  remain  connected  by  fine  pole-threads,  which 
represent  the  interstitial  nuclear  substance.     In  this  stage   the  figure 
resembles  a  spindle. 

6.  The  connection  between  the  two  sets  of  threads  is  broken. 

7.  The  threads  of  each  set  become  convoluted. 

8.  A  membrane  forms  for  each  set,  and  thus  new  daughter  nuclei 
result.     (See  Fig.  6.) 

The  cell-protoplasm  may  commence  to  divide  at  any  stage  between 
the  one  when  the  threads  aggregate  around  the  two  centres  and  the  one 
when  two  distinct  nuclei  are  present ;  or  the  division  of  the  nucleus  may 
be  followed  by  division  of  the  cell,  so  giving  a  cell  with  two  nuclei.  It 
is  not  proved  that  this  is  the  universal  mode  of  divisions  of  nuclei, 
though  it  has  been  observed  in  all  kinds  of  cells  in  the  embryo,  and  to  a 
limited  degree  in  the  adult.  On  the  contrary,  it  is  probable  that  amoeboid 
cells  divide  by  the  direct  method  and  that  other  nuclei  may  also  undergo 
direct  division,  or  Remak's  division,  by  simple  cleavage,  though  all  the 
cases  in  which  constriction  of  nuclei  is  observed  need  not  be  cases  of 
commencing  division,  as  the  change  in- shape  may  be  due  to  pressure  of 
cell-protoplasm,  or  to  nuclear  contractions.  (Klein). 

The  second  form  of  cell-formation  is  termed  by  Kolliker  "  endoge- 
nous cell-formation,"  and  consists  in  the  formation  of  cells  within  the 
membrane  of  the  parent  cell,  which  ultimately  bursts  and  discharges  its 
progeny  of  j^oung  cells.  The  division  of  the  mammalian  ovum,  the 
growth  of  cartilage,  and  many  pathological  cell-formations  are  types  of 

2 


18 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


this  mode  of  cell  reproduction.  The  latter  example  furnishes  many 
instances  in  which  a  number  of  cells  with  entirety  different  attributes 
from  the  parent  cell  develop  in  the  interior  of  a  cell,  such  as  the  develop- 


FIG.  6.— KARYOKINESIS.    (Klein.} 

A,  ordinary  nucleus  of  a  columnar  epithelial  cell ;  B,  C,  the  same  nucleus  in  the  stage  of  convolution : 
D,  the  wreath,  or  rosette  form ;  E,  the  aster,  or  single  star ;  F,  a  nuclear  spindle  from  the  Descemet's 
endothelium  of  the  frog's  cornea ;  G,  H,  I,  the  diaster ;  K,  two  daughter  nuclei. 

ment  of  pus-corpuscles  in  the  interior  of  different  tissue-cells  in  inflam- 
mation (Fig.  7). 

The  best  object  for  the  study  of  cell  reproduction  by  division,  and 

the  one  of  most  interest  tor  us,  is 
found  in  the  fertilized  ovum  of 
mammals. 

As  the  ovum  approaches  maturity, 
even  before  impregnation  takes  place, 
the  germinal  vesicle  becomes  obscure 
and  more  and  more  irregular  in  out- 
line, its  membrane  and  reticulum 
disappear,  and  the  germinal  spot  is 
broken  up.  What  remains  of  the 
germinal  vesicle  becomes  converted 
into  a  striated,  spindle-shaped  body, 
which  moves  to  the  surface  of  the 
ovum,  to  there  undergo  division  into 
two  parts.  One  part  becomes  ex- 
truded from  the  ovum  to  form  what 
is  known  to  embryologists  as  the  polar  cell,  and  is  soon  followed  by  a 
second  similar  cell,  while  the  portion  of  the  spindle  remaining  within 
the  ovum  forms  a  new  nucleus,  the  female  pronucleus,  from  which,  in 
conjunction  with  the  male  elements,  the  future  embryo  is  developed. 


FIG.  7.— THE  FORMATION  OP  PUS-COR- 
PUSCLES IN  THE  INTERIOR  OF  EPITHE- 
LIAL CELLS,  SHOWING  ENDOGENOUS 
CELL-FORMATION.  (Ranke.) 

A,  single  cylindrical  cell  from  the  human  bile-duct : 
B,  a  similar  cell  containing  two,  C  containing  four,  and 
D  numerous  pus-cells:  E,  isolated  pus-corpuscles; 
F,  a  ciliated  epithelial  cell  from  the  human  respiratory 
tract,  containing  a  single  pus-corpuscle :  and  G,  a  pave- 
ment epithelial  cell  from  the  urinary  bladder  of  man, 
containing  numerous  pus-corpuscles. 


OKIGIN    OF   CELLS. 


19 


111  the  unimpregiiated  ovule  spontaneous  contractions  are  generally 
seen  in  the  protoplasmic  cell-contents.  When  the  egg  becomes  fertilized 
these  contractions  become  so  modified  as  to  cause  the  germinal  vesicle 
(or  the  bod}r  resulting  from  the  union  of  the  male  and  female  pronuclei), 
and  then  the  cell-contents  to  split  into  two  parts  contained  within  the 
cell-membrane,  which  takes  no  part  in  this  division.  These  segmentation 
spheres,  as  already  mentioned,  continue  to  subdivide  until  an  immense 
number  of  minute,  nucleated,  membraneless  cells  are  contained  within  the 
vitelline  membrane  (forming  the  so-called  mulberry  mass). 

From  these  elements,  which  become  progressively  smaller  as  cleavage 
goes  on,  all  the  tissues  of  the  embryo  are  formed.  At  first  the}T  all 
possess  mobilit}T  (amoeboid  movements),  showing  their  analogy  to  the 
simple  amoaba,  but.  at  birth  this  property  is  only  retained  by  certain  cells. 
Like  amrebse,  they  also  grow  in  size  and  divide  into  new  individuals. 

At  first  all  the  cells  resulting  from  the  segmentation  of  the  ovum 
are  exactly  alike  :  they  then  undergo  certain  modifications  in  arrange- 


123  A- 

FIG.  8.— OVA  OF  THE  DOG  FROM  THE  FALLOPIAN  TUBE,  SURROUNDED  BY  THE 
ZONA  PELLUCIDA,  IN  WHICH  ARE  FOUND  NUMEROUS  SPERMATOZOA,  AFTER 
BISCIIOFF.     (Rank<>.} 
1,  ovum  with  two  segmentation  spheres,  the  Zona  pellucida  being  surrounded  by  the  Membrana  gran- 

ulosa ;  2,  ovum  with  four  segmentation  spheres ;  3,  ovum  with  eight  segmentation  spheres ;  4,  ovum  with 

innumerable  segmentation  spheres,  forming  the  mulberry  mass. 

ment  and  form,  different  in  different  classes  of  animals,  from  which  the 
different  tissues  of  the  embryo  are  developed. 

The  ova  of  animals  are  divided  into  two  classes, — those  in  which  the 
entire  yelk  is  concerned  in  the  production  of  the  embryo,  and  those  in 
^Yhich  a  part  only  serves  for  this  purpose, — while  the  remainder  of  the  cell- 
contents  is  drawn  upon  for  the  nutritive  needs  of  the  embr3ro.  The  first 
of  these  which  undergoes  total  segmentation  is  termed  a  holoblastic  egg; 
the  second  undergoes  only  partial  segmentation,  and  is  termed  a  mero- 
blastic  egg.  The  ovum  of  mammals  serves  for  a  type  of  the  former 
class ;  the  ovum  of  birds  is  typical  of  the  second  class.  As  already 
mentioned,  the  mammalian  ovum  represents  a  typical  cell;  the  ovum  of 
the  bird  differs  in  many  points.  Beneath  the  yelk-membrane  is  a  layer 
of  minute  flattened  cells,  which  gradually  disappear  during  the  maturing 
of  the  egg ;  while  the  yelk  consists  of  two  parts,  one  serving  for  the 
development  of  the  embryo,  the  other  for  its  nutrition.  The  part  from 


20  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

which  the  embryo  is  formed  is  a  small,  white  disk  lying  directly  beneath 
the  vitelline  membrane  and  termed  the  tread,  the  blastoderm  or  cicatricula. 
In  the  hen's  egg  this  disk  is  about  four  millimeters  in  diameter,  and  is 
always  found  in  the  upper  surface  of  the  yelk.  If  a  hen's  egg  is  hard- 
ened by  boiling,  and  then  cut  in  two  by  a  vertical  section  so  as  to  bisect 
the  yelk,  the  latter  will  be  found  not  to  be  perfectly  homogeneous.  The 
yelk  is  clothed  externally  by  a  thin  layer  of  different  material,  which  at 
the  edge  of  the  blastoderm  passes  beneath  it  and  becomes  thicker  so  as 
to  form  a  bed  on  which  the  blastoderm  rests,  to  become  connected  by  a 
narrow  neck  with  a  mass  of  similar  matter  occupying  the  centre  of  the 


WY 
W.Y.     W 


N.P. 
B.L. 


Y.V 


CH.L 


CH.L. 


W. 


VT. 


FIG.  9.— DIAGRAMMATIC  SECTION  OF  AN  UNINCUBATEB  FOWL'S  EGG,  AFTER 
ALLEN  THOMPSON.    (Foster  and  Balf our.) 

BLi,  blastoderm ;  WY,  white  yelk — this  consists  of  a  central,  flask-shaped  mass  and  a  number  of 
layers  arranged  concentrically  around  this;  YY,  yellow  yelk;  VT,  vitelline  membrane;  X,  layer  of 
more  fluid  albumen  immediately  surrounding  the  yelk ;  W,  albumen,  consisting  of  alternate  denser  and 
more  fluid  layers ;  CHL,  chalazae ;  ACH,  air-chamber  at  the  broad  end  of  the  egg— this  chamber  is 
merely  a  space  left  between  the  two  layers  of  the  shell-membrane  ;  ISM,  internal  layer  of  shell-membrane : 
SM,  external  layer  of  shell-membrane ;  S,  shell ;  NP,  nucleus  of  Pander. 

yelk,  which  nearly  always  remains  partially  fluid  in  the  hard-boiled  egg. 
Within  the  yelk  again  are  several  concentric  layers  of  this  white  yelk, 
separated  from  each  other  b}^  la}Ters  of  yellow  }relk.  The  3Tellow  yelk  is 
composed  of  comparatively  large,  unnucleated  cells  filled  with  highly 
refractive  granules,  and  containing  vitellin,  lecithin,  and  various  fatty 
bodies.  The  cells  which  form  the  white  yelk  are  much  smaller,  are 
nucleated,  and  often  a  large  cell  will  be  seen  to  contain  numerous  similar 
but  smaller  cells. 

When  the  egg  is  laid  by  the  hen  it  has  already  undergone  changes 
which  result  from  fertilization.     We  will  first  describe  the  characters  of 


ORIGIN   OF   CELLS. 


21 


the  blastoderm  when  the  egg  is  first  laid,  and  then  the  changes  which 
have  preceded  it. 

The  blastoderm  of  an  unincubated  fertilized  egg  may  be  recognized 
by  the  naked  eye,  when  viewed  from  above,  to  consist  of  two  parts:  an 
opaque,  white  circumference,  the  area  opaca,  and  a  central  transparent 
portion,  the  area  pellucida.  In  the  unfertilized  egg  these  divisions  are 
not  marked.  They  are  due  simply  to  the  way  the  blastoderm,  which  is 
itself  entirely  transparent,  rests  on  the  white  yelk.  The  opaque,  circular 
ring  is  where  the  blastoderm  is  directly  in  contact  with  the  white  yelk, 
while  the  central  clear  portion  is  due  to  the  fact  that  the  blastoderm  is 
separated  from  the  yelk  by  a  layer  of  liquid.  The  white  spot  often  seen 
in  the  centre  of  the  blastoderm  is  the  central  column  of  white  yelk 
shining  through  the  transparent  membrane  (Nucleus  of  Pander). 

When  the  blastoderm  is  hardened  and  cut  into  vertical  sections,  it 
is  found  to  be  composed  of  two  layers  of  cells :  the  upper,  small,  nucle- 
ated, C3"lindrical  cells  adhering  closely  together  in  a  single  la3Ter  and 


FIG.  10.— SECTION  OF  AN  UNINCUBATED  BT-ASTODERM  OF  CHICK.     (Klein.) 

A,  cells  forming  the  ectoderm  ;  B,  cells  forming  the  endodenn  ;  C,  large,  formative  cells :  F,  segmen- 
tation cavity. 

resting  on  the  white  3Telk ;  the  lower,  an  irregular  net-work  of  larger  cells 
which  are  not  nucleated,  apparently,  but  which  contain  numerous  highly 
refractive  granules.  These  are  probably  identical  with  the  white-yelk 
spheres  already  referred  to,  and  are  spoken  of  as  formative  cells. 

The  processes  which  in  the  hen's  bod}r  result  in  the  formation  of 
such  an  egg  are  about  as  follow  : 

In  the  capsule  of  the  ovary  the  yelk  alone  constitutes  the  egg.  It 
then,  just  before  bursting  its  capsule,  consists  of  a  minute,  yellowish, 
ellipsoidal,  cellular  body,  with  a  delicate  membrane,  the  vitelline  mem- 
brane, immediately  below  which  in  a  granular  cell-contents,  the  yelk,  lies 
a  lenticular, mass  of  protoplasm,  the  germinal  disk;  within  this  again  is 
a  nucleus,  the  germinal  vesicle,  containing  a  nucleolus,  or  germinal  spot. 

When  the  ovum  becomes  mature  the  ovarian  capsule  bursts,  and 
the  ovum  (representing  the  yelk  of  the  egg  as  laid)  escapes  into  the 
oviduct,  undergoes  impregnation  by  the  spermatozoa  found  in  the  upper 
portion  of  the  oviduct,  and  has  deposited  around  it  the  accessory 


22  PHYSIOLOGY   OF    THE   DOMESTIC   ANIMALS. 

portions  of  the  egg  through  secretions  from  the  walls  of  the  oviduct. 
Thus,  the  layer  of  albumen  surrounding  the  yelk  is  first  deposited  in 
the  passage  of  the  ovum  through  the  second,  tubular  portion  of  the 
oviduct,  the  chalazse  (see  Fig.  9),  or  twisted,  denser  portions  of  the 
albumen,  being  due  to  the  rotatory  motion  of  the  egg  against  the  spiral 
ridges  of  the  oviduct.  The  shell-membrane  is  formed  by  the  organiza- 
tion of  the  most  external  layers  of  albumen,  and  the  shell  is  formed  in 
the  third  portion  of  the  oviduct,  or  the  uterus.  The  walls  of  this 
portion  of  the  tube  secrete  a  viscid  fluid  which  surrounds  the  egg,  and  in 
which  inorganic  particles  are  deposited.  The  egg  remains  in  the  uterus 
for  from  twelve  to  eighteen  hours,  and  is  then  expelled  through  the 
cloaca,  narrow  end  downward,  by  its  muscular  contractions. 


1  2  3 

FIG.  11.— SURFACE    VIEW  OF    THE    EARLY    STAGES    OF    SEGMENTATION    IN    A 

Fowi/s  EGG,  AFTER  COSTE.    (Foster  and  Balfour.) 

1  represents  the  earliest  stage.  The  first  furrow,  B,  has  begun  to  make  its  appearance  in  the  centre 
of  the  germinal  disk,  whose  periphery  is  marked  by  the  line  A.  In  2  the  first  furrow  is  completed  across 
the  disk,  and  a  second  similar  furrow  at  nearly  right  angles  to  the  first  has  appeared.  The  disk  thus 
becomes  divided  somewhat  irregularly  into  quadrants  by  four  (half)  furrows.  In  a  later  stage,  3,  the 
meridian  furrows,  B,  have  increased  in  number,  from  four,  as  in  B,  to  nine,  and  cross-furrows  have  also 
made  their  appearance.  The  disk  is  thus  cut  up  into  small  central,  C,  and  larger.  D,  peripheral  segments. 
Several  new  cross-furrows  are  seen  just  beginning,  as  ex.  gr.,  close  to  the  end  of  the  line  of  reference,  D. 

About  the  time  the  shell  is  being  formed,  provided  impregnation 
has  taken  place,  changes  occur  in  the  blastoderm,  which,  though  analo- 
gous to  the  process  of  segmentation  already  mentioned  as  taking  place 
in  the  mammalian  ovum,  yet  differs  from  it.  The  germinal  vesicle  first 
disappears,  and  a  furrow  is  then  seen  to  run  across  the  germinal  disk, 
dividing  it  into  two  halves.  This  furrow  is  then  met  by  a  second  run- 
ning at  right  angles  to  the  first ;  this  is  then  crossed  by  another,  and 
division  of  the  segments  proceeds  rapidly  by  furrows  running  in  all 
•directions  until  the  germinal  mass  is  cut  up  into  an  immense  number  of 
minute  masses  of  protoplasm,  smaller  toward  the  centre  than  at  the 
periphery  of  the  disk. 

The  furrows  thus  formed  are  not  merely  superficial,  but  extend 
through  the  entire  thickness  of  the  germinal  disk:  hence  the  germinal 
disk  is  cut  up  into  minute  masses  of  protoplasm.  In  other  words,  a 


ORIGIN   OF   CELLS. 


23 


large  number  of  cells  has  resulted  from  the  segmentation  of  the  parent 
cell. 

These  cells  arrange  themselves  into  an  upper  layer,  with  their  long 


FIG.  12.— SURFACE  VIKW  OF  THE  GERMINAL  DISK  OF  A  HEN'S  EGG  DURING 
THE  LATER  STAGES  OF  SEGMENTATION.    (Foster  and  Bal four.) 

At  C,  in  the  centre  of  the  disk,  the  segmentation  masses  are  very  small  and  numerous ;  at  B,  nearer 
the  edge,  they  are  larger  and  fewer;  while  those  at  the  extreme  margin,  A,  are  largest  and  fewest  of  all. 
It  will  be  noticed  that  the  radiating  furrows  marking  off  the  segments,  A,  do  not  reach  to  the  extreme 
margin,  E,  of  the  disk. 

The  drawing  is  complete  in  one  quadrant  only.  It  will,  of  course,  be  understood  that  the  whole  circle 
should  be  filled  up  in  a  precisely  similar  manner. 

axes  vertical,  their  nuclei  become  distinct,  while  the  lower  cells  remain 
large  and  granular  and  irregularl}'  placed,  forming  in  this  way  the  unin- 
ciibated  blastoderm  already  described.  (See  Fig.  10.) 


FIG.  13.— SECTION  OF  THE  GERMINAL  DISK  OF  A  FOWL'S  EGG  DURING  THE 
LATER  STAGES  OF  SEGMENTATION.    (Foster  and  Bal/our.) 

This  section,  which  represents  rather  more  than  half  the  breadth  of  the  blastoderm  (the  middle  line 
being  shown  at  C),  shows  that  the  upper  and  central  parts  of  the  disk  segment  faster  than  those  below  and 
toward  the  periphery.  At  the  periphery  the  segments  are  still  very  large.  One  of  the  larger  segments  is 
shown  at  A.  In  the  majority  of  segments  a  nucleus  can  be  seen  ;  and  it  seems  probable  that  a  nucleus  is 
present  in  them  all.  Most  of  the  segments  are  filled  with  highly  refracting  spherules,  but  these  are  more 
numerous  in  some  cells  (especially  the  larger  cells  near  the  yelk)  than  in  others.  In  the  central  part  of 
the  blastoderm  the  upper  cells  have  commenced  to  form  a  distinct  layer.  No  segmentation-cavity  is  present. 

A,  large  peripheral  cell ;  B,  larger  cells  of  the  lower  parts  of  the  blastoderm ;  C,  middle  line  of  blasto- 
derm; E,  edge  of  the  blastoderm  adjoining  the  white  yelk;  W,  white  yelk. 

As  a  result  of  incubation  a  third  layer  of  cells  makes  its  appearance 
between  the  two  layers  of  the  blastoderm  just  described,  forming  an 
upper,  a  middle,  and  a  lower  Ia3*er,  or  the  epiblast,  the  mesoblast,  and  the 


24  PHYSIOLOGY   OF   THE    DOMESTIC   ANIMALS. 

hypoblast  (Fig.  14).     From  these  three  layers  of  cells  the  embryo  is 
developed. 

Leaving  at  this  point  the  changes  which  occur  in  the  egg  of  the  bird, 
we  have  now  to  follow  the  analogous  changes  in  the  mammalian  ovum. 

We  have  already  seen  that  in  the  mammalian  ovum  one  of  the  first 
evidences  of  impregnation  is  the  division  of  the  protoplasm  of  the  ovum 
progressively  into  smaller  and  smaller  segmentation  spheres,  until  the 
cell-membrane  becomes  filled  with  an  immense  number  of  minute  masses 
of  protoplasm.  The  general  character  of  this  process  in  its  earlier  stages 
is  probably  identical  in  all  the  mammalia.  The  ovum  of  the  rabbit  has 
been  most  studied,  and  the  sketch  here  given  is  based  mainly  on  Balfour's 
summary  of  the  early  stages  of  development  in  the  rabbit's  ovum. 

The  ovum  first  divides  into  two  nearly  equal  spheres,  of  which  one 


BD 


BD,  BD.  MC. 


FIG.  14.— SECTION  OF  A  BLASTODERM  OF  CHICK,  AT  RIGHT  ANGLES  TO  THE 
LONG  Axis  OF  THE  EMBRYO,  AFTER  EIGHT  HOURS'  INCUBATION,  ABOUT 
MIDWAY  BETWEEN  FRONT  AND  HIND  ENDS.  (Foster  and  Balfvur.) 

A,  epiblast;  B,  mesoblast;  C,  hypoblast:  PR,  primitive  groove;  F,  fold  in  the  blastoderm  produced 
accidentally  ;  MC.  mesoblast-cell,— the  line  points  to  one  of  the  peripheral  mesoblast-cells  lying  between 
epiblast  and  hypoblast;  BD,  formative  cells. 

The  section  shows:  (1)  the  thickening  of  the  mesoblast  under  the  primitive  groove,  PR,  even  when  it 
is  hardly  present  at  the  sides  of  the  groove :  (2)  the  hypoblast,  C,  early  formed  as  a  single  layer  of  spindle- 
shaped  cells ;  (3)  the  so-called  segmentation  cavity,  in  which  coagulated  albumen  is  present.  On  the 
floor  of  this  are  the  large  formative  cells,  BD. 

is  slightly  larger  and  more  transparent  than  the  other.  The  larger  sphere 
and  its  products  will  be  spoken  of  as  the  epiblastic  spheres ;  the  smaller 
one  and  its  products  as  the  hypoblastic  spheres.  Both  these  original 
spheres  soon  divide  into  two,  and  each  of  these  into  two  more,  thus 
making  eight.  At  first  these  spheres  are  spherical,  and  arranged  in  two 
layers  formed  of  four  epiblastic  and  four  hypoblastic  spheres.  Soonr 
however,  one  of  the  hypoblastic  spheres  passes  into  the  centre,  and  the 
whole  ovum  becomes  spherical  again. 

In  the  next  stage  each  of  the  four  epiblastic  spheres  divides  into 
two,  followed  b}r  the  division  of  the  hypoblastic  spheres  into  two.  The 
ovum  is  then  made  up  of  sixteen  different  spheres,  nearly  of  the  same 
size.  Of  the  eight  hypoblastic  spheres  four  soon  pass  to  the  centre, and  are 
surrounded  by  the  eight  epiblastic  spheres,  arranged  in  the  form  of  a  cup. 
Division  of  both  sets  of  spheres  now  continues,  the  epiblastic  layer  con- 


ORIGIN   OF   CELLS.  25 

tinning  to  surround  the  central  kypoblastic  spheres,  both  sets  continuing 
to  subdivide,  until  finally  the  ovum  consists  of  an  almost  solid  mass  of 
hypoblastic  spheres  surrounded  by  a  layer  of  epiblastic  cells. 

When  the  process  of  segmentation  is  complete  the  epiblastic  cells 
are  clear  and  have  an  irregularly  cubical  form,  while  the  hypoblastic 
cells  are  polygonal  and  granular  and  somewhat  larger  than  the  epi- 
blastic cells. 

The  blastodermic  vesicle  next  forms.  This  results  from  the  forma- 
tion of  a  narrow  cavity  between  the  epiblast  and  h}Tpoblast,  which 
increases  in  size  until  it  entirely  separates  these  two  layers,  except  at  the 
point  where  the  blastoderm  was  last  in  forming  (the  blastopore).  As 
the  cavity  increases  in  size  the  ovum  also  enlarges,  so  that  soon  it  exists 
in  the  form  of  a  large  vesicle,  formed  of  a  thin  wall  of  a  single  layer  of 


EP 


FIG.  15.— OPTICAL,  SECTIONS  OP  A  RABBIT'S  OVUM  AT  Two  STAGES  CLOSELY 
FOLLOWING  UPON  THE  SEGMENTATION,  AFTER  E.  VAN  BENEDEN. 
(Half our.') 


EP,  epiblast;  HY,  primary  hypoblast ;  BP,  Van  Beneden's  blastopore.    The  shading  of  the  epiblast 
and  hypoblast  is  diagrammatic. 


cells, — the  epiblastic  cells,— with  a  large  cavity,  the  hypoblastic  cells 
forming  a  small,  ventricular  mass  attached  to  the  inner  side  of  the  epi- 
blastic cells  (Fig.  16).  The  ovum  of  the  rabbit  has  now  increased  in 
size  from  0.09  mm.,  its  size  at  the  close  of  segmentation,  to  about  0.28 
mm.  It  is  inclosed  by  the  vitelline  membrane  and  a  mucous  layer 
deposited  by  the  walls  of  the  Fallopian  tube. 

As  the  vesicle  continues  to  enlarge,  the  hypoblastic  cells  spread  out 
beneath  the  epiblast,  though  remaining  thicker  in  the  centre  than  at  the 
edges,  where  the  cells  still  possess  the  power  of  amoeboid  movement. 
The  central,  thicker  portion,  which  is  the  commencement  of  the  embryonic 
area,  forms  an  opaque,  circular  spot  on  the  blastoderm. 

The  primitive  hypoblast  now  becomes  divided  into  two  layers,  the 
lower  continuous  with  the  peripheral  hypoblast  and  formed  of  flattened 
cells,  while  the  upper  is  formed  of  small,  rounded  elements, — the  meso- 


26 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


blast.  The  superficial  epiblast,  again,  is  formed  of  flattened  cells,  which 
soon  become  columnar  and  appear  to  unite  with  the  rounded  elements 
below,  except  at  the  lower  part  of  the  embryonic  area.  Here  the  blasto- 


FIG.  16.— RABBIT'S  OVUM    BETWEEN   SEVENTY  TO  NINETY  HOURS  AFTER 
IMPREGNATION,  AFTER  E. .VAN  BENEDEN.    (Sal/our.) 

BV,  cavity  of  blastodermic  vesicle  (yelk-sac) ;  EP,  epiblast ;  H Y,  hypoblast ;  ZP,  mucous  envelope 
(Zona  pellucida). 

derm,  as  in  the  chick,  is  constituted  by  three  layers, — the  epiblast,  the 
mesoblast,  and  the  hypoblast. 


P.R, 


EP. 


M 


HY. 

FIG.  17.— SECTION  THROUGH  THE  OVAL  BLASTODERM  OF  A  RABBIT  IN  THE 
SEVENTH  DAY,  THROUGH  THE  FRONT  PART  OF  THE  PRIMITIVE  STREAK. 
(Balfour.) 

EP,  epiblast;  M,  mesoblast;  HY,  hypoblast;  PR,  primitive  streak. 

The  subsequent  changes  in  the  development  of  the  blastoderm  form 
the  subject  of  Embryology,  and  for  their  consideration  the  reader  is 
referred  to  text-books  on  anatomy. 

III.      THE   MODIFICATION   IN   THE   FOKM   OF   CELLS. 

We  have  seen  that  originally  all  the  cells  formed  by  cleavage  in  the 
egg  are  absolutely  alike.  Like  the  original  egg,  they  are  typical  cells, 
consisting  of  a  cell-membrane  inclosing  finely  granular  protoplasm,  in 
which  a  nucleus  and  nucleolus  may  be  recognized.  They  only  differ  from 


MODIFICATION   IN   THE   FOKM   OF   CELLS. 


27 


the  original  cell  in  size  and  in  as 
vet  unmarked  individual  char- 
acteristics which  in  the  speciali- 
zation of  function  of  the  organ- 
ism will  cause  them  finally,  for 
the:  most  part,  to  lose  all  mor- 
phological resemblance  to  the 
parent  cell. 

These  differences  in  cells 
produced  in  the  development  of 
the  organism  are  very  numer- 
ous. 

First,  as  regards  their  size, 
we  find  cells  varying  from  the  red 
blood-cell  -g-g1^  to  the  large 
ganglion-cell,  ^<y  of  an  inch 
(Figs.  18  and  19). 

In  nearly  all  instances  where 
a  collection  of  cells  develop  into 
an  organ  or  tissue  the  original 
spherical  form  is  lost,  often 
merely  from  mutual  pressure  and 
from  alteration  in  the  cell-con- 
tents, by  which  the  most  varied 
forms  are  produced.  Thus, 
instead  of  the  spherical  form, 
cells  may  take  on  an  oval,  elon- 
gated shape  (Fig.  20),  or  may  be 
cylindrical  (Fig.  21),  or  again 
from  mutual  pressure  may  form 
regular  hexagons.  Others  may 
have  long,  thread-like  attach- 
ments developed,  as  in  the  sperm- 
cells  (Fig.  22),  or  even  a  number 
of  such  prolongations,  which  as 
long  as  the  cell  is  alive  continue 
in  active  movement  (ciliated 
cells).  (See  Fig. '21.) 

Often  the  nucleus  deviates 
from  its  spherical  form,  and  may 
become  oval  or,  irregular  in  out- 
line,, or,  as  in  certain  cells  of 
the  marrow  of  bone  and  in 


FIG.  18.— RED  AND  WHITE  BLOOD-CORPUSCLES, 
ENLARGED    Six    HUNDRED    DIAMETERS. 

(Ellenberger.) 

A,  surface  view  of  red  corpuscles ;  B,  profile  view ;  C,  rou- 
leaux of  red  corpuscles  ;  D,  central  depression  in  red  corpuscles  : 
E,  crenated  red  corpuscles ;  F,  small,  and  G,  large  white  cor- 
puscles. 


FIG.  19.  — AN  ISOLATED  GANGLION-CELL  OF 
THE  ANTERIOR  HORN  OF  THE  HUMAN 
SPINAL  CORD,  AFTER  GERLACH.  (Klein.) 

A,  axis-cylinder ;  B,  pigment.  The  branched  processes  of 
the  ganglion-cell  break  up  into  the  fine  nerve  net-work  shown 
in  the  upper  part  of  the  figure. 


28 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


FIG.  20.— NON-STRIATED  MUSCULAR  FIBRES,  ISOLATED.    (Klein.) 

The  cross-markings  indicate  corrugations  of  the  elastic  sheath  of  the  individual  fibres. 


FIG.  21.— VARIOUS  KINDS  OF  EPITHELIAL  CELLS.    (Klein.) 

A,  columnar  cells  of  intestine ;  B,  polyhedral  cells  of  the  conjunctiva :  C,  ciliated  conical  cells  of  the 
trachea :  D,  ciliated  cell  of  frog's  mouth ;  E,  inverted  conical  cell  of  trachea ;  F,  squamous  cell  of 
the  cavity  of  the  mouth,  seen  from  its  broad  surface ;  G,  squamous  cell,  seen  edgeways. 


FIG.  22.— VARIOUS  KINDS  OF  SPERMATOZOA.    (Klein.) 

A,  spermatozoon  of  guinea-pig  not  yet  matured ;  B,  the  same  seen  sideways,  the  head  being  flattened 
from  side  to  side ;  C,  a  spermatozoon  of  the  horse ;  D,  a  spermatozoon  of  the  newt. 


MODIFICATION   IN   THE   FORM   OF    CELLS. 


29 


striped   muscle,   may   undergo    reduplication    without   division    of  the 
cell  (Fig.  23). 

The  cell-contents,  or  protoplasm,  particularly  as  regards  its  granular 
constituents,  may  undergo  the  greatest  variation.     Often  true  crystalline 


FIG.  23.— BONE-CORPUSCLES,  WITH   THEIR  PROLONGATIONS,   AFTER  ROLLETT. 

(Flint.) 

formations  are  included  in  the  cell-contents ;  or  vacuoles  may  form  in 
which  different  fluids,  sometimes  watery,  sometimes  fatty,  may  collect,  to 
again  disappear  in  later  stages  of  the  life  of  the  cell. 


FIG.  24.— DIAGRAM  OF  DIFFERENT  FORMS  OF  CARTILAGE.    (Ellenberger.) 

A,  hyaline ;  B,  fibro-cartilage ;  C,  elastic  cartilage ;  D,  secondary  cartilaginous  capsule,  containing 
the  primary  capsule. 

Another  modification  in  the  form  of  cells  consists  in  the  alteration 
of  the  border  laj-ers  of  protoplasm,  so  that  the  cell  is  surrounded  by  a 
more  or  less  chemically  or  morphologically  different  area,  or  intercellular 


30 


PHYSIOLOGY   OF   THE    DOMESTIC   ANIMALS. 


substance,  which  may  present  the  greatest  variety  as  to  quantity.  The 
cell-membrane  and  so-called  cell-capsule  belong  to  these  forms  of  proto- 
plasmic modification.  In  cartilage  and  loose  connective  tissue  this 
intercellular  substance  exists  in  such  amount  that  the  still  actively 
moving  protoplasmic  cells  appear  to  be  forced  apart  by  it.  (See  Fig.  24.) 
Since  the  more  active  vital  movements  can  only  originate  in  the 
semi-fluid  protoplasm  of  cells,  it  is  evident  that  the  more  or  less  rigid 
intercellular  substance  could  only  take  a  slight  part  in  organic  processes 
if  there  were  not  some  means  by  which  it  could  be  brought  into  close 


FIG.  25.— NERVE-FIBRES.    (Thanhoffcr.) 

1,  a,  tnedullated  nerve-fibre:  b.  non-medullated  nerve-fibre  from  the  sympathetic  of  the  ox  (after 
Schultze) ;  2,  non-medullated  nerve-fibre  from  Jacobson's  organ  in  the  sheep  (after  Schnltze) ;  3,  nerve- 
fibres  with  Ranvier's  nodes  (R),  from  the  sciatic  of  the  frog:  4,  funnel-shaped  arrangement  of  medulla 
from  sciatic  of  frog,  treated  with  osmic  acid ;  5,  nerve-fibre  from  frog,  with  axis-cylinder  (t)  and  so-called 
horny  mesh-work;  6,  diagram  of  medullated  nerve-fibre:  n,  neurilemma;  v,  medullary  sheath :  t,  axis- 
cylinder. 

association  with  the  active  vital  processes  constantly  occurring  in  the 
interior  of  cells.  Consequent!}'  we  find  the  entire  intercellular  substance 
pierced  of  a  mesh-work  of  fine  canals,  through  which  the  cells  send 
prolongations  of  their  outer  layer,  which,  after  numerous  subdivisions, 
serve  to  connect  neighboring  cells. 

By  means  of  these  juice-canals  interchange  between  the  contents  of 
the  various  cells  is  possible  and  the  intercellular  substance  receives  its 
necessary  supply  of  nourishment,  while  the  connection  of  cell  with  cell 
is  an  illustration  of  the  loss  of  individuality  of  cell-life.  Often  we  find 


DEVELOPMENT   OF   TISSUES   AND    OKGANS.  31 

cells  connected  by  branching  prolongations :  in  other  cases  the  exten- 
sions of  the  cells — which,  to  be  sure,  have  a  very  different  function  and 
structure  from  those  alreacty  alluded  to,  but  which,  nevertheless,  serve  as 
connections  between  cells — so  overbalance  the  cells  in  extent  and  number 
that  the  latter  often  appear  only  as  rounded  swellings  in  the  extensions 
(e.g.,  in  the  nerves).  (See  Figs.  25  and  26.) 


FIQ.  26.— NERVOUS   GANGLIONIC   CEL.L    AND  BRANCHING    FIBRES,   AFTER 
KRAUSE.     (Thanhoffer.) 

xt,  cell  body;  m,  nucleus;  me,  nucleolus;    pn,  protoplasmic  prolongations;    tf,  axis-cylinder  fibres; 
tn,  axis-cylinder  prolongations. 


IV.      THE   DEVELOPMENT   OF   TISSUES   AND   ORGANS. 

The  final  result  of  the  metamorphosis  of  cells  is  the  formation  of 
tissues  out  of  which  the  various  organs  of  the  body  are  built  up. 


32  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

The  development  of  tissue  starts  in  the  earliest  stages  of  develop- 
ment of  the  egg. 

We  have  seen  already  that,  as  a  result  of  fecundation,  the  egg  divides 
into  a  number  of  minute  segmentation  spheres  which  at  first  form  a 
solid,  mulberry -like  mass,  and  we  have  now  to  consider  the  changes 
occurring  in  the  mass  of  simple,  undifferentiated  cells  which  result  in  the 
development  of  the  tissues  and  organs  of  the  completed  organism. 

In  their  early  stages,  as  in  the  amoeba,  each  of  these  cells  possesses 
the  powers  of  development,  reproduction,  growth,  assimilation,  respira- 
tion, and  contractility.  As  the  organism  passes  to  a  higher  stage  we 
find  that  many  of  these  cells  lose  these  general  properties  possessed  in 
their  entirety  by  undifferentiated  protoplasm,  while  certain  of  them  are 
put  aside  to  carry  on  specific  individual  functions.  Thus,  in  the  young 
embryo,  as  in  the  amoeba,  all  the  cells  possess  the  power  of  contractilit}' ; 
as  the  organism  develops,  this  property  becomes  restricted  to  cells  form- 
ing constituents  of  certain  tissues,  the  contractile  tissues,  or  the  muscular 
system.  The  amoeba,  which  we  have  already  seen  maj^  be  regarded  as 
representing  one  of  the  units  of  which  the  higher  organisms  are  built  up, 
possesses  the  power  of  irritability  and  automatism.  In  higher  forms 
this  property  of  undifferentiated  protoplasm  is  restricted  to  a  single 
tissue,  the  nervous  system.  The  amoeba  has  no  part  specialized  for  the 
various  processes  of  nutrition;  any  part  of  its  substance  may  take  in 
nutritive  matter,  may  digest  out  the  portions  capable  of  supplying  its 
nutritive  needs,  may  remove  the  undigestible  residue :  any  portion  of 
the  amoeba  is  capable  of  carrying  on  the  metabolic  processes  by  which 
the  matter  absorbed  as  food  is  converted  into  protoplasm  like  itself,  and 
any  portion  is  capable  of  absorbing  the  gases  necessary  for  these  com- 
plex chemical  processes  and  of  getting  rid  of  the  effete  products  of  its 
nutritive  processes.  In  the  higher  organisms  certain  cells  are  set  aside 
to  form  the  organs  concerned  in  the  prehension  of  food  ;  others  have  for 
their  sole  function  the  secretion  of  solvent  juices  which  will  digest  out 
the  nutritive  matters  of  the  food ;  others  are  the  carriers  of  the  matters 
absorbed  to  remote  corners  of  the  organisms ;  and  the  sole  business  of 
certain  other  cells  is  to  get  rid  of  the  useless  matter  and  the  products 
of  the  waste  of  the  economy.  In  the  amoeba  any  portion  may  divide  off 
from  the  parent  stock  and  so  originate  a  new  individual;  in  the  higher 
animals  certain  tissues  or  collections  of  cells  have  for  their  sole  office 
the  reproduction  of  cells  which  shall  constitute  the  starting  point  of  a 
new  organism.  In  the  amoeba,  therefore,  specialization  of  function  has 
not  commenced ;  each  minute  particle  of  the  protoplasm  which  constitutes 
it  is  capable  of  carrying  on  all  the  vital  functions.  In  the  higher  organ- 
isms, however,  the  elementary  organisms  of  which  they  are  built  up  are 
so  arranged  that  there  may  be  a  division  of  labor.  These  collections  of 


DEVELOPMENT   OF   TISSUES   AND   OEGANS.  33 

cells,  marked  by  a  more  or  less  exclusiveness  of  function,  are  termed 
tissues.  It  must  not  be  overlooked,  however,  that,  though  certain  func- 
tions are  accentuated  in  individual  tissues,  they  all  possess  remnants  of 
all  the  functions  originally  seen  in  undifferentiated  protoplasm.  Thus, 
maii}^  besides  the  muscular  tissues  possess  the  power  of  contractility : 
it  is  not  the  nervous  system  alone  which  retains  the  property  of 
responding  to  irritants.  All  the  tissues  are  capable  of  reproducing  them- 
selves in  part,  and  all  possess  the  power  of  carrying  on  their  own 
nutritive  processes  if  suitable  food  is  supplied  to  them. 

We  have  seen  that  fecundation  of  the  ovum  leads  to  the  develop- 
ment of  an  immense  number  of  new  cells,  and  we  have  referred  to  the 
modifications  in  form  to  which  these  segmentative  spheres  may  be 
subjected. 

Tissues  are  formed  from  these  segmentative  spheres  in  three  different 
ways  (Wundt) : — 

1.  Through  formation  of  layers  of  cells. 

2.  Through  union  of  cells. 

3.  Through  excretions  by  cells. 

Often  all  of  these  methods  are  united  in  the  formation  of  a  compound 
tissue  which  is  functionally  active  as  a  unit.  Such  a  tissue  is  called  an 
organ.  The  classification  of  tissues  is  based  on  anatomical  grounds;  of 
organs,  on  ph}'siological  grounds. 

1.  To  the  first  group  belong  the  epitheliums.  In  most  of  these  the 
only  modifications  which  occur  in  the  form  of  the  cells  are  due  to 
mutual  pressure  from  close  contact.  Such  cells  are  therefore  polygonal 
or  flattened,  or,  when  growth  is  most  marked  in  one  axis,  cylindrical. 
The  epitheliums,  in  series  of  layers  or  in  single  rows,  cover  the  external 
surfaces  of  the  body  as  well  as  the  coatings  of  the  digestive,  urinary, 
genital  and  respiratory  tracts  which  communicate  with  it,  the  ducts  of 
glands,  and  the  closed  serous  sacs.  In  the  latter  localitj^  they  are  called 
endothelia,  in  the  former  epithelia.  The  hair  and  nails  are  modifications 
of  these  tissues  formed  of  small  elongated  cells  grown  together  into 
almost  homogeneous  tissues.  The  terminal  portions  of  the  organs  of 
special  sense  are  also  epithelial  in  nature. 

Epithelial  cells  are  connected  by  a  thin  layer  of  an  albuminous 
cement  substance,  which  during  life  is  in  a  semi-fluid  condition. 
The  shape  of  the  cell  may  be  columnar  or  squamous.  Spindle-shaped  and 
club-shaped  cells,  as  well  as  goblet  cells,  ciliated  cells,  epidermic  cells, 
and  prickle  cells,  are  all  modifications  of  these  shapes.  Endothelial  cells 
are  always  of  the  squamous  variety,  arranged  in  single  layers  of  flattened, 
transparent  cells  with  oval  nuclei.  When  their  form  approaches  the 
columnar,  as  occasionally  is  the  case  in  certain  serous  membranes,  they 
are  then  in  an  active  state  of  division,  are  called  germinating  cells,  and 

3 


34  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

the  small  spherical  lymphoid  cells  which  result  are  carried  to  the  circu- 
lation to  become  white  blood-corpuscles. 

Glandular  tissue  is  also  epithelial  in  nature.  Cells  are  the  essential 
secreting  organs  of  glands,  though  numerous  other  tissues  enter  into 
their  composition.  Such  cells  are  usually  rounded  or  polygonal,  and  are 
soft  in  consistence.  Frequently  the  cells  rapidly  partially  break  down 
and  are  carried  off  as  constituents  of  the  secretion,  as  colostrum  cells, 
or  mucoid  corpuscles  (moulting);  or  the  destruction  of  the  cell  form  may 
be  complete  and  the  constituents  of  the  cell  enter  the  secretion  in  the 
form  of  a  solution. 

Muscular  tissue  forms  the  third  of  the  group.  In  the  muscles  the 
muscular  cells  are  always  closely  associated  with  connective  tissue. 
Such  cells  may  be  of  two  different  kinds,  different  in  structure  and  in 
function, — the  striped  and  unstriped  cells.  Muscle-cells  are  contractile, 
like  amoeboid  cells,  but  contractility  is  only  possible  in  one  definite  direc- 
tion, that  of  their  long  axis ;  muscles,  therefore,  become  shorter  and 
thicker  during  contraction. 

2.  To  the  second  group  of  tissues  formed  by  union  of  cells  belong 
two  tissues  in  which,  in  their  development,  the  cells  have  become  greatly 
elongated,  and  after  absorption  of  the  cell-wall  become  converted  into 
fibres  or  tubes ;  these  are  the  nerves  and  capillaries. 

In  the  nervous  tissues  certain  cells  retain  their  primitive  character, 
the  nerve-cells,  and  only  nerve-fibres  properly  belong  to  this  group  of 
tissues.  Nevertheless  the  nerve-cells  are  in  continuity  with  the  nerve- 
fibres. 

The  capillaries  in  a  similar  manner  originate  from  the  arrangement 
of  nucleated,  spindle-shaped  cells  in  rows,  which  become  hollowed  out 
through  the  formation  of  vaeuoles.  The  formative  cells  manifest  a  ten-' 
dency  to  send  out  sprouts  which  connect  with  other  forming  or  mature 
capillaries  by  which  the  net-work  of  capillaries  is  formed.  Lymphatic 
capillaries  are  developed  in  the  same  way  as  the  blood-vessels. 

3.  Tissues  formed  by  excretions  from  cells,  forming  the  third  group, 
may  also  be  called  intercellular  tissues.     Connective  tissue  is  a  type  of 
this  class.     Connective  tissues  serve  to  bind  together  all  the  organs  of 
the  body  ;  they  exist  in  various  forms,  which  are  to  a  certain  extent 
mutual!}'  convertible ;  they  all  yield  allied  chemical  products. 

Connective  tissue  originates  in  spherical  cells,  with  very  soft  proto- 
plasmic nucleated  contents,  which  ultimately  may  form  a  perfectly  homo- 
geneous, laminated,  or  fibrous  intercellular  substance. 

The  cells  themselves  may  exist  in  various  different  forms,  either  as 
tendon-cells,  when  they  are  flattened,  oblong  masses  of  protoplasm 
arranged  in  rows,  with  round  nuclei  lying  in  bundles  of  fibrils  of  white 
connective  tissue ;  as  branched  cells,  found  in  the  cornea,  serous  mem- 


DEVELOPMENT  OF  TISSUES  AND   ORGANS.  35 

branes,  and  subcutaneous  tissues,  which,  under  certain  conditions,  pre- 
serve their  power  of  movement ;  as  pigment-cells,  which  are  branched 
cells  filled,  with  the  exception  of  their  nucleus,  with  granules  •  as  fat- 
cells,  in  which  the  protoplasmic  cell-contents  are  replaced  by  a  drop  of 
oil,  which  forces  the  flattened  nucleus  against  the  cell-membrane;  and  as 
migratory  cells,  which  are  formed  in  the  spaces  of  fibrous  tissue,  and 
which  possess  the  power  of  amoeboid  movement. 

The  form  of  connective  tissue  in  which  least  change  is  produced  in 
development  is  the  so-called  mucoid  or  gelatinous  tissue.  In  some 
of  the  invertebrates,  as  in  mollusks,  this  tissue  forms  the  greater  part  of 
the  bod}\  It  consists  of  a  soft,  semi-fluid,  intercellular  substance,  in  which 
numerous  granules  and  broken  down  membraneless  cells  are  suspended. 
Many  of  these  cells  possess  the  power  of  amoeboid  movement. 

From  this  tissue  in  vertebrates  the  fibrillar  connective  tissue  is  de- 
veloped by  the  condensation  of  this  intercellular  substance  into  bundles 
of  fibres,  held  together  by  an  albuminous  cement  substance,  in  which 
the  forms  of  the  cells  become  much  changed,  becoming  flattened  and 
elongated  by  mutual  pressure  until  the  diameter  of  the  cell  is  not  greater 
than  that  of  the  nucleus. 

The  elastic  tissues  are  formed  out  of  the  fibrillar  connective  tissues, 
which  become  so  modified  chemically  as  to  yield  elastin  and  not  gelatin. 
The  fibres  of  elastic  tissue  are  bright  j'ellow  in  color,  usually  anastomose, 
and  are  sometimes  straight,  but  more  often  coiled  up  in  bundles. 

The  different  "forms  of  development  of  connective  tissue,  especially 
of  the  intercellular  substance,  depend  upon  its  different  chemical  meta- 
morphoses. Thus,  the  gelatinous  tissues  owe  their  properties  to  a  semi- 
fluid albuminous  booty,  the  connective  tissue  proper  to  gelatin-forming 
bodies,  cartilage  or  chondrin,  and  the  elastic  tissues  to  elastin,  etc. 

Bone  is  characterized  by  the  deposit  of  inorganic  compounds  in  its 
intercellular  substance.  This  hardened  tissue  then  incloses  the  partially 
broken  down  cells,  which  form  the  lacunae  or  bone-corpuscles,  in  which 
the  thickened  membrane  and  nucleus  are  often  visible,  though  they  dis- 
appear in  old  bones  and  their  place  is  then  taken  \)y  serous  fluids,  etc. 

The  bones  are  also  rich  in  vessels  which  traverse  the  Haversian 
canals. 

As  the  deposit  of  salts  occurs  partly  from  these  and  partly  from 
the  external  membrane,  the  bones  become  laminated  in  structure,  some 
layers  being  parallel- with  the  canals,  others  with  the  exterior. 

Cartilage  is  characterized  by  a  sparse  intercellular  substance  which 
yields  chondrin,  and  by  large  cells  which  are  often  the  seat  of  endoge- 
nous multiplication.  As  in  bone,  so  in  cartilage,  the  intercellular  sub- 
stance becomes  arranged  in  the  form  of  capsules  around  the  cells,  and 
may  either  remain  homogeneous  (hyaline)  or  become  fibrillar  (fibrp- 


36  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

cartilage  or  elastic  cartilage,  in  which  a  dense  net-work  of  elastic  fibres 
occupies  the  intercellular  matrix).  Most  cartilages,  except  on  articulating 
surfaces,  are  covered  by  a  fibrous  membrane,  the  perichondrium,  supplied 
with  blood-vessels,  lymphatics,  and  nerves. 

Bone  is  surrounded  by  a  fibrous  membrane,  the  periosteum,  with  an 
inner  layer  of  oblong  nucleated  cells,  which,  from  the  fact  that  the  bone 
is  developed  from  them,  are  termed  osteoblasts.  Similar  cells  are  also 
found  in  the  marrow  of  bones. 

The  organs  of  the  animal  body  are  always  composed  of  several 
tissues;  they  may  be  of  three  classes,  in  each  one  of  which  some  one 
tissue  is  especially  prominent  in  function  : — 

1.  Organs  whose  chief  function  depends  upon  tissues  of  the  first 
class  (cells  without  intercellular  substance). 

a.  Glands,  which  always  in  addition  to  the  epithelium  contain  nerves 
and  blood-vessels.  The  epithelium  is  the  essential  part  of  glands,  skin, 
mucous  and  serous  membranes. 

/;.  Muscles.  In  these  are  found  muscle-cells  as  the  functionally 
prominent  tissues,  though  associated  with  them  are  connective  tissue, 
blood-vessels,  and  nerves. 

2.  Organs  whose  chief  function  is  manifested  through  tissues  of  the 
second  class. 

a.  Compound  vessels,  arteries,  veins,  and  rvmph-vess-els.     Although 
the  capillaries  are  formed  by  union  of  cells,  in  larger  trunks  this  mode 
of  formation  only  applies  to  the  endothelium,  on  which  the  other  tissues 
— elastic  tissue,  connective  tissue,  and  pale  muscular  fibres — subsequently 
develop  in  layers. 

b.  The  organs  of  the  nervous  system.     Nerve-cells  and  nerve-fibres, 
formed  by  union  end  to  end  of  cells,  here  form  the  essential  tissues, 
though  blood-vessels  and  connective  tissue  are  associated  with  them. 

3.  Organs  whose  function  is  due  to  intercellular  substance.  The  bony 
skeleton  is  the  only  representative  of  this  group,  and  the  modification 
of  connective  tissue  known  as  bone,  or  its  antecedent  cartilage,  is  the 
characteristic  tissue;  as  secondary  tissues,  connective  tissue  and  blood- 
vessels and  nerves,  representatives  of  the  second  class,  are  also  met  with. 

For  the  mode  of  development  of  the  compound  organs  in  the 
embryo  the  reader  must  be  referred  to  text-books  on  anatomy  or 
embryology. 


SECTION   II. 
CELLULAR  PHYSICS. 

I.      THE  PHYSICAL  PEOCESSES  IN   CELLS. 

As  the  tissues  and  organs  of  the  animal  body  originate  in  ceils,  we 
should  expect  that  the  functions  of  the  higher  organisms,  which  we  know 
to  be  identical  with  those  of  the  most  elementary  forms  of  life,  would  to 
a  certain  extent  be  accomplished  by  the  same  general  processes.  We 
have  already  divided  the  functions  of  animal  life  into  the  vegetative,  or 
nutritive,  functions  and  the  functions  of  relation,  and  have  called  atten- 
tion to  the  attempt  which  has  been  made  to  reduce  the  working  of  these 
processes  to  physical  and  chemical  laws.  Although  in  many  points  this 
endeavor  fails,  the  operation  of  the  ordinary  physical  and  chemical  laws 
serves  to  explain  many  of  the  complex  phenomena  of  animal  life.  This 
is  especially  seen  in  the  maintenance  of  the  nutrition  of  the  organism. 

That  cells  may  retain  a  nutritive  balance  it  is  requisite,  in  the  first 
place,  that  they  be  .supplied  with  a  proper  pabulum,  which  must  pass 
from  the  exterior  to  the  interior  of  the  cells.  We  have  found  that  the 
typical  cell  is  surrounded  by  a  homogeneous  or  striated  membrane, 
which,  like  all  other  organic  tissues,  contains  a  large  amount  of  water 
closely  associated  with  the  ultimate  molecules  of  which  that  membrane 
is  made  up.  Hence,  the  cell-membrane  may  be  regarded  as  a  porous 
partition  whose  pores  are  filled  with  water,  and  which  separates  the 
cell-contents  from  the  surrounding  media.  These  media  may  be  either 
gaseous,  as  the  atmosphere ;  fluid,  like  the  lymph  and  blood  in  higher 
animal  forms,  or  water  in  aquatic  forms  of  life;  or  semi-fluid,  like  the 
more  or  less  solid  intercellular  substance. 

This  passage  of  nutriment  from  the  exterior  to  the  interior  of  cells 
is  mainly  accomplished  b}^  purely  physical  means,  not  only  in  simple 
unicellular  organisms  but  also  in  higher  forms  of  life,  where  digestion, 
or  the  preparation  of  food  for  absorption,  has  for  its  object  the  reduc- 
tion of  food  into  such  forms  that  the  operation  of  the  physical  laws  of 
imbibition,  capillarity,  filtration,  diffusion,  and  osmosis,  aided  perhaps 
by  chemical  affinity,  will  be  sufficient  to  enable  the  nutritive  matters  to 
pass  to  the  interior  of  cells. 

When  once  in  the  interior  of  the  cells  the  raw  food-products  must 
be  transformed  into  protoplasm  similar  to  that  of  which  the  cell-contents 

(37) 


38  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

is  composed.  This  is  a  purely  chemical  process,  is  accompanied  by  the 
liberation  of  force,  and  requires  for  its  performance  the  free  access  of 
oxygen.  Gases,  also,  must  therefore  pass  from  the  exterior  to  the 
interior, — a  process  which  the  laws  of  absorption  and  diffusion  of  gases 
are  quite  sufficient  to  explain.  Again,  the  chemical  processes  concerned 
in  the  assimilation  of  food  result  in  the  formation  of  carbon  dioxide, 
urea,  kreatin,  and  other  crystalline  bodies  which  are  no  longer  of  use 
and  which  must  be  removed ;  or  the  cell  activity  may  take  on  the  form 
of  a  secretion, — that  is,  the  cell-protoplasm  ma}7,  from  the  matter  sup- 
plied to  it,  manufacture  certain  substances  which  in  the  higher  organisms 
have  to  be  used  elsewhere.  In  either  case  the  products  of  the  proto- 
plasmic operations  must  be  removed.  Here,  also,  physical  laws  are  all 
sufficient.  Gases  are  removed  under  the  laws  of  gaseous  diffusion  and 
absorption.  All  ciystallized  products  are  eliminated  by  equally 
simple  means.  The  absorption  of  fluid  by  the  cell-contents  through  imbi- 
bition leads  to  increase  of  volume,  and  hence  to  increased  pressure  on  the 
cell-membrane.  Filtration  thus  comes  into  operation.  Or,  if  the  pres- 
sures within  and  without  the  cell  are  equal,  interchange  of  matters  in 
solution  may  take  place  through  diffusion  and  osmosis.  All  these  proc- 
esses may  occur  equally  well  in  membraneless  cells ;  for,  in  all  cases,  to 
permit  interchange  the  dividing  membrane  must  be  capable  of  absorbing 
the  fluids  or  solutions  with  which  it  is  in  contact.  The  conditions,  then, 
are  analogous  to  those  of  a  body  containing  fluid  by  imbibition  in  con- 
tact with  another  fluid. 

We  have  now  to  consider  some  of  the  physical  processes  concerned 
in  these  operations.  The  chemical  processes  will  subsequently  receive 
attention. 

The  explanation  of  the  physical  processes  in  cells  is  to  be  found  in 
the  molecular  forces  which  fluid  molecules  exert  on  each  other  and  on 
solids  with  which  they  may  be  in  contact. 

1.  COHESION  is  the  force  which  binds  together  adjacent  molecules  of 
the  same  nature ;  for  example,  two  molecules  of  water  or  two  molecules 
of  iron.  This  attractive  force  is  strongly  exerted  in  solids,  less  so  in 
liquid,  and  is  absent  in  gases.  It  is  measured  by  the  force  which  is 
required  to  tear  a  body  asunder.  The  closer  the  molecules  of  a  body 
are  together,  the  greater  their  cohesive  force. 

Cohesion  varies  inversely  with  the  square  of  the  distance  which 
separates  the  molecules  ;  anything,  therefore,  which  drives  the  molecules 
apart  will  tend  to  weaken  their  cohesive  force.  When  bodies  are  heated 
the  expansion  which  they  undergo  is  due  to  the  separation  of  their  mole- 
cules. Hence,  when  solids  are  heated  their  molecules  are  further  and 
further  separated  until  finally  their  cohesive  force  is  balanced  by  the 
repulsive  force,  and  the  bodies«pass  from  a  solid  to  a  liquid  state.  This 


PHYSICAL   PEOCESSES  IN   CELLS.  39 

occurs  in  all  cases,  provided  the  heat  to  which  they  are  subjected  does 
not  cause  them  to  undergo  chemical  change.  If  a  body  which  has  been 
fused  by  heat  has  its  temperature  still  further  raised  its  molecules 
become  so  much  further  separated  that  the  force  of  cohesion  is  not 
sufficient  to  keep  them  in  contact,  and  the  body  then  becomes  vaporized. 

In  liquids  the  force  of  cohesion  is  not  great ;  hence  their  molecules 
are  readily  displaced  and  a  mass  of  liquid  assumes  the  shape  of  the  vessel 
which  contains  it ;  in  other  words,  the  force  of  gravity  overcomes  the 
force  of  cohesion.  Cohesive  force  is,  nevertheless,  present  in  liquids,  and 
may  be  demonstrated  by  the  difficulty  with  which  a  plate  of  glass  placed 
horizontally  in  contact  with  the  surface  of  water  is  removed  vertically 
upward.  This  difficulty  is  due  to  the  fact  that  the  adhesion  of  the  glass 
to  the  water  being  greater  than  the  cohesion  of  the  water,  the  molecules 
of  water  must  be  violently  separated  to  permit  of  the  removal  of  the 
glass. 

The  spheroidal  form  assumed  by  small  masses  of  liquid,  as  in  a  drop 
of  dew,  a  globule  of  mercury,  is  due  to  the  working  of  the  force  of  cohe- 
sion of  the  molecules  of  the  liquid.  In  a  small  drop  of  mercury  placed 
on  a  surface  for  which  it  has  no  adhesion,  as  wood  or  glass,  the  sum  of 
the  mutual  attractions  of  all  its  molecules  being  greater  than  the  force 
of  gravity  acting  on  them,  the  globule  assumes  the  spherical  form.  If, 
however,  the  drop  of  mercury  is  large,  then  the  force  of  gravity  increas- 
ing with  the  mass  of  the  body  becomes  greater  than  its  cohesion  and  the 
drop  becomes  flattened. 

The  molecules  of  all  liquids  attracting  each  other,  it  is  evident  that 
the  molecules  in  the  free  surface  of  a  liquid  will  be  attracted  by  and  will 
attract  those  below  them,  but  will  exert  or  will  be  subjected  to  no  exter- 
nal attraction.  At  the  surface  of  liquids,  therefore,  there  is  always  an 
inward  attraction,  which  is  called  surface  tension.  Of  course,  in  these 
considerations  external  accidental  pressures  and  attractions  to  which  the 
liquid  may  be  subjected  are  neglected. 

The  surface  tension  of  liquids  is  well  illustrated  by  blowing  a  soap- 
bubble  on  the  end  of  a  glass  tube ;  as  long  as  the  other  end  of  the  tube 
remains  closed  the  elastic  tension  of  the  air  in  the  bubble  balances  the  sur- 
face tension  of  the  soap-film,  but  when  the  end  of  the  glass  tube  is  opened 
the  tension  of  the  film  leads  to  the  contraction  and  final  disappearance 
of  the  bubble.  So  also  insects  can  move  on  the  surface  of  water  without 
sinking,  for  the  water,  not  being  able  to  wet  their  feet,  forms  a  depression, 
and  the  elastic  reaction  of  the  surface  supports  them.  The  case  is  simi- 
lar when  a  sewing-needle  is  floated  on  water ;  as  the  needle  is  coated 
with  a  thin  film  of  oil  the  water  does  not  adhere  to  it,  the  surface  becomes 
depressed,  and  its  increased  tension  serves  to  support  the  weight.  Wash- 
ing the  needle  first  in  alcohol,  ether,  or  potash  causes  it  at  once  to  sink. 


40 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


The  importance  of  these  facts  will  be  seen  in  the  explanation  of 
capillary  phenomena. 

2.  ADHESION  is  the  molecular  attraction  exerted  between  the  surfaces 
of  bodies  in.  contact ;  it  may  be  manifested  between  solids  (as  between 
two  freshly-cut  surfaces  of  a  leaden  bullet,  or  two  pieces  of  plate-glass), 
between  solids  and  liquids  (as  when  a  drop  remains  clinging  to  a  glass 
rod  which  has  been  dipped  in  water),  and  between  solids  and  gases  (as 
shown  by  the  bubbles  of  air  which  adhere  to  a  glass  or  metal  plate  when 
immersed  in  water). 

The  adhesion  of  liquids  to  solids,  which  alone  of  the  above  will 
receive  attention  at  present,  is  greater  than  the  cohesion  of  liquids,  as 
already  mentioned.  Thus,  when  a  drop  of  water  is  placed  on  a  glass 
surface  it  does  not  assume  the  spheroidal  form,  but  becomes  flattened 
out,  showing  that  the  adhesion  of  the  water  to  the  glass  is  greater  than 
the  cohesion  of  the  water.  If,  however,  the  glass  plate  be  greasy,  then 
the  drop  of  water  will  exert  no  adhesion  to  the  glass  and  will  remain 
spheroidal.  This  adhesion  of  liquids  to  solids  is  not  universal,  but 


.FIG.  27.        FIG.  28.  FIG.  29.  FIG.  30. 

CAPILLARY  PHENOMENA.    (Ganot.) 

depends  on  the  nature  of  both  the  solid  and  the  liquid.  Certain  liquids 
are  capable  of  adhering  to,  or  wetting,  certain  solids  and  not  others  ;  and 
a  solid  to  which  one  liquid  will  adhere  will  be  inert,  or  even  repulsive  to 
another.  These  facts  also  are  of  importance  in  the  explanation  of 
capillarity. 

3.  CAPILLARITY. — When  a  solid  body  is  placed  in  contact  with  a  liquid 
the  phenomena  (attraction  or  repulsion)  which  result  are  termed  capillary 
phenomena  from  the  fact  that  they  are  best  seen  when  capillary  tubes 
(capillus,  a  hair)  are  immersed  in  liquids. 

As  already  stated,  water  is  capable  of  adhering  to  glass.  When  a 
glass  rod  is  dipped  into  water,  the  water  is  raised  up  against  the  sides 
of  the  rod  to  form  a  concave  surface  above  the  level  of  the  water,  as  if 
no  longer  subject  to  the  laws  of  gravity  (Fig.  27).  If,  on  the  other 
hand,  a  glass  rod  be  dipped  into  mercury,  which  does  not  adhere  to 
it,  the  mercury  is  depressed  around  the  rod,  forming  a  convex  surface 
below  the  level  of  the  surrounding  fluid  (Fig.  28).  If  glass  tubes 
with  narrow  bore  are  immersed  in  water  and  mercury,  in  the  former 


PHYSICAL  PKOCESSES   IN   CELLS. 


41 


the  water  will  rise  within  the  tube  considerably  above  the  level  of 
the  water  outside,  and  the  surface  of  the  water  in  the  tube  will  be 
concave  (concave  meniscus);  while  the  mercury  will  be  depressed  in 
the  glass  tube  below  the  level  of  the  mercury  on  the  outside  and  the 
surface  of  the  mercury  within  the  tube  will  be  convex  (convex  meniscus) 
(Figs.  29  and  30).  If  any  two  bodies,  such  as  two  glass  plates,  are 
immersed  sufficiently  near  to  each  other  in  a  liquid,  the  liquid  will 
rise  or  be  depressed  between  them,  according  as  the  liquid  has  or 
has  not  any  adhesion  to  the  plates  (Fig.  31),  the  degree  of  elevation  or 
depression  being  one-half  what  it  would  be  if  a  tube  of  glass  whose 
diameter  equals  the  distance  between  the  two  plates  were  immersed  in  the 
same  liquids.  If  a  drop  of  water  be  placed  in  a  conical  glass  tube  of 
small  angle  and  horizontal  axis,  each  end  of  the  drop  will  have  a  concave 
meniscus  and  it  will  move  from  the  large  to  the  small  end  of  the  tube : 
if  the  liquid  be  mercury,  each  end  will  have  a  coiiA*ex  meniscus  and  it 
will  move  in  the  reverse  direction  (Figs.  32  and  33). 

In  the  explanation  of  capillary  phenomena 
two  causes  deserve  attention :  first,  the  cause  of 
the  curvature  of  the  surface,  and,  second,  the  cause 
of  the  ascent  or  depression  of  the  liquid  within 
the  tube. 


FIG.  31. 


FIG.  32. 


FIG.  33. 


The  form  of  the  surface  of  a  liquid  in  contact  with  a  solid  depends 
on  the  relation  between  the  attraction  exerted  by  the  solid  on  the  liquid 
and  the  mutual  attractions  of  the  molecules  of  the  liquid.  Any  molecule 
of  a  liquid  in  which  a  solid  is  immersed  is  acted  on  by  three  forces :  1st, 
gravity;  2d,  the  attractive  force  of  the  solid  for  the  liquid  molecule  ;  and 
3d,  the  cohesive  attractions  of  the  other  molecules  of  the  fluid. 

According  to  the  relative  intensities  of  these  forces  their  resultant 
may  occupy  one  of  three  positions  : — 

First. — If  the  attraction  of  the  solid  balances  the  cohesive  attrac- 
tion of  the  fluid,  the  resultant  of  these  two  forces  will  coincide  with  the 
force  of  gravity  and  the  surface  of  the  fluid  will  be  horizontal;  for  to 
be  in  equilibrium  the  surface  of  a  liquid  must  be  at  right  angles  to  the 
direction  of  the  resultant  of  all  the  forces  acting  on  that  liquid 
(Fig.  34). 

Second. — If  the  attractive  force  of  the  solid  for  the  fluid  increases, 
or  if  the  cohesive  force  of  the  liquid  diminishes,  the  resultant  will  fall 
outside  of  the  line  of  gravity  or  between  the  line  of  attraction  of  the 


42 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


solid  and  the  line  of  gravit.y,  and  the  surface  of  the  liquid  being  at  right 
angles  to  that  resultant  will  be  concave  (Fig.  35). 

Third. — If  the  attraction  of  the  solid  for  the  liquid  decreases,  or 
the  cohesive  attraction  of  the  liquid  increases,  the  resultant  will  fall  to 
the  other  side  of  the  line  of  gravity,  or  between  the  line  of  cohesive 
force  of  the  liquid  and  the  line  of  gravity,  and  the  surface  of  the  liquid, 
being  perpendicular  to  that  resultant,  will  be  convex  (Fig.  38). 


FIG.  34. 


FIG.  35. 


FIG. 


DIAGRAMS  ILLUSTRATING  CAUSE  OF  CURVATURE  OF  LIQUID  SURFACES  IN 
CONTACT  WITH  SOLIDS.    (Ganot.) 

The  molecule  m  is  acted  on  by  gravity,  in  the  vertical  line  m  P :  is  attracted  by  the  plate  n.  in  the  line 
n  m,  and  by  the  liquid  F,  in  the  line  m  F.  The  direction  of  the  resultant  m  R  will  depend  upon  the  relative 
intensities  of  these  forces.  If  n  m  and  m  F  balance,  the  resultant  is  vertical,  m  R  (Fig.  34),  and  the  surface 
is  horizontal.  If  n  m  increases,  or  m  F  decreases,  the  resultant  R  is  within  the  angle  n  m  P,  and  the  surface 
is  concave  (Fig.  35).  If  m  F  increases,  or  n  m  decreases,  the  resultant  R  is  within  the  angle  I'm  F,  and  the 
surface  is  convex,  for  the  surface  of  a  liquid  is  always  perpendicular  to  the  resultant  of  forces  acting  on 
its  molecules  (Fig.  36). 

The  ascent  or  descent  of  liquid  within  a  capillary  tube  is  dependent 
on  the  manner  in  which  the  curvature  of  the  surface  modifies  the  prin- 
ciples of  hydrostatic  equilibrium. 

When  a  tube  of  large  calibre  is  immersed  in  a  vessel  containing 
liquid  the  conditions  of  equilibrium  are  the  same  as  in  two  communicating 
vessels  containing  the  same  fluid.  Equilibrium  is  only  possible  when  the 

surface  of  the  liquid  in  both  vessels  is 
on  the  same  horizontal  plane.  For,  take 
any  molecule  in  the  plane  MN  (Fig.  37). 
It  will  be  subjected  to  a  downward  pres- 
sure equal  to  the  weight  of  a  column  of 
the  same  fluid,  the  height  of  which  is  equal 
to  the  distance  of  that  molecule  from  the 
surface  of  the  fluid  within  the  tube.  It 
will  also  be  subjected  to  an  upward  pres- 
sure which  is  equal  to  the  weight  of  a 
column  of  liquid  whose  height  is  equal  to 
the  distance  of  that  plane  from  the  surface 

of  the  liquid  without  the  tube.  These  weights  are,  however,  equal. 
Therefore  every  molecule  in  the  plane  MN  will  be  subjected  to  equal  and 
contrary  pressures,  and  will  consequently  be  in  equilibrium. 

Suppose,  however,  the  tube  have  a  diameter  less  than  one  millimeter. 
The  concave  surfaces  produced  by  the  adhesion  of  the  fluid  to  the 


FIG.  37.— DIAGRAM  ILLUSTRATING 
LIQUID  PRESSURES. 


PHYSICAL  PROCESSES  IN  CELLS.  43 

walls  of  the  tube  will  then  intersect,  and  the  surface  of  the  fluid  within 
the  tube  will  be  a  concave  meniscus.  In  other  words,  every  portion  of 
the  surface  of  the  liquid  within  the  tube  will  be  under  the  attractive  influ- 
ence of  the  walls  of  the  tube.  A  certain  portion  of  the  fluid  within  the 
tube  will  so  be  held  up  by  adhesion  to  the  tube,  and  will  hence  exert 
no  downward  pressure.  As  a  consequence  the  downward  pressure  within 
the  tube  will  be  less  than  the  upward  pressure  of  a  column  of  fluid  of 
the  same  height  without  the  tube.  Any  molecule  on  any  plane  below 
the  surface  of  the  fluid  in  the  tube  would  so  be  subjected  to  two 
unequal  pressures,  a  greater  upward  pressure  and  a  lesser  downward 
pressure ;  the  column  of  liquid  will  therefore  rise  within  the  tube  until 
these  two  pressures  are  equal. 

When,  however,  the  force  of  cohesion  of  the  liquid  is  greater  than 
that  of  adhesion  to  the  walls  of  the  tube,  as  already  explained,  the  sur- 
face becomes  convex  and  the  surface  tension  is  increased.  Since  the 
molecular  forces  are  greater  than  gravity,  the  downward  pressure  in  the 
tube  is  greater  than  the  upward  pressure  to  which  any  plane  is  subjected 
by  the  weight  of  the  liquid  outside  of  the  tube.  The  fluid  then  is  de- 
pressed in  the  tube  until  these  two  pressures  are  equal. 

Capillarit}-  partly  explains  the  ascent  of  the  sap  in  trees,  the  ascent, 
of  oil  in  a  lamp-wick,  to  a  certain  extent  the  movement  of  the  blood  and 
lymph  in  the  capillaries,  but  more  especially  the  entrance  of  fluid  into 
porous  bodies, — a  fact  of  the  greatest  importance  as  underlying  the  expla- 
nation of  imbibition,  filtration,  and  osmosis. 

4.  SOLUTION. — That  a  substance  may  enter  the  interior  of  cells  it 
must,  as  a  rule,  be  in  a  state  of  solution;  though  we  shall  find,  when  we 
study  the  process  of  absorption,  that  there  are  several  exceptions  to  this 
statement. 

The  process  of  solution  of  solids  in  fluids  is  of  very  general  occur- 
rence in  cell  life.  Almost  all  food-stuffs  are  solid,  and  to  be  of  nutritive 
value  must  first  be  reduced  to  the  form  of  a  solution  ;  even  the  con- 
sumption of  organic  matter  in  the  vital  processes  of  a  cell  results  in  the 
formation  of  a  watery  solution,  as  in  the  formation  of  urine,  sweat,  and 
the  various  secretions. 

When  a  solid  dissolves  in  a  liquid,  the  cohesion  of  the  molecules 
of  the  solid  is  broken  by  their  adhesion  for  the  molecules  of  the  liquid. 
When,  therefore,  the  attraction  of  the  liquid  for  the  solid  is  greater 
than  the  cohesion  of  the  solid,  the  latter  is  said  to  be  soluble  and  its 
molecules  separate.  The  limit  of  solubility  is  reached  when  the  attrac- 
tions of  adhesion  and  cohesion  are  balanced. 

Anything  that  reduces  the  cohesion  of  a  solid  favors  its  solution; 
thus,  heat  accelerates  solution  by  separating  solid  molecules  through 
the  expansion  which  it  produces,  and,  by  increasing  the  distance  between 


44  PHYSIOLOGY  OF  THE   DOMESTIC  ANIMALS. 

the  molecules,  thereby  weakens  their  cohesive  force.  Pulverizing,  by 
mechanically  separating  the  molecules  to  a  certain  extent,  also  assists 
solution. 

Heat  is  always  essential  to  the  conversion  of  a  solid  into  a  solution. 
Ordinarily  the  heat  is  abstracted  from  the  surrounding  media,  and  is 
rendered  latent  in  the  solution,  thus  explaining  the  mode  of  action  of 
freezing  mixtures.  The  amount  of  heat  so  rendered  latent  in  forming  a 
solution  is  nearly  always  equivalent  to  the  amount  required  to  melt  the 
body. 

In  certain  cases,  however,  instead  of  the  temperature  being  lowered 
in  the  process  of  solution,  it  actually  rises,  as  when  caustic  potash  is  dis- 
solved in  water.  This  depends  upon  the  fact  that  two  contrary  proc- 
esses are  going  on  at  the  same  time ;  the  solution,  which  tends  always 
to  produce  a  reduction  of  temperature,  and  the  chemical  union  of  the 
potash  with  the  water,  which,  like  many  other  chemical  processes,  tends  to 
cause  an  increase  of  temperature.  Consequently,  as  one  or  the  other  of 
these  processes  predominates  the  temperature  will  fall  or  rise ;  or,  if  the 
two  balance,  will  remain  unchanged. 

Solubility  varies  greatly  in  different  bodies  and  in  different  liquids. 
Some  solids  are  soluble  only  in  hot  media,  and  are  deposited  on  cool- 
ing ;  others  only  in  cold  liquids,  and  are  thrown  out  of  solution  when 
the  temperature  of  the  liquid  is  raised.  As  a  rule,  bodies  dissolve  in 
liquids  which  have  similar  properties ;  thus  crystalline  bodies  are  soluble 
in  water,  fats  in  oil,  metals  in  mercury,  and  resins  in  alcohol. 

u  When  two  or  more  salts  are  dissolved  in  water  without  chemical 
action  on  each  other,  three  conditions  result :  1st.  The  quantity  of  each 
salt  held  in  solution  is  less  than  when  it  alone  is  present,  though  the 
combined  quantity  is  greater  than  when  only  one  salt  is  used.  2d.  The 
quantity  of  each  is  as  great  as  when  one  only  is  used ;  then  the  total 
quantity  dissolved  is  the  sum  of  that  taken  up  in  each  single  solution. 
3d.  The  quantity  dissolved  is  greater  than  when  one  alone  is  used, 
the  addition  of  the  second  salt  in  this  case  increasing  the  solubility  of 
the  first,  and  often  the  first  increasing  also  the  solubility  of  the  second" 
(Draper). 

When  the  cohesion  of  the  solid  and  its  adhesion  for  the  liquid  mole- 
cules balance,  the  solution  is  then  said  to  be  saturated.  In  the  case  of 
certain  fluids,  like  alcohol  and  water,  there  is  no  limit  to  solubility ;  their 
molecules  will  freely  mingle  with  each  other,  and  the  resulting  liquid  is 
said  to  be  a  mixture,  or  an  emulsion.  On  the  other  hand,  two  liquids 
may  offer  an  example  of  true  solution,  one  being  only  capable  of  passing 
to  a  certain  degree  between  the  molecules  of  the  other,  as  in  the  case  of 
volatile  oils  and  water,  where  the  limit  of  solubility  is  readily  reached. 

5.   IMBIBITION. — Every  porous  solid  may  be  considered  as  formed  of 


PHYSICAL  PKOCESSES  IN   CELLS.  45 

a  collection  of  capillary  tubes.  When  such  a  solid  (e.g.,  a  piece  of  chalk) 
is  immersed  in  a  fluid  which  is  capable  of  wetting  it,  the  fluid  will  enter 
into  the  pores  of  the  solid  through  capillarity,  and  will  remain  even  after 
the  body  is  removed  from  the  fluid.  The  solid  is  then  said  to  have 
absorbed  fluid  by  imbibition.  Organic  bodies  also  are  capable  of  absorb- 
ing fluid  by  imbibition,  but  the  process  is  somewhat  different  from  that 
of  the  inorganic  porous  body. 

Every  organic  bod}^,  no  matter  what  its  consistency,  contains  always 
a  large  amount  of  water  in  its  composition,  to  which  fluid,  as  we  shall 
find  later,  many  of  the  physical  properties  of  the  tissues  are  due.  When 
inorganic  bodies  contain  fluid,  that  fluid  is  held  in  one  of  two  ways, — 
either  chemically  united  with  the  body,  as  in  hydrates,  or  as  water  of 
crystallization ;  or  mechanically  in  the  pores  of  the  solid.  Organic  bodies 
occupy  a  mean  between  these  two.  The  water  in  their  composition  is 
not  in  a  form  of  chemical  combination,  nor  is  it  held  mechanicalty  in 
pores,  as  in  the  porous  inorganic  body,  though  the  conditions  are  some- 
what similar  to  the  latter  case.  That  there  is  a  difference,  however,  is 
proved  by  the  different  effects  of  the  abstraction  of  water  from  organic 
and  porous  inorganic  bodies.  The  physical  characters  of  porous,  inor- 
ganic solids,  such  as  baked  clay,  are  not  seriously  altered  by  the  removal 
of  water  contained  in  their  pores.  The  abstraction  of  water  from  semi- 
solid  organic  bodies,  on  the  other  hand,  entirely  changes  their  physical 
and  physiological  properties.  A  piece  of  connective  tissue  in  its  fresh 
condition  is  soft,  white  and  glistening,  flexible,  extensible  and  elastic. 
When  the  water  which  it  contains  is  removed  by  drying,  it  shrivels  up, 
becomes  rigid,  yellowish  in  color,  brittle,  and  loses  weight.  If  it  be  then 
immersed  in  water  its  previous  characters  will  be  restored.  This  differ- 
ence in  the  manner  in  which  the  water  entering  into  the  composition  of 
organic  and  inorganic  bodies  is  held  is  explained  by  the  assumption  that 
in  the  porous  inorganic  body  the  water  occupies  comparatively  large 
spaces  between  particles  of  solid,  while  in  the  organic  body  the  water 
surrounds  the  ultimate  molecules  of  the  body.  Organic  tissues,  ma}' 
therefore  be  defined  as  bodies  whose  intermolecular  spaces  are  filled 
with  fluid. 

As  the  fluids  are  held  in  a  different  manner  in  inorganic  and  organic 
bodies,  it  is  natural  to  find  that  the  way  in  which  the  fluid  is  absorbed 
differs  in  the  two  cases. 

When  a  dry,  porous,  inorganic  body,  such  as  a  piece  of  chalk,  is 
thrown  into  wrater,  the  water  enters  the  pores  of  the  chalk  by  capillarity 
and  displaces  the  air  which  was  contained  in  its  pores.  It  increases  in 
weight  by  the  addition  of  the  weight  of  the  absorbed  water,  but  does 
not  increase  in  volume.  When  a  dry  organic  body,  such  as  a  piece  of 
gelatin,  is  thrown  into  water  no  air  is  displaced,  and  yet  many  times 


46  PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 

its  own  volume  of  water  may  be  absorbed.  The  gelatin  must  therefore 
increase  in  volume.  The  fluid  in  organic  imbibition  passes  into  the  inter- 
molecular  spaces  and  separates  the  molecules.  That  an  organic  body  may 
imbibe  fluid  it  is  consequently  necessarj^  that  its  molecules  be  freely 
movable. 

The  power  of  imbibition  possessed  by  the  organic  tissues  is  espe- 
cially due  to  their  albuminoid  constituents.  Protoplasm  is,  therefore, 
above  all  capable  of  imbibition,  and  the  rapid  formation  or  disappear- 
ance of  vacuoles  in  protoplasmic  cells  may  be  due  to  rapid  changes  in 
imbibition. 

Every  organic  substance  has  a  limit  be}rond  which  imbibition  is 
impossible.  This  limit  is  lower  when  the  water  contains  solids  in  solu- 
tion, provided  the  solids  are  not  chemically  acted  on  by  the  tissues,  from 
the  fact  that  imbibed  water  is  held  with  greater  tenacity  by  the  tissues 
than  are  the  substances  held  in  solution  in  the  water.  Thus,  when  a 
tissue  saturated  with  a  salt  solution  is  subjected  to  pressure,  the  solution 
first  pressed  out  is  more  concentrated  than  that  which  is  forced  out  when 
the  pressure  is  subsequently  increased ;  and  in  general  the  fluids  lose  in 
concentration  in  imbibition.  Organic  tissues  therefore  absorb  water  with 
greater  readiness  than  saline  solutions.  The  importance  of  this  fact  will 
be  seen  in  the  explanation  of  osmosis. 

The  extent  of  imbibition  depends,  therefore,  on  the  membrane  and 
the  nature  of  the  fluid  with  which  it  is  in  contact.  Thus  it  has  been 
found  by  Liebig  that  one  hundred  parts  of  ox-bladder  absorb,  of — 

Water, 268  volumes. 

Salt  solution  (1.204  sp.  gr.),     .        .        .        .133 
Alcohol  (84  per  cent.),      .        .        .        .        .38        " 
Marrow  oil,        .        .        .        .  .  17     -   " 

Membrane,  therefore,  has  less  affinity  for  a  salt  solution  than  for 
water.  This  may  also  be  shown  by  soaking  a  bladder  in  water,  wiping 
it  dry,  and  then  sprinkling  it  with  common  salt.  The  salt  comes  in 
contact  with  some  of  the  water  in  the  bladder,  dissolves,  and  forms  a 
salt  solution.  But  as  the  membrane  can  contain  less  salt  solution  than 
water,  some  of  the  solution  is  expelled  and  the  bladder  shrivels  up. 
So  also  a  moistened  bladder  thrown  into  alcohol  shrivels  up,  because 
the  alcohol  mixes  with  the  water  in  the  bladder ;  and  as  the  bladder, 
as  shown  above,  can  only  absorb  one-seventh  as  much  alcohol  as 
water,  the  solution  is  driven  out.  This  is  the  explanation -of  the  use 
of  alcohol  and  various  saline  solutions  for  hardening  tissues  for  making 
microscopic  sections. 

In  the  nutrition  of  animal  cells  the  process  of  imbibition  is  an 
important  factor.  Every  substance  which  is  soluble  in  water  is  capable 
of  being  appropriated  by  the  protoplasm  and  maj^,  through  imbibition, 


PHYSICAL   PEOCESSES   IN   CELLS.  47 

obtain  access  to  the  interior  of  cells,  to  there  undergo  the  transformations 
which  the  needs  of  the  economy  necessitate.  In  cells  which  possess  a 
closed  membrane,  capillarity  may  also  be  concerned ;  for  there  is  reason 
to  suppose  that  the  striated  appearance  which  is  seen  on  examining  most 
cell-membranes  with  a  high  power  under  the  microscope  is  in  reality  due 
to  the  presence  of  minute  apertures,  or  canaliculi.  Fluid  will  therefore 
enter  the  pores  in  the  membranes  of  cells,  and  so  obtain  access  to  the 
protoplasmic  cell-contents.  The  passage  of  fluids,  however,  through  the 
cell-membrane  is  not  necessarily  dependent  on  capillarity.  For  the 
cell-membrane,  like  other  organic  tissues,  is  capable  of  absorbing  water 
by  imbibition  in  the  same  way  in  which  water  is  absorbed  b}T  gelatin,  i.e, 
by  entering  into  its  intermolecular  spaces.  The  state  of  affairs  is  thus 
similar  to  the  conditions  described  in  the  experiment  with  the  bladder 
and  salt.  We  have  an  organic  tissue  soaked  with  a  fluid  in  contact  with 
a  substance  (protoplasm)  having  an  affinity  for  that  fluid  greater  than 
the  affinit}^  of  the  membrane  for  the  fluid;  the  fluid,  therefore,  leaves 
the  cell-membrane  to  enter  the  protoplasm  by  organic  imbibition. 

The  affinity  of  protoplasm  for  water  is  never  satisfied  during  life : 
or,  in  other  words,  the  maximum  amount  of  water  capable  of  being 
absorbed  by  cell-contents  is  never  reached.  Cells  will,  therefore,  always 
absorb  fluid  when  brought  into  contact  with  it,  and  by  so  doing  will 
tend  to  increase  in  volume.  As,  however,  the  extensibility  of  cell- 
membranes  is  in  most  cases  very  limited,  the  increase  in  volume  of  the 
cell-contents  will  tend  to  cause  filtration  of  the  fluid  contained  in  the 
meshes  of  the  protoplasm  back  through  the  cell-membrane  to  the 
exterior. 

These  facts  which  we  have  learned  in  reference  to  the  imbibition  of 
fluids  by  organic  tissues  give  but  an  imperfect  idea  of  the  processes  of 
imbibition  which  take  place  in  living  cells.  Many  fluids  which  are 
absorbed  by  dead  tissues  are  perfectly  indifferent  to  living  cells,  and 
there  can  be  no  doubt  but  that  imbibition  in  living  tissues  is  largely 
governed  by  the  nature  of  the  chemical  affinities  caused  by  the  chemical 
processes  continually  taking  place  in  the  interior  of  active  cells.  Thus, 
living  tissues  (muscles)  are  incapable  of  absorbing  dilute  solutions  of 
sodium  salts ;  the  same  tissues  when  dead  will  absorb  it  in  large  amounts. 
Potassium  salts,  on  the  other  hand,  are  rapidly  absorbed  by  the  same 
tissue  and  almost  instantly  cause  its  death,  though  even  in  this  case  the 
power  of  imbibition  for  the  potassium  salt  is  greatly  increased  after 
death.  Again,  we  shall  find  that  the  prolonged  activity  of  many  tis- 
sues, especially  the  muscles,  is  manifested  in  the  production  of  an  acid 
reaction  in  the  cell-contents;  under  such  circumstances,  sodium  solutions, 
which  are  indifferent  to  these  tissues  at  rest,  will  now  be  absorbed  by 
them. 


48  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

The  following  figures  represent  the  behavior  of  the  muscular  tissue 
to  solutions  of  different  salts  (Ranke) : — 

MAXIMUM  IMBIBITION. 

1  PER  CENT.  Na'Cl.  1  PER  CENT.  K  Cl. 

Living,  resting  muscle,          .      0  Positive,  but  not   capable  of 

estimation,  as  the  muscle 
instantly  died. 

Living,  tetanized  muscle,     .     13  Positive  :  not  to  be  estimated, 

for  the  same  reason  as  above. 
Dead  muscle,          .        .        .35  136  per  cent. 

Perfectly  analogous  observations  have  also  been  made  in  the  case  of 
the  nervous  tissues. 

It  would,  therefore,  appear  that  living  tissues  only  absorb  by 
imbibition  when  their  vital  forces  are  diminished  in  energy.  In  the 
organism  the  cells  are  continually  bathed  in  a  fluid  which  contains  the 
matters  necessary  for  the  nutrition  of  the  cells.  If  the  cells  have  been 
at  rest  their  nutritive  equilibrium  lias  not  been  disturbed  and  imbibition 
does  not  take  place.  If,  however,  they  are  exhausted  by  previous 
activity,  imbibition  is  then  inaugurated,  nutritive  substances  enter,  the 
results  of  cell  activity  are  extruded  (acids,  etc.),  nutritive  equilibrium  is 
restored,  and  imbibition  not  only  ceases,  but  from  the  increased  volume 
of  the  cell-contents  pressure  is  produced  on  the  cell-membrane  and  the 
excess  of  fluid  is  forced  through  again  to  the  exterior  b}T  filtration. 
Consequently  cells  which  are  most  weakened  by  prolonged  activity  are 
the  cells  which  carry  ont  as  a  direct  result  of  the  chemical  affinities 
created  by  that  activity,  the  most  active  imbibition.  By  these  peculi- 
arities in  the  conditions  which  govern  imbibition  in  living  cells  is  to  be 
explained  the  peculiar  distribution  of  the  inorganic  salts  in  the  animal 
bod}T, — sodium  in  the  fluids,  potassium  in  the  solid  organs  of  the  body. 
For,  as  we  know,  sodium  solutions  are  indifferent  fluids  and  are  not 
absorbed  by  the  tissues  unless  they  have  undergone  some  depression  in 
energy,  while  potassium  salts  in  solution  are  rapidly  absorbed  and  lead 
to  the  death,  the  drowning  out  of  protoplasm. 

6.  FILTRATION  OR  TRANSUDATION  is  the  passage  of  fluid  through  a 
membrane  dependent  upon  inequality  of  hydrostatic  pressures  ;  but  that 
a  fluid  should  so  pass  it  is  essential  that  the  membrane  be  capable  of 
absorbing  the  fluid  by  imbibition. 

The  greater  the  affinit}^  of  the  fluid  for  the  membrane  (see  Imbibition} 
the  more  rapidly  will  the  fluid  under  a  moderate  pressure  pass  through 
the  membrane:  thus  water,  or  even  a  saline  solution,  will  filter  more 
rapidly  than  oil.  Filtration  will  occur  more  rapidly  through  a  thin  than 
a  thick  membrane. 

The  rapidity  of  filtration  is,  further,  in  direct  proportion  to  the  pres- 
sure which  the  fluid  exerts  on  the  membrane,  and  increases  with  increas- 


PHYSICAL  PROCESSES  IN   CELLS.  49 

ing  temperature.  Solutions  of  different  salts  pass  almost  unaltered 
through  membranes,  though  the  filtrate,  from  the  fact  that  the  membrane 
keeps  back  some  of  the  water  of  solution,  may  be  more  concentrated. 
The  reverse  is  true  in  the  filtration  of  colloids  (bodies  like  glue) ;  there 
the  filtrate  contains  a  smaller  percentage  of  the  colloid  than  the  original 
fluid, — from  the  fact  that  the  membrane  allows  more  water  to  pass  than 
gum,  albumen,  etc. 

This  explains  the  fact  that  colloid  bodies,  perhaps  on  account  of 
the  great  size  of  their  molecules,  are  with  great  difficulty  removed  from 
the  pores  of  animal  and  vegetable  tissues,  especially  since  it  has  been 
found  that  if  the  fluid  which  contains  colloids  in  solution  also  contains 
crystalloids,  less  colloid  will  filter  through  than  if  the  crystalloids  had 
been  absent,  and  the  filtrate  is  richer  in  crystalloids  than  the  fluid  in  the 
filter.  Crystalloids,  therefore,  hinder  the  filtration  of  colloids  ;  and  as 
protoplasm  is  always  associated  with  certain  saline  bodies,  the  latter 
prevent  the  loss  of  the  albuminoids  of  the  cell-contents. 

Many  of  the  phenomena  of  filtration  may  be  explained  under  the 
working  of  the  laws  of  capillarity,  especially  when  the  filter  is  an  inorganic, 
porous  solid.  When,  however,  it  is  an  organic  membrane,  as  of  course 
is  always  the  case  in  the  animal  or  vegetable  cell,  there  the  laws  of  imbi- 
bition are  of  prime  importance. 

Cell  life  furnishes  many  examples  of  the  process  of  filtration.  When 
the  cell-contents  increase  in  bulk  through  imbibition  the  pressure  on  the 
interior  of  the  cell-membrane  is  greater  than  on  the  exterior;  substances 
in  solution  within  the  cell  may  then  pass  through  the  cell-membrane. 
The  formation  of  the  saline  constituents  of  the  various  secretions  is 
probably  accomplished  in  this  way.  When  the  flow  of  blood  is  obstructed 
in  a  vein  the  pressure  back  of  the  obstruction  becomes  greatly  increased, 
and  the  water  and  saline  constituents  of  the  blood  pass  through  the 
walls  of  the  vessel.  In  this  way  O3dema  and  dropsies  are  produced.  In  the 
liver,  so  long  as  the  pressure  in  the  bile-ducts  is  low,  the  bile  filters  from 
the  liver-cells  into  the  bile-ducts.  But  if  the  flow  of  bile  is  interfered 
with  so  as  to  make  only  a  slight  resistance  in  the  bile-ducts,  the  bile  then 
filters  into  the  hepatic  parenchyma,  from  there  into  the  lymphatics,  by 
which  it  is  carried  throughout  the  body,  and  jaundice  is  produced. 

When  the  renal  secretion  comes  under  consideration  it  will  be  found 
that  the  process  of  filtration  there  fills  a  very  important  role. 

When  fluids  pass  from  the  interior  to  the  exterior  of  cells,  or  the 
reverse,  they  usually  come  into  contact  with  other  fluids.  Under  certain 
circumstances  these  fluids  will  mix ;  under  others  mixing  will  not  occur. 
Those  conditions  now  demand  consideration. 

7.  DIFFUSION  OF  LIQUIDS. — The  molecules  of  liquids,  as  has  been 
already  seen,  are  held  together  by  a  force  of  attraction,  or  cohesion  ;  the 

4 


50  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

molecules  of  liquids  are  also  capable  of  exerting  an  attractive  force  on 
solids,  or  adhesion.  In  addition  to  these  two  modes  of  manifestation 
of  molecular  force,  molecules  of  liquids  are  capable  of  attracting  mole- 
cules of  other  liquids.  If  in  two  different  liquids  brought  into  contact 
the  cohesive  force  between  the  molecules  of  each  liquid  is  greater  than 
the  attractive  force  between  the  molecules  of  the  different  liquids,  the 
liquids  remain  separate  and  apart,  and  are  said  not  to  be  miscible. 
Water  and  oil  furnish  examples  of  such  liquids. 

If,  however,  the  attraction  between  the  molecules  of  the  different 
liquids  is  greater  than  the  cohesive  force  of  either,  then  the  liquids  will 
mix,  even  against  gravity,  until  the  mixture  becomes  uniform.  Such  a 
process  of  mixing  is  called  diffusion  of  liquids.  It  follows,  therefore, 
that  whenever  two  chemically  indifferent  fluids  are  brought  into  contact 
with  one  another  the}^  mix,  even  without  any  disturbing  cause,  until  a 
perfectly  uniform  mixture  results. 

Diffusion  may  be  illustrated  by  filling  a  small  bottle  with  some  saline 
solution  and  then  placing  it  in  a  large  jar,  which  is  then  carefully  filled 
with  distilled  water,  so  poured  in  as  to  cover  the  mouth  of  the  small  jar 
which  contains  the  saline  solution,  at  the  same  time  avoiding  any  mixing 
of  the  fluids  by  movement. 

If  a  small  portion  of  the  water  in  the  large  jar  is  then  drawn  off 
carefully  from  time  to  time  with  a  pipette,  it  will  be  found  that  the 
water  will  contain  a  gradually  increasing  quantity  of  the  salt,  until 
finally  the  jar  will  be  filled  with  a  perfectly  uniform  saline  solution. 

From  such  experiments  it  has  been  found  that  the  rapidity  of  dif- 
fusion increases  with  the  extent  of  surfaces  in  contact,  with  the  tempera- 
ture, and  with  the  difference  in  concentration  of  the  two  fluids ;  it  is, 
therefore,  more  rapid  at  the  beginning  of  the  experiment,  when  the  outer 
jar  contains  distilled  water,  than  later,  when  it  contains  a  saline  solution. 
The  rapidity  of  diffusion  also  varies  with  the  chemical  nature  of  the 
solutions ;  thus,  potassium  salts  diffuse  much  more  readily  than  sodium 
salts, — a  point  which  we  shall  later  see  is  of  great  importance.  Acids  dif- 
fuse very  rapidly;  alkaline  salts  and  sugar  slower,  and  colloids,  perhaps 
from  the  fact  that  they  cannot  form  true  solutions,  scarcely  at  all,  though 
colloids  in  solutions  with  crystalloids  do  not  interfere  with  the  diffusion 
of  the  latter ;  while,  when  two  salts  undergo  diffusion  together,  the  least 
diffusible  salt  diffuses  more  rapidly  than  it  would  alone. 

In  the  different  animal  tissues,  in  addition  to  the  intermolecular 
spaces  filled  with  fluid,  we  have  also  larger  spaces,  or  sensible  pores, 
which  contain  fluids,  and  which  form  a  system  of  more  or  less  fine  canals 
traversing  the  different  parts  of  the  body  (lymph-spaces,  lymph-  and 
blood-capillaries).  Therefore  every  internal  part  of  the  animal  body  is 
continually  bathed  in  liquid  into  which  fluids  leaving  the  cells  are 


PHYSICAL  PROCESSES  IN   CELLS.  51 

capable  of  diffusion.  In  most  cases,  however,  these  fluids  are  in  con- 
stant motion,  and  the  purely  physical  phenomena  of  diffusion  are  of 
little  importance,  particularly  when  the  extreme  slowness  of  ordinary 
diffusion  is  remembered.  As  the  composition  of  the  fluids  of  the  body 
is  continually  changing,  diffusion,  greatly  aided  by  the  motion  of  the 
fluids,  will,  nevertheless,  serve  to  maintain  a  certain  degree  of  constancy 
of  composition. 

It  has  been  already  shown  that  when  watery  solutions  are  found  on 
different  sides  of  a  membranous  partition,  as  in  the  case  of  the  cell-con- 
tents of  two  neighboring  cells  whose  contents  are  more  or  less  fluid,  the 
membrane  does  not  serve  to  keep  the  fluids  apart.  For,  the  membrane 
being  capable  of  absorbing  liquids  by  imbibition,  the  liquids  fill  the 
intermolecular  spaces  of  the  membrane,  and  so  come  in  contact  with  each 
other;  the  phenomena  of  diffusion  then  commence,  though  the  process  is 
very  greatly  modified  by  the  behavior  of  the  intervening  membrane.  As 
already  mentioned,  diffusion,  with  the  exception  of  the  part  it  plays  in 
distributing  fluids  uniformly  through  the  interior  of  cells,  fills  quite  a 
secondary  role  in  the  physical  processes  of  the  animal  economy.  Dif- 
fusion as  modified  by  the  passage  of  liquids  through  an  animal  membrane 
occupies  a  much  higher  position  in  point  of  importance. 

8.  OSMOSIS. — When  two  liquids  capable  of  mixing  are  separated  by  a 
membrane  which  possesses  the  power  of  imbibing  these  liquids,  a  gradual 
union  of  the  two  liquids  takes  place  through  the  membrane. 

This  interchange,  which  is  called  osmosis,  continues  until  the  two 
liquids  are  equally  mixed  ;  consequently,  the  final  result  is  the  same  as  if 
no  membrane  separated  the  two  liquids,  though  the  process  is  essentially 
different ;  for  the  diffusion  currents  must  be  modified  by  the  molecular 
forces  which  the  molecules  of  the  membrane  exert  on  the  liquids  in  con- 
tact with  them.  If  two  liquids  are 
poured  into  the  arms  of  a  U-tube 
(Fig.  38)  so  that  they  are  in  con- 
tact at  A  they  will  mix,  but  the 
level  will  remain  the  same  in  both 
tubes,  i.e.,  equal  portions  of  each 
liquid  pass  into  one  another  in  equal 
time  ;  if,  on  the  other  hand,  a  mem-  FIG.  38. 

brane  is  placed  at  A  the  liquids  will 

mix,  but  the  column  of  liquid  will  rise  in  one  tube  above  the  original 
level  and  sink  to  a  corresponding  amount  in  the  other.  From  which  it 
follows  that  in  the  mixing  of  liquids  through  a  membrane  the  interchange 
is  unequal,  i.e.,  more  of  one  liquid  passes  than  of  the  other.  The  current 
through  the  membrane  is  a  double  one.  Thus,  if  a  saturated  salt  solu- 
tion is  placed  in  one  arm  of  the  tube  and  an  equal  quantity  of  distilled 


52  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

water  be  placed  in  the  other,  the  salt  solution  will  soon  be  found  to  have 
increased  in  volume  and  the  water  to  have  decreased.  If  the  character 
of  the  two  liquids  is  then  examined  it  will  be  found  that  the  distilled 
water  is  no  longer  pure,  but  that  it  contains  salt ;  while  the  saline  solu- 
tion will  be  no  longer  saturated,  but  of  much  less  density.  Salt  has 
therefore  passed  through  to  the  water  and  water  passed  through  to  the 
salt  solution.  There  has  been,  however,  as  is  evident,  a  difference  in 
the  rapidity  with  which  the  two  substances  have  traversed  the  mem- 
brane. That  this  process  is  not  at  all  analogous  to  nitration — in  fact  is 
directly  opposed  to  it — is  seen  in  the  continued  ascent  of  the  column  of 
liquid  in  one  arm  of  the  tube,  showing  that  the  water  passes  to  the  salt 
solution  even  against  a  continually  increasing  hydrostatic  pressure. 
The  tendency  is  therefore  for  nitration  currents  to  form  in  the  opposite 
direction  to  the  osmotic  current.  If  one  liquid  is  water  and  the  other 
salt  solution,  the  amount  of  water  passing  to  the  salt  solution  for  each 
equivalent  of  salt  passing  to  the  water  is  called  the  osmotic  equivalent 
of  the  salt.  The  osmotic  equivalent  is  dependent  upon  the  chemical 
nature  of  the  body  and  the  concentration  of  its  solution. 

Thus,  for  sodium  chloride  it  is  4.3,  meaning  that  for  every  gramme 
of  salt  which  passes  through  the  membrane  4.3  grm.  of  water  will  pass 
in  the  opposite  direction  to  the  salt.  For  sodium  sulphate  it  is  11.6; 
potassium  sulphate,  12  ;  magnesium  sulphate,  11.7  ;  alcohol,  4.2  ;  sugar,  7.1. 

In  general  the  osmotic  equivalent  increases  with  the  temperature, 
and  varies  very  greatty  with  the  concentration  of  the  solutions. 

The  rapidity  with  which  different  bodies  diffuse  through  a  porous 
membrane  is  independent  of  their  osmotic  equivalent,  but  is  directly 
dependent  upon  their  chemical  nature  and  solubilit}T,  increasing  with 
solubility  ;  and  bodies  nearly  related  as  to  their  chemical  composition 
are  also,  nearly  related  as  to  rapidity  of  diffusion.  The  rapidity  also 
increases  with  increasing  difference  of  concentration  between  the  two 
liquids  and  with  increase  of  temperature. 

When  two  solutions  of"  the  same  substance  but  of  different  densities 
are  allowed  to  diffuse  into  one  another,  the  denser  decreases  in  density 
and  the  lighter  increases,  and  the  same  alterations  of  volume  occur  as 
would  be  the  case  were  one  of  the  liquids  pure  water.  The  osmotic 
equivalent  is  in  both  cases  the  same,  but  in  the  former  case  the  rapidity 
of  osmosis  is  much  less. 

If  two  solutions  of  substances  of  different  chemical  composition  are 
allowed  to  diffuse,  the  rapidity  will  increase  with  increase  in  the  chemical 
affinity  between  the  two  substances. 

All  colloids  pass  with  difficulty  through  organic  membranes,  but  as 
they  have  a  strong  affinity  for  water  they  draw  it  with  vigor  through 
organic  membranes  ;  hence,  their  osmotic  equivalent  is  very  high,  though 


PHYSICAL   PKOCESSES   IX   CELLS.  53 

the  current  of  water  to  the  colloid  is  ver}'  slow,  possibly  because  the 
large  molecules  of  the  colloids  readily  stop  the  pores  of  the  membrane. 
Albumen  in  solution  passes  more  readily  through  a  membrane  to  mix 
with  salt  solution  than  with  water.  A  very  concentrated  solution  of 
salt,  however,  prevents  osmosis  of  albumen  by  simply  removing  the  water 
from  the  albuminous  solution. 

When  a  solution  of  a  diffusible  substance,  together  with  a  solution 
of  a  colloid,  is  placed  on  one  side  of  a  membrane  and  pure  water  on  the 
other,  at  first  none  of  the  colloid  passes  through  the  membrane,  but 
simply  water  to  the  colloid  and  the  diffusible  substance  to  the  water; 
hence,  albumen  may  be  freed  of  its  salts  by  diffusion  (dialysis),  or,  if  a 
mixed  solution  of  sugar  and  gum  is  subjected  to  dialysis,  only  the  sugar 
passes  through  the  membrane. 

An  exception  to  this  is  seen  when  albumen  and  salts  dialyze  with  water. 
First  the  salts  pass,  then  the  albumen  passes  into  the  salt 'solution. 

Just  as  we  found  there  were  two  kinds  of  imbibition, — the  capillary 
and  molecular, — so  are  there  two  kinds  of  osmosis,  which  differ  somewhat 
according  as  the  partition  between  the  two  fluids  is  a  porous,  inorganic 
solid,  or  an  organic  tissue  capable  of  absorbing  liquid  by  imbibition.  In 
the  case  of  a  porous,  inorganic  partition  the  phenomena  of  osmosis  are 
entirely  governed  by  capillarity  and  the  laws  of  diffusion  of  liquids. 
Certain  liquids  have  a  greater  tendency  to  enter  capillary  tubes  than 
others.  When,  therefore,  two  miscible  liquids  are  separated  by  a  porous 
solid,  which  may  be  regarded  as  a  collection  of  capillary  tubes,  the  liquid 
which  has  the  greater  affinity  for  the  walls  of  the  tube  will  enter  to  a 
greater  extent  than  the  other,  and  will  meet  the  other  fluid  advancing  in 
the  opposite  direction,  but  with  less  force  on  account  of  its  lesser  affinit3\ 
The  two  liquids  thus  coming  into  contact  with  each  other  will  diffuse  into 
each  other,  and  the  pores  will  be  occupied  with  a  mixture  of  two  liquids, 
for  one  of  which  the  walls  of  the  tube  will  have  a  greater  affinity  than 
for  the  other.  Then,  although  diffusion  will  take  place  from  this  mixture 
into  the  liquid  of  greater  affinity,  the  latter  continually  forcing  out  some 
of  the  mixture,  the  liquid  of  lesser  affinity  will  continually  increase  in 
volume. 

In  the  case  of  organic  membranes,  the  power  possessed  by  the  mem- 
brane of  imbibing  different  liquids  enables  osmosis  to  take  place,  while 
the  direction  of  the  current  is  governed  by  the  affinity  of  the  liquids  for 
the  membrane.  Whichever  liquid  has  the  greater  affinity  for  the  mem- 
brane will  pass  in  greatest  amount.  Here,  for  the  sake  of  simplifying 
the  matter,  we  may  assume  that  the  liquid  wrhich  has  entered  the  inter- 
molecular  spaces  of  the  membrane  is,  to  a  certain  extent,  governed  by 
the  same  conditions  which  apply  to  the  entrance  of  liquids  into  capil- 
lary tubes. 


PHYSIOLOGY  OF   THE  DOMESTIC   ANIMALS. 


When  an  organic  tissue  has  absorbed  liquid  by  imbibition,  its  inter- 
molecular  spaces  being  filled  with  that  liquid,  the  liquid,  which  becomes 
superficial  on  the  far  side  of  the  membrane,  is  in  direct  continuity  with 
the  body  of  the  liquid  having  the  greater  affinity  for  the  membrane,  and 
in  direct  contact  with  the  liquid  of  lesser  affinity.  Diffusion  phenomena 
therefore  commence. 

When  a  membrane  has  a  tendency  to  imbibe  water,  it  will  absorb 
more  water  than  salt  solution,  if  placed  between  water  and  a  salt  solu- 
tion, and  will  increase  in  volume.  In  every  pore  or  intermolecular 
space  of  the  membrane,  therefore,  the  layer  of  liquid  in  contact  with 
the  sides  of  the  pores,  or  with  the  solid  molecules,  will  contain  less 
salt  than  water. 

From  the  affinity  which  the  two  liquids  exert  on  one  another  this 

condition  will  not  remain  constant, 
and  the  rapidity  with  which  the  inter- 
change takes  place  will  depend  upon 
the  affinity  of  the  two  liquids  for 
one  another ;  but  the  interchange 
will  not  occur  in  the  same  manner 
as  if  no  membrane  were  present,  i.e., 
equal  quantities  of  salt  solution  and 
water  will-  not  substitute  one  an- 
other. Such  an  interchange  will 
only  occur  in  the  centre  of  the  pore, 
while  on  the  wall  of  the  pores  only 
water  will  pass ;  consequently  the 
salt  solution  will  increase  in  volume 
and  the  water  will  diminish  corre- 
spondingly, while  the  rapidity  of 
motion  along  the  walls  will  be  less 
than  in  the  centre  of  the  pores  on 
account  of  the  attraction  of  the 
walls  for  the  water. 

Therefore,  the  greater  the  concentration  of  the  salt  solution  the 
higher  will  be  the  osmotic  equivalent,  since  the  difference  of  affinity  of 
the  membrane  for  the  water  as  compared  with  the  salt  solution  will  be 
the  more  marked.  This,  however,  only  applies  to  salts  whose  solutions 
are  also  imbibed  by  the  membrane ;  where  this  is  not  the  case  increased 
concentration  produces  a  decrease  in  the  osmotic  equivalent,  for  in  the 
latter  case  there  will  be  more  tendency  for  the  membrane  to  hold  the 
layer  of  water  in  contact  with  the  walls  of  its  pores. 

Different  membranes  will  consequently  modify  the  osmotic  exchange 
of  liquids  taking  place  through  them. 


FIG.  39.— DIAGRAM  ILLUSTRATING 
OSMOSIS. 

This  figure  represents  a  diagrammatic  section  of  a 
single,  capillary  pore  in  an  organic  membrane  separating 
salt  solution  and  water.  From  the  greater  affinity  of  the 
membrane  for  water  than  for  salt  solution,  the  former 
passes  in  a  layer  in  contact  with  the  circumference  of  the 
tube,  while  the  salt  solution  passes  only  in  the  centre  of 
the  tube.  Therefore,  more  water  than"  salt  solution  will 
traverse  the  membrane. 


PHYSICAL   PROCESSES   IN   CELLS.  55 

Thus,  dr}"  membrane  will  show  a  higher  osmotic  equivalent  than 
fresh  membranes  or  dried  membranes  moistened,  from  the  fact  that  the 
membrane  retains  more  water  by  imbibition,  while  the  passage  of  the 
salt  is  facilitated. 

If  an  animal  membrane  separates  water  and  alcohol,  the  water  will 
pass  in  much  greater  amount,  for  membrane  absorbs  water  mifch  more 
readily  than  alcohol  or  a  mixture  of  water  and  alcohol. 

Rubber  or  collodium  membranes,  on  the  other  hand,  allow  alcohol 
to  pass  with  greatest  readiness,  as  such  membranes  absorb  alcohol  more 
readily  than  water. 

The  general  phenomena  of  osmosis  may  he  well  illus- 
trated by  the  egg-osmometer  (Fig.  40).  This  is  prepared 
by  picking  off  a  little  of  the  shell  from  one  end  of  an  egg, 
taking  care  to  leave  the  shell-membrane  intact,  while  a 
glass  tube  is  cemented  around  a  small  hole  pierced  through 
both  shell  and  shell-membrane  at  the  opposite  end.  The 
end  at  which- the  shell  has  been  removed  and  the  membrane 
left  undisturbed  is  then  immersed  in  distilled  water.  After 
a  time  it  will  be  found  that  water  has  passed  from  the  out- 
side to  the  interior  of  the  egg,  as  shown  by  the  increased 
volume,  the  white  of  the  egg'being  forced  up  into  the  tube 
cemented  on  the  open  end  of  the  egg.  At  the  same  time 
the  addition  of  nitrate  of  silver  to  the  water  in  which  the 
egg  was  immersed  will  show,  by  the  white  precipitate 
formed,  that  the  chlorides  have  passed  from  the  inside  to 
the  outside  of  the  egg.  No  trace  of  albumen,  however,  is 
to  be  seen  in  the  distilled  water.  The  salts  of  the  egg,  or 
its  crystalloids,  have  thus  passed  by  osmosis  through  the 
egg-membrane,  water  has  also  passed,  while  the  egg-albu- 
men, a  colloid,  has  been  retained. 

These  facts,  already  alluded  to,  that  crystalloids  in  solu- 
tion will  pass  through  an  animal  membrane,  while  colloids 
will  not,  has  been  made  use  of  in  a  process  which  is  fre- 
quently employed  by  the  chemist  to  separate  bodies  of  these 
two  classes.  Thus,  albumen,  or  any  other  colloid,  may  be 
entirely  freed  from  crystalloids,  such  as  salt  or  sugar,  by 
placing  it  on  one  side  of  a  membrane  with  a  large  quantity 
of  distilled  water,  which  is  frequently  renewed,  on  the  other. 
The  salts  pass  through  the  membrane  to  the  water,  their  FlG-  A4°K~  s 

place  being  taken  by  water,  while  the  albumen,  with  the  ILLUSTRATE  Os- 
exception  of  becoming  more  diluted,  remains  unchanged.  MO  TIC  ACTION. 
This  process  is  termed  dialysis.  .  (Flint.) 

Osmotic  phenomena,  consequently,  may  be  referred  to  the  following 
causes  (Wundt)  : — 

1.  The  affinity  which  the  two  liquids  exert  on  one  another. 

2.  The  relative   affinity  which  the  membrane  exerts  on  the   two 
liquids. 

3.  On  the  narrowness  of  the  pores  through  which  the  liquids  diffuse. 

4.  On  the  overcoming  of  the  adhesion  of  the  liquids  to  the  walls  of 
the  pores  through  increase  of  temperature. 

The  importance  of  this  process  in  the  action  of  the  animal  organism  is 
very  evident.  Nearly  all  animal  tissues  are,  during  their  entire  life,  in 


56  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

a  state  of  tension  from  imbibition  (swollen)  ;  therefore,  all  tissues  permit 
the  entrance  of  watery  and  saline  solutions,  and  prevent  entrance  of 
liquids  not  miscible  with  water.  The  absorption  of  most  of  the  dissolved 
food-stuffs,  and  the  removal  of  deleterious  matters,  etc.,  by  the  glands 
from  the  blood  rest  on  osmotic  processes.  The  results  as  to  the  different 
osmotic*  equivalent  of  different  substances  ;  the  behavior  of  different 
membranes  to  diffusion  ;  the  different  capability  of  animal  matter  for 
imbibing  different  solutions,  all  point  to  the  way  in  which  the  glands 
remove  different  substances  from  the  blood  where  no  other  explanation 
can  be  found  but  a  membrane  and  cells  capable  of  absorbing  certain 
solutions.  The  presence  of  certain  salts  in  the  contents  of  certain  cells 
is  without  doubt  instrumental  in  shaping  the  capability  of  those  cells 
for  absorbing  definite  solutions. 

9.  DIFFUSION  OF  GASES.— In  the  living  organism,  in  the  cell,  the 
vital  activities  are  only  carried  on  when  there  is  an  unbroken  supply  of 
oxygen  conveyed  to  the  cells  either  in  the  form  of  a  free  gas  or  in 
haemoglobin.  And,  on  the  other  hand,  the  organism  cannot  exist  unless 
there  is  some  provision  made  for  the  removal  of  C02,  continually  formed 
in  physiological  oxidation,  and  which  itself  is  a  dead^  poison  to  cell 
activity.  These  two  gases  are,  therefore,  the  most  important  which  have 
to  be  considered. 

In  pulmonated,  air-breathing  animals  there  is  also  a  continual  exhala- 
tion of  watery  vapor  ;  there  is  also  a  continual  circulation  of  N  in  the 
lungs  of  animals,  as  N  forms  four-tifths  of  the  atmosphere. 

Gaseous  interchange  in  the  organism  rests  mainly  on  the  laws  of 
diffusion  and  absorption  of  gases,  though  these  laws  are  subject  to  some 
slight  modification  as  contrasted  with  their  application  to  inorganic 
matter. 

Ity  gaseous  diffusion  is  meant  the  mutual  mixing  of  two  or  more 
free  gases ;  and,  as  in  liquid  diffusion,  it  results  in  a  uniform  mixture. 

Gases  which  pass  into  a  vacuum  fill  it  completely  and  uniformly;  this 
is  also  the  case  when  the  space  into  which  a  gas  streams  is  already  occu- 
pied by  a  gas  which  is  chemically  indifferent  to  the  first ;  a  space  filled 
with  an  indifferent  gas  behaves  to  another  gas  precise^  like  a  vacuum. 

If  two  flasks,  each  provided  with  a  stop-cock,  are  connected,  one 
vertically  above  the  other,  and  the  upper  one  filled  with  Irydrogen,  the 
lightest  of  gases,  and  the  lower  one  with  carbon  dioxide,  a  heavy  gas,  if 
the  stop-cocks  are  now  opened,  in  a  short  time  it  will  be  found  that  half 
of  the  hydrogen,  in  spite  of  its  lighter  specific  gravit}^,  has  descended 
into  the  lower  flask,  while  half  of  the  carbon  dioxide  has  ascended 
against  gravity  into  the  upper  flask,  so  that  each  flask  will  contain  a 
uniform  mixture  of  the  two  gases  (Fig.  41).  Each  gas  has  diffused  into 
the  other  as  into  a  vacuum,  and  what  holds  for  the  diffusion  of  two 


PHYSICAL   PKOCESSES   IX   CELLS. 


57 


erases  applies  also  to  the  diffusion  of  several  gases ;  so  that  the  general 
rule  may  be  formulated  :  If  a  number  of  gases  exerting  no  chemical 
influence  on  each  other  are  allowed  to  enter  a  space,  each  gas  will  diffuse 
itself  uniformly  through  that  space. 

If  the  amount  of  gas  in  any  given  space  is  small  or  large,  or,  in 
other  words,  no  matter  what  the  gaseous  pressure  may  be,  another  gas 
will  enter  that  space  precisely  as  if  it  were  a  vacuum. 

The   importance   of  these   laws    in    explaining  the  mechanism  of 
gaseous  interchange  in  respiration  is  very  evident.     The  atmosphere  is 
composed  of  a  mechanical  mixture  of  about  f  nitrogen  and  |  oxygen. 
In  the  process  of  inspiration  a  variable  amount   of  this 
gaseous  mixture  is  drawn  into  the  lungs.     It  then  meets 
with  a  gaseous  mixture  which  contains  less  ox}-gen  than 
the  atmosphere    (for    a  certain    amount  of  the   ox}Tgen 
taken  in  in  previous  inspirations  has  been  removed  by 
the  blood),  and  which  contains  a  considerable  volume  of 
carbon  dioxide  removed  from  the  blood. 

Phenomena  of  diffusion,  therefore,  at  once  commence 
between  the  air  alread}'  in  the  lungs  and  that  which  has 
entered  in  inspiration.  The  air  in  the  lungs  becomes 
gradually  poorer  in  oxygen  and  richer  in  carbon  dioxide, 
as  the  air-cells  are  approached.  Diffusion  tends  to  equal- 
ize this  difference  ;  the  oxygen  of  the  inspired  air  diffuses 
into  the  deeper  portions  of  the  lungs,  the  carbon  dioxide 
diffuses  from  the  deeper  to  the  upper  portion,  the  process 
being  a  constant  one;  for  the  difference  in  the  relative 
volumes  of  the  two  gases  in  the  upper  air-passages  is 
maintained  by  repeated  expirations,  by  which  C02  is 
removed,  anil  inspirations,  by  which  more  oxygen  is  FlG  ^ 

brought  into  the  lungs. 

The  COa  formed  in  respiration  by  animal  organisms,  and  thus 
removed  from  them  in  respiration,  distributes  itself  uniformly  through 
the  atmosphere,  so  that  there  is  everywhere  a  uniform  percentage, 
unless  there  is  a  local  temporary  increase ;  but  then  this  soon  becomes 
equalized  by  diffusion,  permanent  increase  being  prevented  by  the 
absorption  processes  in  the  vegetable  kingdom. 

The  tension  of  0  in  the  atmosphere  is  far  greater  than  that  of  C02, 
as  the  0  is  present  in  far  larger  proportion,  and  conversely. 

Diffusion  leads  finally  to  the  theoretical  result,  that  all  gases  in  any 
given  space,  as  in  the  atmosphere,  exist  under  the  same  pressure ;  when, 
therefore,  there  is  anywhere  a  temporary  increase  in  the  tension  of  a  gas, 
diffusion  commences  and  tends  to  continue  until  there  is  a  uniform 
distribution  and  mixing  of  the  different  gases. 


58 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


If  two  different  gases  are  separated  by  a  porous  partition,  the  gases 
will  mix  through  that  partition.  The  phenomena  under  such  circum- 
stances are  similar  to  what  has  been  described  in  the  case  of  liquids 
under  osmosis ;  that  is,  that  different  gases  pass  with  different  degrees 
of  rapidity  through  the  partition,  so  that  the  volume  of  gas  increases  on 
one  side  of  the  partition  and  decreases  on  the  other.  If  an  unglazed, 
porous,  earthenware  cup  (such  as  is  used  in  a  Grove  battery)  is  closed 
witli  a  cork  through  which  passes  a  long,  vertical,  glass  tube,  whose  end 
dips  into  a  vessel  below  containing  water,  and  the  cup  is  covered  with  a 
bell-jar  containing  hydrogen  or  illuminating  gas,  the  hydrogen  will  pass 
through  the  walls  of  the  cup  to  the  inside  faster  than  the  air  from  the 
inside  can  diffuse  out.  The  volume  of  gas  in  the  interior  increasing^ 
bubbles  of  air  will  escape  through  the  water  from  the  end  of  the  tube. 
If  now  the  bell-jar  be  removed  the  hydrogen  will 
diffuse  out  from  the  cup  faster  than  the  air  can 
enter,  the  volume  of  gas  within  the  cup  will  decrease 
and  the  water  will  rise,  from  atmospheric  pressure, 
within  the  tube.  If  oxygen  be  used  within  the  cup 
instead  of  atmospheric  air,  it  will  be  found  that  the 
hydrogen  will  diffuse  four  times  as  fast  as  the  oxygen. 
The  density  of  hydrogen  is  1.;  that  of  oxygen  16.; 
therefore,  the  law  has  been  made  that  the  rapidity 
with  which  different  gases  under  similar  conditions 
(equal  pressures)  diffuse  through  thin,  porous  par- 
titions into  a  vacuum  or  into  other  gases  is  in  inverse 
proportion  to  the  square  root  of  the  density  of  the 
gases  (Graham's  law). 

These  general  facts  may  be  illustrated  by  another 
very  simple  experiment.  If  an  unglazed  earthenware 
cup  be  closed  by  a  cork  in  which  a  water-manometer 
is  inserted  and  then  placed  in  a  larger  glass  vessel  containing  vapor 
of  ether,  the  air  from  the  inside  of  the  cup  will  diffuse  out  faster  than 
the  five-times-heavier  vapor  of  ether  will  diffuse  in,  and  the  water  in 
the  open  arm  of  the  manometer  will  sink  (Fig.  42). 

There  is,  however,  here  a  marked  difference  from  osmosis,  for  in  the 
diffusion  of  gases  through  inorganic  partitions  or  dry  organic  membranes 
the  nature  of  the  partition  is  without  influence  on  the  rapidity  of  diffusion. 
The  rapidly  of  diffusion  depends  only  on  the  specific  gravit3T  of  the  gas. 
10.  ABSORPTION  OF  GASES. — Exactly  as  gases  diffuse  into  spaces 
already  occupied  by  other  gases,  so  also  will  they  diffuse  into  the  inter- 
molecular  spaces  of  liquids,  without  any  chemical  attraction  between  the 
gas  and  the  fluid  being  essential.  If  a  glass  tube,  closed  at  one  end,  is 
filled  with  dry,  ammoniacal  gas,  its  open  end  immersed  in  mercur}-,  and 


FIG.  42. 


PHYSICAL   PROCESSES    IN   CELLS.  59 

then  a  small  quantity  of  water  introduced  into  the  tube,  the  water  will 
almost  instantly  absorb  the  gas,  which  will  entirely  disappear,  and  the 
mercury  will  rise  in  the  tube,  and,  with  the  water,  entirely  fill  it. 

Just  as  without  so  also  within  liquids,  gases  exert  no  pressure  on 
each  other;  so  that  a  number  of  gases  may  diffuse  at  the  same  time  into 
any  given  liquid. 

We  meet,  in  this  solution  of  gases  in  liquids,  with  laws  analogous 
to  those  which  govern  the  solution  of  solids  in  liquids.  Every  liquid 
absorbs  at  amr  given  temperature  a  fixed  quantity  of  an y  given  gas,  just 
as  a  certain  quantit}'  of  liquid  will  only  dissolve  a  given  quantit}^  of 
a  salt.  The  volumes  which  a  given  liquid  at  a  fixed  temperature  will 
absorb  of  different  gases  are  very  different,  the  most  readily-liquefied 
gases  being  most  readily  absorbed.  The  volume  of  any  gas  that  may 
be  absorbed  b}-  a  liquid  varies  greatly  with  the  temperature.  As  the 
temperature  increases  capability  of  absorption  decreases,  until  at  100°  C. 
water  absorbs  no  gas  at  all.  The  exact  opposite  holds  in  the  case  of 
solutions. 

The  co-efficient  of  absorption  is  the  volume  of  gas  which  a  liquid  in 
free  communication  with  a  gas  can  absorb.  It  varies  with  every  liquid, 
every  gas,  and  every  temperature.  According  to  Bunsen,  a  unit  of 
volume  of  water  absorbs — 

Gas.  Temperature.  Volume. 

<    00  1.7967 


CO2 

N 


0 


200 
00 

200 
00 

200 


H  .  00 


.9046 
0.02034 
0.01401 
0.04114 
0.02838 
0.0163 


With  every  increase  of  pressure  the  liquid  will  absorb  uniformly- 
increased  amounts  of  gas. 

Gases  absorbed  by  liquids  do  not  lose  their  power  of  diffusion. 
Hence,  if  we  bring  a  liquid  which  contains  a  gas  under  a  definite  tension, 
e.g.,  H20  with  C02.  in  communication  with  a  space  containing  another 
gas,H,  the  C02  diffuses  out  of  the  HaO  into  the  space  containing  the  H. 
C02  will  continue  to  leave  the  water  until  it  exists  in  equal  pressure 
without  and  within  the  liquid  ;  so,  also,  H  will  diffuse  into  the  water  until 
it  has  a  uniform  tension  without  and  within  the  liquid.  An  absorbed 
gas  is  therefore  given  up  when  the  tension  of  the  gas  is  less  in  the  space 
in  communication  with  the  liquid  than  the  tension  of  the  gas  in  the  liquid. 
When  two  or  more  gases  are  mixed  together  their  absorption  by  a  liquid 
is  proportional  to  the  relative  volumes  of  the  gases  present  in  the  mix- 
ture, or  to  the  different  gaseous  tensions. 

In  the  cell  in  the  animal  organism  this  gaseous  interchange  occurs 


60  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

through  the  cell-wall  or  the  walls  of  capillaries,  etc.  These  organic 
tissues,  which  we  have  seen  to  be  always  filled  with  liquid,  offer  very  little 
resistance  to  the  passage  of  a  gas.  The  animal  fluids  communicate 
through  these  delicate  moist  tissues  almost  directly  writh  the  gases  of  the 
atmosphere. 

Gases  formed  by  cells,  or  gases  which  pass  from  the  exterior  to  the 
interior  of  cells,  or  even  the  passage  of  gases  through  the  membranes  of 
the  lungs  or  gills  of  animals,  are  not  governed  by  the  law  of  the  dif- 
fusion of  gases  given  above,  but  their  transfer  through  an  animal  mem- 
brane is  governed  by  the  co-efficient  of  absorption  of  that  tissue  for  the 
different  gases.  This  may  be  illustrated  by  a  very  simple  experiment 
devised  by  Draper,  who  does  not  appear,  however,  to  have  appreciated 
its  application  to  gaseous  interchange  in  the  animal  bod}'.  The  law  of 
the  diffusion  of  gases  through  porous  partitions  is  that  the  rapidity  of 
the  diffusion  is  inversely  as  the  square  root  of  the  densit}'  of  the  gas. 
If  the  finger  be  dipped  in  soap-water  and  then  rapidly  passed  over  the 
mouth  of  an  empty  bottle  so  as  to  leave  a  horizontal  film,  and  the  bottle 
then  placed  under  a  bell-jar  filled  with  carbon  dioxide,  the  film  soon 
swells  up  into  an  almost  hemispherical  dome.  Or,  if  the  bottle  be  filled 
with  carbon  dioxide,  and  then  exposed  to  the  atmosphere  after  its  mouth 
has  been  covered  with  a  sonp-film  as  before,  the  film  is  promptly 
depressed  into  a  deep  concavity  and  bursts.  Now,  if  the  film  is  regarded 
as  a  porous  partition,  the  air,  being  of  many  times  less  density  than  the 
C03,  should  diffuse  much  more  rapidly,  according  to  Graham's  law.  The 
reverse,  however,  is  the  case.  Water,  however,  of  which  the  film  consists, 
has  a  much  higher  co-efficient  of  absorption  for  C02  than  it  has  for  oxygen 
or  nitrogen.  The  C02  is  therefore  absorbed  more  rapidly  by  the  film 
than  the  gases  of  the  atmosphere,  and  from  its  solution  in  the  film  dif- 
fuses rapidly  into  the  atmosphere.  The  state  of  affairs  is  similar  in  the 
case  of  gaseous  interchange  in  animal  cells. 

The  membranes  of  cell  are  not  porous  partitions,  but  are  tissues 
whose  molecular  interspaces  are  filled  with  liquids.  That  a  gas  may  pass 
through  such  a  membrane  it  is  necessary,  therefore,  that  the  gas  be  first 
absorbed  by  the  liquid  in  the  cell-membrane.  The  readily-absorbed  gases, 
such  as  CO2,  will  thus  diffuse  through  cell-membranes  more  rapidly  than 
those  with  a  lower  co-efficient  of  absorption,  such  as  N,  H,  or  O,  the 
rapidity  of  absorption  being  further  governed,  not  only  by  the  co-efficient 
of  absorption,  but  by  the  gaseous  tension  and  the  temperature.  After 
having  passed  through  the  cell-membrane  gases  will,  of  course,  diffuse 
into  the  liquid  or  gaseous  media  surrounding  those  cells,  according  to  the 
tension  of  those  gases  already  present. 

In  the  case  of  terrestrial  animals  this  medium  is  the  atmosphere, 
which  is  composed  of  21-volume  per  cent,  of  0  and  79  per  cent,  of  N, 


PHYSICAL  PROPERTIES  OF  TISSUES.  61 

with  traces  of  C03.  If  we  imagine  in  the  first  place  that  the  tissues  are 
at  first  free  from  gas,  according  to  the  co-efficients  of  absorption  and 
pressure,  they  will  absorb  definite  volumes  of  these  gases. 

If  we  assume  that  the  co-efficient  of  absorption  of  the  animal  liquids 
for  these  gases  is  the  same  as  water,  as  is  actually  nearly  the  case,  the 
co-efficient  of  absorption  for  O  will  be  nearly  double  that  of  N,  and  the 
volumes  absorbed  will  be  as  34.91  to  65.09.  This  is  actually  the  case  in 
large  bodies  of  water,  as  lakes,  etc. 

Under  the  conditions  we  have  imagined,  of  course,  only  a  trace  of 
C02  would  be  absorbed.  '  We  know,  however,  that  C0a  is  a  constant 
result  of  cell  life  ;  therefore  the  tension  of  C02  in  animal  fluids  is  far  in- 
excess  of  that  in  the  atmosphere ;  consequently,  instead  of  an  absorp- 
tion of  C02  by  the  tissues  from  the  air,  we  will  have  an  exhalation  taking 
place.  Similar  conditions  apply  in  the  case  of  watery  vapor. 

Hence,  the  gaseous  interchanges  between  the  organism  and  the 
atmosphere  under  the  laws  of  absorption  and  diffusion  are  as  follow : — 

Absorption  of  O  and  N. 
Exhalation  of  CO2  and  H2O  vapor. 

In  animals,  however,  by  far  the  greater  part  of  0  and  COa  are 
carried  in  chemical  combination  with  haemoglobin,  and  not  in  mere  solu- 
tion in  the  fluids  of  the  body.  These  conditions,  as  well  as  the  mechanism 
of  gaseous  interchange  in  the  lungs  and  tissues,  will  be  considered  in 
greater  detail  under  the  subject  of  Respiration.  At  present  enough  has 
been  said  to  show  that  the  laws  of  diffusion  and  absorption  are  the 
fundamental  principles  which  underlie  these  processes. 

II.   THE   PHYSICAL   PROPERTIES   OF   TISSUES. 

We  have  found  that  the  different  animal  tissues  furnish  illustrations 
of  both  the  solid  and  liquid  forms  of  matter,  var3*ing  from  a  perfect 
fluid  to  a  solid  of  almost  mineral  consistence,  and  that  midway  between 
these  extremes  what  may  be  termed  the  semi-fluid  tissues  are  of  the 
greatest  importance  in  the  physical  and  chemical  operations  of  the 
organism.  We  know,  further,  from  anatysis  of  the  organic  tissues,  that, 
no  matter  what  their  consistence,  they  all  contain  a  large  proportion  of 
water  in  their  composition ;  it  is  to  the  amount  and  the  manner  in  wrhich 
this  water  is  held  by  the  tissues  that  nearly  all  the  physical  properties 
of  the  tissues,  particularly  of  the  semi-solid  tissues,  are  due. 

We  have  already  seen  that  in  inorganic  bodies,  though  they  may 
be  rich  in  water,  the  water  is  either  chemically  united  to  that  body,  or  is 
held  mechanically  in  capillary  pores ;  while  in  organic  matter  the  water 
occupies  the  intermolecular  spaces.  The  tissues,  therefore,  resemble 
solutions  in  this  respect ;  thus,  in  a  salt  solution  the  water  occupies  the 


62  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

intermolecular  spaces  of  the  salt.  In  solutions,  however,  the  solids  are 
bound  to  the  water;  in  tissues,  the  reverse. 

Since  all  fresh,  organic  tissues  contain  water,  their  specific  gravity 
must  be  comparatively  low  ;  drying,  by  driving  off  the  water,  while 
decreasing  their  weight  by  the  amount  of  water  displaced,  will  increase 
their  specific  gravity,  though  even  then,  like  all  organic  bodies,  they  will 
be  specifically  lighter  than  most  minerals.  The  specific  gravity  of  dif- 
ferent tissues  will  also  vary  according  to  the  nature  of  their  special  con- 
stituents;  thus,  adipose -tissue  will  represent  one  extreme,  bones  and 
teeth  the  other,  and  tissues  which  are  rich  in  fat,  like  the  nervous  tissues, 
will  be  of  less  specific  gravity  than  those  which  contain  inorganic 
matters. 

As  the  specific  gravity  of  the  tissues  depends  upon  their  constitu- 
ents, it  will  vary  according  to  the  relative  proportions  of  those  con- 
stituents at  different  ages,  in  different  individuals,  and  in  different 
nutritive  states.  No  fixed  figures  can,  therefore,  be  given  to  represent 
the  specific  gravity  of  the  different  tissues,  but,  though  not  constant,  the 
following  represents  the  average  specific  gravity  of  the  most  important 
tissues  of  the  human  body : — 

Bones,     ...........  1.656 

Elastic  tissue  and  tendons, 1.12 

Muscles,  .        , •      .        .  1.073 

Arteries,  . '  .  1.096 

Veins, .        .        .        .  1.05 

Nerves,    .  '     .        .        .        .        .        ...        .         .  1.046 

1.  COHESION. — It  follows  from  what  has  been  said  as  to  the  freedom 
of  molecular  movement  in  most  organic  tissues,  as  shown  in  their  capa- 
bility of  imbibition,  that  their  cohesion  must  be  less  than  that  of  most 
inorganic  solids.  It  is  highest"  in  the  bones,  lowest  in  glands  and  , brain, 
though  it  is  comparatively  high  in  nerves.  Cohesion  is  there  due  to  the 
fibrous  envelope  (neurilemma)  and  not  to  the  nerve-fibre;  and  as  these 
sheaths  relatively  increase  as  the  nerve-trunks  subdivide,  the  cohesion  of 
the  fine  nervous  twigs  of  the  skin  is  relatively  higher  than  that  of  the 
nerve-trunks. 

The  greater  the  amount  of  water  contained  in  a  tissue  the  less  its 
cohesion,  for  the  wider  apart  will  be  the  molecules,  and  the  molecular 
attraction  decreases  as  the  square  of  the  distance  which  separates  them. 
Consequently  desiccation  increases  cohesion.  The  order  of  cohesiveness 
is  inversely  as  the  quantity  of  water;  thus,  the  following  list  is  arranged 
with  tissues  of  greatest  cohesion  and  least  water  first,  and  as  water 
increases  cohesion  decreases : — 

1.  Bones.  4.   Muscles.  7.   Intestines. 

2.  Tendons.  5.   Veins.  8.    Glands. 

3.  Nerves.  6.   Arteries.  9.   Brain. 


PHYSICAL  PROPERTIES   OF  TISSUES.  63 

In  youth  the  tissues  have  less  cohesion  than  in  adult  life,  from  the 
greater  preponderance  in  the  former  period  of  water ;  while  the  cohesion 
again  declines  in  old  age,  especially  in  bone  and  muscle,  even  though 
the  proportion  of  water  present  also  diminishes,  from  changes  in  the 
quantity  of  inorganic  elements. 

The  cohesion  of  airy  tissue  is  not  uniform  in  all  directions,  but,  as  is 
well  known,  certain  tissues  may  be  ruptured  in  one  direction  more 
readily  than  in  another ;  thus,  a  costal  cartilage  is  more  readily  broken 
transversely  than  longitudinally.  This  is  even  .more  marked  in  fibrous 
tissues,  such  as  a  tendon,  where  it  is  much  easier  to  separate  the  longi- 
tudinal fibres  than  it  is  to  rupture  them  by  traction.  This  may  be 
explained  by  the  fact  that  the  cohesion  of  any  tissue  is  the  resultant  of 
the  forces  which  holds  the  ultimate  molecule  of  the  tissues  together,  as  in 
a  single,  fibre  of  connective  tissue,  and  of  the  adhesive  force,  which 
through  the  mediation,  ordinarily  of  cement  substance,  holds  several 
collections  of  similar  molecules  together. 

The  forces  which  may  act  on  a  tissue  to  destroy  its  cohesion  mny 
operate  in  four  different  ways :  by  traction,  b}'  pressure,  by  flexion,  and 
by  torsion.  All  the  different  tissues  behave  differently  to  each  of  these 
modes  of  action. 

The  resistance  to  traction  is  measured  by  the  force  required  to  tear 
apart  the  molecules  of  any  tissue ;  hence,  the  force  required  to  produce 
tearing  in  any  tissue  must  increase  with  the  cross-section  of  the  tissue 
subjected  to  strain,  and  when  the  cohesion  of  two  different  tissues  is 
compared  in  this  respect  the  comparison  must  always  be  reduced  to  a 
unit  of  cross-section.  Thus,  in  the  following  table  the  numbers  represent 
the  breaking  weight  in  kilogrammes  for  every  square  millimeter  of 
surface  (Wertheim): — 

Bones,  .        .         .        ....  7  76 

Tendons, .  694 

Muscles, 0.054 

Nerves, .  0.93 

Arteries, .  0.16 

Veins,        . .  012 

This  resistance  to  traction  is  of  great  importance  in  the  mechanics 
of  the  organism.  The  cohesion  of  the  bones,  tendons,  ligaments,  and 
muscles  permit*  of  the  accomplishment  of  mechanical  work,  while  the 
resistance,  to  distension  of  the  different  membranes  of  the  body,  such  as 
the  aponeuroses,  fibrous  membranes,  etc.,  is  of  great  value  in  numerous 
physiological  operations. 

The  resistance  to  pressure  is  especially  seen  in  the  bony  skeleton, 
articular  cartilage,  and  intervertebral  disks.  In  the  bones  this  is  especially 
very  marked.  Thus,  it  has  been  found  that  from  1110  to  2300  kilo  were 
required  to  crush  a  cube  of  bone  from  the  compact  substance  of  the 


64  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

bones  of  the  extremity  5  millimeters  thick,  while  only  100  kilo  were 
required  to  crush  a  cube  of  the  same  size  from  the  spongy  substance. 
The  cohesion  of  the  compact  substance  measured  in  this  way  decreases 
to  about  the  same  degree  when  either  the  organic  matter  or  the  lime  salts 
are  removed;  it  also  decreases  greatly  when  the  water  is  removed, 
showing  a  deviation  from  the  general  statement  above  made.  This  resist-' 
ance  to  pressure  plays  an  important  role  in  the  support  of  the  body  in 
standing,  walking,  and  jumping,  and  in  the  protection  from  injury  of  such 
important  organs  as  the  brain,  spinal  cord,  lungs,  and  heart. 

The  resistance  to  pressure  in  the  osseous  system  decreases  with  age. 
Thus,  Fick  has  found  that  a  prism  of  bone  1  square  millimeter  in  size 
from  a  man  30  years  of  age  was  crushed  by  a  weight  of  15.03  kilo,  while 
a  similar  piece  from  a  man  aged  74  years  would  not  sustain  a  weight  of 
4.33  kilo.  The  bones  of  different  animals  also  show  great  differences  in 
their  resistance  to  pressure. 

The  resistance  to  flexion  and  torsion  possessed  by  the  different  tissues 
of  the  body  also  comes  into  play  in  certain  physiological  operations. 
Thus,  in  inspiration  the  ribs  and  costal  cartilages  undergo  a  slight 
amount  of  twisting  and  bending  through  the  action,  of  the  inspiratory 
muscles,  and  regain  their  position  during  expiration.  So,  when  a  weight 
is  lifted  and  held  horizontal  by  the  hand  the  resistance  to  flexion  pre- 
vents bending  of  the  bones  of  the  arm. 

The  cohesion  of  the  tissues  is  always  greatest  in  the  direction  in 
which  the  forces  which  act  on  those  tissues  is  usually  exerted.  Thus, 
when  tissues  are  ordinarily  subjected  to  the  force  of  traction,  their  co- 
hesive force  is  most  developed  in  a  longitudinal  direction,  and  such  tis- 
sues, like  tendons  and  ligaments,  are  fibrous  in  structure.  When  the 
pressure  or  force  to  which  tissues  may  normally  be  subjected  does  not 
lie  in  any  one  but  in  many  different  directions,  as  in  the  resistance 
which  serous  membranes  and  aponeuroses  offer  to  distension,  such  mem- 
branes are  also  fibrous  in  structure ;  but  the  fibres,  instead  of  being 
parallel  to  each  other  as  in  tendons,  in  which  traction  is  the  only  force 
to  which  they  are  subjected,  are  interlacing  and  cross  each  other  in 
every  direction.  Finally,  when  pressure  is  the  force  which  must  be 
resisted,  we  find  the  tissues  taking  the  form  in  which  such  resistance 
may  be  best  offered  ;  the  compact  bony  tissues  are  therefore  arranged  in 
arches,  as  in  the  head  of  the  femur,  or  in  the  form  of  hollow  tubes, 
as  in  the  shafts  of  the  long  bones, — two  forms  which,  with  the  greatest 
economy  of  material,  offer  the  greatest  resistance  to  pressure.  In  the 
case  of  the  femur  its  upper  end  is  not  only  subjected  to  pressure  from 
the  weight  of  the  bod}r,  but  also  to  flexion ;  for  the  head  of  the  femur 
is  not  in  a  line  with  the  long  axis  of  the  bone,  but  lies  to  one  side  and 
is  connected  with  the  shaft  of  the  bone  by  an  oblique  neck.  The 


PHYSICAL   PROPERTIES   OF   TISSUES. 


65 


sirrangement  of  the  compact  substance  of  the  bone  is  especially  fitted  to 
overcome  these  direct  or  indirect  pressures  (Fig.  43). 

2.  ELASTICITY. — The  elasticity  of  the  tissues  varies  in  the  same  way 
AS  their  cohesion.  The  moist  tissues  have,  as  a  rule,  a  very  slight  elas- 
ticity ;  that  is,  they  offer  slight  resistance  to  external  forces  which  tend 
to  change  their  form,  and  in  most  of  the  tissues  which  are  rich  in  water, 
as  the  brain  and  glands,  the  elasticity  is  incomplete ;  that  is,  the  original 
form  is  not  regained  after  the  distorting  force  ceases  to  act.  On  the 
other  hand,  in  the  elastic  tissues  and  muscles  the  force  must  be  excessive 
to  produce  permanent  distortion. 

The  cohesion  of  a  body  is  its  resistance  to  tearing  forces ;  elasticity  is 
•developed  as  resistance  to  alteration  in  form,  and  refers  to  the  property  by 
which  the  original  form  is  regained.  The  elasticity  of  a  body  is  therefore 
great  when  a  great  force  is  required 
to  produce  change  in  form,  and 
vice  versa;  while  the  completeness 
of  the  elasticity  is  expressed  by  the 
perfection  with  which  the  original 
form  is  regained  after  the  distorting 
force  ceases  to  act.  Thus,  the  elas- 
ticity of  lead  is  great  but  incom- 
plete ;  of  rubber,  is  small  but 
perfect. 

Elasticity  cannot  be  measured 
toy  stretching  force  alone,  but  com- 
pressing, twisting,  and  bending 
forces  must  also  be  considered. 
The  resistance  to  each  of  these 
forces  is  the  same.  The  less  exten- 
sible a  body  is,  the  less  compressible 
is  it  also,  and  the  more  rapidly  it 
vibrates  when  bent  from  its  position  of  equilibrium. 

Organic  tissues  which  are  poor  in  water,  as  wood  and  bone,  and 
which  possess  high  elasticity,  behave  to  stretching  weights  like  inorganic 
bodies,  i.e.,  the  increase  in  length  is  proportionate  to  the  weight.  In 
the  soft  tissues,  of  less  but  more  complete  elasticity,  the  increase  in 
length  produced  by  heavy  weights  is  proportionately  less  than  that  due 
to  smaller  weights.  The  cause  of  this  lies  in  the  greater  extensibility  of 
such  tissues,  through  which  they  are  more  stretched  by  small  weights 
than  is  possible  in  rigid  bodies,  because  in  the  latter  a  much  smaller  ex- 
tension would  exceed  the  limit  of  cohesion  ;  though  the  use  of  weights 
of  very  great  difference  shows  that  the  extensibility  of  rigid  bodies  is 
probably  also  governed  by  the  same  laws. 

5 


FIG.  43.— DIAGRAM  OF  THE  STRUCTURE 
OF  THE  NECK  OF  THE  HUMAN  FEMUR. 
(Ward.) 

The  fibres.  A,  by  their  rigidity,  and  the  fibres,  B,  by 
their  tenacity,  tend  to  the  support  of  the  weight,  as 
illustrated  in  the  bracket,  while  the  latter  fibres  inter- 
lace with  the  arciform  fibres,  F. 


66 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


The  laws  for  elastic  changes  in  form  of  all  bodies,  including  the  soft 
organic  tissues,  is  expressed  in  the  diagram  given  below  (Fig.  44). 

The  spaces  on  the  line  A  B  represent  the  extending  weights.  The 
spaces  on  the  line  B  C  represent  the  increase  in  length.  Thus,  if  the 
extension  of  any  given  tissue  by  any  given  weight  equal  the  ordinate, 
A  D,  the  increase  in  extending  weight  by  regularly  increasing  amounts 
will  not  produce  a  proportional  increase  in  length.  Each  increase  will 
be  less  than  that  produced  by  the  previous  lesser  extending  weight,  and 
the  line  which  connects  the  limits  of  extension  will  be  a  curve  which 
gradually  tends  to  form  a  horizontal  line, — in  other  words,  a  hyperbola. 
In  a  corresponding  figure,  representing  the  extension  of  an  inorganic  bod}', 
the  line  D  C,  instead  of  being  a  curve,  would  be  a  straight  line,  and  the 
spaces  on  the  line  B  C  from  B  to  C  would  be  equal,  showing  that  the 
extension  increases  regularly  with  uniform  increase  in  extending  weight, 
A  p  with  the  exception  above 

alluded  to,  when  very 
great  difference  in  ex- 
tending weights  is  made 
use  of.  This  difference 
between  organic  and  in- 
organic bodies  is,  without 
doubt,  attributable  to  the 
greater  extensibility  of 
the  former. 

The  organic  tissues 
have  still  another  char- 
acteristic which  distin- 
guishes them  from  the  inorganic  bodies,  viz.,  when  a  tissue  has  been 
extended  by  a  weight,  if  the  weight  is  allowed  to  remain  the  extension 
gradually  increases,  and  may  not  be  complete  for  days  or  months  ;  this 
is  called  elastic  after-working.  It  is  present  in  all  elastic  bodies,  though 
in  rigid  bodies  it  is  much  less  marked,  and  its  limit  is  sooner  reached. 

The  weight  which  will  stretch  a  prism  one  square  millimeter  in  area 
and  one  meter  long  one  meter,  provided  the  limit  of  cohesion  is  not 
thereby  passed,  is  called  the  co-efficient  of  elasticity. 

The  following  figures,  according  to  Wundt,  give  the  co-efficients  of 
elasticity  of  some  of  the  more  important  organic  tissues  : — 

Bones,     .  -    .        .    ..".        .-       .         .        .         .        2264. 

Tendons,  .'        .....         .         .        .     1.6693 

Nerves,    .  ....'..        .        .         .     1.0905 

Muscles,.         ,         ...     ;- 0.2734 

Arteries,  .,       .        .    "... 0.0726 

The  smallness  of  these  co-efficients  is  recognized  when  it  is  remembered 
that  for  cast-steel  it  is  19881. 


C 


FIG.  44. 


PHYSICAL   PROPERTIES   OF   TISSUES.  67 

Elasticity  is  a  property  of  the  tissues  of  the  animal  body  which  is 
of  great  importance  in  man}'  physiological  operations.  It  is  a  force 
which  acts  either  against  constant  forces,  such  as  gravity,  or  temporary 
forces,  such  as  muscular  action.  Thus,  the  intervertebral  disks,  through 
their  elasticit}',  serve  to  deaden  the  shock  given  to  the  spinal  column  in 
jumping;  the  elastic  ligaments  of  the  spinal  column  serve  to  preserve  it 
in  its  normal  position  without  there  being  a  constant  strain  on  the  muscles, 
and  in  animals  in  whom  the  backbone  is  horizontal  it  serves  to  counteract 
the  weight  of  the  abdominal  viscera.  In  the  herbivorous  animals  the 
3'ellow  elastic  tissue  of  the  ligament-urn  uuchae  serves  to  assist  the  muscles 
in  supporting  the  head. 

In  expiration  the  elastichy  of  the  costal  cartilages  and  ribs,  together 
with  that  of  the  lungs, — forces  which  have  to  be  overcome  in  inspiration, 
— tend  to  restore  the  thorax  to  its  natural  form,  and  thus  drive  the  air  out 
of  the  lungs. 

The  elastic  tissue  of  the  arteries  tends  to  aid  the  intermittent  pro- 
pelling force  of  the  heart  in  producing  a  constant  forward  motion  of  the 
blood.  When  the  heart  contracts  it  drives  a  definite  quantity  of  blood 
into  the  arterial  system,  already  filled  with  blood,  and  thus  still  further 
distends  the  arteries.  During  the  pauses  between  the  contractions  of  the 
ventricles  the  elastic  tissue  recoils,  from  the  removal  of  the  distending 
force,  on  the  contents  of  the  blood-vessels,  and,  backward  motion  being 
prevented  by  the  closure  of  the  semi-lunar  valves,  drives  the  current  of 
blood  forward  in  the  vessels.  This  point  will  again  be  alluded  to  in  more 
detail  under  the  subject  of  the  Circulation. 

In  addition  to  these  properties  most  of  the  tissues  of  the  animal 
body  are  also  flexible  and  extensible,  the  degree  varying  great!}-  accord- 
ing to  the  structure  of  the  parts.  Flexibility  and  extensibility  must  not 
be  confounded.  Flexibility  means  capability  of  being  bent  or  twisted  ; 
extensibility  means  capability  of  being  increased  in  length.  Thus,  the 
tendons  are  flexible,  but  not  extensible  ;  were  they  capable  of  being  in- 
creased in  length  it  would  be  at  the  expense  of  the  force  developed  by 
muscles.  Tendons  are,  however,  very  flexible;  they  adjust  themselves 
to  the  position  the  part  may  occupy,  so  that  sometimes  they  transmit 
muscular  force  at  right  angles  to  the  line  in  which  the  muscle  acts.  Liga- 
ments, again,  are  flexible,  and  also  somewhat  more  extensible  than  tendons. 
In  joints  they  permit  of  the  free  play  of  one  bony  surface  on  the  other, 
and  yet  by  their  inextensibility  serve  to  keep  the  articular  surfaces  in 
apposition.  In  dislocations  the  articular  ligaments  are  rent,  and  the  bony 
articular  surfaces  are  no  longer  in  contact:  in  sprains  the  limit  of  elas- 
ticity of  the  ligaments  has  been  passed ;  that  is,  they  have  been  stretched 
beyond  the  point  at  which  their  elasticity  enables  them  to  regain  their 
original  form,  and  partial  ruptures  take  place. 


68  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

All  the  connective  tissues  are  originally  flexible  and  extensible ; 
these  properties  become  greatly  modified  in  the  subsequent  development 
of  the  tissues  of  this  group.  Thus,  in  cartilage  and  bone,  extensibility 
has  very  largely  disappeared,  especially  in  the  latter,  but  they  are  of  high 
elasticit}'.  In  dense  fibrous  tissue,  such  as  aponeuroses,  flexibility  re- 
mains, but  extensibility  has  become  greatly  reduced ;  hence  the  intense 
pain  produced  in  inflammation  below  such  tissues ;  for  being  inextensible 
swelling  is  restrained,  and  the  pressure  produced  by  the  products  of  in- 
flammation on  the  nerve-endings  is  greatly  increased. 

3.  OPTICAL  CHARACTERISTICS  OF  TISSUES  (Wundt). — (a)  Ee fraction. — 
All  organic  tissues  possess  a  higher  refractive  index  than  water.  By  this 
is  meant  that  when  a  ray  of  light  passes  obliquely  out  of  one  medium 
into  another  of  different  density,  it  is  bent  out  of  its  path  in  a  straight 
line  at  the  surface  of  separation  of  the  two  media,  the  ratio  between  the 
angle  of  incidence  and  the  angle  of  refraction  being  the  index  of  refrac- 
tion. Though  comparative  measurements  of  the  different  tissues  have  not 
been  made,  we  can  recognize  the  difference  by  the  sharpness  of  outline 
in  microscopic  examination.  Thus,  cell-wall,  nucleus,  and  nucleolus  are 
recognized  by  their  difference  in  refractive  powers.  When  two  tissues 
have  the  same  refractive  power  they  cannot  be  distinguished  by  the  eye, 
and  if  no  refractive  power  is  possessed  they  are  homogeneous. 

Fat,  elastic  tissue,  and  horn  have  the  highest  refractive  power. 
Watery  solutions,  as  in  the  vacuoles  of  plant-cells  and  in  secretions,  have 
least  refractive  power.  Albuminous  matters,  gelatin-giving  intercellular 
substance,  and  mucin  have  about  the  same  refractive  index. 

(b)  Power  of  Absorbing  Color*. — In  very  thin  sections  most  vegetable 
and  animal  tissues  appear  colorless.     In  thick  sections,  when  examined 
by  transmitted  light,  the  different  colors  are  absorbed  in  different  degrees. 
Yegetable  tissues  absorb  the  most  refractive  rays  ;  therefore,  in  sections 
of  increasing  thickness  they  appear  at  first  yellow  and  then  red.     The 
same  rule  applies  to  animal  tissues,  even  when  freed  from  blood,  e.g., 
epithelium  and  cartilage.     Many  tissues  owe  their  color  to  deposits  in 
them  of  special  coloring  matters.     When  this  is  intense  many  rays  of 
light  are  entirely  extinguished,  and  in  the  spectra  of  such  bodies  portions 
of  the  spectrum  are   either  entirety  absent  or  dark  absorption-bands 
appear  in  different  parts  of  the  spectrum. 

The  points  of  occurrence  of  these  absorption-bands  are  definite  and 
characteristic  for  each  different  substance.  The  spectra  of  certain  bodies 
of  physiological  importance,  such  as  the  blood,  biliary  coloring  matters, 
etc.,  will  be  referred  to  under  their  appropriate  headings  in  the  sections 
on  Special  Physiology. 

(c)  Double  Refraction. — A   large  number  of  bodies  of  crystalline 
structure  have  the  property  of  splitting  a  single  incident  ray  of  light  pass- 


PHYSICAL  PROPERTIES   OF  TISSUES.  69 

ing  through  them  into  two  rays  ;  hence,  when  an  object  is  seen  through 
such  a  crystal  it  appears  double,  the  bifurcation  of  the  ray  of  light  being 
spoken  of  as  double  refraction. 

Many  of  the  animal  tissues  are  doubly  refractive,  though  this  prop- 
erty is  weaker  in  fresh  tissue  than  after  drying.  Double  refraction  is 
only  faintly  developed  in  connective  tissue,  especially  in  its  youngest 
stages.  Elastic  tissue  is  more  highly  doubly  refractive,  as  are  also  car- 
tilage, bone,  nerves,  muscles,  nails,  and  hair. 

Double  refraction  permits  the  recognition  of  the  molecular  structure 
of  organized  tissues.  A  body  whose  molecules  in  all  directions  are 
arranged  in  the  same  manner  produces  only  single  refraction  ;  one  whose 
molecules  are  arranged  in  different  directions  in  different  proportions 
produces  double  refraction,  i.e.,  splits  the  ray  of  light  into  two  ra}^s, 
which  are  polarized  perpendicularly  to  one  another,  and  whose  vibrations 
are  therefore  in  two  planes  perpendicular  to  one  another.  Simple  glass 
is  a  single  refractive  medium,  but  if  compressed  or  stretched  in  one 
direction  it  becomes  doubly  refractive.  The  double  refractive  body  can 
either,  as  in  the  last  example,  refract  the  ray  more  or  less  in  one  direction 
than  in  the  direction  perpendicular  to  it,  or  the  light  can  be  transmitted 
in  three  perpendicular  directions  with  different  velocities.  In  the  inor- 
ganic world  crystals  furnish  examples  of  all  three  cases. 

Crystals  of  the  regular  system  (tesseral)  are  isotropic  (singly 
refractive).  In  tetragonal  and  hexagonal  forms,  which  possess  an  unequal 
axis  and  two  or  three  perpendicular  equal  axes,  the  refraction  is  either 
greater  (positive)  or  less  (negative)  in  the  direction  of  the  unequal  axis, 
and  such  bodies  are  said  to  have  a  single  optic  axis.  Other  crystalline 
forms  have  three  axes,  characterized  by  the  transmission  of  light  with 
different  velocities.  They  have  two  optic  axes  not  coinciding  with  the 
axes  of  crystallization. 

In  organized  bodies  all  of  the  above  cases  are  also  met  with.  Most 
mature  tissues  are  doubly  refractive.  The  optic  characteristics  are  not, 
however,  changed  by  pressure  or  stretching. 

We  must  conclude  from  this  that  the  doubly-refractive  tissue-mole- 
cule is  suspended  in  a  singly-refractive  medium,  and  that  this  molecule 
is  unaffected  in  pressure  or  stretching  just  as  it  remains  unaffected  in 
imbibition.  Organic  tissues  are  therefore  analogous  to  crystals  in  their 
molecular  arrangement ;  and  this  view  is  strengthened  by  the  fact  that 
many  organic  substances  which  are  apparently  anything  but  crystalline 
in  their  structure,  such  as  albumen,  gluten,  and  chondrin,  possess  the 
power  of  rotating  the  plane  of  polarized  light. 

The  most  important  examples  of  double  refractive  power  are  seen  in 
the  muscles  and  nerves.  These  will  be  considered  under  their  special 
headings. 


70  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

4.  ELECTRICAL  PHENOMENA. — Electrical  phenomena  may  occur  in 
animal  and  vegetable  tissues  under  various  conditions. 

Frictional  electricity  occurs  when  dry  epidermal  tissues  (hair,  outer 
epidermis)  and  other  bodies  of  rough  surface  are  rubbed  together,  as  on 
the  skin  and  clothing.  It  has  no  physiological  significance. 

Currents  produced  by  chemical  differences  in  tissues  may  be  seen  in 
plants  when  a  point  of  the  exposed  interior  is  connected  with  a  point  of 
the  external  surface,  the  internal  section  being  negative  to  the  exterior. 
Such  currents  probably  only  exist  when  contact  by  conductors  is  made 
between  these  two  surfaces. 

In  certain  animal  and  vegetable  tissues  there  appear  to  be  elementary 
parts,  which  are  actively  efficient  in  developing  an  electrical  current. 
Among  such  phenomena  belong  the  electrical  phenomena  observed  in 
certain  plants,  as  the  Dionaea  muscipula;  in  certain  animals,  as  the  torpedo 
and  electric  eel,  and  in  the  currents  developed  in  muscles  and  nerves  of 
all  animals.  The  latter  will  receive  consideration  under  the  subjects  of 
Nerve  and  Muscle. 

III.    MECHANICAL   MOVEMENTS   IN   CELLS. 

It  has  been  seen  that  the  processes  by  which  cells  absorb  and  give 
up  liquids  and  gases  are  reducible  to  purely  physical  laws.  We  have 
further  alluded  to  the  fact  that  the  characteristics  of  the  nutritive  proc- 
esses in  animal  as  distinguished  from  vegetable  cells  is  the  reduction  of 
complex  organic  compounds  in  the  former  to  simple,  inorganic  substances ; 
while  in  the  vegetable  cell,  simple,  inorganic,  elementary  compounds  are 
built  up  into  complex  organic  matter.  In  vegetable  cells  force  is,  there- 
fore, rendered  latent ;  in  animal  cells  force  is  liberated. 

In  the  animal  cell  this  liberation  of  energy  may  take  on  the  form  of 
animal  movements  from  ttie  contractility  of  protoplasm  ;  or  it  may  result 
in  the  development  of  heat  or  of  electricity.  The  consideration  of  the 
processes  which  lead  to  this  liberation  of  energy  will  be  deferred  until 
after  the  chemical  constituents  of  cells  have  been  discussed,  while  heat- 
formation  and  the  development  of  electricity  will  be  studied  under  their 
appropriate  headings  in  Special  Physiology. 

The  movements  seen  in  animal  and  vegetable  organisms  may  be  the 
result  of  external  causes,  such  as  friction,  heat,  or  chemical  action,  or 
they  may  be  apparently  spontaneous. 

Two  classes  of  movement  may  be  distinguished  : — 

1.  Those  which  are  produced  by  varying  tension  in  the  cell-mem- 
brane, from  varying  degrees  of  imbibition  of  the  cell-contents. 

2.  Those  which  are  peculiarly  protoplasmic  in  nature. 

1.  MOTION  PRODUCED  BY  IMBIBITON  IN  CELLS. — The  first  of  these  is 
especially  illustrated  by  many  of  the  forms  of  motion  which  occur  in  the 


MECHANICAL   MOVEMENTS   IN   CELLS.  71 

vegetable  kingdom,  such  as  the  turning  of  leaves  toward  or  away  from 
the  light,  the  regular  motion  of  certain  algae,  such  as  diatoms,  desmidia, 
oscillatoria,  as  well  as  the  irritative  motions  of  certain  plants,  such  as  the 
sensitive  plant  (Mimosa  pudica),  or  the  Venus'  Fty-Trap  (Dionxa  mus- 
cipula);  all  of  these  motions  depend  upon  a  change  in  the  physical  state 
of  imbibition  of  certain  cells.  In  the  Mimosa  pudica,  the  plant  in  which 
motion  is  most  marked,  and  apparently  most  closely  analogous  to  that 
occurring  in  the  animal  kingdom,  motion  of  three  different  parts  may  be 
recognized. 

While  at  rest  during  the  day-time  the  leaf-stems  of  the  sensitive 
plant  form  an  acute  angle  with  the  main  stem,  the  secondary  leaf-stems 
diverge,  and  the  leaves  are  opened  out  so  that  they  form  a  plane  surface. 
When  evening  comes  the  leaf-stem  sinks  downward,  the  leaves  approach 
each  other,  as  when  the  fingers  of  'the  open  hand  are  adducted  to  the 
middle  finger,  and  the  leaflets  themselves  close  up  so  that  the  sur- 
faces which  during  the  da3r-time  are  the  uppermost  now  come  in  contact 
with  each  other.  If  the  entire  plant  is  shaken  the  same  changes  occur 
as  have  been  just  described  to  take  place  during  the  night ;  or  if  the 
under  part  of  any  one  of  the  leaf-stems  is  gently  touched,  the  closing 
motion  is  localized  in  that  part  of  the  plant.  If,  however,  the  upper 
portion  of  the  leaf  is  touched,  no  change  is  produced  in  the  position  of 
the  leaves  or  of  the  stem.  The  under  part  of  the  leaf-stem  is  seen  to  be 
cylindrical  in  shape,  and  this  represents  the  sensitive  portion  of  the 
plant. 

Briicke,  to  whom  we  are  indebted  for  the  explanation  of  the 
mechanism  of  this  movement,  has  found  that  this  cylindrical  structure 
which  underlies  the  leaf-stem  is  composed  of  a  bundle  of  vessels  running 
through  the  centre,  and  between  it  and  the  outer  green  bark  there  is  a 
layer  of  very  succulent  cells,  which  on  the  upper  and  non-sensitive  side 
of  the  stem  are  comparatively  thick  walled,  while  on  the  under  side  the 
cells  are  provided  with  very  delicate  membranes.  If  a  portion  is  cut 
out  of  this  cylindrical  stem,  the  ends  immediately  become  retracted  so 
that  each  extremity  takes  on  a  funnel-like  form.  If  such  a  cylindrical 
piece  is  then  divided  in  the  direction  of  its  long  axis,  each  part  becomes 
bent  in  the  form  of  a  bow,  so  that  the  external  epidermal  side  is  longer 
than  that  bounded  by  the  vascular  bundle.  This  change  in  tension  of 
the  cells  is  due  to  a  change  in  distribution  of  the  cell-juice.  When  the 
membrane  of  the  under  portion  of  the  leaf-stem  is  touched  the  cell-juice 
flows  from  the  lower  to  the  upper  cells  and  into  the  intercellular  spaces; 
the  tension  of  the  upper  cells  therefore  becomes  increased,  while  that  of 
the  lower  cells  becomes  reduced.  The  stem,  therefore,  sinks  and  the 
leaves  close.  Movement  occurring  in  the  mimosa  as  a  consequence  of 
mechanical  irritation,  therefore,  depends  upon  differences  in  degree  of 


72  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

turgescence  of  certain  cells,  and  has  nothing  in  common  with  animal 
motion. 

The  Dionxa  muscipula,  or  Venus'  Fly-Trap,  furnishes  another  illus- 
tration of  movement  of  parts  occurring  in  the  vegetable  kingdom.  The 
form  of  the  bilobed  leaf,  which  is  the  movable  part  of  this  plant,  is 
shown  in  Fig.  45.  The  two  lobes  stand  at  rather  less  than  a  right 
angle  to  each  other,  and  on  each  of  the  inner  surfaces  are  three  minute 
filaments  projecting  inward.  The  margins  of  the  leaf  are  prolonged 
into  spikes,  into  each  of  which  a  bundle  of  spiral  vessels  enters.  When 
any  one  of  these  filaments  is  touched,  even  by  so  slight  a  pressure  as 
would  be  produced  by  contact  with  a  hair,  the  leaves  instantly  come  into 
apposition,  and  the  spikes  interlock  like  the  teeth  of  a  rat-trap.  The 
upper  surface  of  the  leaf  is  covered  with  minute  glands,  which  furnish  a 
secretion  having  the  power  of  digesting  organic  substances.  When 

insects  come  in  contact  with 
these  filaments,  the  leaves  close 
so  as  to  imprison  them,  and 
the  insects  are  digested  by  the 
acid  secretion  stimulated  by 
their  contact,  and  absorbed. 

In  this  plant  the  chief  seat 
of  the  movement  is  in  the  thick 
mass  of  cells  which  overlies  the 
central  bundles  of  vessels  in 
the  mid-rib.  When  any  one 

FIG.  45.— VENUS'  FLY-TRAP  (Dionoea  musdpuia).     of  these   filaments   on   the  in- 
LEAF  VIEWED  LATERALLY  IN  ITS  EXPANDED  ,  «  ^^1,1 

STATE.    (Darwin.)  ternal  surface  of  the  leaves  is 

touched  the  impulse  travels  in 

all  directions  through  the  cellular  tissue,  independently  of  the  course  of 
the  vessels,  to  the  cells  at  the  mid-rib.  Fluid  thus  flowing  from  the 
upper  cells  to  the  lower,  the  lower  cells  greatly  increase  in  tension,  while 
the  upper  ones  become  relaxed  and  the  leaves  come  into  apposition. 
Opening  of  the  leaves  is  accomplished  by  a  reverse  process.  In  this 
plant  there  is  therefore  to  be  seen  not  only  a  mechanical  irritation, 
which  produces  mechanical  motion  by  purely  mechanical  means,  but  also 
a  chemical  irritation  through  contact  of  various  substances  with  the 
leaf,  which  results  in  the  production  of  a  digestive  secretion. 

2.  PROTOPLASMIC  MOVEMENTS. — Protoplasmic  movements,  which  may 
be  seen  in  both  the  animal  and  vegetable  kingdoms,  may  be  of  various 
kinds.  We  may  meet  with  movements  of  free  protoplasm,  or  of  proto- 
plasm while  contained  within  cell-walls. 

The  peculiarity  of  protoplasmic  motion  lies  in  the  fact  that  the 
particles  of  the  contractile  mass  do  not  move  around  any  fixed  point, 


MECHANICAL  MOVEMENTS  IN  CELLS.  73 

but  that  all  the  particles,  as  in  a  liquid,  are  capable  of  mutual  rearrange- 
ment of  position.  Further,  the  stimulus  to  motion  is  not  invariably 
applied  from  without,  but  may  be  self-originating  in  the  interior  of  the 
mass.  Protoplasm  is  thus  contractile,  irritable,  and  automatic. 

Protoplasm,  wherever  found,  is  a  transparent,  colorless,  apparently 
homogeneous  mass,  refracting  light  somewhat  more  strongly  than  water, 
but  less  than  oil.  Where  protoplasm  may  be  separated  into  layers,  as  in 
the  ectosarc  and  endosarc  of  some  of  the  lower  animalcules,  protoplasm 
may  be  doubly  refractive,  and  when  the  direction  of  motion  of  the 
protoplasm  is  constant  the  optic  axis  coincides  with  the  line  of  motion. 
Protoplasm,  as  previously  indicated,  possesses  considerable  power  of 
imbibition,  moderate  cohesion,  and  great  extensibility,  the  degree  of  each 
of  these  physical  attributes  varying  in  different  forms  of  protoplasm, 
and  at  different  times  and  under  different  conditions  for  the  same 
protoplasm. 

Protoplasm  also  usually  contains  a  variable  number  of  granules  of 
foreign  matter,  which  are  passive  in  the  motions  of  protoplasm,  but 
which  themselves  may  manifest  oscillatory  movement  (Brownian  motion). 
The  reaction  of  protoplasm  is  usually  faintly  alkaline  or  neutral. 

Protoplasm  may  produce  movement  by  means  of  prolongations  of 
cells,  or  by  the  contraction  of  organized  matter  resulting  from  the 
metamorphosis  of  cell-contents.  We  have  therefore  to  consider — 

First. — Protoplasmic  and  cellular  motion,  whether  limited  by  a  cell- 
membrane,  or  occurring  in  free  protoplasm. 

Second. — Motion  of  the  protoplasmic  prolongations  of  cells,  as  seen 
in  ciliary  movement ;  and 

Third. — The  contraction  of  substances  resulting  from  the  metamor- 
phosis of  cell-contents,  as  seen  in  muscular  tissue. 

1.  Movements  in  Protoplasmic  Contents  of  Cells. — In  addition  to 
the  Brownian  movement,  or  oscillatory  movement  of  granules  which  is 
seen  whenever  minute  particles,  whether  organic  or  inorganic,  are  sus- 
pended in  a  fluid,  and  which  are  simply  due  to  varying  currents  produced 
by  differences  of  temperature,  the  motion  in  the  protoplasmic  contents 
of  cells  may  be  either  circulatory  (cyclosis)  or  may  result  in  changes  of 
form.  Circulatory  movements  are  seen  in  numerous  vegetable  cells, 
particularly  when  the  protoplasmic  contents  have  decreased  somewhat 
in  amount  so  as  not  to  fill  the  entire  interior  of  the  cell;  the  protoplasm 
is  then  heaped  up  against  the  walls  of  the  cells,  and  sends  prolongations 
across  the  interior.  These  cell-contents  may  then  manifest  movements, 
either  of  changes  of  form  or  of  circulation  of  starch  granules,  etc., 
which  are  imbedded  in  the  protoplasm. 

If  a  cell  of  the  Tradescantia  virginica  is  examined  under  the  micro- 
scope, the  protoplasmic  cell-contents  will  be  found  to  be  arranged  in  the 


74 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


form  of  an  irregular  net-work,  as  represented  in  Fig.  46.  These  proto- 
plasmic threads  are  the  seat  of  changes,  both  of  form  and  position.  The 
single  filaments  may  become  thicker  or  thinner,  or  a  new  filament  may 
spring  out  from  and  enter  and  unite  with  adjoining  filaments,  or  may 
undergo  division  into  several  others,  the  process  being  analogous  to  that 
already  described  as  characterizing  the  amoeba.  In.  addition  to  this 
motion  in  the  cell-contents,  rotatory  movements  may  also  be  seen  to  take 

place  in  the  protoplasm  which  is  in 
contact  with  the  walls  of  the  cell, 
rotation  occurring  in  a  constant 
direction  and  with  almost  uniform 
rapidity  around  the  cell-nucleus,  the 
imbedded  chlorophyll  and  starch- 
granules  rotating  in  a  mass  without 
any  decisive  change  in  their  relative 
positions.  Such  rotatory  move- 
ments are  seen  in  the  leaf-cells  of 
the  Vallisneria,  and  various  other 
plants.  Similar  motions  are  also 
seen  in  the  paramoecium  and  other 
infusoria. 

In  young  animal  cells  the  same 
character  of  movement  is  often 
present  ;  often  when  a  membrane  is 
absent  or  is  very  flexible  the  pro- 
toplasmic movements  cause  a  change 
in  the  entire  shape  of  the  cell,  and 
the  motion  so  produced  cannot  be 
distinguished  from  those  of  free 
protoplasm. 

Occasionally     protoplasm      be- 
FIG.  46.-TRADESCANTIA   CELLS,"  AFTER    comes   free    by   escaping   from   the 

interior  of  cells,  such  as  the  so-called 

r»laarrmirl«5  of  m  VJTOTnvPPtPS  1T1  whioll 
Piabn  IliyXOIiryCt  «!3,  11. 

not  only  an  internal  granular  move- 
ment but  also  a  change  of  external 

shape  may  be  made  out.  Similar  phenomena  are  also  seen  in  those 
organisms  which  consist  of  masses  of  free  protoplasm,  such  as  the 
monera,  rhizopods,  polyps,  and  infusoria.  Such  protoplasm  possesses 
in  an  eminent  degree  the  property  of  contractility,  —  a  term  originally 
applied  to  striped  and  unstriped  muscles.  The  changes  in  form  of 
masses  of  free  protoplasm  is  identical  in  nature  with  that  observed  in 
muscular  contraction. 


*  «. 

A  represents  the  fresh  cell  suspended  in  water  ;  B  the 
same  cell  after  moderate,  local  electrical  stimulation. 
The  irritated  region  extends  from  a  to  b,  the  protoplasm 

int°  clumps'  at  c  and  d'  as  a  result  of  the 


MECHANICAL  MOVEMENTS  IN   CELLS. 


75 


The  contractility  of  protoplasm  may  be  manifested  by  either 
partial  or  total  contractions,  the  latter  tending  to  cause  the  protoplasm 
to  assume  a  spherical  shape.  Partial  contractions  are  much  more 
common,  and  consist  in  contractions  along  certain  circumferences  of  the 
mass  of  protoplasm,  and  thus  lead  to  the  production  of  irregularity  in 
outline.  Movements  so  produced  are  described  as  amoeboid  movements 
from  the  fact  that  they  are  best  seen  in  the  amoeba. 

Amoeboid  movements  have  already  been  described,  and  are  exempli- 
fied in  many  of  the  cells  of  which  the  bodies  of  the  higher  animals  are 
made  up.  Thus,  the  colorless  blood-corpuscles,  lymph-cells,  and  corneal 
corpuscles  possess  throughout  their  entire  life  the  power  of  changing 
their  form  in  a  manner  entirely  similar  to  that  possessed  by  the  aimsba 
(Fig.  47). 


FIG.  47.— AMCEBOID  MOVEMENT  IN  A  COLORLESS  BLOOD-CORPUSCLE  OF  THE 
FROG.     (Engelmann.) 

The  temperature  was  gradually  raised  from  a  tow,  and  then  gradually  reduced. 

The  most  striking  illustration  of  this  form  of  protoplasmic  move- 
ment, seen  in  adult  animals,  is  exemplified  in  the  motions  of  pigment- 
cells  in  the  skin  of  the  chameleon.  As  is  well  known,  the  chameleon  is 
capable  of  changing  the  hue  of  its  skin,  and  this  is  simply  due  to  the 
varying  degrees  of  contraction  of  the  pigment-cells,  which  are  situated 
below  the  epidermis.  When  these  cells  send  out  branching  prolonga- 
tions to  the  exterior,  the  skin  surface  of  the  chameleon,  from  the  larger 
amount  of  pigment  exposed,  will  take  on  a  dark  hue.  In  the  different 
stages  of  contraction  of  these  pigment-cells  the  tint  of  the  skin  will 
vary  according  as  the  pigment-cells  are  seen  through  a  thicker  or  thinner 
layer  of  yellowish  or  almost  colorless  epidermal  cells. 


76 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


The  two  extremes  of  position  of  these  pigment-cells  are  represented 
in  Figs.  48  and  49. 


FIG.  48. 


FIG.  49. 


PIGMENT  LAYER  OF  THE  SKIN  OF  THE  CHAMELEON  IN  DIFFERENT  DEGREES 
OF  CONTRACTION.    (Briicke.) 

The  frog  also,  as  is  well 
known,  is  another  illustration 
of  a  change  of  tint  produced 
by  precisely  similar  processes. 

From  the  fact  that  the 
movements  of  these  pigment- 
cells  appear  to  be  under  the 
control  of  the  nervous  system, 
they  offer  an  illustration  of  a 
transition  stage  between  the 
independent,  automatic  move- 
ment of  free  protoplasm,  as  in 
the  body  of  the  amoeba,  and 
the  specialization  of  the  func- 
tion of  movement  in  the  nerv- 
ous ganglia,  nerves,  and  muscle- 
cells  of  higher  animals. 

In  certain  of  the  low  forms 
of  life  protoplasmic  motion 
may  take  on  the  form  of  minute 
contractile  threads  thrown  out 
from  the  body  of  variovis  rhiz- 
opods  and  monera,  which  dif- 
ers  from  the  amoeboid  move- 
ments just  described.  In  this 
case  long  and  thin  protoplasmic 
threads  in  great  number  extend  in  every  direction  from  the  central  mass  ; 
these  threads,  on  whose  surfaces  fine  granules  are  often  seen  in  active 


FIG.  50. 


MECHANICAL   MOVEMENTS   IN    CELLS. 


77 


motion,  are  not  themselves,  usually,  the  seat  of  an}*  active  change  in  form, 
although  they  slowly  and  gradually  become  longer  or  shorter,  or  perhaps 
even  divided.  They  are  also  capable  of  being  entirely  withdrawn  into 
the  contractile  body-mass.  Such  a  form  of  motion,  or  rather  the  forms 
resulting  from  such  motion,  are  represented  in  Fig.  50. 

2.  Ciliary  Movement. — By  ciliary  movement  is  meant  the  pendulum- 
like  motion  possessed  by  protoplasmic  prolongations  of  fine  hair-like 
threads  of  numerous  animal  and  vegetable  cells. 

In  many  of  the  infusoria  the  entire  external  body  surface,  or  a  certain 
limited  portion  of  it,  is  supplied  with  minute  hair-like  appendages,  which, 
by  their  oscillation,  serve  as  organs  of  propulsion.  In  vegetable  spores 
cilia  are  distributed  in  a  similar  manner,  and  likewise  serve  as  propulsive 
organs. 


FIG.  51.— CILIATED   EPITHELIAL  CELLS   FROM  THE  NASAL  Mucous  MEM- 
BRANE OF  THE  Cow,  MAGNIFIED  500  DIAMETERS.    (C.  F.  Mutter.) 

In  the  animal  kingdom  ciliary  movement  is  seen  under  numerous 
forms  on  ciliated  epithelial  cells  lining  the  nasal  passages,  antrum,  tear- 
duct  and  sacs,  pharynx  and  Eustachian  tube,  middle  ear,  trachea, 
bronchi,  uterus  and  Fallopian  tube,  vas  defferens,  epididymus,  central 
canal  of  the  spinal  cord  and  brain-ventricles,  while  cilia  also  serve  as  the 
organ  of  movement  in  spermatozoa. 

The  form  of  the  cilium  is,  as  a  rule,  that  of  a  narrow,  hair-like 
thread.  In  all  of  the  ciliated  epithelial  cells  of  the  higher  animals,  as 
well  as  in  most  spermatozoa,  and  in  man}7  of  the  lower  animals  and 
plants,  the  length  of  such  cilia  may  vary  from  0.05  mm.  to  0.005  mm. 
(Fig.  51).  They  are  structureless  in  appearance  and  colorless,  and 
possess  a  considerable  amount  of  flexibility  and  elasticit}'.  Under  the 
influence  of  various  agents  they  may  either  swell  up  by  imbibition  or 


78  PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 

shrivel  when  desiccated,  and  their  appearances  then  undergo  the  same 
changes  as  will  be  described  under  the  alterations  of  protoplasm.  The 
solutions  which  coagulate  albuminoid  bodies  also  coagulate  the  ciliate 
prolongations  of  cells.  Caustic  alkalies  and  most  of  the  concentrated 
acids  dissolve  them.  In  fact,  cilia  behave  to  all  reagents  in  a  very 
similar  manner  to  protoplasm.  All  cilia  are  invariably  connected  with 
a  protoplasmic  base,  and  are  never  on  firm  membranes.  Therefore, 
when  cilia  are  found  in  the  higher  animals  on  epithelial  membranes  the 
free  surface  of  the  cell  possesses  no  membrane,  but  the  protoplasmic  cell- 
contents,  in  a  manner  similar  to  that  which  is  found  in  the  epithelial  cells 
of  the  villi  of  the  small  intestine,  is  somewhat  condensed,  apparently 
non-contractile,  homogeneous,  or  striated,  and  not  capable  of  imbibition. 
Such  a  surface  might  therefore  be  described  as  a  protoplasmic  cuticle. 

Cilia  pass  through  this  condensed  layer  of  protoplasm  to  be  directly 
in  contact  with  the  protoplasmic  contents  of  the  cell  below.  On  each  cell 
of  a  ciliated  epithelial  membrane,  from  ten  to  twenty  such  cilia  will  be 
distributed  over  the  external  surface.  In  lower  forms  of  animals, .as  in 
the  spermatozoa  of  all  vertebrates,  ciliated  cells  ma}^  possess  but  a  single 
cilium,  as  seen  in  many  of  the  unicellular  algae  and  flagellata. 

Ciliated  epithelial  cells  are  always  cylindrical  in  shape  and  are 
nucleated.  When  a  portion  of  ciliated  membrane  such  as  that  obtained 
from  the  mouth  or  nasal  pharynx  of  the  frog,  or  from  the  nasal  chamber 
of  almost  anjr  animal,  is  placed  under  the  microscope,  the  thread-like 
prolongations  of  these  cells  will  be  found  to  be  in  constant  motion,  by 
which  the  cells  of  one  locality  make  a  rapid  bending  motion  in  one 
direction,  and  then  more  slowly  bend  themselves  back  to  their  original 
position.  The  amplitude  of  these  oscillations  varies  greatly  with  the 
character  of  the  cell  and  certain  external  conditions,  but  on  all  cylin- 
drical epithelial  cells  taken  from  the 'same  localit}^  is  about  equal,  and, 
although  the  bending  may  be  as  much  as  90°,  it  usually  varies  from 
about  20°  to  50°.  The  rapidity  of  oscillation  of  eacli  cilium  may  be 
about  six  or  eight  in  the  second,  although  under  certain  circumstances 
it  may  be  considerably  higher,  since  it  is  influenced  by  a  number  of 
external  conditions,  such  as  temperature,  amount  of  water  contained  by 
imbibition,  etc. 

The  mechanical  force  exerted  by  this  pendulum-like  motion  of  the 
cilia  is  very  considerable.  In  cells  which,  like  the  spermatozoa,  are 
supplied  with  a  single  cilium  (Fig.  52),  the  screw-like  motion  of  this 
appendage  is  sufficient  to  produce  rapid  motion  of  the  entire  organism. 
In  the  case  of  ciliary  membranes,  the  vibration,  having  a  greater  intensity 
in  one  direction  than  in  another,  is  sufficient  to  produce  forward  motion 
of  light  bodies  brought  in  contact  with  them.  Thus,  if  the  mucous  mem- 
brane is  dissected  from  the  pharynx  of  the  frog  and  fastened  by  pins  on 


MECHANICAL   MOVEMENTS   IN   CELLS. 


79 


a  board,  any  light  bodies  placed  in  contact  with  the  ciliated  surface  of 
the  membrane  will  be  moved  comparatively  rapidly  forward  in  the 
direction  of  oscillation  of  the  cilia;  or  if  the  body  of  the  frog  is  bisected, 
and  a  glass  tube  passed  in  the  month  and  out  the  oesophagus,  which  is 
cut  off  at  the  point  where  it  enters  the  stomach,  the  motion  of  the  ciliated 
epithelium  lining  the  pharynx  and  oesophagus  will  be  sufficient  to  cause 


FIG.  52.— SPERMATOZOA  OF  DIFFERENT  ANIMALS.    (Thanhoffer.) 

P,  b,  a,  spermatozoa  of  Paludina  vivipara:  Hn,  of  Helix  nemoralis  ;  B,  of  Blaps  mortisaga  ;  Bi,  of 
bull;  V,  of  mole;  K,  of  dog;  D.  of  bat:  Em,  of  man;  E,  of  mouse;  C,  of  canary-bird  ;  L,  of  horse;  Pa,  b, 
of  rat,  with  sperinatoblasts ;  J,  of  sheep ;  B*-,  of  frog ;  R,  of  Raja  batis ;  Pa,  a",  spermatoblasts. 

the  body  of  the  frog  to  advance  at  a  comparatively  rapid  rate, — as 
much  possibly  as  one  millimeter  in  the  second,  or  even  more.  It  has  been 
estimated  that,  in  oblique  or  vertical  upward  movements,  each  square 
centimeter  of  ciliated  membrane  can  perform  in  one  hour  0.8  gramme 
millimeters  of  wor.k,  or  the  cells  can  lift  their  own  weight  more  than  four 
meters  high  (Bowditch).  This  motion  of  bodies  placed  in  contact  with 


SO  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 


-- 


'.ciliated  surfaces  is  evidently  dependent  upon  the  fact  that  the  intensity 
of  motion  is  greater  in  one  direction  than  in  the  other;  otherwise,  of 
course,  the  effect  would  be  negative. 

Since  ciliated  epithelium,  as  has  been  already  shown,  lines  most  of 
the  tubular  structures  of  the  animal  body,  the  effect  of  the  vibratory 
motion  of  the  cilia  will  be  to  propel  onward  fluids  and  light  particles  in 
contact  with  the  surfaces  of  the  membrane.  Thus,  the  cilia  of  the 
Fallopian  tube,  by  their  vibrations,  serve  greatly  to  assist  the  onward 
passage  of  the  ovum  through  the  oviduct. 

Ciliary  motion  persists  only  as  long  as  the  cilia  are  in  contact  with 
the  protoplasmic  contents  of  cells,  although  Briicke  has  found  that  it  is 
not  necessary  that  the  entire  cell  be  in  contact  with  the  cilia ;  for  if  the 
free  surface  of  .a  ciliated  membrane  is  carefully  shaved  with  a  sharp 
knife  and  the  portions  cut  off  examined  under  a  microscope,  it  will  be 
found  that  many  of  the  ciliated  cells  have  been  divided,  and  yet,  provided 
a  certain  portion  of  the  cell-contents  is  still  in  contact  with  the  cilia,  the 
latter  will  still  manifest  their  normal  movements.  Ciliary  movement 
may  persist  after  the  death  of  the  individual  where  that  ciliary  motion 
is  not  concerned  in  producing  movement  of  the  entire  organism ;  thus, 
in  the  ciliated  infusoria  anything  which  destroys  the  life  of  the  animal- 
cules will  arrest  ciliary  movement;  but,  in  the  higher  animals,  in  the 
cold-blooded  groups,  motion  of  ciliated  epithelium  may  persist  for  days 
after  the  death  of  the  animal;  while,  even  in  the  warm-blooded  animals, 
a  number  of  hours  after  the  death  of  the  organism,  the  cilia  will  still  be 
in  vibration.  This  indicates  that,  in  the  first  place,  ciliary  movement  is 
not  under  the  control  of  the  nervous  system;  and,  secondly,  that  it.  is 
independent  of  the  state  of  the  entire  organism, — at  any  rate,  in  the 
higher  forms  of  life, — since  it  may  persist  long  after  the  irritability  of 
nerves  and  muscles  has  disappeared.  Temperature  produces  the  same 
effects,  nearly,  on  ciliary  movement  as  it  exerts  on  other  protoplasmic 
movements ;  thus  above  45°  C.  ciliated  motion  ceases,  while  at  0°  C.  it 
also  is  arrested,  to,  however,  return  again  when  the  temperature  is  raised. 

Increase  of  temperature  between  these  two  limits  produces  increase 
in  the  rapidity  of  oscillation  of  cilia,  while  decrease  of  the  temperature 
produces  retardation. 

Every  alteration  in  degree  of  watery  imbibition  of  epithelial  cells 
exerts  an  influence  on  the  ciliary  movement ;  especially  on  the  degree  of 
frequency  and  amplitude  of  vibration.  Increasing  the  amount  of  water 
in  the  epithelial  cells  above  the  normal  amount  may,  at  first,  increase  the 
vigor  of  oscillation,  but  when  a  certain  maximum  is  passed  motion  is 
gradually  arrested,  as  in  heat-tetanus  ;  the  cilia  coming  to  rest  while  bent 
forward,  both  cells  and  cilia  being  swollen  and  more  transparent,  and  the 
nucleus  appearing  as  a  distended,  watery  vesicle.  When  such  a  con- 


MECHANICAL  MOVEMENTS  IN  CELLS.  81 

dition  is  reached  the  normal  condition  of  the  cells  may  be  again  restored 
through  the  use  of  desiccating  agents,  such  as  salts,  which  have  an 
affinity  for  water,  provided  the  watery  distension  has  not  lasted  too  long, 
nor  has  passed  a  certain  degree.  Abstraction  of  water  again,  on  the 
other  hand,  reduces  the  rapidity,  amplitude,  and  mechanical  force  of 
movement,  while  the  cells  and  cilia  become  shriveled  and  motion  is 
arrested.  Like  all  other  evidences  of  protoplasmic  activity,  a  certain 
supply  of  oxygen  is  necessary  for  the  maintenance  of  ciliary  motion, 
and  here  again  the  same  conditions  may  be  determined  as  will  be 
described  under  the  conditions  necessary  for  protoplasmic  movement. 
So  also  various  chemical  influences,  alkalies,  acids,  anaesthetics,  and 
poisons  produce  disturbances  of  motion  dependent  upon  their  influence 
on  the  protoplasmic  contents  of  the  cells.  The  influences  of  electricity 
on  ciliary  movement  have  not  been,  as  yet,  very  clearly  made  out, 
although  they  also  appear  to  be  in  accord  with  the  results  obtained  from 
the  action  of  electricity  on  protoplasm. 

These  facts  serve  to  show  that  ciliary  movement  is  a  form  of  pro- 
toplasmic movement ;  for,  not  only  is  such  motion  dependent  on  the  con- 
nection of  the  cilia  with  the  cell-contents,  but  all  cilia  on  a  single  cell 
vibrate  synchronously,  and  their  motion  is  dependent  upon  the  condition 
of  the  protoplasmic  contents  of  the  cells.  Anything  which  interferes  with 
the  manifestations  of  force  in  protoplasm  will  interfere  with  ciliary  motion. 
Ciliary  motion,  nevertheless,  differs  from  other  forms  of  protoplasmic 
movement  in  that  it  occurs  in  definite  directions,  and,  with  the  exception 
of  the  spermatozoa  and  other  ciliated  organisms,  on  fixed  surfaces. 

Cilia  are  contractile  but  not  automatic  or  irritable,  while  the  con- 
tents of  ciliated  cells  have  apparently  lost  their  power  of  independent 
contractility.  Cilia  may,  therefore,  be  regarded  as  the  organs  of  move- 
ment of  certain  cells.  They,  consequently,  represent  a  certain  stage  of 
specialization  of  function. 

3.  Movement  in  Specialized  Contractile  Tissue. — In  the  contraction 
of  muscular  tissue,  specialization  of  function  has  advanced  a  step  farther. 
Free  protoplasm  originates  its  own  stimulus  to  contraction,  is  therefore 
automatic,  and  is  itself  contractile.  In  ciliated  cells  the  contractile 
impulse  originates  in  the  protoplasmic  contents  of  the  cells,  which,  how- 
ever, have  lost  their  power  of  contractility,  and  transfers  the  stimulus 
to  contractile  organs,  the  cilia,  which  are  not  themselves  automatic. 

In  muscular  tissue  movement  depends  upon  three  histologically 
different  tissues :  the  nervous  ganglion,  which  is  automatic  and  originates 
the  contractile  impulse ;  the  nerves,  which  conduct  this  impulse  to  the 
muscles,  which,  like  cilia,  are  contractile  but  not  automatic. 

The  phenomena  of  muscular  contraction  will  be  considered  under 
Special  Physiology. 


82  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


GENEKAL   CONDITIONS   GOVEKNING  PROTOPLASMIC   MOVEMENT. 

The  motions  of  protoplasm  are  governed  by  a  large  number  of  con- 
ditions which  are  similar  for  protoplasm,  whether  of  animal  or  vegetable 
origin.  This  fact  therefore  points  to  the  identity  of  protoplasm  of  ani- 
mal and  vegetable  forms  of  life. 

1.  Temperature.— For   every   variety  of   protoplasm   there   is  an 
upper  and  lower  temperature  beyond  which  spontaneous  motion  ceases. 
The  minimum  temperature  at  which  motion  is  possible  is  usually  0°  C.; 
the  maximum  is  40°  C.     Between  these  limits  the  rapidity  of  motion 
usually  increases  with  the  increase  of  temperature,  and  the  temperature 
at  which  the  motions  are  most  active  usually  lies  several  degrees  below 
the  maximum  temperature,  at  which  point  heat-tetanus,  or  heat-rigor, — 
in  other  words,  universal  contraction  of  protoplasm, — occurs,  resulting 
in  the  assumption  of  spherical  forms  analogous  to  the  condition  pro- 
duced by  prolonged  mechanical,  chemical,  or  electrical  irritation.    If  the 
temperature  is  then  reduced,  the  protoplasm  may  regain  its  power  of 
spontaneous  contractility.     At  the  maximum   temperature  no  optical 
changes  occur  in  the  protoplasm,  but  if  the  temperature  is  raised  above 
this  point  the  protoplasm  becomes  shriveled  and  opaque  from  the  coagu- 
lation of  the  albuminoids  of  protoplasm.     Vacuoles  often  form,  and  the 
power   of   contractility   is   permanently   lost.     As   the   temperature   is 
reduced  toward  the  minimum  the  movements  become  slower,  and  con- 
tractility is  finally  extinguished.     No  optical  changes  are,  however,  so 
produced,  and  an  increase  of  temperature  will  now  renew  the  power  of 
contractility.    Contractility  is  therefore  destroyed  by  an  excess  of  heat, — 
is  suspended  by  a  low  temperature. 

The  changes  in  shape,  as  a  consequence  of  change  in  temperature,  are 
represented  in  Fig.  53.  From  a  to  c  the  temperature  was  12°  C.  The 
protoplasm — the  white  blood-corpuscles  of  the  frog — during  that  time 
changed  its  form  but  little.  The  preparation  was  then  placed  on  the 
warm  stage  of  the  microscope  and  heated  to  50°  C.  Almost  imme- 
diately the  movements  became  more  active,  passing  through  the  forms  as 
shown  from  d  to  Z.  At  m  commencing  and  at  n  complete  heat-rigor  is 
shown,  while  at  o  and  p  are  shown  the  commencing  movements  restored 
by  subsequent  cooling. 

2.  The  Degree  of  Imbibition. — The  amount  of  water  held  in  com- 
position by  the  protoplasm  is  also  of  influence   on   the   capability  for 
spontaneous  motion.    For  every  form  of  protoplasm  there  is  a  maximum 
and  minimum  quantity  of  water  of  imbibition  be}Tond  which  movement 
ceases.      Contraction  is  impossible  when,  as  a  rule,  less   than  60   per 
cent,   or   more   than    90    per   cent,    of  water   is    held   by    protoplasm. 
Within  these  limits  the  rapidity  of  contraction  increases  with  the  amount 


CONDITIONS   GOVERNING  PROTOPLASMIC  MOVEMENT. 


83 


of  water,  and  consequently  with  the  increase  of  volume  and  decrease  in 
the  index  of  refraction  of  the  protoplasm.  As  the  maximum  amount  of 
water  becomes  approached  the  spherical  form  is  assumed  ;  so  that,  there- 
fore, distilled  water,  as  pointed  out  in  the  section  on  imbibition,  kills 
protoplasm,  possibly  by  the  extraction  of  the  salts  which  are  necessary- 
for  the  life  of  protoplasm.  Thus,  salt-water  fish  are  killed  by  placing  in 
fresh  water;  the  fresh  water  is  then  found  to  increase  in  its  inorganic 
constituents,  which  thus  evidently  must  be  extracted  from  the  tissues 
of  the  animals  with  which  it  is  in  contact.  So  also  desiccation  produces 
shriveling  of  the  protoplasm  and  an  entire  disappearance  of  all  power  of 
movement,  although  in  the  lower  forms  of  life  vitality  is  not  destroyed, 


FIG.  53.— AM<EBOID  MOVEMENT  IN  A  COLORLESS  BLOOD-CORPUSCLE  OF  THE 
FROG.     (Engelmann.) 

The  temperature  was  gradually  raised  from  atom,  and  then  gradually  reduced. 

but  becomes  latent ;  and  when  the  proper  percentage  of  moisture  is  again 
supplied  the  protoplasm  will  regain  its  power  of  contracting. 

This  is  seen  in  the  infusoria  and  various  low  forms  of  animal  and 
vegetable  life,  which  may  be  preserved  indefinite!  jr  when  desiccated,  and 
ma}*  be  restored  to  active  life  by  placing  them  in  a  condition  to  absorb 
moisture. 

3.  TJie  Supply  of  Oxygen. — Protoplasmic  movements  require  the 
constant  supply  of  oxygen,  although  they  may  continue  to  live  in  a 
medium  of  much  lower  oxygen-tension  than  is  seen  in  the  atmosphere. 
Higher  tensions  of  oxygen  than  are  found  in  the  atmosphere  will  reduce 
the  motions  of  protoplasm,  which  are,  however,  again  renewed  when  the 


84  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

pressure  of  oxj^gen  is  diminished.  All  protoplasmic  motion  is  rapidly 
arrested  in  a  vacuum. 

4.  Various  Chemical  and  Physical  Agents. — Various  chemical  agents 
are  capable  of  modifying  the  contractility  of  protoplasm.  Thus,  a  slight 
excess  of  acid  or  of  alkali  will  arrest  protoplasmic  movement;  hence, 
protoplasmic  motions  in  the  cells  of  various  vegetable  organisms,  such 
as  cara,  will  be  arrested,  after  two  or  three  minutes,  in  a  one-tenth  of  one 
per  cent,  soda  solution.  Dilute  acids  cause  coagulation  of  protoplasm, 
and  will  perhaps  explain  the  poisonous  action  of  carbon  dioxide  and  the 
necessity  of  its  removal  from  cells  as  rapidly  as  formed.  Various  poisons, 
such  as  ether  and  chloroform,  interfere  with  the  activity  of  protoplasm 
of  all  forms,  and  the  similarity  of  action  serves  to  still  further  demon- 
strate the  identity  of  protoplasm.  Thus,  the  alkaloid  veratrine  produces 
effects  on  all  forms  of  protoplasm  similar  to  those  so  well  marked  in 
muscular  tissue. 

Protoplasm,  also,  like  muscular  and  other  irritable  tissue,  responds 
to  various  forms  of  artificial  stimuli,  though  the  degree  of  susceptibility 
to  such  stimuli  may  vary  in  different  forms  of  protoplasm.  Electrical 
currents,  when  powerful,  are  capable  of  killing  protoplasm,  causing  it  to 
assume  a  spherical  shape,  and  to  become  opaque,  shriveled,  and  granular. 
Feeble  currents  slow  the  spontaneous  motions  of  protoplasm,  while 
strong  currents  arrest  them.  Where  the  contractile  tissue  is  inclosed 
in  tubular  sheaths  and  the  assumption  of  the  spherical  form  so  rendered 
impossible,  as  in  muscular  tissue,  an  attempt  is  made  to  approach  the 
form  as  nearly  as  possible.  Such  protoplasmic  cylinders  when  stimulated 
become  shorter  and  thicker. 

Sudden  changes  of  temperature  are  also  capable  of  producing  either 
increase  or  decrease  in  the  contractility  of  protoplasm,  the  change  being 
more  marked  the  more  rapidly  the  variation  in  temperature  occurs. 

Absence  of  light  also  serves  finally  to  arrest  protoplasmic  motion, 
while  its  presence  will  lead  to  increased  vigor  of  contraction,  as  already 
referred  to  in  the  changes  in  the  contractile  pigmented  cells  of  the  skin 
of  the  chameleon  and  frog. 


SECTION  III. 
CELLULAR  CHEMISTRY. 

I.   CHEMICAL  CONSTITUENTS  OF  CELLS. 

IN  the  consideration  of  the  structure  of  organized  bodies  we  found 
that,  no  matter  how  complicated  their  form,  all  organized  matter  was 
capable  of  being  resolved  into  a  unit  of  organization,  which  we  termed, 
with  Briicke,  an  elementary  organism  or  cell. 

Cells,  therefore,  are  the  simplest  schematic  form  to  which  all  the 
various  forms  of  organized  bodies  are  capable  of  being  reduced.  Chemi- 
cal investigation  of  organized  bodies  further  shows  that  they  are  equally 
simple  as  regards  their  elementary  composition.  Of  the  sixt3'-five  chemi- 
cal elements  only  seven  enter  with  any  degree  of  constancy  into  the  forma- 
tion of  organic  compounds  ;  these  are  oxygen,  nitrogen,  hydrogen,  carbon , 
sulphur,  phosphorus,  and  iron.  By  far  the  greatest  number  of  all  organic 
compounds  are  composed  only  of  the  three  elements,  carbon,  hydrogen, 
and  oxygen,  va^ing  in  the  different  relative  proportions  of  each.  In 
one  group,  represented  by  the  organic  acids  (succinic  acid,  C4H604),  even 
if  we  assume  that  all  the  hydrogen  present  is  associated  with  oxygen  in 
the  proportion  to  form  water,  there  always  remains  a  considerable  excess 
of  oxygen  unaccounted  for.  In  the  second  group,  represented  by  the 
carbo-hydrates  (glycogen,  C6H1006),  we  have  twice  as  much  hydrogen  as 
oxygen,  or,  in  other  words,  the  oxygen  and  hydrogen  exist  only  in  the 
proportion  to  form  water.  In  the  third  group,  composed  of  these  ele- 
ments, carbon,  hydrogen,  and  oxygen,  and  represented  by  the  fatty  acids 
(oleic  acid,  C^Hs/^),  if  we  suppose  that  all  the  oxygen  is  united  with 
the  hydrogen  in  the  proportion  to  form  water,  we  have  still  a  consider- 
able excess  of  hydrogen  unaccounted  for.  Such  bodies  are,  therefore, 
termed  h}'dro-carbons. 

In  another  group  of  organic  compounds,  and  one  of  the  most  im- 
portant of  the  constituents  of  cells,  we  find  nitrogen  associated  with 
carbon,  hydrogen,  and  oxygen.  Such  a  group  we  would  therefore  term 
the  nitrogenous,  in  contradistinction  to  the  non-nitrogenous. 

To  this  group  belong  the  highly  complex  organic  products  (complex 
as  regards  their  molecular  arrangement),  which  contain  sulphur  and  occa- 
sionally phosphorus,  arid  still  more  rarely  iron,  and  which  are  represented 
by  the  albuminous  bodies ;  the  nitrogenous  organic  acids  and  bases,  the 

(85) 


86  PHYSIOLOGY  OF  THE   DOMESTIC  ANIMALS. 

organic  alkaloids  and  indifferent  crystalline  bodies,  some  of  which  contain 
sulphur,  are  other  members  of  this  group.  As  yet  only  three  substances 
of  organic  origin  are  known  to  contain  phosphorus ;  these  are  lecithin 
(found  in  the  blood,  bile,  and  serous  fluids),  glycerin-phosphoric  acid 
(derived  from  the  former,  and  found  in  the  same  localities),  and  nuclein 
(found  in  pus-corpuscles,  yelk  of  egg,  and  semen).  In  the  living  organism 
these  organic  compounds  are  in  a  state  of  solution  in  a  relative^  large 
amount  of  water,  and  either  associated  or  chemically  united  with  a  small 
percentage  of  inorganic  matter,  which  modifies,  in  all  probability,  the 
nature  of  the  former,  and  is  itself  not  without  value  in  the  vital  processes. 
All  organic  compounds  are  readily  decomposable,  either  through  the 
action  of  various  chemical  reagents,  elevation  of  temperature,  or  through 
the  processes  of  fermentation  and  putrefaction.  As  the  result  of  all  these 
changes  in  organic  matters  simpler  compounds  are  produced.  The  more 
complex  the  molecule  of  organic  matter,  the  more  readily  is  it  subjected  to 
decomposition.  The  character  of  these  changes,  as  well  as  the  nature  of 
some  of  the  substances  which  result  from  change  of  various  kinds  in 
organic  matter,  will  be  subsequently  discussed. 

Of  the  inorganic  constituents  of  cells  by  far  the  most  abundant  is 
water,  which  forms  the  great  bulk  of  organic  bodies.  Many  vegetable 
matters  may  contain  as  much  as  90  per  cent,  of  water,  while  the  animal 
tissues  may  contain  75  per  cent,  or  more,  though  the  percentage  is  by  no 
means  constant,  and  may  vary  in  single  tissues  according  to  different 
plrysiological  or  pathological  conditions.  The  inorganic  constituents  of 
cells  are  taken  up  by  the  cells  already  preformed,  and,  as  a  rule,  again 
leave  the  cells  in  the  form  in  which  they  entered  it.  The  most  prominent 
exception  to  this  rule  is  found  in  the  case  of  carbon  dioxide  and  sul- 
phuric acid ;  the  former  originating  in  the  oxidation  of  the  hydrogen 
contained  in  the  water  of  organic  constituents,  and  the  latter  coming 
from  the  oxidation  of  the  sulphur  contained  in  albuminoids.  The  inor- 
ganic constituents  of  animal  and  vegetable  cells  in  110  way  differ  from 
similar  bodies  found  in  inorganic  matter.  When  found  as  constituents 
of  cells  they  have  invariably  been  derived  from  the  atmosphere  or  the 
earth,  have  been  absorbed,  often  without  undergoing  any  change,  by 
vegetable  cells,  and  have  passed  from  the  latter  into  the  interior  of  animal 
tissues.  Inorganic  matter  is  found  in  all  animal  fluids  and  tissues, 
although  with  great  variation  as  to  amount.  Certain  inorganic  constitu- 
ents— such,  for  example,  as  water  and  sodium  chloride — are  found 
invariably  in  all  animal  tissues  and  fluids,  while  other  of  the  inorganic 
cell-constituents  are  limited  to  the  cells  of  certain  special  tissues. 

The  inorganic  constituents  of  cells  may  exist  either  in  the  form  of 
gases,  salts,  free  acids,  or  in  certain  forms  of  combination  whose  exact 
arrangement  has  not  yet  been  made  out. 


CHEMICAL   CONSTITUENTS   OF   CELLS.  87 

In  addition  to  the  elements  which  have  been  already  mentioned  as 
forming  part  of  the  organic  constituents  of  cells,  and  which,  of  course, 
may  exist  in  other  forms,  we  find  also,  when  organic  matter  is  subjected 
to  combustion,  chlorine,  fluorine,  silicon,  potassium,  sodium,  calcium, 
magnesium,  manganese,  iron,  and  occasionally  copper  and  lead,  in  the 
ash.  Of  the  other  elements  of  organic  bodies  in  incineration  the  carbon 
is  converted  into  carbon-dioxide,  part  of  which  remains  in  the  form  of 
carbonates  in  the  ash,  part  of  the  hydrogen  uniting  with  oxj-gen  to  form 
water.  Another  portion  unites  with  nitrogen  to  form  ammonia,  while  the 
phosphorus  and  sulphur  remain  as  oxygen  compounds,  sulphuric  and 
phosphoric  acids,  united  with  different  bases  also  in  the  ash. 

Of  the  various  chemical  compounds  which  are  found  in  the  interior 
of  cells,  and  which  have  entered  it,  either  from  accidental  contact  or  as 
foods,  or  as  resulting  from  the  chemical  processes  in  cells,  we  may  make 
three  different  groups  : — 

1.  Those  which,   already  formed,   exist   in  inanimate   nature,   are 
absorbed,  and  again  leave  cells  without  undergoing  any  change  while 
forming  constituents  of  organized  bodies.     Such  substances  are  repre- 
sented by  the  inorganic  constituents  of  animal  cells. 

2.  This  group  comprises  those  which  are  already  formed  exterior  to 
the  cells,  and  which,  in  the  process  of  assimilation  by  the  cells,  undergo 
a  change  simply  in  their  mode  of  molecular  arrangement,  without  under- 
going any  profound  chemical  metamorphosis.     Such   constituents  are 
seldom,  if  ever,  removed  from  the  cells  in  the  form  in  which  they  entered 
it,  and  are,  in  the  chemical  process  occurring  in  the  interior  of  the  cells, 
always  reduced  to  simpler  forms.    The  organic  constituents  of  cells  form 
this   group.     They  may  be   either  nitrogenous   or  non-nitrogenous   in 
composition. 

3.  We  meet  also  with  a  class  of  compounds  which  are  themselves 
developed  in  the  vital  processes  in  cells,  as  the  result  of  the  metamorphosis 
of  either  the  organic  constituents  of  cells  or  of  the  food-products  which 
have  been  assimilated  by  the  cells.     Such  bodies  may  be  removed  from 
cells  either  as  complex,  organic,  excretory  products  (as  types  of  which 
urea  and  kreatin  may  be  mentioned),  or  they  themselves  may  undergo 
more  profound  decomposition  before  being  removed  from  the  interior  of 
the  cells.    The  examination  of  protoplasm,  wherever  found  in  the  animal 
or  vegetable  kingdom,  will  show  that  it  contains  examples  of  each  of 
these  three  classes  of  compounds. 

The  chemical  constituents  of  organic  bodies  may,  then,  be  divided 
into  two  different  groups, — the  organic  and  the  inorganic.  The  organic 
may  again  be  subdivided  into  the  nitrogenous  and  the  non-nitrogenous. 
Proteids,  with  their  derivatives,  represent  the  nitrogenous  group ;  the 
hydro-carbons  and  carbo-hydrates,  with  their  derivatives,  the  non- 


88  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

nitrogenous  group.     Water  and  various  salts  belong  to  the  second,  or 
inorganic  group.     These  will  be  taken  up  in  turn : — 

CONSTITUENTS  OF  CELLS. 


I.  ORGANIC.  II.  INORGANIC.  • 

Water  and  Salts. 


A.  Nitrogenous.  B.  Non-nitrogenous. 

Proteids  and 
their  Derivatives. 


1.  Carbo-hydrates.  2.  Hydro-carbons. 

Starches  and  Sugars  and  Fats  and  Oils, 

their  Derivatives. 

A.      NITROGENOUS    ORGANIC    CELL-CONSTITUENTS — PROTEIDS    AND 

THEIR  DERIVATIVES. 

General  Characteristics  of  Proteids. — Proteid,  or  albuminous 
bodies,  is  the  name  given  to  a  number  of  neutral,  nitrogenous  products 
of  complex  nature  widely  distributed  throughout  the  animal  and  vege- 
table kingdoms,  and  agreeing  more  or  less  in  chemical  composition  and 
properties  with  the  white  of  an  egg.  They  are  found  dissolved  in  the 
fluid  media  of  the  animal  body,  as  constituents  of  the  digestive  juices, 
and  in  different  degrees  of  solidit}*  in  the  various  tissues.  They  are 
never,  during  health,  eliminated  from  the  body  in  excretions.  They  are 
present  during  all  periods  of  life.  The  higher  plane  of  organization  of 
man  and  the  higher  animals  depends  mainly  upon  the  abundance  and 
variety  of  the  albuminous  constituents  of  their  tissues;  for,  while  in 
plants  the  cell-walls  are  largely  composed  of  non-nitrogenous  matter, 
such  as  cellulose,  in  animals  analogous  parts  are  formed  of  various 
complex  albuminoids. 

Proteids  are  organic,  colloidal  bodies,  composed  of  carbon,  hydrogen, 
oxygen,  nitrogen,  sulphur,  and  occasionally  phosphorus.  They  are 
absolutely  essential  to  life,  whether  animal  or  vegetable,  but  are  exclu- 
sively of  vegetable  origin ;  that  is,  although  they  may  be  assimilated 
and  modified  by  the  vital  processes  occurring  in  animal  cells,  they 
must  first  have  been  preformed  by  the  chemical  processes  occurring  in 
vegetable  cells.  When  found  as  constituents  of  the  tissues  of  car- 
nivorous animals  they  have  been  derived  directly,  with  but  slight 
modification,  from  the  herbivora  which  have  served  for  their  food, 
while  the  herbivorous  animals  find  them  invariably  ready  formed  in 
the  tissues  of  vegetables  which  serve  as  their  food,  and  which  require 
but  slight  modification  to  be  converted  into  the  constituents  of  the 


NITROGENOUS   ORGANIC   CELL-CONSTITUENTS.  89 

animal  tissues.  Animals,  therefore,  do  not  have  the  power  of  manu- 
facturing albuminoids,  although  they  may  transform  albuminous  bodies 
of  one  kind  into  those  of  another.  Thus,  casein  may  be  transformed 
into  the  albuminous  constituents  of  muscle-tissue ;  it  may  be  combined 
with  other  substances  so  as  to  form,  for  example,  the  haemoglobin  of 
the  blood-corpuscles,  or  may  become  so  modified  as  to  form  what  are 
termed  the  derived  albuminoids  of  the  different  tissues. 

After  serving  the  purposes  of  the  organism  such  bodies  are  excreted, 
not  as  proteids,  but  as  products  resulting  from  their  retrograde  meta- 
morphosis. All  albuminous  bodies  are  so  intimatety  associated  with 
inorganic  matter  that  their  isolation  in  a  pure  state  is  a  matter  of  the 
greatest  difficulty,  or,  it  may  be,  impossibility  ;  consequently  the  inciner- 
ation of  albuminous  bodies — a  process  which  is  accompanied  with  the 
development  of  an  odor  like  burning  horn — always  leaves  an  ash  composed 
of  potassium  and  magnesium  phosphates  and  small  quantities  of  carbo- 
nates. If  sulphur  is  regarded  as  a  constant  and  normal  component  of 
proteids  and  not  as  an  occasional  accidental  addition,  they  all  possess  a 
very  high  molecular  weight.  In  all  forms  of  proteids  the  percentage  of 
chemical  elements  entering  into  their  composition  is  only  subject  to 
slight  variation  in  the  different  classes.  Thus,  according  to  Hoppe-Se}"ler, 
C.  may  vary  from  52.7  to  54.5  per  cent.;  H.,  6.9  to  7.3  .per  cent.;  N., 
15.4  to  16.5  per  cent. ;  O.,  20.9  to  23.5  per  cent.;  S.,  0.8  to  2.0  per  cent. 

Physical  Properties. — When  dry,  albuminous  bodies  form  perfectly 
amorphous,  yellowish,  brittle  masses  without  odor  or  taste,  and  closely 
resembling  gums  in  appearance,  and,  like  gums,  hygroscopic  to  a  high 
degree:  they  rotate  the  plane  of  polarized  light  to  the  left, and  in  watery 
solutions,  which  are  nearly  always  opalescent,  are  not,  as  a  rule,  capable 
of  osmosis, — a  fact,  which  seems  to  show,  as  Brucke  has  pointed  out, 
that  their  condition  in  the  form  of  fluid  is  more  one  of  particulate 
suspension  than  of  true  solution.  When  shaken  with  fluid  oils,  the  latter 
are  mechanically  separated  into  minute  particles,  each  of  which  is  sur- 
rounded by  a  layer  of  the  albuminous  solution  (emulsion).  Some  are 
soluble  in  wrater,  others  not;  nearly  all  are  insoluble  in  alcohol  and 
ether ;  most  are  soluble  in  strong  alkalies  and  acids,  but'  in  the  process 
of  solution  undergo  chemical  change.  Most  of  the  albuminous  bodies 
may  exist  in  two  modifications,  either  in  a  soluble  or  in  an  insoluble 
form.  They  exist  usually  in  the  soluble  form  in  animal  and  vegetable 
cells,  but  become  insoluble  by  the  action  of  heat  and  various  chemical 
reagents. 

When 'watery  solutions  of  albuminous  bodies  are  evaporated  in  a 
vacuum,  or  at  40°  to  50°  C.,  a  yellowish,  brittle,  soluble  residue  is  left; 
in  other  words,  albumen  may  be  recovered  unaltered  in  general  prop- 
erties in  the  dry  form  from  solutions  when  subjected  to  evaporation  by 


90  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

gentle  heat.  When  heated  much  above  this  point  albuminous  bodies 
then  pass  into  the  insoluble  form  (coagulated  proteids). 

Chemical  Properties. — Proteids  are  precipitated  out  of  their  solu- 
tions by  the  following  reagents  :  the  stronger  mineral  acids,  acetic  acid 
and  potassium  ferro-C}*anide ;  acetic  acid  and  sodium  sulphate,  lead 
acetate,  mercuric  chloride,  tannic  acid,  powdered  potassium  carbonate 
added  in  bulk  to  saturation,  alcohol,  ether,  and  several  other  substances. 

Iodine  stains  most  proteids  yellow, — a  point  which  may  aid  in  their 
recognition  under  the  microscope. 

Their  presence  in  solution  may  be  recognized  by  the  following 
processes  : — 

First,  by  coagulation.  When  solutions  of  albuminoids  are  gently 
heated,  provided  the  amount  of  albumen  contained  is  at  all  appreciable, 
a  firm  coaguluin  results  when  the  solution  has  been  warmed  up  to  60° 
or  70°  C.  The  temperature  at  which  coagulation  occurs  will  vary  in 
different  forms  of  albuminous  bodies,  and  according  to  the  reaction  and 
chemical  characteristics  of  the  solvent.  If  a  small  amount  of  a  dilute 
acid  is  added  to  a  solution  of  an  albuminous  body  coagulation  will  be 
found  to  occur  at  a  lower  temperature  than  if  the  solution  be  neutral ; 
while,  on  the  other  hand,  the  presence  of  a  small  amount  of  alkali  will 
prevent  coagulation  occurring  until  the  temperature  has  been  raised 
above  the  point  at  which  it  occurs  when  the  solution  is  neutral.  If  a 
large  amount  of  alkali  be  present  coagulation  by  heat  will  be  rendered 
impossible.  Neutral  salts  in  small  amount  in  albuminous  solution  will 
also  lower  the  temperature  of  coagulation,  whether  the  solution  be 
faintly  acid,  faintly  alkaline,  or  neutral.  The  coagulation  of  albuminous 
bodies  by  heat  is  only  possible  when  they  are  in  solution,  and  therefore 
seems  to  show  that  the  change  from  the  soluble  to  the  insoluble  form 
produced  by  heat  is  not  so  much  dependent  upon  the  heat  as  upon  the 
heat  combined  with  moisture ;  for  if  the  albumen  be  separated  from 
solution  by  evaporation  below  the  point  of  coagulation,  the  dried  albumen 
so  obtained  will  still  possess  the  power  of  solubility  in  water :  and  yet, 
if  placed  in  a  perfectly  dry  tube  the  temperature  of  the  albumen  ma\'  be 
raised  far  above  the  point  of  coagulation  without  any  change  occurring 
in  the  albumen,  i.e.,  without  its  losing  its  power  of  subsequent  solubility 
in  water,  and  of  being  coagulated  when  that  solution  is  raised  to  tha 
coagulating  point. 

Second :  If  a  solution  which  is  supposed  to  contain  albumen  is 
acidulated  with  acetic  acid,  a  few  drops  of  potassium  ferrocyanide  then 
added,  and  the  fluid  boiled,  albuminous  bodies  will  be  precipitated. 

Third :  If  the  fluid  is  acidulated  with  acetic  acid  and  a  small 
quantity  of  a  strong  solution  of  sodium  sulphate  then  added,  and  the 
fluid  then  boiled,  a  firm,  white  coagulum  will  result. 


*      NITROGENOUS   ORGANIC   CELL-CONSTITUENTS.  91 

The  first  and  third  of  these  tests  may  be  used  for  separating  albu- 
minous bodies  from  other  substances  in  solution, — a  process  which  is 
often  necessary  in  the  examination  of  organic  fluids.  So  also  if  the  fluid 
is  acidulated  with  acetic  acid,  and  then  added  to  a  large  bulk  of  strong 
alcohol,  albuminous  bodies  may  thus  be  coagulated,  and  their  separation 
from  other  ingredients  of  the  solution  rendered  possible. 

A  precipitate  produced  by  boiling  alone  is  not  a  sufficient  proof 
of  the  presence  of  albumen,  since  certain  substances,  such  as  calcium 
phosphate  in  human  urine  and  calcium  carbonate  in  the  urine  of  her- 
bivora,  will  be  thrown  down  by  boiling.  If  the  precipitate  is  permanent 
on  the  addition  of  nitric  acid  after  boiling,  albumen  is  present,  since  the 
salts  above  mentioned  will  be  redissolved  by  the  acid.  Alkali  may  also 
hinder  the  coagulation  of  albumen  by  heat,  and  an  acid  reaction  is  there- 
fore essential  for  the  emplo3^ment  of  this  test. 

Occasionally  albumen  is  present  in  solution  in  amount  too  small  to 
be  detected  by  any  of  the  preceding  tests.  The  detection  of  traces  of 
albumen  is  then  rendered  possible  by  various  color  reactions. 

The  Biuret  Reaction. — When  a  small  amount  of  caustic  potash 
solution  is  added  to  a  dilute  solution  of  cupric  sulphate  a  precipitate  of 
cupric  hydrate  will  be  thrown  down.  If  an  excess  of  potash  is  now 
added,  the  precipitate  will  be  redissolved  and  the  fluid  take  on  a  light- 
blue  color.  If,  however,  albuminous  bodies  be  present  in  solution,  and 
this  procedure  be  carried  out,  on  solution  of  the  precipitate  of  cupric 
hydrate  the  fluid  will  take  on  a  violet  color  instead  of  u  blue.  This  test 
may  be  used  to  detect  the  presence  of  albuminous  bodies  in  extremely 
small  amount  in  solution.  It  may  be  also  used  for  the  recognition  of 
the  albuminous  nature  of  solids.  If  a  solid  body  which  is  supposed  to 
contain  albuminous  bodies  be  touched  first  with  a  drop  of  cupric  sul- 
phate solution,  then  with  a  drop  of  potash  solution,  and  then  washed 
with  water,  the  spot  so  treated  will  be  found  to  have  a  violet  color. 
This  test  is  also  used  for  the  recognition  of  peptone.  A  solution  of 
peptone  so  treated  will  become  red  instead  of  violet. 

Xantho-proteic  Reaction. — When  albuminous  bodies  in  solution  are 
boiled  with  nitric  acid,  the  solution  and  coagulum,  if  one  be  present, 
take  on  a  yellow  color.  If  the  solution  be  then  allowed  to  cool  and 
strong  ammonia  added,  the  upper  layers  of  the  solution,  or  the  coagu- 
lum, if  any  be  present,  will  become  orange  colored. 

Millon's  Reaction. — If  a  little  Millon's  reagent*  be  added  to  a  solu- 
tion which  contains  albumen,  if  the  albumen  be  present  in  considerable 

*  Millon's  reagent  is  prepared  by  dissolving  mercury  in  its  own  weight  of  nitric 
acid  by  the  aid  of  gentle  heat.  The  solution  is  then  poured  into  a  glass  vessel,  and  twice 
its  volume  of  water  added  ;  a  crystalline  precipitate  will  separate  in  a  few  hours,  and  the 
yellowish  supernatant  fluid,  which  may  be  readily  decanted  off,  is  Millon's  reagent. 


92  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

quantity,  a  dense,  white  precipitate  will  be  formed,  and  when  subjected 
to  heat  the  precipitate  will  become  condensed  into  the  form  of  a  firm 
coagulum,  and  will  turn  red.  If  but  a  trace  of  albumen  is  present  the 
fluid  will  simply  take  on  a  pinkish  color. 

Schnitzels  Test. — When  albuminoids  in  solution  are  treated  with  a 
cane-sugar  solution  in  small  quantities  and  concentrated  sulphuric  acid 
then  added  a  beautiful  red  color  is  formed. 

Adamkiewicz's  Test.— If  a  solution  of  an  albuminous  body  is  strongly 
acidulated  with  acetic  acid  and  sodium  chloride  added  in  bulk,  and  then 
strong  sulphuric  acid,  the  fluid  will  gradually  assume  a  violet-blue  color, 
slightly  phosphorescent,  and  gradually  turning  dark  purple. 

Frohde's  Test. — When  a  mixture  of  sulpho-molybdic  acid  is  added 
to  a  solution  of  albuminous  bodies  a  dark-blue  color  is  produced. 

Of  the  above  tests  the  xantho-proteic  and  Millon's  reaction  may  be 
used  for  the  microscopical  detection  of  the  albuminoids. 

Albuminous  bodies  may  be  divided  into  the  following  classes : — 

I.  ALBUMENS. — Albumens  are  bodies  which  are  soluble  in  water,  and 
when  in  solution  are  coagulated  by  heat  (about  70°  C.).  They  are  not 
precipitated  from  their  solutions  by  dilute  acids,  carbonates  of  the  alka- 
lies, sodium  chloride,  or  platino-hydrocyanic  acid.  When  dried  at  about 
40°  C.,  or  if  evaporated  at  a  lower  temperature  in  a  vacuum,  they  leave 
a  yellowish,  friable,  inodorous,  gummy  mass,  which  is  still  soluble  in 
water,  and  whose  solutions  possess  all  the  properties  of  the  original 
solution.  Albumens  are  precipitated  from  their  solution  by  alcohol,  if 
alkaline  salts  are  present.  Albumens  may  exist  in  three  different  forms, 
—serum-albumen,  egg-albumen,  and  vegetable  albumen. 

1.  Serum- Albumen. — Serum-albumen  is  found  in  blood,  serum, 
lymph,  serous  transudations,  and  animal  secretions. 

Serum-albumen  may  be  obtained  from  blood-serum,  or  any  serous  transuda- 
tion,  by  adding  dilute  acetic  acid,  drop  by  drop,  until  a  flocculent  precipitate  forms. 
This  precipitate  is  then  filtered  off,  and  the  filtrate,  after  neutralization  with  a 
little  sodium  carbonate,  is  evaporated  in  a  shallow  dish  to  a  small  volume,  not 
allowing  the  temperature  to  rise  above  40°  C.  The  salts  may  then  be  removed  by 
dialysis,  changing  the  water  frequently  outside  of  the  dialyzer,  and  again  evapo- 
rating at  40°  C.  to  dryness. 

So  obtained,  serum-albumen  always  contains  a  slight  percentage  of 
salts,  but  is  soluble  in  water,  forming  a  clear  solution,  which  is  somewhat 
tenacious  when  concentrated. 

In  the  dry  condition  it  is  a  yellowish,  brittle,  transparent  body 
capable  of  being  redissolved  in  water,  and  its  solutions  are  then  coagu- 
lable  by  heat.  Its  solutions  are  opalescent,  and  possess  a  specific  laevo- 
rotation  for  yellow  light  of — 56°.  It  is  precipitated  out  of  its  solutions 
by  alcohol,  the  precipitate  being  partially  redissolved  when  the  alcohol 
is  immediately  poured  off,  but  is  not  coagulated  l>y  ether.  Most  of  the 


NITROGENOUS   ORGANIC   CELL-CONSTITUENTS.  93 

salts  of  the  heavy  metals  precipitate  serum-albumen,  as  do  the  mineral 
acids  in  large  quantities,  especially  nitric  acid.  Its  point  of  firm  coagu- 
lation is  from  72°  to  73°  C.,  although  turbidity  sets  in  at  about  60°  C. 
The  presence  of  acetic  or  phosphoric  acids,  sodium  chloride,  or  other 
neutral  salts,  lowers  the  coagulation-point  of  serum-albumen,  while  the 
presence  of  sodium  carbonate  necessitates  a  higher  temperature.  It  is 
precipitated  by  the  strong  mineral  acids  from  its  solution  in  dilute  acids, 
and  the  precipitate  is  readily  soluble  in  concentrated  acids ;  egg-albumen 
is  not. 

2.  Egg-Albumen. — In  many  points  egg-albumen,  which  is  contained 
in  the  meshes  of  the  fibrous  net-work  of  birds'  eggs,  closely  resembles 
serum-albumen.    The  points  of  contrast  are  that  its  specific  rotation  is  only 
— 35.5°,  and  when  agitated  with  ether  it  is  gradually  precipitated.    When 
injected  into  a  vein  or   the  connective  tissue,  or  when  introduced  in  large 
quantities  into  the  stomach  or  rectum  of  an  animal,  egg-albumen  is  found 
unaltered  in  the  urine,  while  the  injection  of  serum-albumen  produces  no 
such  albuminuria. 

A  solution  of  comparatively-pure  egg-albumen  may  be  obtained  for  testing 
by  breaking  the  whites  of  several  hens'  eggs  into  a  beaker,  cutting  up  the  mem- 
branes with  scissors  so  as  to  free  the  albumen  from  their  meshes,  stirring  well 
with  an  equal  volume  of  water,  and  filtering  through  muslin.  The  salts  may  then 
he  removed  by  dialysis. 

Dry  egg-albumen  may  be  obtained  by  evaporating  the  above  solution 
to  dryness  at  40°  C.  So  prepared,  its  physical  properties  agree  closely 
with  those  of  serum-albumen.  Its  solutions  have  several  properties  which 
enable  it  to  be  distinguished  from  serum-albumen.  Hydrochloric  acid 
in  small  amount  produces  no  precipitate ;  in  larger  amount  it  causes  a 
firm  coagulum,  which  is  only  with  difficulty  soluble  in  excess  of  acid  and 
in  water  and  neutral  salt  solutions. 

3.  Vegetable  Albumens. — Albuminous  bodies  are  found  dissolved  in 
plant-juices  and  in  the  form  of  a  solid  in  various  seeds,  and  form  the 
most  important  albuminoids  for  the  nutrition  of  the  herbivorous  domestic 
animals.     Their  general  properties  agree  with  those  of  egg-  arid  serum- 
albumen,  though  they  present  certain  variations  among  themselves  in 
composition  and  chemical  properties.     Thus,  the  coagulable  substances 
which  may  be  extracted  from  peas  and  horse-beans  dissolve  readily  in 
lime-water  and  acetic  acid,  while  the  other  vegetable  albumens  do  not. 

The  vegetable  albumens  are,  as  a  rule,  poorer  in  carbon  but  richer  in 
nitrogen  than  albumen  of  animal  origin, — a  fact  possibly  accounting  for 
their  lesser  nutritive  value  and  readiness  of  assimilation.  They  usualty 
have  phosphorus  associated  with  them.  Vegetable  altnimen  is  soluble  in 
cold  water,  and  its  solutions  are  coagulable  by  heat ;  with  dilute  acids 
and  alkalies  it  is  converted  into  an  albuminate.  In  the  seeds  of  certain 


94  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

plants  there  is  contained  a,  variety  of  albumen  which,  when  extracted 
with  warm  salt  solution  and  then  allowed  to  cool,  forms  octahedral 
cr}rstals. 

Various  forms  of  vegetable  albuminous  bodies  have  been  described : — 

Vegetable  Caseins. — The  seeds  of  the  leguminous  plants  and  oleagi- 
nous grains  differ  from  the  cereals,  properly  so  called,  in  that  they  do 
not  contain  gluten,  soluble  in  alcohol,  but,  in  addition  to  the  albuminoids 
coagulable  by  heat,  various  other  albuminous  bodies  which  are  insoluble 
in  pure  water  but  soluble  in  alkaline  solutions,  from  which  they  may  be 
precipitated  by  acetic  acid,  the  precipitate  being  soluble  in  excess. 
According  to  Dumas  and  Cavours,this  substance  may  even  be  coagulated 
by  rennet,  and  is  therefore  closely  analogous  to  the  casein  of  milk,  to  be 
subsequently  considered.  Three  different  forms  of  vegetable  casein-like 
bodies  have  been  described.  Legumin,  which  forms  the  greater  part  of 
the  proteid  constituents  of  the  leguminous  plants ;  almonds  and  the 
lupins  contain  a  substance  analogous  to  vegetable  casein  to  which  the 
name  of  amandin,  or  conglutin,  has  been  given ;  while  the  part  of  gluten 
which  is  insoluble  in  alcohol  is  of  similar  nature,  and  has  been  termed 
gluten-casein. 

Legumin. — The  watery  extract  of  the  seeds  of  the  leguminous  plants 
often  has  an  acid  reaction,  without  doubt  due  to  the  presence  of  phos- 
phoric acid,  which  appears  to  be  a  necessary  component  of  vegetable 
casein.  Legumin  may  be  obtained  by  the  agitation  of  powdered  legu- 
minous seeds  with  seven  or  eight  times  their  weight  of  a  one-tenth  of 
one  per  cent,  solution  of  potassium  hydrate.  After  about  six  hours  the 
fluid  is  decanted  and  allowed  to  stand  from  twelve  to  twent3r-four  hours 
at  a  low  temperature,  and  the  residue  which  then  forms  is  again  washed 
with  water.  The  washings  are  then  collected  and  precipitated  with  dilute 
acetic  acid,  and  the  precipitate,  washed  again  with  dilute  alcohol,  is 
finally  precipitated  by  concentrated  alcohol  and  ether. 

Freshly  precipitated  legumin  is  only  very  slightly  soluble  in  cold 
water.  Legumin  may,  however,  be  extracted  from  the  powdered  seeds 
of  the  leguminous  plants  by  cold  water,  its  solubility  in  water  being  then 
due  tO'the  phosphoric  acid  of  the  seeds.  It  is  readily  soluble  in  alkaline 
solutions,  from  which  it  is  precipitated  by  acids  and  solutions  of  metallic 
salts.  It  is  soluble  in  dilute  hydrochloric  and  acetic  acids.  When  boiled 
with  water  it  becomes  coagulated  and  insoluble  in  alkaline  solutions  and 
in  acids.  By  prolonged  ebullition  with  sulphuric  acid  it  undergoes 
decomposition,  with  the  formation  of  leucin  and  ty rosin  and  small  quan- 
tities of  aspartic  acid.  Legumin  is  also  present  in  oats. 

Amandin,  or  conglutin,  is  contained  in  sweet  and  bitter  almonds, 
and  is  separated  from  them  in  the  same  manner  as  legumin.  It  is  dis- 
tinguished from  legumin  by  a  greater  solubility  in  dilute  acids,  though 


NITROGENOUS   ORGANIC    CELL-CONSTITUENTS.  95 

its  general  properties  coincide  with  those  of  legumin.  It  is  distinguished 
from  it,  however,  by  being  more  soluble  than  legumin  in  dilute  acids.  A 
substance  analogous  to  vitellin  has  also  been  found  in  the  seeds  of 
various  plants.  It  is  also  termed  crystallized  vegetable  casein. 

Gluten,  or  vegetable  fibrin,  exists  in  a  large  number  of  grains,  par- 
ticularly those  of  the  cereals,  and  plays  an  important  part  in  the  nutritive 
value  of  vegetable  foods.  It  also  exists  in  the  growing  parts  of  plants, 
and  in  various  vegetable  juices.  It  is  a  compound  albuminous  body, 
which  differs  from  all  others  in  that  it  is  soluble  in  water  and  in  alcohol 
when  traces  of  free  acid  or  alkali  are  present.  It  is  only  partly  and 
imperfectly  soluble  in  pure  water.  It  may  be  readily  obtained  by 
washing  flour  under  a  stream  of  water,  by  which  the  starch  is  removed, 
and  the  gluten  then  remains  in  the  form  of  an  elastic,  grayish  mass. 
Gluten  is  only  partly  soluble  in  alcohol.  According  to  Ritthausen, 
gluten  contains  at  least  four  albuminous  substances  in  addition  to 
vegetable  albumen,  which  has  been  already  described;  a  body  insoluble 
in  alcohol,  which  is  gluten-casein,  or  the  vegetable  fibrin  of  Liebig,  and 
three  nitrogenous  substances  soluble  in  alcohol,  to  which  the  name  of 
gluten  fibrin,  gliadin,  and  mucedin  have  been  given. 

1.  Gluten-Casein. — To  prepare  this  body,  fresh  gluten  is  washed  first 
with  alcohol,  and  the  insoluble  residue  is  then  agitated  with  two-tenths  of 
one  per  cent,  potash  solution,  which  dissolves  out  the  gluten  and  leaves  an 
insoluble  residue  of  starch  and  fatty  matters.     From  the  fluid  gluten- 
casein  is  precipitated  in  flocculi  by  the  addition  of  acetic  acid  sufficient 
to  give  a  faint  acid  reaction.     It  is  then  washed  with  water  and  alcohol, 
and  after  desiccation  the  gluten-casein  so  prepared  is  insoluble  in  hot 
and   cold  water.     Boiling  water,  however,  causes  it  to  undergo  some 
modification,  which  renders  it  insoluble  in  alkalies  and  acids.     In  the 
fresh  state  it  is  soluble  in  acetic  acid,  and  in  alcohol  acidulated  with 
acetic  acid.     All  weak  alkaline  solutions  dissolve  fresh  gluten-casein, 
and  cause  it  when  dry  to  first  swell  up  and  then  dissolve.     It  is  precipi- 
tated out  of  these  solutions  by  acids  and  the  mineral  salts,  forming 
combinations  with  the  latter.     Its  properties  are  very  similar  to  those  of 
legumin   and  conglutin.     It  contains  more  sulphur  and  less   nitrogen 
than  legumin. 

2.  Gluten-Fibrin. — This  body  is  obtained  by  distilling  the  alcoholic 
solution  of  gluten  until  the  fluid  does  not  contain  more  than  40  percent, 
of  alcohol ;  a  mucilaginous  mass  rich  in  gluten-fibrin  is  then  deposited, 
and  may  be  purified  by  washing  with  absolute  alcohol  and  precipitating 
with  ether.     It  then  forms  a  coherent,  tenacious  mass,  insoluble  in  water. 
Its  separation  from  the  gliadin  and  mucedin  of  gluten  depends  upon  the 
fact  that  all  are  soluble  in  dilute  alcohol,  and  that  gluten-fibrin  is  almost 
insoluble  in  water  and  very  weak  alcohol.    As  the  alcohol  is  distilled  off 


95  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

the  gluten-fibrin  separates.  It  dissolves  in  warm,  dilute  alcohol,  and 
forms  a  brownish-yellow  solution.  When  such  solutions  cool,  and  as 
they  undergo  evaporation,  a  white  or  grayish  pellicle  forms  on  the  surface, 
which  disappears  on  agitation.  It  is  more  soluble  in  absolute  alcohol 
than  either  gliadin  or  mucedin.  Gluten-fibrin  is  readily  dissolved  in 
dilute  acid  and  alkaline  solutions,  and  is  precipitated  from  these  solutions 
by  neutralization,  or  by  the  addition  of  metallic  salts. 

3.  Gliadin,  or  Vegetable  Gelatin. — This  body  is  one  of  the  principles 
of  gluten  which  is  soluble  in  dilute  alcohol.     It  is  obtained  by  agitating 
gluten  with  strong  alcohol,  which  removes  gluten-fibrin,  dissolving  the 
residue  in  1  per  cent,  potash  solution,  and,  after  having  precipitated  the 
solution  with  acetic  acid,  by  extracting  the  precipitate  with  alcohol  of 
75  per  cent,  at  a  temperature  of  38°  C.     By  this  means  only  gliadin  is 
dissolved,  while  the  mucedin  remains.    Vegetable  gelatin  then  separates, 
as  the  fluid  cools,  in  the  form  of  a  gelatinous  mass.     It  may  be  purified 
by  dissolving  in  acetic  acid  and  neutralizing  the  clear  solution  with 
potash;  the  precipitate  is  then  again  washed  with  alcohol  and  ether.     In 
the  fresh  state  vegetable  gelatin  has  the  consistence  of  a  thick  mucilage. 
Absolute  alcohol  causes  it   to  contract  to  a  hard  and  yellowish-white 
mass.     Cold  water  causes  it  to  again  swell  up  and  dissolves  part  of  it, 
and  the  solution  may  be  precipitated  by  tannic  acid.     Submitted  to  long 
boiling  with  water,  gliadin  becomes   insoluble   and   undergoes    partial 
decomposition.     Dilute  alcohol  dissolves  it  more  readily  than  pure  water. 
It  is  insoluble  in  absolute  alcohol.     It  is  very  soluble  in  acids  and  dilute 
alkalies,  and  while  in  solution  in  alkalies  may  be  precipitated  by  the 
metallic   salts,   but  its   solution  in  acetic  acid  is  not  precipitated   by 
mercuric  chloride.     It  contains  a  considerable  percentage  of  sulphur. 

4.  Mucedin. — This  substance  has  been  but  little  studied,  and  is  only 
to  be  distinguished  from  vegetable  gelatin  by  its  greater  solubilit3r  in 
water.     Its  method  of  isolation  has  been  already  indicated  in  the  pre- 
ceding paragraphs. 

These  substances  approach  one  another  very  closely  in  chemical 
composition,  and  it  would  appear  from  the  processes  employed  in  their 
isolation  that  it  is  by  no  means  certain  that  they  have  been  obtained 
pure.  On  the  other  hand,  their  analogy  to  corresponding  bodies  of 
animal  origin  is  not  sufficiently  striking  to  justify  an  analogous  nomen- 
clature. 

For  the  preceding  account  of  their  properties  we  are  indebted 
mainly  to  Wiirtz  (  Chimie  Biologique}. 

II.  GLOBULINS. — Globulins  are  bodies  which  are  insoluble  in  water 
but  soluble  in  dilute  solutions  of  sodium  chloride.  They  are  coagulable 
by  heat  when  in  solution,  and,  while  soluble  in  dilute  acids  and  alkalies, 
are  in  the  process  of  solution  changed  into  derived  albumens.  They  are 


NITROGENOUS   ORGANIC   CELL-CONSTITUENTS.  97 

precipitated  by  alcohol  and  by  carbonic  acid,  and  by  the  addition  of  a 
large  quantity  of  water  to  their  solutions ;  sodium  chloride  added  in 
bulk  to  their  solutions,  as  a  rule,  precipitates  them. 

Five  different  kinds  of  globulins  have  been  recognized. 

1.  Vitellin. — Yitellin  is  found  in  the  yelk  of  eggs  and  in  the  crys- 
talline lens.     It  may  be  prepared  by  shaking  the  yelks  of  eggs  with 
separate  portions  of  ether  until  all  the  yellow  color  is  removed,  dissolv- 
ing the  residue  in  dilute  sodium  chloride  solution,  filtering  and  precipi- 
tating the  filtrate  with  excess  of  water.     So  obtained,  it  always  contains 
lecithin.     It  is  not  precipitated  by  the  addition  of  sodium  chloride  in 
substance  to  its  solutions.     It  is  soluble  in  dilute  acids,  and  is  readily 
converted   into    syntonin,   and    by   neutralization   and  re-solution   with 
alkalies  into  alkali  albuminate.     Its   point  of  coagulation  ranges  from 
70°  to  80°  C.     It  is  also  coagulable  by  alcohol. 

2.  Myosin. — Myosin  is  formed  in  the  rigor  mortis  of  muscles,  and 
probably  also  in  the  gradual  death  of  all  forms  of  protoplasm.     It  is 
precipitated  from  its  solutions  in  dilute  sodium  chloride  by  the  addition 
of  common  salt  in  excess.     It  is  also  precipitated  from  its  solutions  by 
excessive  dilution  with  water.    Its  general  properties  will  be  more  closely 
considered  under  the  chemistry  of  muscles. 

3.  Paraglobulin. — This  substance  will  be  described  under  the  con- 
sideration of  the  coagulation  of  the  blood.     Hammarsten  states  that  a 
very  much  larger  quantity  of  this  body  is  found  in  the  blood  of  domestic 
animals   than  has  been  heretofore  supposed.     According  to  him,  more 
than  half  of  all  the  albuminoids  in  the  blood  consists  of  paraglobulin. 

4.  Fibrinogen. — This  is  also  a  globulin  found  in  the  blood,  and  its 
consideration  will  likewise,  for  the  present,  be  deferred. 

5.  Globulin,  or  Crytstallin,  is  contained  in  the  crystalline  lens,  and 
it  resembles  vitellin  in  that  it  is  not  precipitated  from  its  solutions  by 
saturation  with  sodium  chloride,  but  it  is  readily  precipitated  by  alcohol. 

Representatives  of  the  group  of  globulins  are  also  found  in  the  vege- 
table kingdom.  According  to  Dr.  Sidney  Martin,  vegetable  globulins' 
may  be  divided  into  two  classes,  namely,  vegetable  myosins  and  vege- 
table paraglobulins.  The  myosins,  obtained  from  the  flour  of  wheat, 
rye,  and  barley,  have  similar  properties ;  they  are  all  readity  soluble  in 
10  to  15  per  cent,  sodium  chloride  solution,  and  are  precipitable  from  this 
solution  by  saturation  with  sodium  chloride  or  magnesium  sulphate. 
They  are  soluble  in  10  per  cent,  magnesium  sulphate  solution,  and  are 
coagulated  in  this  solution  at  a  temperature  of  55°  to  60°.  If  the  salt  is 
dialyzed  away  from  the  saline  solution  of  myosins,  the  latter  is  precipi- 
tated ;  but  the  precipitate  is  no  longer  a  globulin,  since  it  is  insoluble  in 
saline  solutions.  It  is  soluble  in  dilute  acids  and  alkalies  (0.2  per  cent.)  ; 
it  is  precipitable  from  these  solutions  by  neutralization,  the  precipitate 

7 


98  PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 

being  soluble  in  excess  of  alkali  or  acid ;  that  is,  the  myosin  has  been 
converted  into  a  proteid  having  the  properties  of  an  albuminate.  If 
the  saline  solution  of  myosin  be  placed  in  an  incubator  at  a  temperature 
of  35°  to  40°,  in  twelve  to  eighteen  hours  a  fine  flocculent  precipitate 
falls,  while  the  globulin  disappears  from  the  solution ;  this  takes  place 
more  rapidly  if  the  saline  solution  is  diluted.  The  precipitate  exhibits 
the  same  properties  as  the  precipitate  of  the  globulin  by  dialysis ;  that 
is,  at  a  temperature  of  35°  to  40°  the  globulin  is  transformed  into  an  albu- 
rn mate.  The  ready  transformation  of  the  soluble  globulin  of  wheaten 
nour  into  an  insoluble  albuminate  is  one  of  the  phenomena  which  take 
place  during  the  formation  of  gluten. 

The  second  class  of  vegetable  globulins,  the  paraglobulins,  is  in  dis- 
tinct contrast  with  that  of  the  myosins.  Two  proteids  of  this  class 
have  been  found,  one  in  papaw-juice,  the  other  in  the  seeds  of  Abrus 
precatorius  (jequirity).  Both  these  globulins  exhibit  the  following 
properties :  they  are  soluble  in  saline  solutions,  and  are  precipitated  by 
saturation  with  sodium  chloride  and  magnesium  sulphate.  In  a  10  per 
cent,  solution  of  magnesium  sulphate,  they  coagulate  between  70°  and 
75°  C.  When  precipitated  from  their  saline  solutions  by  dialysis,  they  are 
still  soluble  in  solutions  of  sodium  chloride  and  magnesium  sulphate  of 
10  to  15  per  cent.,  not  being  transformed  into  albuminates.  Nor  are 
they  precipitated  by  long  exposure  (over  three  days)  to  a  temperature 
of  35°  to  40°.  >  u  .,«! 

III.  FJBRINS. — Fibrins  are  solid  albuminous  bodies  .'insoluble  in 
water  and  sodium  chloride,  and  which  swell  up  to  a  stiff'  jelly  in  dilute 
acids.  When  so  treated  iibrin  is  coagulable  by  heat.  The  fibrin  of  the 
blood  is  produced  in  the  process  of  coagulation  of  the  blood  ;  its  prop- 
erties will  be  studied  with  the  subject  of  blood  coagulation. 

IV..  DERIVED  ALBUMINATES. — Derived  albuminates  are  bodies  which 
are  insoluble  in  water  or  sodium  chloride  solutions,  but  are  readily  soluble 
in  dilute  acids  or  alkalies.  Their  solutions  are  not  changed  by  heat. 
When  neutralized  they  are  precipitated  from  their  solutions,  the  pre- 
cipitate being  soluble  in  excess.  Derived  albuminates  may  exist  in  two 
different  forms, — acid  albumens  and  alkali  albumens. 

1.  Acid  Albumen. — When  a  native  albumen  in  solution  is  subjected 
to  the  action  of  a  dilute  acid,  such  as  hydrochloric  acid,  at  a  tolerably 
warm  temperature  its  solutions  readily  lose  their  power  of  coagulating 
when  boiled.  If,  however,  the  acid  is  exactty  neutralized  by  the  addition 
of  any  alkali  the  albumen  is  at  once  precipitated,  and  the  precipitate  is 
again  redissolved  by  an  excess  of  alkali.  The  native  albumen  is  thus 
converted  into  a  form  of  albuminous  body  which  has  become  insoluble  in 
water  and  uncoagulable  by  heat. 

When   acid   albumen   is   precipitated    out   of   its  solution    by   the 


NITROGENOUS   ORGANIC   CELL-CONSTITUENTS.  99 

addition  of  an  alkali  and  then  subjected  to  heat,  the  acid  albumen  so 
suspended  in  water  becomes  coagulated,  and  is  then  indistinguishable 
from  any  other  coagulated  proteid.  After  precipitation  by  neutrali- 
zation, if  the  precipitate  be  then  dissolved  in  lime-water,  its  solution  in 
lime-water  will  be  coagulable  on  boiling.  Acid  albumen  is  precipitated 
out  of  its  solution  by  the  neutral  salts,  such  as  sodium  chloride,  and  by 
gallic  acid  and  metallic  salts. 

The  conversion  of  albumen  into  acid  albumen  from  the  action  of  a 
dilute  acid  is  a  gradual  process.  If  a  solution  of  egg-albumen  be  acidu- 
lated with  dilute  hydrochloric  acid,  and  subjected  to  a  temperature  of 
about  40°  C.,  it  will  be  found,  if  tested  from  time  to  time,  that  a  coagulum 
still  occurs  on  boiling.  The  amount  of  proteid  so  coagulated  by  heat 
will  steadily  decrease,  and  the  amount  of  precipitate  obtained  by  neutral- 
ization will  increase  correspondingly.  After  only  ten  or  fifteen  minutes  it 
will  be  found  that  if  the  solution  of  acid  albumen  is  exactly  neutralized 
all  the  albumen  will  have  been  converted  into  acid  albumen,  and  if 
the  precipitate  is  then  filtered  off  and  the  filtrate  tested  with  the  various 
proteid  tests  it  will  be  found  that  all  the  proteid  has  apparently  disap- 
peared ;  or,  in  other  words,  has  been  converted  into  acid  albumen. 

A  certain  degree  of  temperature  is  necessary  for  this  conversion. 
If  a  mixture  of  albumen  solution  and  dilute  acid  be  surrounded  by  ice, 
the  process  of  conversion  into  acid  albumen  will  be  extremely  slow.  If 
warmed  up  to  about  40°  C.,  or,  in  fact,  any  distance  below  the  tempera- 
ture of  coagulation  of  the  albumen,  the  process  of  conversion  will  be 
very  much  more  rapid. 

If  finely-chopped  muscle  is  washed  in  water  so  as  to  remove  all  the 
soluble  albuminous  bodies  and  blood,  and  the  remainder  be  covered  with 
a  large  quantity  of  dilute  hydrochloric  acid  (0.2  per  cent.),  and  kept  for 
about  twenty-four  hours  at  a  temperature  of  40°  C.,  it  will  be  found  that 
the  greater  part  of  the  muscle  will  be  dissolved  ;  if  the  supernatant  fluid  be 
filtered  off  and  neutralized,  an  abundant  precipitate  of  acid  albumen  will 
be  thrown  down  in  flocculi,  which  will  gradually  settle.  The  acid 
albumen  in  this  case  is  derived  from  the.n^osin  of  the  muscle,  and 
indicates  that  the  globulins  as  well  as  the  albumens  are  capable  of  being 
converted  into  derived  acid  albumen.  Acid  albumen  so  obtained  from 
muscle  is  frequently  spoken  of  as  S3'ntonin,  but  is  apparently  identical 
in  its  general  behavior  under  the  different  tests  to  the  acid  albumen 
derived  from  either  egg-  or  serum-albumen.  So  also  in  the  preliminary 
stages  of  gastric  digestion  of  proteids  a  product  is  first  formed  which 
appears  to  be  identical  in  character  with  acid  albumen,  or  syntonin,  and 
is  termed  parapeptone.  It  also  is  precipitated  from  its  solutions  by 
neutralization,  and  is  apparently  formed  solely  through  the  action  of  the 
acid  of  the  gastric  juice  on  proteids. 


100  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

Any  of  the  coagulated  proteids  may  be  converted  into  acid  albumen 
through  solution  in  the  mineral  acids.  If  a  solution  of  albumen  is 
gently  heated  to  boiling  with  dilute  hydrochloric  acid,  no  coagulum  will 
be  formed,  from  the  fact  that  in  the  gradual  elevation  of  temperature  the 
albumen  in  solution  has  had  time  to  be  converted  quickly  into  acid 
albumen  through  the  action  of  the  acid.  If,  now,  a  small  quantity  of  a 
concentrated  mineral  acid,  especially  hydrochloric,  be  added,  an  abundant 
precipitate  will  form,  and  this  precipitate  is  soluble  in  an  excess  of 
mineral  acid,  especially  if  subjected  to  heat. 

It  is  thus  shown  that  acid  albumen  is  soluble  in  concentrated  mineral 
acids.  It  is  insoluble  in  them  when  they  are  moderate^  concentrated, 
and  it  is  soluble  again  when  they  are  ver}'  dilute.  Egg-albumen,  in 
certain  respects,  differs  from  serum-albumen  in  its  behavior  to  dilute 
acids.  If  dry  serum-albumen  is  dissolved  in  a  concentrated  mineral 
acid,  it  is  readily  converted  in  its  process  of  solution  into  acid  albumen. 
If  this  solution  of  serum-albumen  in  concentrated  acid  is  then  diluted 
with  twice  its  volume  of  water,  acid  albumen  will  be  precipitated,  and  if 
the  precipitate  is  filtered  off  it  may  readily  be  dissolved  in  water,  from 
the  fact  that  it  still  holds  clinging  to  it  enough  acid  to  make  a  dilute 
acid  solution.  Therefore,  it  is  not  a  solution  of  acid  albumen  in  water, 
but  in  dilute  acid.  Egg-albumen  is  less  soluble  in  concentrated  nitric 
acid  or  hydrochloric  acid,  and  when  precipitated  from  such  a  solution  it 
is  less  readily  dissolved  in  water. 

Fibrin  also  is  soluble  in  concentrated  mineral  acids,  and  is  rapidly 
converted  into  syntonin ;  therefore,  it  may  be  said  that  all  proteids  are 
capable  of  being  converted  into  derived  albumens. 

Syntonin,  dissolved  in  dilute  hydrochloric  acid,  rotates  the  plane  of 
yellow  light  — 72°  to  the  left,  and  this  degree  of  rotation  is  independent  of 
the  concentration  of  the  solution,  but  may  be  increased  to  — 84.8°  if  the 
solution  is  heated.  Syntonin  contains  sulphur,  as  may  be  readily  shown 
by  dissolving  some  syntonin  in  liquor  potassse,  and  adding  a  solution  of 
lead  acetate  and  boiling ;  the  fluid  will  then  become  brown  from  the 
formation  of  lead  sulphide.  When  precipitated  from  its  solutions  by 
neutralization  acid  albumen  forms  a  white,  gelatinous  substance  insoluble 
-in  water  and  sodium  chloride  solutions,  but  soluble  in  lime-water  (in 
which  solution,  as  already  stated,  it  undergoes  partial  coagulation  when 
boiled),  and  in  dilute  acids  and  alkaline  solutions.  If,  to  the  solution  in 
>  lime-water,  after  having  undergone  partial  coagulation  through  boiling, 
magnesium  sulphate  be  added,  a  still  further  precipitation  will  be  caused. 
Cold  solutions  of  acid  albumen  are  not  precipitated  by  magnesium  sul- 
phate, even  if  the  acid  albumen  be  dissolved  in  an  alkaline  solution.  If, 
however,  the  solution  of  acid  albumen  and  alkali  be  warmed,  it  is  then 
precipitated  by  the  addition  of  magnesium  sulphate  or  calcium  chloride, 


NITKOGENOUS   OBGANIC   CELL-CONSTITUENTS.  101 

indicating  that,  in  all  probability,  the  boiling  has  served  to  convert  the 
acid  albumen  into  an  alkali  albumen.  Acid  albumen  shows  all  the 
reactions  of  proteids  already  described.  It  may  be  separated  from 
liquids  in  which  it  is  dissolved  by  boiling  with  hydrated  oxide  of  lead. 

2.  Alkali  Albumen. — If  any  native  albumen  in  solution  is. subjected 
to  the  action  of  a  dilute  alkali,  such  as  sodium  or  potassium  hydrate,  it 
will  undergo  changes  somewhat  similar  to  those  produced  by  the  action 
of  an  acid.  Alkali  albumens,  or  alkali  albuminates,  may,  therefore,  be 
described  as  albuminous  bodies  which  are  insoluble  in  water  or  sodium 
chloride,  but  readily  soluble  in  dilute  acids  or  alkalies.  Their  solutions 
are  not  changed  by  heat.  When  neutralized  the}''  are  precipitated  from 
their  solutions,  the  precipitate  being  soluble  in  excess  of  acid,  unless 
alkaline  phosphates  are  present ;  an  excess  of  acid  is  then  required  to 
produce  precipitation.  In  this  conversion  heat  facilitates  the  process, 
and,  as  in  the  case  of  formation  of  acid  albumen,  the  conversion  is  a 
gradual  one.  When  alkali  albumen  is  precipitated  from  its  solution  in 
alkalies  by  neutralization  with  an  acid,  if  an  excess  of  acid  be  added  it 
is  again  rapidly  dissolved,  through  its  conversion  into  acid  albumen. or 
S3rntonin.  This  conversion  of  alkali  albumen  into  acid  albumen  is  more 
readily  accomplished  when  the  alkali  albumen  has  been  freshly  precipi- 
tated. If  some  time  has  been  allowed  to  elapse  after  the  precipitation 
b}'  neutralization,  it  will  still  be  converted  into  syntonin  by  the  action 
of  an  acid,  but  not  so  readily  as  when  freshly  precipitated,  unless  sub- 
jected to  heat  (about  60°  C.).  If  alkaline  phosphates  are  present  in  the 
solution  the  alkali  albumen  is  not  precipitated  on  neutralization,  but 
enough  acid  must  be  added  to  convert  the  basic  phosphate  into 
acid  phosphate,  and,  when  this  is  accomplished,  the  slightest  addition 
of  an  acid,  even  of  C02,  will  then  be  sufficient  to  precipitate  alkali 
albumen. 

Alkali  albuminate  may  exist  either  in  the  form  of  solution  or  as  a 
solid.  If  undiluted  white  of  egg  is  stirred  up  with  a  concentrated  solu- 
tion of  caustic  potash,  or  with  undissolved  caustic  potassium  hydrate, 
it  will  gradually  be  converted  into  a  stiff  jelly.  If  this  jelly  is  washed 
with  water  so  as  to  remove  the  excess  of  alkali,  it  may  be  dissolved 
in  warm  water,  and  will  then  behave  like  alkali  albumen  obtained  by  the 
action  of  alkalies  on  albuminous  solutions.  If,  before  solution  in  water, 
the  solid  alkali  albuminate  has  been  washed  until  most  of  the  alkali  has 
been  removed,  passing  a  stream  of  carbon  dioxide  through  the  solution 
will  be  sufficient  to  cause  precipitation. 

If  some  pieces  of  solid  alkali  albuminate  are  placed  in  an  acid  just 
strong  enough  to  show  an  acid  reaction  after  the  introduction  of  the 
albuminate,  the  latter  will  become  milky-white,  shrivel  up,  and  form  an 
elastic  mass,  the  so-called  pseudo-fibrin,  which  will  swell  up  in  dilute 


102  PHYSIOLOGY  OF   THE  DOMESTIC   ANIMALS. 

(0.1  per  cent.)  acids  without  dissolving,  but  which  is  soluble  in  the  caustic 
alkalies,  and  may  be  precipitated  by  neutralization. 

Alkali  albumen,  like  other  albuminous  bodies,  is  also  precipitated 
from  its  solutions  by  metallic  salts.  With  alcohol  no  precipitate  is 
yielded,  and  alkali  albumen  is  said  to  contain  no  sulphur,  the  sulphur  of 
the  albumen  from  which  it  is  made  being  removed  by  the  alkali  in  the 
process  of  conversion.  It  therefore  differs  from  acid  albumen  and  from 
casein,  which  contains  sulphur. 

Alkali  albumen  or  albuminate  is  present  in  all  young  cells,  in  blood- 
corpuscles  and  blood-serum,  in  muscle,  pancreas,  nerves,  crystalline  lens, 
and  cornea.  It  would  seem  that  alkali  albuminate  may  exist  in  various 
forms,  judging  by  the  difference  in  effect  produced  on  polarized  light  by 
alkali  albumen  produced  from  different  sources.  Thus,  alkali  albumen 
produced  from  serum-albumen  has  a  Isevo-rotatory  power  of — 86°  ;  from 
egg-albumen,  of — 47°,  and  if  prepared  from  coagulated  egg-albumen  it 
may  be  as  high  as  — 58.8°. 

Casein  is  a  form  of  alkali  albuminate  which  is  present  in  milk.  It 
yields  potassium  sulphide  when  left  to  stand  with  liquor  potassae,  and 
still  more  quickly  when  heated  with  it.  It  may  be  prepared  from  milk  by 
shaking  the  milk  with  caustic  potash  and  ether,  removing  the  ether  and 
precipitating  the  albuminate  with  acetic  acid,  and  washing  the  coagulum 
with  water,  alcohol,  and  ether.  The  other  properties  of  casein  will  be 
further  studied  under  the  subject  of  Milk. 

Alkali  albumen,  therefore,  differs  from  acid  albumens  in  its  not  being 
precipitated  on  neutralization  if  alkaline  phosphates  be  present ;  by  its 
being  precipitated  by  magnesium  sulphate  in  substance  in  cold  solution, 
but  in  not  being  coagulated  when  boiled  in  lime-water ;  and  it  contains  no 
sulphur. 

V.  COAGULATED  PROTEIDS. — It  has  already  been  seen  that  the  action 
of  heat  on  solutions  of  egg-  and  serum-albumen,  globulins,  or  on  fibrin 
when  suspended  in  water,  or  dissolved  in  saline  solutions,  serves  to 
coagulate  them  and  to  convert  them  into  an  insoluble  form.  Absolute 
alcohol  produces  a  similar  effect  on  the  same  bodies ;  coagulated  proteids 
are  insoluble  in  water,  dilute  acids  and  alkalies  and  neutral  saline  solu- 
tions, and,  although  they  are  soluble  in  the  strong  mineral  acids,  their 
solubility  is  dependent  upon  the  fact  that  through  the  action  of  the  acid 
they  are  converted  into  dem^ed  albumens.  They  are  readil}7  converted 
into  peptones  through  the  action  of  the  different  digestive  juices  (gastric 
and  pancreatic  juices).  When  freshty  formed  the}r  are  white,  flocculent,  or 
cheesy  masses  which,  under  the  microscope,  are  entirely  amorphous; 
they  hold  water  and  salt  solutions  with  great  tenacity.  Their  chemical 
characteristics  have  been  very  little  studied. 

YI.  AMYLOID  SUBSTANCES  OR  LARDACEIN. — This  is  a  substance  which 


NITROGENOUS   ORGANIC   CELL-CONSTITUENTS.  103 

appears  to  be  a  derivative  of  fibrin,  and  is  found  as  a  deposit  in  numerous 
of  the  organs  of  the  bod3^  such  as  the  spleen,  liver,  etc.  It  is  insoluble 
in  water,  alcohol,  ether,  dilute  acids,  and  alkaline  carbonates,  and  is  not 
dissolved  by  the  digestive  juices.  When  acted  on  by  concentrated  hydro- 
chloric  acid  it  passes  into  solution  and  is  converted  into  syntonin,  which 
may  be  precipitated  by  dilution  with  water.  With  sulphuric  acid  it  dis- 
solves when  boiled,  forming  a  violet  solution,  and  with  strong  sulphuric 
acid  it  is  converted  into  leucin  and  tyrosin.  In  its  composition  it  appears 
identical  with  other  proteids.  It  behaves  differently,  however,  to  certain 
of  the  proteid  tests,  and  must,  therefore,  be  regarded  as  a  modified 
proteid.  Thus,  with  iodine,  instead  of  the  yellow  color  produced  with 
other  proteids,  a  reddish-brown  color  is  formed.  With  iodine  and 
chloride  of  zinc  or  sulphuric  acid  a  violet-bluish  color  is  produced,  thus 
resembling  cellulose  in  its  reaction,  to  which  similarity  it  owes  its  name 
of  amyloid,  though  it  must  be  remembered  that  this  is  the  only  point  of 
similarity  between  amyloid  substances  and  the  starchy  bodies  ;  for  it 
contains  nitrogen,  which  is  absent  from  all  starches,  and  it  cannot  be 
converted  into  sugar.  Aniline  violet  on  amyloid  substance  causes  a 
reddish-violet  color,  and  is  a  test  which  may  be  readily  used  for  detecting 
the  presence  of  amyloid  degeneration  in  various  animal  organs.  Amyloid 
substance  yields  the  Millon's  and  xantho-proteic  reactions. 

VII.  PEPTONES. — A  peptone  is  a  modified  form  of  proteid  which 
occurs -when  any  of  the  albuminous  bodies,  with  the  exception  of  lardacein, 
are  subjected  to  the  action  of  gastric  or  pancreatic  juices,  prolonged 
boiling  at  high  temperature  under  great  pressure,  or  by  the  action  of 
heat  and  dilute  , acids  at  moderate  temperature.  Their  general  charac- 
teristics will  be  referred  to  under  the  subject  of  Digestion. 

In  addition  to  the  above  classes  of  albuminous  bodies,  albumen  has 
been  said  to  exist  under  two  other  forms,  that  of  meta-albumen  and  para- 
albumen,  although  as  37et  very  little  is  known  about  their  characteristics,  or 
in  fact  whether  they  are  not  simply  ordinary  albuminous  bodies  modified  by 
the  accidental  addition  of  some  other  substance.  Thus,  meta-albumen 
might  possibly  be  regarded  as  a  mixture  of  albumen  and  mucin,  since  it  is 
precipitated  by  alcohol  without  undergoing  coagulation  ;  it  is  not  coagu- 
lated by  boiling,  although  its  solutions  become  cloudy  when  heated,  and 
it  is  not  precipitated  by  acetic  or  hydrochloric  acids,  or  acetic  acid  and 
potassium  ferrocyanide.  It  is,  however,  precipitated  by  mercuric  chloride 
and  gallic  acid.  It  has  been  found  in  ovarian  cysts,  and  in  the  fluid  of 
ascites.  When  precipitated  by  alcohol  the  precipitate  is  again  soluble  in 
water.  Para-albumen  has  also  been  found  in  the  fluid  of  ovarian  cysts, 
where  its  presence  was  supposed  to  be  characteristic,  but  has  also  been 
found  elsewhere.  It  is  precipitated  b}^  alcohol,  and  when  so  precipitated 


104  PHYSIOLOGY   OF   THE   DOMESTIC  ANIMALS. 

may  redissolve  again  in  water.  It  is  not  completely  coagulated  by  boil- 
ing. It  is  rendered  turbid  by  acetic  acid,  the  cloudiness  being  removed 
by  an  excess  of  acid  or  sodium  chloride.  It  is  precipitated  by  nitric 
acid,  potassium  ferrocyanide  and  acetic  acid,  mercuric  chloride,  and  ace- 
tate of  lead. 

ALBUMINOIDS. 

In  the  development  of  the  different  tissues  of  the  animal  body 
the  native  albumens  already  described,  which  exist  in  the  ovum  and 
embryonic  cells,  assume  a  modified  form,  the  condition  under  which 
such  a  modified  albumen  is  present  varying  considerably  in  dif- 
ferent tissues ;  as  already  pointed  out,  the  difference  in  the  different 
tissues,  especially  in  the  different  members  of  the  connective-tissue 
group,  is  dependent  upon  the  modification  which  the  albuminous  con- 
stituents of  those  cells  have  undergone.  Such  bodies  have  a  chemical 
composition  very  closely  allied  to  that  of  native  albumens.  They 
are  complex,  nitrogenous  compounds,  but  they  present  certain  proper- 
ties in  contrast  with  the  true  albuminous  bodies.  As  they  appear  to 
result  from  the  transformation  of  those  bodies  in  the  animal  econonvr, 
not  as  a  rule  being  found  in  the  vegetable  kingdom,  they  may  be  spoken 
of  as  the  albuminoids  of  special  tissues. 

In  the  connective-tissue  group  are  included  a  number  of  different 
tissues,  such  as  white  connective  tissue,  elastic  tissue,  tendon,  bone, 
cartilage,  and  dentine,  which  at  first  sight  appear  to  have  few  if  any 
points  in  common.  Yet  all  these  tissues  fulfill  the  same  subservient 
function  of  connection  and  support,  all  originate  from  the  same  layer 
of  the  blastoderm,  and  in  different  periods  of  life  are  often  changed 
from  one  form  into  the  other.  The  cells  of  all  these  tissues  are  capable 
of  developing  a  more  or  less  homogeneous  intercellular  substance,  whose 
chemical  composition  differs  in  the  different  members  of  this  group. 

When  any  of  the  various  forms  of  connective  tissue  proper  are 
macerated  for  some  days  in  lime-water  or  baryta-water,  the  various 
elements  fall  asunder  from  solution  of  the  connecting  cement,  which 
may  be  precipitated  from  its  solution  by  dilute  acids.  This  body  is 
mucin.  If  the  ground  substance  of  the  different  connective  tissues  after 
the  removal  of  mucin  is  boiled  in  water,  they  nearly  all  yield  substances 
somewhat  similar  to  glue  ;  hence  they  are  called  collagenous  bodies. 

We  will  take  these  up  in  turn. 

1.  Mucin. — Mucin,  or  the  cement  substance,  is  found  in  all  mucous 
secretions  as  a  result  of  special  cell  action,  and  jn  the  tissue  of  mollusks, 
and  is  the  substance  to  which  their  tenacious  character  is  due.  It  is 
found  in  embryonic  connective  tissue,  and  serves  to  bind  together  the 
fibres  of  tendons,  and  of  connective  tissue  and  epidermis,  and  is  found 


NITROGENOUS   ORGANIC   CELL-CONSTITUENTS.  105 

in  synovial  secretions.  Mucin  may  be  prepared  from  the  salivary  glands 
by  making  a  watery  extract,  filtering  and  precipitating  mucin  by  acetic 
acid  ;  the  precipitate  may  then  be  washed  with  water,  with  alcohol,  and 
with  ether  to  remove  fat.  Mucin  may  also  be  obtained  from  tendons  by 
washing  well,  cutting  up  into  small  pieces,  extracting  them  with  water  to 
remove  soluble  albuminous  bodies  and  salts,  and  then  allowing  them  to 
stand  for  several  days  in  lime-  or  bai'3'ta-water.  After  filtration,  acetic 
acid  will  precipitate  the  mucin,  which  at  first  is  granular,  but  afterward 
flocculent  in  appearance,  and  which  may  be  washed  with  dilute  alcohol 
or  dilute  acetic  acid.  It  also  may  be  prepared  from  ox-gall  by  precipi- 
tating with  its  own  volume  of  alcohol  to  remove  the  coloring  matter  and 
proteids,  dissolving  the  precipitate  in  lime-water,  after  washing  with 
fresh  alcohol,  and  precipitating  the  mucin  from  its  solution  in  lime- 
water  by  acetic  acid. 

When  freshly  precipitated,  mucin  is  a  glutinous  body  which  may  be 
suspended  but  not  dissolved  in  water.  Mucin  is  soluble  in  concen- 
trated but  not  in  dilute  mineral  acids.  It  is  also  soluble  in  liquor 
potassae  and  lime-water,  and  the  solution  is  viscid  and  nearly  neutral. 
When  in  solution  it  is  not  coagulated  by  boiling,  but  is  precipitated 
in  an  insoluble  form  by  acetic  acid.  Its  solutions  are  precipitated  by 
mineral  acids,  the  precipitate  being  soluble  in  a  slight  excess  of  acid. 
It  is  not  precipitated  by  metallic  salts,  with  the  exception  of  acetate 
of  lead.  When  boiled  for  twenty  or  thirty  minutes  with  dilute  sul- 
phuric acid  it  acquires  the  power  of  reducing  the  ordinary  sugar  tests. 
It  again  loses  this  power  on  prolonged  boiling.  A  body  similar  to 
acid  albumen  is  formed  at  the  same  time.  No  precipitate  is  produced 
with  solutions  of  mucin  by  acetic  acid  and  potassium  ferroc3Tanide 
unless  other  albuminoids  are  also  present.  It  gives  no  precipitate 
with  mercuric  chloride,  and  does  not  give  the  biuret  reaction  for  albu- 
minous bodies ;  with  Millon's  reagent  it  gives  a  red  color.  It  therefore 
possesses  several  properties  which  are  divergent  from  those  of  or- 
dinary albuminous  bodies,  and  is  evidently  a  proteid  body  modified 
through  the  differentiation  of  the  protoplasm  of  the  cells  of  the  con- 
nective-tissue group. 

Mucin  appears  to  be  digested  by  pancreatic  but  not  by  gastric  juice. 
Mucin  is  not  soluble  in  water  or  alcohol,  but  swells  up  very  much  in  the 
former,  particularly  in  the  presence  of  certain  salts.  When  the  mixture 
is  filtered  part  of  the  mucin  often  passes  through,  and  causes  a  turbid 
precipitate.  The  mixture  in  water  possesses  no  viscidity;  it,  however, 
becomes  clearer  and  more  tenacious  if  sodium  chloride  is  added. 

2.  CollagenoKS  Albuminoids. — Collagenous  albuminoids,  of  which 
gelatin  is  the  type,  are  albuminous  bodies  found  in  connective  tissue, 
cartilage,  and  bone.  They  contain  a  little  less  carbon  and  more  nitrogen 


106  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

than  the  true  albuminous  bodies.  They  are  termed  gelatinous  because 
gelatin,  which  is  formed  by  the  action  of  boiling  water  on  these  tissues, 
is  the  most  important  representative  of  the  group.  It  contains — , 

a.  Collagen. 

b.  Gelatin. 

c.  Chondrogen. 

d.  C  lion  drill. 

a.  Collagen,  or  gelatinous  substance,  forms  the  organic  basis  of 
bones  and  teeth,  and  of  the  fibrous  parts  of  tendons,  ligaments,  and 
fascia.  It  derives  its  name  from  the  fact  that  by  prolonged  boiling  it  is 
converted  into  gelatin  or  glue  (Ko/l/ld).  Collagen  is  prepared  from  bones 
by  soaking  in  repeated  changes  of  dilute  hydrochloric  acid;  or  from 
tendons  by  removing  mucin  by  means  of  lime-  or  baryta-water,  then  by 
repeated  washing  with  water,  and  finally  with  very  dilute  acetic  acid. 
When  fresh  it  is  soft,  but  it  shrinks  and  becomes  hard  when  dry,  or  when 
alcohol  is  added.  Collagen  is  insoluble  in  cold  water;  it  swells  up  on 
dilute  acids,  and  becomes  transparent ;  through  the  prolonged  action  of 
dilute  acids  collagen  dissolves,  the  solution  containing  gelatin  and  acid 
albumen,  the  latter,  perhaps,  being  produced  by  the  action  of  the  acid  on 
the  residual  matter  of  the  connective-tissue  cells.  It  dissolves  in  liquor 
potassse,  and  in  'boiling  dilute  acids  or  in  boiling  water  it  dissolves  and 
is  rapidly  converted  into  gelatin. 

6.  Gelatin. — Gelatin  is  prepared,  as  already  indicated,  by  boiling 
collagen,  or  any  of  the  connective-tissue  group,  in  water,  and  when  the 
solution  cools  it  forms  a  jelly  the  consistence  of  which  depends  upon 
the  percentage  of  gelatin  present. 

Gelatin,  prepared  as  indicated  above,  is  a  product  of  the  trans- 
formation of  connective  tissue  by  the  prolonged  action  of  boiling  water. 
It  is  favored  by  high  temperature  (120°  C.),  as  in  Papin's  Digester,  and 
the  presence  of  a  minute  quantity  of  acid.  When  dry  it  forms  a 
yellowish  or,  if  pure,  a  transparent,  tasteless  solid,  closely  resembling  a 
gum  in  its  general  appearance  and  characteristics.  It  is  insoluble  in 
cold  water,  but  when  immersed  in  cold  water  is  able  to  absorb  by 
imbibition  forty  times  its  own  weight.  It  then  will  form  a  stiff,  tenacious, 
jelly-like  mass.  If  dry  gelatin  is  boiled  in  water,  it  is  readily  dissolved, 
and  when  the  solution  in  water  cools  the  gelatin  sets  into  a  stiff  jelly  if 
more  than  1  per  cent,  of  gelatin  is  present,  the  consistence  of  the  jelly 
depending  upon  the  quantity  of  gelatin  dissolved.  When  boiled  for  a 
long  time  in  water,  or  if  boiled  with  an  acid  or  alkali,  this  property  of 
gelatinizing  is  lost  and  two  peptone-like  bodies  result. 

Gelatin  is  insoluble  in  alcohol,  ether,  and  chloroform.  It  is  soluble 
in  warm  glycerin,  such  solutions  having  the  power  of  gelatinizing  when 
cooled. 


NITROGENOUS   ORGANIC   CELL-CONSTITUENTS.  107 

In  solution  gelatin  rotates  the  plane  of  polarized  light  to  the  left 
( — 130°  at  25°  C.).  In  watery  solutions  gelatin  is  precipitated  by  tannic 
acid, alcohol,  and  mercuric  chloride  ;  but  not  hy  acetic  acid,  which  serves 
to  distinguish  it  from  chondrin ;  nor  by  potassium  ferrocyanide  and  acetic 
acid,  which  separates  it  from  other  proteids;  nor  acetate  of  lead,  which 
precipitates  chondrin.  When  boiled  with  cupric  sulphate  and  potassium 
hydrate,  the  blue  solution  becomes  red  without  depositing  oxide  of 
copper.  Gelatin  readily  undergoes  putrefaction,  and  among  the  products 
leucin,  ammonia,  and  some  of  the  fatty  acids  are  found. 

c.  Chondrogen. — Chondrogen  is  found  in  the  intercellular  substance 
of  l^aline  cartilage,  and  in  the  cartilage  of  bone  before  ossification.    It 
derives  its  name  from  the  fact  that  when  boiled  with  water  it  forms 
chondrin, — a  point  which  serves  to  distinguish  it  from  fibro-cartilage, 
which,  when  treated  in  the  same  way  with  boiling  water,  forms  gelatin,  and 
not  chondrin.    Chondrogen  is  insoluble  in  cold  water,  but  if  dried  before- 
hand, when  immersed  in  cold  water  will  swell  up  slightly.    It  swells  very 
slightly  in  acetic  acid,  and  may  be  dissolved  by  the  concentrated  mineral 
acids  and  caustic  alkalies.     When  subjected  to  prolonged  boiling  with 
water  it  dissolves  and  forms  an  opaline  solution,  which  forms  a  jelly 
when  cooled. 

d.  Chondrin. — As  just  stated,  chondrin  is  the  result  of  prolonged 
boiling  of  .chondrogen  in  water.     When  solutions  of  chondrin  in  water 
cool  the}"  form  a  stiff  jelly,  which  is  insoluble  in  cold  water,  but  soluble 
in  alkalies  and  ammonia.     When  solutions  of  chondrin  are  evaporated, 
a  hard,  translucent,  yellowish,  gummy  mass  results,  which  is  insoluble 
in   alcohol  and   ether,  swells  slightly  in  cold   and   dissolves   tolerably 
readily  in  hot  water  and  solutions  of  the  alkalies.     Prolonged  boiling  of 
watery  solutions  of  chondrin  destroys  its  power  of  gelatinizing,  though 
the  other  properties  of  chondrin  are  not  thereby  altered.     It  is  precipi- 
tated from  its  solutions  by  alcohol.     It  differs  from  gelatin  in  that  it  is 
precipitated  by  the  mineral  acids  even  when  they  are  dilute ;  an  excess 
of  the   reagent  dissolves   the   precipitate.      It  is   also   precipitated   by 
solutions   of  sulphurous   acid.     It   is   precipitated   by   acetic  acid,  the 
precipitate  not  being  soluble   in  excess   unless   some   alkaline   salt   be 
present.     It  is  precipitated  in  abundant  flocculi  by  solutions  of  alum, 
which   readily  dissolve  in  an  excess,  and  the  fluid  becomes  clear  and 
transparent.     It   is  precipitated  with  acetate  and    subacetate   of  lead, 
nitrate  of  silver,  and  cupric  sulphate.     Tannic  acid  and  chlorine  water 
precipitate  it,  as  in  the  case  of  gelatin.     It  rotates  the  plane  of  polarized 
light  to  the   left.     Chondrin   also  is   readily   decomposable,  and  when 
subjected   to    prolonged    heat   with    concentrated   l^drochloric   acid    is 
decomposed,  with  the  formation  of  nitrogenous  compounds  which  have 
the  power  of  reducing  the  cupro-potassium  test ;  a  body  resembling  acid 


108  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

albumen  is  formed  at  the  same  time.  The  same  changes  follow  prolonged 
boiling  with  dilute  sulphuric  acid.  There  are  some  grounds  for  supposing 
that  chondrin  is  not  an  individual  albuminoid,  but  that  it  is  rather  a 
mixture  of  gelatin,  mucin,  and  salts,  since  its  general  characteristics  are 
similar  to  what  might  be  possessed  by  a  combination  of  these  bodies. 
All  the  connective  tissues,  therefore,  possess  a  body  which  may  be 
transformed  into  gelatin  by  boiling,  and  a  cement  substance,  mucin. 

The  following  statements  represent  in  a  few  words  the  distinctive 
characteristics  of  mucin,  cliondrin,  gelatin,  and  albumen: — 

Mucin. — Precipitated  by  acetic  acid,  the  precipitate  is  not  dissolved 
by  sodium  sulphate. 

Chondrin. — Precipitated  by  acetic  acid,  the  precipitate  is  dissolved 
by  sodium  sulphate.  Precipitated  by  lead  acetate,  alum,  silver  nitrate, 
and  copper  sulphate. 

Gelatin. — Not  precipitated  by  acetic  acid,  nor  by  acetic  acid  and 
potassium  ferrocyanide,  nor  by  lead  acetate. 

Albumen. — Dissolved  by  acetic  acid,  the  solution  is  precipitated  by 
potassium  ferrocyanide,  or  by  the  addition  of  alkaline  salts  and  heat. 

Gelatin  and  chondrin  are  mostly  to  be  recognized  by  their  hot 
solutions  forming  a  jelly  when  cooled.  This,  as  already  mentioned,  is  not 
invariably  the  case,  as  the  property  is  lost  by  prolonged  boiling,  or  by 
boiling  with  acids. 

Closely  allied  to  these  collagenous  albuminoid  constituents  of  the 
connective  tissues  we  meet  with  two  other  albuminoids  which  have  many 
points  in  common  with  the  above,  with  the  exception  that  they  do  not 
form  jellies  when  their  solutions  cool.  These  two  bodies  are  Elastin, 
obtained  from  elastic  tissue,  and  Keratin,  a  nitrogenous  body  of  epithelial 
origin. 

3.  Elastin. — Elastin  is  the  albuminoid  principle  contained  in  yellow 
elastic  tissue.  When  yellow  elastic  connective  tissue  is  boiled  with 
water,  after  mucin  has  been  removed,  collagen  is  dissolved.  The  residue 
which  remains  is  mainly  composed  of  elastin.  Elastin  may  be  prepared 
by  macerating  the  ligamentum  nuchae  of  the  ox  with  ether,  and  then  hot 
alcohol,  to  remove  the  fats ;  boiling  water,  to  remove  collagen  and  convert  it 
into  gelatin,  and  10  per  cent,  caustic  soda,  and  then  acetic  acid,  allowing 
the  boiling  in  water  to  continue  for  at  least  thirty-six  hours,  and  in  the 
acetic  acid  for  at  least  six  hours.  After  being  subjected  to  the  soda,  the 
remaining  tissue  is  again  boiled  with  dilute  acetic  acid,  well  washed  with 
water,  and  afterward  the  acid  neutralized.  After  washing  with  hot 
water  a  brittle,  yellowish  mass  is  obtained,  which  recovers  its  elasticity 
and  fibrous  appearance  if  soaked  in  dilute  acetic  acid. 

Elastin  is  insoluble  in  cold  or  boiling  water,  and  offers  remarkable 
resistance  to  chemical  agents,  unless  boiled  for  a  very  long  time.  It  is 


NITROGENOUS   ORGANIC   CELL-CONSTITUENTS.  109 

insoluble  in  alcohol,  ether,  ammonia,  or  acetic  acid,  but  it  dissolves  in 
caustic  potash.  Its  solutions,  however,  do  not  gelatinize.  When  once 
dissolved  in  caustic  potash  the  alkali  may  be  neutralized  without  throw- 
ing the  elastin  out  of  solution.  Tannic  acid  is  the  only  acid  which  will 
precipitate  it.  Elastin  gives  the  xantho-proteic  and  Millon's  reactions, 
and  its  place  among  the  albuminoids,  therefore,  seems  warranted.  When 
boiled  for  a  long  time  with  sulphuric  acid  it  undergoes  decomposition, 
with  the  formation  of  leucin  and  tyrosin.  Elastin  contains  no  sulphur. 

4.  Keratin. — The  epithelial  tissues  of  the  animal  body — nails,  bone, 
epidermis,  and  epithelium,  as  well  as  horns  and  feathers — are  mainly 
composed  of  a  substance  closely  allied  to  albumen,  as  it  gives  leucin  and 
tyrosin  on  decomposition,  to  which  the  name  of  keratin  has  been  given. 

Keratin  contains  sulphur  in  loose  combination,  and  is  in  some  re- 
spects closely  related  to  elastin.  Keratin  is  insoluble  in  alcohol  and 
ether,  swells  up  in  boiling  water,  and  is  soluble  in  the  caustic  alkalies. 
It  is  not  liable  to  decomposition.  When  one  of  the  epithelial  structures, 
such  as  horn,  is  subjected  to  the  action  successively  of  boiling  water  and 
alcohol,  ether,  and  dilute  acids,  this  substance,  keratin,  remains  behind. 
But  when  so  obtained  it  has  by  no  means  a  constant  composition, 
and  it  is  probable,  therefore,  that  keratin  is  rather  a  mixture  of  several 
nitrogenous  bodies  than  a  single  albuminoid. 

Decomposition  of  the  Albuminous  Bodies. — As  already  mentioned, 
albuminous  bodies  are  the  most  unstable  of  all  organic  compounds,  and 
we  have  the  strongest  reason  for  believing  that,  even  while  in  the  interior 
of  animal  and  vegetable  organisms,  the  albuminous  constituents  of  proto- 
plasm are  continually  the  seat  of  various  forms  of  decomposition  which 
result  in  the  production  of  simpler  organic  and  inorganic  forms.  As  we 
know  but  very  little  as  to  the  molecular  constitution  of  the  proteid 
bodies,  nothing  positive  can  be  said  as  to  the  complex  chemical  processes 
which  result  in  the  production  of  simpler  organic  forms.  The  subject 
has  been  a  favorite  field  of  research  for  organic  chemists,  but  as  yet 
scarcely  anything  tangible  has  resulted  from  their  labors.  An  immense 
amount  of  valuable  information  has  been  attained,  but  the  applicability 
of  the  facts  so  reached  to  physiological  processes  is  not  as  yet  clearl}^ 
assured.  The  chief  end  products  of  the  decomposition  of  proteids  in 
the  animal  cell,  which  is  essentially  one  of  oxidation,  are  water,  carbon 
dioxide,  and  urea.  What  the  nature  of  the  substances  are  which  are  in- 
termediary between  these  end  products  and  albuminoids  we  do  not  clearly 
know,  except  that  certain  ones,  such  as  leucin,  tyrosin,  certain  of  the 
carbo-hydrates,  such  as  glycogen  and  fats,  are  of  constant  occurrence 
and  of  great  importance.  The  subject  of  the  decomposition  of  albumen 
under  various  chemical  and  physical  agents  is  an  extremely  interesting 
one,  but  it  falls  more  within  the  province  of  works  on  organic  chemistry. 


110  PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 

In  our  study  of  the  processes  of  metabolism  of  the  animal  body,  in 
which  we  will  attempt  to  trace  the  course  of  the  food-stuffs  after  their 
entrance  into  the  body  and  in  their  elimination  as  various  effete  products, 
this  subject  must  necessarily  be  touched  upon ;  the  consideration  of  the 
part  of  this  subject  which  is  at  all  capable  of  practicable  application  will 
be  deferred  until  then. 

It  may  only  be  mentioned  here  that  the  simpler  an  organism  the 
simpler  must  be  the  chemical  changes  in  its  constituents.  Thus,  we  find 
that  in  the  elementary  vegetable  organisms  their  entire  structure  is  made 
up  of  protoplasm,  which  is  practically  almost  solely  albuminoid  ;  we  have 
then  appearing  chlorophyll,  cellulose,  starch,  and  in  still  higher  forms  the 
various  sugar  groups,  vegetable  acids,  alkalies,  etc.  In  the  animal  body 
a  similar  state  of  affairs  holds.  We  m&y  say  that  the  body  of  an  amoeba 
is  composed  of  simple  albuminous  matter.  In  the  development  of 'organs 
we  have  a  development  of  supposed  chemical  derivatives  of  protoplasm, 
and  the  higher  the  state  of  development  of  the  organism  the  more  com- 
plex will  be  the  changes  which  have  resulted  from  the  original  proto- 
plasm. As  we  have  already  mentioned,  these  cell-constituents  are  organic, 
nitrogenous  and  non-nitrogenous,  and  inorganic  bodies.  All  of  the  sub- 
stances which  we  have  heretofore  considered  are  examples  of  derivatives 
or  modifications  of  protoplasm,  and  as  protoplasm  is  essentially  albumi- 
nous they  are,  therefore,  the  examples  of  a  modification  of  albumen.  In 
the  waste  of  albuminous  tissues  we  have  an  immense  number  of  inter- 
mediary bodies,  partly  belonging  to  the  various  aromatic  series,  between 
albuminous  bodies  and  the  simpler  end  products,  water,  carbon  dioxide, 
and  urea.  These  bodies  result  from  a  progressive  series  of  oxidations, 
and  will  receive  consideration  under  the  subject  of  Nutrition. 

FEKMENTS. 

Various  animal  and  vegetable  cells  will  often  be  found  to  contain 
a  class  of  bodies  which  are  closely  allied  in  composition  to  albuminous 
substances,  since  they  contain  carbon,  nitrogen,  hydrogen,  ox3^gen,  and 
sulphur.  From  the  fact  that  they  are  able,  under  certain  conditions,  to 
produce  reduction  in  the  complexity  of  organic  compounds  with  the 
action  of  water  without  acting  through  the  development  of  chemical 
affinities,  and  without  themselves  undergoing  change,  such  bodies  are 
termed  soluble  ferments,  and  are  derived  directly  from  modifications  of 
the  protoplasm  of  the  living  organisms  in  which  they  originate.  Al- 
though they  are  apparently  allied  to  albuminoids  in  their  chemical  con- 
stitution, yet  when  purified  they  fail  to  give  the  proteid  reactions ;  and 
although  we  may  be  pretty  sure  that  such  bodies  are  derived  from 
the  physiological  splitting  up  of  proteids,  we  have  no  exact  knowledge 
as  to  their  structure.  When  obtained  dry  by  various  processes,  which 


NITROGENOUS   ORGANIC   CELL-CONSTITUENTS.  Ill 

will  be  considered  under  the  study  of  the  individual  ferments  in  the 
section  on  Digestion,  they  are  amorphous,  colorless  powders,  which  are 
highly  soluble  in  water,  resemble  gums  somewhat  in  appearance,  and  are 
precipitated  from  their  solutions  by  alcohol,  corrosive  sublimate,  and 
lead  acetate.  One  of  their  remarkable  points  of  contrast  to  albuminous 
bodies  is  that,  when  precipitated  from  solution  in  water  or  glycerin  by 
absolute  alcohol,  if  the  precipitates  are  filtered  off  and  dried,  they  are 
again  perfectly  soluble  in  water,  and  are  still  capable  of  exerting  all  their 
actions  ;  hence,  their  precipitation  is  more  of  a  mechanical  nature  than 
chemical.  Further,  when  the  precipitates  formed  by  the  above  reagents 
are  decomposed  by  sulphuretted  hydrogen  a  wateiy  extract  of  the  pre- 
cipitate will  still  preserve  the  original  properties  of  the  ferment ;  in  other 
words,  the  soluble  matter  is  restored  to  the  water  unchanged,  and  still 
preserves  its  specific  properties.  The  ferments  are  with  difficulty  freed 
from  albuminoids,  and  it  is  in  all  probability  the  albuminoid  which  is 
chemically  precipitated  from  their  solutions  by  the  above  reagents,  and 
which  in  this  precipitation  carries  with  it  mechanically  the  ferment. 
Consequently,  this  property  of  the  ferment  of  being  precipitated  by  the 
above  reagents  is  dependent  upon  the  albuminous  bodies  which  are 
nearly  always  associated  with  it.  We  shall,  further,  find  that  this  prop- 
erty of  being  carried  down  by  precipitates  from  solutions  is  the  basis 
of  nearl}r  all  the  methods  which  have  been  employed  for  the  isolation  of 
the  different  digestive  ferments. 

Ferments  obtained  from  the  animal  and  vegetable  kingdom  may 
have  the  most  varied  functions.  We  have  but  little  information 
concerning  the  soluble  ferments  from  a  chemical  point  of  view.  We 
do  not  even  know  whether  they  all  have  the  same  chemical  compo- 
sition, and  differ  only  in  some  unknown  manner  in  their  specific  activit3r. 
They  only  are  active  at  a  temperature  below  60°  C.,  and  when  in  the 
presence  of  water ;  at  the  temperature  of  boiling  water  they  are  perma- 
nently destroyed;  at  lower  temperatures  their  activity  is  suspended. 
They  do  not  themselves  appear  to  be  influenced  in  the  phenomena  offer- 
mentation  which  they  inaugurate ;  ferments  are  also  inactive  in  the  pres- 
ence of  various  chemical  agents,  such  as  alcohol,  the  stronger  mineral 
acids,  and  all  the  large  group  of  substances  which  are  known  as  antisep- 
tics. Ferments  may  be  of  two  kinds ;  either  organized  ferments,  such 
as  the  yeast-plant,  malt,  vibrios,  bacteria,  etc., — substances  which  are 
themselves  elementary,  cellular  organisms, — or  the  so-called  unformed 
ferments,  or  enzymes,  substances  which  invariably  originate  in  the  interior 
of  animal  and  vegetable  protoplasm,  and  are  soluble  and  not  organized. 

This  latter  group  comprises  all  the  ferments  with  which  we  are  par- 
ticularly interested.  Their  specific  action  is  in  many  cases  closely  analo- 
gous to  that  of  the  formed  ferments.  There  are,  however,  several  points 


112  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

of  contrast  between  them.  Organized  ferments  are  destroyed  by  com- 
pressed oxygen ;  soluble  ferments  are  not.  Solutions  of  borax  prevent 
the  action  of  the  unformed  ferments,  but  are  without  influence  on  the 
formed  ferments.  The  organized  ferments  during  their  action  reproduce 
themselves  ;  the  soluble  ferments  do  not  act.  All  the  soluble  ferments 
have  a  high  percentage  of  ash,  sometimes  as  much  as  8  per  cent.  Under 
the  action  of  ferments,  fermentable  bodies  yield  substances  whose  nature 
is  dependent  on  that  of  the  ferment.  So  that  any  individual  ferment- 
able substance  under  the  influence  of  different  ferments  will  split  up  into 
different  substances. 

The  following  are  the  important  ferments  found  in  animal  organ- 
isms :  ptyalin,  found  in  the  saliva  and  converting  starch  into  sugar ; 
pepsin,  found  in  the  gastric  juice  and  in  the  presence  of  a  dilute  acid 
converting  albuminous  bodies  into  peptones  ;  the  milk-curdling  ferment, 
or  rennet,  found  in  the  gastric  juice  and  coagulating  milk  in  neutral  or 
acid  media;  the  amylolytic  ferment  of  pancreatic  juice,  converting  starch 
into  sugar  ;  the  proteolytic  ferment  of  pancreatic  juice,  converting  proteids 
into  peptones  in  an  alkaline  medium;  the  fat-ferment  of  pancreatic  juice, 
splitting  up  neutral,  fatty  bodies  into  fatty  acids ;  the  milk-curdling  fer- 
ment, also  said  to  exist  in  pancreatic  juice  ;  the  inversive  ferment,  found 
in  intestinal  juice  and  converting  cane-sugar  into  inverted  sugar;  and 
the  liver-ferment,  converting  gtycogen  into  sugar.  The  general  subject 
of  the  nature  of  the  changes  produced  by  these  substances  will  be  con- 
sidered in  the  next  section  ;  the  mode  of  action  of  the  digestive  ferments 
will  be  considered  under  the  subject  of  Digestion. 

B.    NON-NITROGENOUS    ORGANIC   CELL-CONSTITUENTS. 

I.  CARBO-HYDRATES.  —  The  carbo-hydrate  tissue-constituents  are 
composed  of  carbon,  hydrogen,  and  oxygen,  the  latter  two  in  the  propor- 
tion to  form  water.  Although  occasionally  present  as  constituents  of 
animal  cells,  they  are  almost  exclusively  produced  by  the  vegetable  king- 
dom, and  present  many  interesting  examples  of  isomerism.  They  may 
be  divided  into  the  three  following  groups : — 

(a)  STARCHES  (C6H10O5). 

(6)   GRAPE-SUGAR  GROUP  (C6HiaO6). 

(c)  CANE-SUGAR  GROUP  (CMH22On). 

The  members  of  the  first  group  may,  through  the  action  of  dilute 
acids  or  the  di astatic  ferments,  be  transformed  in  great  part  into  the 
second  group.  The  latter  undergoes  alcoholic  fermentation  when  in 
contact  witli  malt. 

(a)  THE  AMYLOSES,  OR  STARCH  GROUP  7?(C«H1006). — This  group 
includes  starch,  dextrin,  glycogen,  cellulose,  granulose,  and  inulin. 


NON-NITBOGENOUS   OEGANIC   CELL-CONSTITUENTS. 


113 


1.  Starch,  or  amylum  (??(C6H10O6)  or  CmllaoOjg),  is  almost  univers- 
al^ distributed  throughout  the  vegetable  kingdom,  and  is  the  first  evi- 
dence of  the  decomposition  of  CO2  of  the  atmosphere  by  vegetable  cells 
(6  CO3-{-5  H2O  =  C6H10O6-|-12  0).  It  is  particularly  abundant  in  the 
cereals,  in  seeds  of  the  leguminous  plants,  and  in  the  potato,  and  in  cer- 
tain roots,  tubers,  soft  stems,  and  seeds.  It  forms  rounded  masses  which 
lie  in  the  plasma  of  the  plant-cells,  becoming  converted,  in  the  process  of 
germination  in  seeds  and  bulbs,  into  soluble  dextrin  and  sugar.  Under 


FIG.  54.— STARCH-GRANULES,  AFTER  LOEBISCH. 

A,  pea-starch ;  B,  rice-starch  ;  C.  oat-starch  ;  D,  wheat-starch :  E,  bean-starch :  F,  millet-starch ;   G,  corn-starch  ;  H,  rye- 
starch  ;   I,  lentil-starch  ;    K,  potato-starch ;  L,  buckwheat-starch ;   M,  barley -starch. 

microscopic  examination  starch  appears  as  rounded,  glistening  granules 
composed  of  a  series  of  concentric  rings.  These  granules  vary  in  appear- 
ance and  size  according  to  their  source.  In  size  they  may  vary  from 
0.004  mm.  in  diameter,  as  when  found  in  beet-seeds,  to  0.16  mm.,  as  in 
potato-starch  (Fig.  54). 

In  the  following  table  (after  Karmarsch)  the  diameter  of  the  starch- 
granules  from  different  sources  is  given.     Microscopic  examination  of 

8 


114 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


0.140  (0.10-0.185). 

0.140 

0.07 

0.063 

0.050 

0.050 

0.036 

0.031 

0.02-0.03 

0.028 

0.022 

0.025 

0.009 


different  "  meals,"  by  the  shape  and  size  of  the  granules,  will  thus  permit 
of  the  recognition  of  adulteration  with  inferior  meals  : — 

Mm. 

Starch  granules  from  Potatoes  (average), 
Arrowroot, 
Sago, 
Beans, 

Peas,  " 

Wheat, 
Rye, 
Oats, 
Corn, 
Tapioca, 
Rice, 
Barley, 
Buckwheat, 

The  striated  appearance  is  due  to  the  fact  that  starch  is  composed 
of  two  substances, — cellulose  and  granulose,  arranged  in  concentric 
layers,  the  cellulose  always  being  external.  Granulose  stains  blue  with 
iodine, — not  by  the  formation  of  a  chemical  compound,  but  by  the  deposit 
of  the  iodine  around  the  starch-molecules, — and  cellulose  stains  a  faint 
yellow.  These  two  substances  may  be  separated  by  digesting,  at  60°  C., 
one  part  of  starch  in  forty  parts  of  saturated  salt  solution  containing 
1  per  cent,  of  free  hydrochloric  acid.  The  granulose  then  passes  into 
solution,  while  the  cellulose  remains.  Examined  in  this  waf ,  potato- 
starch  has  been  found  to  contain  5.7  per  cent,  cellulose,  wheat-starch 
2.3  per  cent.,  and  arrowroot  3.10  per  cent.  Under  the  action  of  dias- 
tatic  ferments  granulose  is  converted  into  sugar,  while  cellulose  remains 
unaltered.  A  third  substance  has  been  distinguished  in  starch  which  is 
termed  erythrogranulose,  and  it  differs  from  granulose  in  taking  on  a  red 
coloration  when  treated  with  iodine.  It  has  a  stronger  affinity  for  fodine 
than  granulose.  Hence,  when  starch-mucilage  is  treated  with  very  dilute 
iodine  solution  a  red  color  is  produced,  but  when  a  large  quantity  of 
iodine  is  added,  a  deep-blue  coloration,  from  the  fact  that  the  reaction 
of  the  iodine  with  the  granulose  masks  the  erythrogranulose  reaction. 

Pure  starch  is  a  white,  tasteless,  and  odorless  substance  which  is 
almost  entirely  insoluble  in  cold  water.  In  boiling  water  the  granules 
swell  up  from  the  imbibition  of  water  by  the  granulose,  the  cellulose 
envelopes  burst,  and  the  granulose  dissolves.  It  is  to  the  presence  of 
the  cellulose  envelope  that  the  insolubility  of  raw  starch  in  cold  water  is 
due.  When  the  cellulose  membranes  are  destroyed  or  comminuted,  as  by 
grinding  with  powdered  glass,  a  part  of  the  granulose  is  then  dissolved 
in  the  water,  and  by  repeated  washing  nearly  all  the  granulose  ma}7  be 
removed  and  the  cellulose  envelopes  alone  remain.  In  boiling  water, 
while  the  starch  is  said  to  be  soluble,  the  condition  is  more  strictly  one 
of  a  high  degree  of  imbibition  of  the  starch.  Like  other  colloids,  starch 
is  incapable  of  dialysis,  and  forms  a  mucilaginous  emulsion.  A  solution 


NON-NITROGENOUS   ORGANIC   CELL-CONSTITUENTS.  115 

of  granulose  in  water  rotates  the  plane  of  polarized  light  strongly  to  the 
right.  According  to  Pay  en,  when  starch  is  placed  in  a  saturated  solu- 
tion of  potassium  iodide,  or  potassium  bromide,  it  swells  up  to  a  stiff 
jelly  and  increases  twenty-five  to  thirty  times  in  volume.  This  mass 
may  then  be  dissolved  in  water,  with  only  a  slight  residue  of  starch- 
cellulose.  Dilute  acids  will  also  dissolve  granulose. 

The  alteration  of  starch  through  the  action  of  the  dia static  ferments 
will  be  described  under  the  consideration  of  the  action  of  the  digestive 
juices  on  the  different  food-stuffs.  When  starch  is  boiled  with  dilute 
acids  similar  products  result. 

When  starch  is  subjected  to  dry  heat  at  150°  to  160°  C.  it  is  gradu- 
ally transformed  into  dextrin.  When  moisture,  however,  is  present,  quite 
different  compounds  result,  the  starch  being  completely  decomposed,  with 
the  formation  of  carbon  dioxide,  formic  acid,  etc.  In  still  higher  tem- 
peratures small  quantities  of  brenzcatechin  are  formed, — a  fact  which  is 
pf  especial  interest,  as  it  indicates  the  possibility  of  the  conversion  of 
carbo-hydrates  into  members  of  the  aromatic  series.  Oxalic  acid  results 
from  heating  starch  with  nitric  acid. 

The  test  for  starch  is  iodine,  which,  with  raw  starch,  or  with  starch- 
mucilage,  gives  a  deep-bine  coloration  which  disappears  on  heating,  to 
return  on  cooling,  if  the  heat  has  not  been  too  prolonged.  Starch  is 
also  precipitated  from  its  solutions  by  tannic  acid  in  the  form  of  a  yellow, 
flocculent  sediment  which  is  dissolved  on  heating. 

.  •  ^  2.  Cellulose  (C6H10O6). — Cellulose  forms  the  wall  or  cell-membrane 
of  vegetable  cells,  and  may  be  regarded  as  the  skeleton  of  plants.  It  is 
formed  by  vegetable  protoplasm  out  of  other  carbo-li3Td rates,  such  as 
starch  and  sugar,  and  is  capable  of  being  again  reconverted  into  other 
members  of  the  same  group.  It  only  very  seldom  occurs  in  a  perfectly 
pure  condition.  Young  plants  contain  purer  cellulose  than  older  plants; 
in  the  latter  there  is  a  greater  percentage  of  ash.  Cotton  and  Swedish 
filter-paper  are  forms  of  comparatively  pure  cellulose.  Cellulose  is  very 
hygroscopic,  but  ammoniacal  cupric  oxide  solution  (Schneider's  reagent) 
is  its  only  solvent.  In  sulphuric  acid  it  first  swells  up  and  then  dissolves 
and  forms  a  substance  which  is  stained  blue  with  iodine.  This  substance  is 
termed  ani3'loid,  but  must  not  be  confounded  with  the  amyloid  substance 
of  pathologists,  which  has  been  already  described  under  the  albuminous 
bodies.  Cellulose  is  also  capable  of  being  converted  into  the  sugar 
group  by  prolonged  action  of  acids.  Woody  fibre  is  a  modified  form  of 
cellulose,  which  is  due  to  the  deposit  within  the  cellulose  of  nitrogenous 
substances  ;  it  then  has  acquired  a  greater  power  of  resistance  to  various 
mechanical  and  chemical  agents.  In  woody  fibre  cellulose  has  become 
associated  with  a  body  richer  in  carbon  and  poorer  in  oxygen  than  cellu- 
lose, and  which  is  termed  lignin  ;  its  formula  is  C10H240U.  The  lignin 


116  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

constitutes  about  50  per  cent,  of  wood,  the  other  half  being  composed  of 
cellulose,  upon  which  the  lignin  is  deposited.  Iodine  stains  cellulose  of  a 
yellowish  color  unless  hydriodic  acid,  potassium  iodide,  zinc  iodide,  sul- 
phuric acid,  phosphoric  acid,  or  zinc  chloride  are  added  with  the  iodine. 
With  any  of  these  reagents,  combined  with  the  iodine,  the  cell-membrane 
or  cellulose  is  stained  blue.  It  is  not  known,  however,  in  what  way  these 
agents  assist  the  reaction. 

3.  Dextrin  (C6H1006). — Dextrin,  or  British  gum,  is  the  name  given 
to  a  group  of  substances  which  may  be  regarded  as  intermediary  products 
in  the  conversion  of  starch  into  sugar.  It  may  also  be  obtained  by  boil- 
ing starch  with  dilute  acid,  although  in  this  operation  the  sugars  are  also 
obtained.  There  is  some  doubt  as  to  whether  it  exists  ready  formed  as 
a  constituent  of  vegetable  cells.  In  commerce  it  is  manufactured  by 
heating  dry  starch  up  to  400°.  Through  the  action  of  the  dry  heat  the 
starch  becomes  yellowish  in  color  and  soluble  in  water.  Dextrin  is  in- 
soluble in  alcohol  and  ether;  it  should  not  reduce  the  sugar  test  unless, 
as  is  apt  to  be  the  case,  it  is  associated  with  sugar.  It  rotates  the  ray 
of  polarized  light  strongly  to  the  right,  from  which  it  derives  its  name 
( dexter  =  right),  and  is  readily  converted  by  the  action  of  dilute  acids, 
or  the  diastatic  ferments,  into  sugar.  According  to  Bernard,  dextrin  is 
found  in  the  blood  of  both  the  herbivora  and  carnivora,  though  in  greater 
amount  in  the  former.  When  found  in  the  animal  body  it  originates 
partly  from  the  giycogen  of  the  liver  and  partly  from  the  food.  The  test 
for  dextrin  is  the  formation  of  a  mahogany-red  color  when  iodine  is  added 
to  its  solutions.  When  heated  this  color  disappears  and  does  not  return  on 
cooling, — a  point  of  importance  as  serving  to  distinguish  dextrin  from 
giycogen,  another  member  of  this  group.  Dextrin  is  precipitated  out 
of  its  watery  solutions,  which  are  alwa}^s  turbid,  by  alcohol,  lime-water 
and  ammonia,  and  acetate  of  lead.  With  iodine  in  solution  in  potassium 
iodide,  dextrin  gives  a  violet  coloration. 

4.  Giycogen. — Giycogen, or  animal  starch, or, more  properly  speaking, 
animal  dextrin,  wiU  be  discussed  at  length  under  the  subject  of  Special 
Physiology. 

5.  Inulin  (C6H1006). — In  its  composition  and  characteristics  inulin 
is  closely  allied  to  starch.     It  is  found  in  the  roots  of  the  Lobeliaceae, 
Campanulaceae,  and  Gordeniaceas  ;  it  owes  its  name  to  the  fact  that  it  wras 
first  discovered  in  the  root  of  the  Inula  helenium.     Dried  dahlia-bulbs 
contain    42   per   cent,   of  inulin.     In   the   autumn   inulin   is   found    in 
greatest  amount ;    in  the   spring   it  becomes  converted   into   Isevulose. 
Inulin  is   only   found   dissolved    in   plant-juices,  and  never  as  a  solid 
deposit ;  and  since  inulin  by  itself  is  insoluble  in  water,  it  must  then  owe 
its  solubility  to  the  presence  of  some  other  substance. 

Inulin  may  be  obtained  \>y  boiling  dahlia-bulbs   in  water,  enough 


NON-NITKOGENOUS   ORGANIC   CELL-CONSTITUENTS.  117 

calcium  carbonate  being  added  to  neutralize  the  acid  reaction.  After 
filtering  and  concentration,  inulin  separates  from  the  extract  in  the  form 
of  crystals.  By  boiling  with  dilute  acid,  inuliu  is  converted  into 
Isevulose. 

(6)  THE  GLUCOSES,  OR  GRAPE-SUGAR  GROUP  ?i(C6H1206). — This  group 
comprises  grape-sugar,  or  dextrose,  galactose,  inosite,  and  Isevulose,  or 
sugar  of  fruits. 

1.    Grape-Sugar  (C6H12O6-|-H2O). — Grape-sugar,  or  glucose,  is  widely 
distributed  throughout  the  vegetable  kingdom,  as  a  rule  accompanying 
fruit-sugar,  and  Js  also  normally  found  dissolved  in  many  of  the  animal 
j  uices.    It  owes  its  name  to  its  being  found  in  grapes,  where  it  is  associated 
with  Isevulose.     It  rotates  the  plane  of  polarized  light  to  the  right,  and  is 
consequently  designated  as  dextrose.     As  a   product  of  the  action  of 
the  diastatic  ferments  on  starch  and  the  majorit3T  of  the  carbo-l^-drates, 
it  acquires  an  especial  importance  for  the  animal  organism.    Grape-sugar 
also  occurs  in  the  vegetable  kingdom  associated  with  other  bodies  to  form 
glucosideSj  from  which  it  may  be  separated  by  treatment  with  acids  or 
ferments.     Most  of  these  bodies  contain  only  C,  H,  and  O;  some,  such 
as  solanin  and  amygdalin,  contain  N  in  addition,  and  in  others  S  is  also 
found.     Grape-sugar  seldom  occurs  in  well-formed  crystals,  but  ordinarily 
in  crumbly,  white  masses,  which,  under  the  microscope,  are  seen  to  consist 
of  small,  rhombic  tables.    It  has  a  sweetish  taste,  and  is  soluble  in  water 
and   alcohol.     At    100°    C.   grape-sugar   melts   and   loses  its  water  of 
ciystallization.     At  higher  temperatures  it  becomes  brown,  and  is  con- 
verted   into    caramel,   CuH^Oj,.      At    still   higher    temperatures    it    is 
completely  decomposed  into  CO,  C02,  marsh-gas,  acetic  acid,  acetone, 
aldehyde,  and    other   products.     If  heated   with  a   strong  solution  of 
caustic  potash  grape-sugar  decomposes,  with  heat  production,  into  lactic 
acid,  brenzcatechin,  formic  acid,  and  other  products,  accompanied  by 
the  development  of  a  brown  color.     If  nitric  acid  is  then  added,  an  odor 
of  burnt   sugar  and  formic  acid  is  produced.      Grape-sugar  is  readily 
soluble  in  water,  but  less  so  than  cane-sugar.     It  is  also  less  sweet  than 
cane-sugar.     It  is  very  slightly  soluble  in  alcohol  and  insoluble  in  ether. 
Glucose  combines  with  different  acids  and  bases  to  form  glycosates  or 
saccharates.      Grape-sugar   has  a    great   affinity  for  oxygen,  and  it  is 
therefore   a   powerful   reducing   agent.     This   property  is  seen   in   the 
reduction  of  cupric  oxide  in  an  alkaline  solution,  and  has  been  made  use 
of  for  a  qualitative  and  quantitative  test  of  its  presence.     Thus,  if  one 
molecule  of  grape-sugar  is  mixed  with  five  molecules  of  cupric  sulphate 
and  eleven  molecules  of  sodic  hydrate  the  copper  will  be  precipitated 
completely,  and  the  filtrate  will  be  free  from  sugar.     In  watery  solutions 
grape-sugar  is  unstable,  since  it  is  readily  decomposed  under  the  action 
of  ferments.     This  fermentation,  produced  under  the  influence  of  yeast 


118  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

or  malt,  is  termed  alcoholic  fermentation,  and  is  accompanied  by  tlie 
development  of  carbon  dioxide,  with  small  amounts  of  glycerin  and 
formic  acid.  The  fermentation  caused  by  the  lactic  acid  ferment,  or 
decomposing  nitrogenous  matter,  results  in  the  final  development  of 
butyric  acid. 

Various  tests  have  been  proposed  for  the  qualitative  and  quantitative 
estimation  of  grape-sugar.  Of  these  it  may  be  mentioned  that  in 
solutions  of  cupric  hydrate  in  the  presence  of  free  alkalies,  when  subjected 
to  boiling,  grape-sugar  reduces  the  cupric  oxide  into  red  or  yellow 
anhydrous  cuprous  oxide  (Trommer's  and  Fehling's  test).  Basic  nitrate 
of  bismuth  is  reduced  by  grape-sugar  to  bismuth  oxide  (Bottger's  test). 
When  boiled  with  half  its  volume  of  liquor  potassse  grape-sugar  solutions 
acquire  a  bright-brown  color,  due  to  the  formation  of  melassic  acid.  If 
nitric  acid  is  now  added,  the  odor  of  formic  acid  is  evolved  (Moore's 
test).  For  the  methods  of  quantitative  estimation  of  sugar  solutions 
and  further  details  as  to  testing  for  sugar,  references  must  be  made  to 
text-books  on  physiological  chemistry. 

2.  Lsevulose. — As  with  dextrose  and  cane-sugar,  Isevulose  is  also 
abundantly  distributed  through  the  vegetable  kingdom,  especially  in  the 
acid  fruits.     It  forms  a  colorless,  non-e^stallizable  s}rrup,  with  almost 
as  much  sweetness  as  cane-sugar.     It  derives  its  name  from  its  property 
of  rotating  the  plane  of  polarized  light  strongly  to  the  left  (at  15°  C.= 
— 106°).     It  is  as  powerful   a  reducing  agent  as  grape-sugar.     When 
placed  in  contact  with  malt  it  undergoes  alcoholic  fermentation  without 
first  being  converted  into  dextrose.     Lsevulose  is  also  formed  in  what  is 
termed  the  inversion  of  cane-sugar.     When  cane-sugar  is  subjected  to 
the  action  of  dilate  mineral  acids,  or  the  intestinal  juices  of  animals,  it 
is  turned  into  the  so-called  inverted  sugar,  which  may  be  regarded  as  a 
mixture  of  equal  portions  of  dextrose  and  Isevulose. 

3.  Inosite  (C6H12O6  -|-  2H2O). — Inosite  is  a  saccharine  body  which 
is  found  in  the  heart-muscle  and  in  most  of  the  organs  of  the  body, 
especially  of  the  horse  and  ox.     It  is  also  found  in  certain  plants,  es- 
pecially in  the  unripe  fruit  of  the  Papilionacese.     Inosite  crystallizes  in 
long,   colorless,   efflorescent   tables,  and   in   cabbage-like   aggregations, 
which  when  dried  break  down  into  a  white  mass.     It  has  a  sweetish 
taste,  is  easily  soluble  in  water,  but  insoluble  in  alcohol  and  ether.     Its 
solutions  are  optically  inactive.     It  does  not  reduce  the  copper  test  for 
sugar.     It  is  incapable  of  undergoing  alcoholic  fermentation,  and  is  not 
decomposed  by  caustic  alkalies  or  weak  acids.     It  is  precipitated  from 
its   solutions  by  lead  acetate  and  ammonia.     If   inosite  is  evaporated 
almost  to  dryness  on  a  strip  of  platinum-foil  with  nitric  acid,  and  the 
residue  moistened  with  a  little  ammonia  and  calcium  chloride  solution; 
and  again  evaporated,  a  beautiful  red  coloration  is  produced  (Scherer's 


NON-NITROGENOUS   ORGANIC   CELL-CONSTITUENTS.  119 

test).  By  means  of  this  test  it  is  claimed  that  the  presence  of  0.005 
grain  of  inosite  may  be  recognized.  In  contact  with  decomposing  organic 
matters  inosite  may  undergo  lactic  acid  or  butyric  acid  fermentation. 

(c)  SACCHAROSES,  OR  CANE-SUGAR  GROUP  ft(C12H220u). — This  group 
comprises  saccharose,  or  cane-sugar,  lactose  or  milk-sugar,  maltose  or 
malt-sugar,  and  arabin,  found  in  gum  arable. 

1.  Saccharose,  or  Cane-Sugar  (C12H22OU). — This  substance  is  found 
widely  distributed  throughout  the  vegetable  kingdom  in  the  juices  of 
various  plants,  trees,  and  fruits.  It  is  derived  from  changes  occurring 
in  starch  in  the  ripening  of  the  fruits.  Cane-sugar  is  said  to  be  the 
origin  of  all  forms  of  vegetable  sugar,  which  in  the  process  of  vegetation 
is  partly  broken  up  into  glucose  and  laevulose.  Cane-sugar  crystallizes 
in  large,  colorless  rhomboidal  prisms,  which  are  soluble  in  one-third 
their  weight  of  water,  the  solubility  being  greatly  increased  b\r  heat ; 
thus,  at  0°  C.,  100  grammes  of  a  saturated  sugar  solution  contain  65 
grammes  of  sugar  ;  at  14°  C.,  66  grammes  ;  and  at  40°  C.,  75.75  grammes. 
The  solutions  of  cane-sugar  rotate  the  plane  of  polarized  light  to  the 
right  (-f-  73.80°);  with  various  metallic  salts  and  oxides  it  forms  chemical 
compounds,  which  are  termed  saccharates.  When  carefully  heated  to 
160°  C.,  it  melts  into  a  clear,  pale,  yellowish  fluid,  which  on  cooling 
forms  a  transparent,  amorphous  mass — -the  so-called  barley-sugar.  If 
the  temperature  of  160°  is  prolonged,  cane-sugar  is  transformed  into 
laevulose  and  glucose.  When  subjected  to  a  higher  temperature  with 
moisture  more  profound  chemical  changes  are  produced.  Carbon  dioxide 
is  developed,  and  a  firm,  carbonaceous  mass  containing  a  trace  of 
brenzcatechin  and  caramelin  may  result.  In  the  dry  distillation  of 
sugar  large  quantities  of  carbon  dioxide  and  small  quantities  of  carbon 
monoxide  and  marsh-gas  are  set  free,  while  the  distillate  contains  acetic 
acid,  as  well  as  substances  allied  to  aldehyde  and  acetone.  Under  various 
circumstances,  such  as  the  action  of  dilute  mineral  acids,  ferments,  and 
prolonged  heating  of  a  watery  solution  in  a  closed  vessel,  cane-sugar 
becomes  inverted;  that  is,  divided  into  a  mixture  of  glucose  and 
laevulose. 

Cane-sugar  is  not  directly  fermentable,  but  when  converted  into 
dextrose  and  Isevulose  may  then  undergo  fermentations  similar  to  those 
of  grape-sugar.  Cane-sugar  is  easily  acted  on  by  oxidizing  agents,  but 
less  readily  than  is  grape-sugar.  It  does  not  reduce  alkaline  cupric 
hydrate  solutions,  nor  is  it  precipitated  by  acetate  of  lead,  although 
ammonic  lead  acetate  precipitates  it.  Strong  sulphuric  acid  chars  cane- 
sugar,  but  dissolves  grape-sugar.  Cane-sugar  is  not  directly  assimilable 
by  the  animal  economy.  When  introduced  into  the  intestinal  canal  it  is 
first  changed  into  invert  sugar  before  being  dissolved.  When  injected 
into  the  veins  it  is  eliminated  unchanged  by  the  kidneys. 


120  PHYSIOLOGY  OF   THE  DOMESTIC   ANIMALS. 

2.  Maltose. — Maltose  is  the  form  of  sugar  which  results  from  the 
action  of  a  diastatic  ferment,  or  dilute  acids  with  heat,  on  starches.     It 
resembles  cane-sugar  in  many  respects,  but  has  the  power  of  reducing 
alkaline  solutions  of  cupric  hydrate,  although  its  reducing  power  is  one- 
third  less  than  that  of  dextrose.     It  rotates  the  plane  of  polarized  light 
strongly  to  the  right,  even  more  so  than  dextrose  (-{-150°).    It  is  capable 
of  undergoing  fermentation,  and,  through  the  action  of  dilute  acids  with 
heat,  may  be  converted  into  dextrose.     It  is  this  form  of  sugar  which  in 
all  probability  invariably  results  from  the  digestion  of  the  carbo-hydrates 
in  the  animal  body  under  the  influence  of  an  amylolytic  ferment,  and  will 
be  again  alluded  to  in  the  chapters  on  Digestion. 

3.  Lactose,    or    Milk-Sugar   (C12H220u-J-HaO). — Lactose   resembles 
cane-sugar  closely  in  its  properties,  but  is  more  stable,  and,  like  dextrose, 
1ms  the  power  of  reducing  the  sugar  tests.     It  rotates  the  plane  of  polar- 
ized light  to  the  right,  the  degree  of  the  rotation  diminishing  with  the 
age  of  the  solution.     It  is  found  only  in  milk;  it  crystallizes  in  hard, 
white,  rhomboidal  prisms ;  is  soluble  in  six  parts  of  cold  and  two  and 
one-half  parts  of  hot  water  ;  insoluble  in  alcohol,  ether,  and  only  slightly 
sweetish.    It  is  only  fermentable  with  difficulty.    It  will  again  be  alluded 
to  more  at  length  under  the  subject  of  Milk. 

4.  Arabin. — Arabin  is  capable  of  being  converted  by  means  of  dilute 
sulphuric  acid  into  a  sugar  which  is  termed  arabinose,  and  is  closely 
analogous  to  dextrose.     It  is  the  main  constituent  of  gum  arabic.     It 
polarizes  light  to  the  right,  reduces  the  copper  sugar  tests,  but  is  in- 
capable of  fermentation. 

II.  HYDRO-CARBONS,  OR  FATS. — Fats  may  be  either  of  animal  or  vege- 
table origin,  and  occur  either  deposited  within  the  interior  of  cells,  or  in 
the  form  of  solution  or  suspension  in  animal  or  vegetable  juices.  In  the 
animal  body  fat  is  especially  formed  in  the  cells  of  the  connective-tissue 
group,  either  through  fatty  degeneration  of  the  protoplasmic  cell-contents 
of  the  connective-tissue  corpuscles,  or  by  the  absorption  of  fat  brought 
to  them  by  the  cells  by  a  vital  process  analogous  to  the  feeding  of  the 
timceba,  or  the  absorption  of  fat  from  the  intestinal  canal  of  animals.  In 
the  formation  of  adipose  tissue  by  either  of  these  processes  the  proto- 
plasmic cell-contents  gradually  become  displaced,  the  nucleus  lying 
against  the  cell-membrane,  while  the  cell-contents  consist  mainly  of  a 
globule  of  oil.  During  the  life  of  the  organism  the  fatty  contents  of 
cells  are  always  of  a  fluid  consistence,  and,  in  the  case  of  animals,  only 
solidify  when  cooled  below  a  certain  point,  which  is  characteristic  of 
the  different  individual  fats.  In  the  vegetable  cell  the  fats  remain  per- 
manently fluid,  with  but  few  exceptions,  in  the  form  of  oils.  As  animal 
fats  solidify,  a  partial  process  of  crystallization  into  groups  of  acicular 
crystals  often  takes  place.  When  within  the  interior  of  cells  fats  are 


NON-NITROGENOUS  ORGANIC   CELL-CONSTITUENTS.  121 

stained  black  by  perosmic  acid ;  this  reagent  is,  therefore,  a  delicate 
microscopic  test  for  the  detection  of  fats,  and,  since  fat  is  a  constant 
constituent  of  nervous  tissue,  is  used  as  a  means  of  recognizing  this 
tissue.  In  vegetable  cells  fat  is  partly  produced  directly  from  CO2  and 
H2O,  and  also  through  the  transformation  of  starch ;  the  latter  is  its 
mode  of  origin  in  oily  seeds  and  fruits  where  it  is  stored  up  until  required 
for  germination  and  growth. 

The  natural  fats  are,  without  exception,  compounds  of  a  triatomic 
radical,  propenyl  or  glyceryl,  combined  with  three  atoms  of  a  monatomic 
fatty  acid,  namely,  either  palmitic,  stearic,  or  oleic  acids.  The  fats 
formed  by  the  union  of  these  acids  with  the  radical  glyceryl  are  termed 
palmitin,  stearin,  and  olein. 

A  few  fats  contain  other  glycerin  ethers,  such,  for  example,  as  are 
found  in  butter.  At  the  ordinary  temperatures,  fats  are  either  solid,  like 
tallow;  semi-solid,  like  butter  and  lard  ;  or  fluid,  like  oils.  These  differ- 
ences depend  upon  the  differences  in  their  composition.  The  more 
stearin  or  palmitin  there  is  present,  the  more  the  fats  tend  to  solidify  ; 
while  the  more  olein  there  is,  the  more  fluid  are  they.  All  fatty  bodies 
become  fluid  considerably  below  the  temperature  of  boiling  water.  In 
the  pure  condition  fats  are  odorless,  tasteless,  and  of  alkaline  reaction. 
When  kept  in  contact  with  the  air,  they  become  rancid  from  the  setting 
free  of  fatty  acids  and  the  oxidation  of  glyceryl,  with  the  resulting  pro- 
duction of  volatile  fatty  acids  and  glycerin.  In  this  process  they  acquire 
odor  and  taste,  and  have  an  acid  reaction.  Fats  have  a  lower  specific 
graA7ity  than  water.  All  fats  are  completely  insoluble  in  water,  but  when 
water  contains  bodies  such  as  gum  or  albumen  in  solution,  fats  will  then 
remain  mechanically  suspended  in  the  form  of  an  emulsion,  which  is 
merely  the  breaking  up  of  the  oil  into  minute  globules.  When  fluid,  fats 
render  paper  which  is  coated  with  them  transparent  (grease-spots). 
Many  of  the  fats  are  soluble  in  alcohol,  especially  when  hot,  and  all  are 
soluble  in  ether,  chloroform,  the  volatile  oils,  benzol,  and  carbon  disul- 
phide.  When  fats  contain  small  quantities  of  free  fatty  acids  they  will 
form  a  permanent  emulsion  with  sodium  carbonate  solution.  This  prop- 
erty has  been  used  by  Briicke  as  the  means  of  detecting  the  presence  of 
free  fatty  acids,  and,  in  all  probability,  the  production  of  an  emulsion  in 
the  digestion  of  fats  by  pancreatic  juice  is  due  partly  to  this  fact.  When 
subjected  to  dry  distillation,  acrolein  is  formed  in  conjunction  with  other 
acrid  and  aromatic  products.  When  fats  are  boiled  with  alkalies,  soap 
is  produced  by  union  of  the  alkali  with  the  fatty  acid,  forming  a  soluble 
salt,  or  soap,  while  glycerin  passes  into  solution.  The  glycerin  may  like- 
wise be  displaced  by  inorganic  bases,  such  as  lead,  and  glyceryl  hydrate 
or  glyceryl  alcohol  (glycerin)  is  produced.  This  replacement  of  glyceryl 
by  other  bases  is  termed  saponification.  The  presence  of  glycerin  may 


122  PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 

be  recognized  by  the  development  of  acrolein  when  boiled  with  glacial 
phosphoric  acid.  Under  the  influence  of  certain  ferments  fats  split  up 
into  glycerin  and  a  &tty  acid  by  combining  with  the  elements  of  water, 
thus : — 

C3H5(OC16H310)3+3H20:=C3H5(OH)3+3(C16H310,OH). 
Tripalmitin.  Water.  Glycerin.  Palmitic  Acid. 

The  composition  of  the  four  principal  fats  is  represented  in  the 
following  formulae  : — 

Glycerin,  C3H5(OH)3. 

Palmitin,  C3H5(OC16H31O)3.         Palmitic  Acid,  C16H31O,OH. 
Stearin,  C3H5(OC18H35O)3.  Stearic  Acid,  C18H35O,OH. 

Olein,  C3H5(OC18H330)3.  Oleic  Acid,  CI8H33O,OH. 

Butyrin,  C3H5(OC4H7O)3.  Butyric  Acid,  C4H8O2. 

Stearin. — Stearin  is  the  chief  constituent  of  the  more  solid  fats. 
Its  melting  point  varies  between  53°  and  66°  C.  It  is  insoluble  in  cold 
alcohol  and  in  ether,  but  is  soluble  in  both  when  boiled.  It  never  occurs 
in  the  vegetable  fats.  It  crystallizes  from  boiling  alcoholic  solutions  in 
brilliant  quadrangular  plates. 

Palmitin. — This  fat  is  the  chief  component  of  the  animal  fats,  but 
also  is  largely  found  in  fats  of  vegetable  origin.  It  is  more  soluble  in 
cold  and  hot  ether  and  alcohol  than  is  stearin.  Its  melting  point  is 
45°  C.  It  crystallizes  in  fine  needles. 

Olein. — When  pure,  olein  is  a  colorless  oil  which  is  fluid  at  the 
ordinary  temperature  and  solidifies  at  0°  C.  When  exposed  to  the  air 
it  absorbs  oxygen  and  becomes  yellow.  It  dissolves  all  other  fats, 
especially  at  30°  C.  It  is  soluble  in  cold  absolute  alcohol  and  ether. 
It  is  more  abundant  in  vegetable  than  in  animal  fats. 

Butyrin. — Butyrin  is  found  in  butter.  It  is  a  pungent  liquid  ;  and 
when  it  decomposes,  butyric  acid,  to  which  the  odor  and  taste  of  rancid 
butter  are  due,  is  set  free. 

Spermaceti  is  found  in  the  cranial  sinuses  of  whales,  and  is  a  deriva- 
tive of  cetyl  alcohol  (C16H33)O.  This  is  a  solid  body  which  melts  at 
50°  C.,  and  when  saponified  yields  in  addition  stearic,  myristic,  and 
lauric  acids. 

Bees-wax  is  also  a  form  of  animal  fat,  which  is  likewise  capable  of 
saponification,  the  radical  here  being  cetyl  alcohol.  Waxes  possess 
many  points  in  common  with  the  fats,  but  are  not  acted  on  by  the 
digestive  juices. 

Margarin. — Formerly  this  name  was  given  to  a  substance  which  was 
supposed  to  be  a  special  fat,  but  which  is  now  known  to  be  a  mixture  of 
stearin  and  palmitin.  It  occurs  in  the  form  of  needle-like  crystals  which 
are  often  found  in  the  interior  of  fat-cells,  and  which  were  supposed  to 
be  a  glycerin  ether  of  a  hypothetical  acid, — margaric  acid. 


INORGANIC   CELL-CONSTITUENTS.  123 

The  percentage  composition  of  the  animal  fats  varies  only  within 

narrow  limits  : — 

c.  H.  o. 

Horse-fat,  .        .        .        .        .  77.07  11.69  11.24 

Ox  7650  11.90  11.59 

Sheep  " 76.61  12.03  11.36 

Pig  16.54  11.94  11.52 

Dog      " 76.63  12.05  11.62 

Cat  76.56  11.90  11.44 

The  Average. 
76.5          12.0          11.5 
Formula,  C62H99O6. 

Of  the  different  domestic  animals,  horse-fat  is  3rellow,  and  begins  to 
melt  at  30°  C.  Its  essential  component  is  olein.  Ox-fat  contains  prin- 
cipally stearin  and  palmitin,  and  but  little  olein.  It  is  white,  melts  at 
43°  C.,  and  solidifies  after  melting  at  36°  or  37°  C.  Mutton-fat  contains 
principally  stearin.  Its  melting  point  is  46°.  It  solidifies  at  from  35°  to 
40°  C.  Pig.fat  is  white,  and  contains  large  quantities  of  olein ;  melts 
at  41°,  and  solidifies  after  melting  at  about  30°  C. 

Adipose  tissue  is  made  up  as  follows : — 

"Water.  Membranes.  Fat. 

Ox, 9.96               1.16  88.88 

Sheep, 10.48               1.64  8788 

Pig, 6.44               1.35  92.21 

C.    INORGANIC   CELL-CONSTITUENTS.* 

The  inorganic  constituents  of  cells  enter  them  already  formed,  and, 
as  a  rule,  leave  them  without  undergoing  change'.  About  the  only 
exceptions  to  this  statement  are  found  in  the  case  of  carbon  dioxide, 
the  water  formed  by  oxidation  of  the  hydrogen  of  organic  compounds, 
and  the  sulphur  of  various  excretory  products,  which,  eliminated 
through  the  intestines  and  kidneys,  originates  in  the  sulphur  of 
albuminous  compounds.  The  inorganic  cell-constituents  differ  in  no 
way  from  similar  compounds  found  elsewhere.  They  originate  in  the 
earth  and  atmosphere,  become  constituents  of  vegetable  organisms, 
and  then,  through  absorption  in  foods,  enter  into  the  composition 
of  animal  bodies.  The  amount  of  inorganic  matter  found  in  cells, 
including  of  course  water,  is  greater  in  weight  than  the  organic  cell- 
constituents.  The  inorganic  constituents  may  exist  in  the  form  of 
water,  salts,  gases,  and  certain  elements  whose  exact  mode  of  combina- 
tion has  not  yet  been  thoroughly  determined.  All  the  inorganic  constit- 
uents of  the  body,  in  some  period  of  their  existence  as  such,  are  in  the 
form  of  solutions.  They  enter  the  organism  in  solution,  are  deposited 

*  In  the  preparation  of  this  section  the  author  is  especially  indebted  to  Gorup- 
Besanez,  "  Lehrbuch  der  Physiologischen  Chemie." 


124 


PHYSIOLOGY  OF   THE   DOMESTIC  ANIMALS. 


as  constituents  of  tissues  perhaps  in  the  solid  or  even  crystalline  form, 
but  are  again  eliminated  from  the  body  in  solution  ;  this  applies  not  only 
to  the  salts,  but  also  to  the  gases  and  acids.  Many  of  the  physical  prop- 
erties of  various  tissues  depend  aJmost  solely  upon  their  inorganic 
constituents.  In  this  connection  it  is  only  necessary  to  mention  the 
bones  and  teeth.  Wherever  cell  growth  is  taking  place  certain  salts  are 
essential,  since  no  form  of  protoplasm  is  able  to  carry  on  its  existence 
without  a  supply  of  salts,  the  nature  of  which  may  differ  in  the  case  of 
different  cell  forms ;  thus,  for  example,  calcium  salts  are  not  only 
essential  for  the  development  of  the  bone-cells,  but  accompany  the 
albuminoids  of  all  growing  tissue  ;  blood-corpuscles  require  iron  and 
potassium  phosphate,  and  all  forms  of  cell  growth  require  sodium 
chloride. 

1.  WATER.  (H20). — Of  the  inorganic  constituents  of  cells  water  is  by 
far  the  most  abundant,  and  is  the  most  important.  In  fact,  all  organisms 
may  be  said  to  live  in  water ;  for  if  their  entire  body  is  not  surrounded  by 
water,  all  contain  water  in  large  amounts,  and  all  their  vital  processes  are 
dependent  on  watery  solutions.  Water  is  destined,  by  entering  by  imbi- 
bition into  solid  tissues,  not  only  to  preserve  the  physical  condition 
which  is  essential  to  the  preservation  and  manifestations  of  the  vital 
phenomena  of  protoplasm,  but  it  holds  in  solution  many  of  the  salts 
essential  to  the  vital  processes  of  the  economy.  It  also  constitutes  a 
large  proportion  of  the  fluids  of  the  body,  such  as  the  blood,  lymph,  chyle, 
and  secretions.  It  is  in  greater  amount  in  embryonic  tissue,  and  decreases 
as  adult  life  and  old  age  are  reached.  In  the  higher  animals  it  may 
exist  in  70  per  cent,  or  more,  while  in  some  of  the  lower  forms  of  life  as 
much  as  90  per  cent,  may  be  reached.  The  amount  of  water  in  different 
organisms,  and  in  the  same  organism  at  different  times,  is  subject  to 
very  great  variation.  It  not  only  constitutes  the  great  part  of  the  secre- 
tions of  the  animal  body,  but  it  also  forms  a  large  proportion  of  even 
the  densest  tissues  of  the  animal  or  vegetable  body.  Thus,  in  the 
enamel  of  teeth  two-tenths  of  one  per  cent,  of  water  is  present,  while  in 
dentine  10  per  cent,  and  in  bones  22  per  cent,  of  water  is  found. 

The  following  table  represents  the  amount  of  water  in  1000  parts  of 
different  animal  tissues : — 


Organs.                                                                           Water.         Solids. 

Enamel, 

2            998 

Ivory, 

100           900 

Bone,  . 

216            784 

Fat,     . 

299            701 

Elastic  tissi 

le, 

496    .       504 

Cartilage, 

550            450 

Liver, 

693            307 

Bone-marrow, 

^ 

697            303 

White  brain-substance,                                           700           300 

INORGANIC   CELL-CONSTITUENTS. 


125 


Organs. 

Skin,  . 
Brain, 
Muscles, 
Spleen, 
Thymus, 
Nerves, 
Connective 
Heart, 
Kidneys, 
Gray  brain- 
Vitreous  bo 

tissn 
subsi 

dy, 

e, 
tance 

Water.         Solids. 

720            280 
750            250 
757            243 
758            242 
770            230 
780           220 
796            204 
792            208 
827            173 
858            142 
987              13 



Fluids. 


Water. 


Solids. 


Blood,     $  . 

...        .        .791 

209 

Bile,    .... 
Milk  
Plasma, 

864 
891 
901 

136 
109 
99 

Chyle,         ... 
Lymph, 
Serous  fluids, 
Gastric  juice, 
Intestinal  juice, 

928 
983 
959 
973 
975 

72 
17 
41 
27 
25 

Tears, 
Aqueous  humor, 
Cerebro-spinal  fluid,  . 
Saliva, 
Sweat, 

982 
986 
988 
995 
995 

18 
14 
12 
5 
5 

The  condition  of  semi-solidity  of  organic  tissues,  which  we  found  to 
be  so  essential  to  the  carrying  out  of  the  physical  processes  in  cell  life, 
is  rendered  possible  by  the  amount  of  water  and  the  condition  in  which 
it  is  held  by  the  different  cells.  A  remarkable '  fact  in  connection  with 
the  manner  in  which  water  is  held  by  the  animal  organism  is  that  there 
are  certain  tissues  and  organs  in  which  the  percentage  of  water  found  is 
in  excess  of  the  percentage  of  solids,  without  the  organs  assuming  the 
fluid  form;  indeed,  again,  there  are  certain  semi-solid  organs  whose  per- 
centage of  water  is  even  greater  than  that  of  the  animal  fluids  ;  thus,  the 
kidneys  contain  a  larger  percentage  of  water  even  than  the  blood.  This 
shows  therefore  that  the  manner  in  which  the  water  is  held  by  such 
tissues  must  be  different  from  that  in  which  it  exists  in  the  animal  fluids, 
where  it  occupies  more  or  less  the  role  of  a  medium  of  solution.  The 
consistence  of  many  fluids  in  the  animal  body  is  not  dependent  so  much 
on  the  amount  of  water  present  as  on  the  nature  of  the  substances  which 
are  in  solution;  thus,  mucus  has  a  considerably  larger  percentage  of 
water  than  blood,  and  yet  is  apparently  a  denser  fluid.  As  already  de- 
scribed in  the  section  on  Physical  Processes  in  Cells,  the  water  of  the 
semi -solid  organic  bodies  enters  their  elementary  intermolecular  spaces, 
and  it  is  a  peculiarity  of  organized  bodies  that  they  may  absorb  a 
quantity  of  water  greatly  in  excess  of  their  own  weight  without  losing 
their  semi-solid  condition.  In  such  cases  it  is  not  water  alone  that  is 
absorbed,  but  water  always  containing  different  inorganic  salts  in  solution. 


126  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

A  certain  part  of  the  water  found  in  animal  tissues  is  held  in  com- 
bination, as  in  water  of  crystallization,  both  in  organic  and  inorganic 
molecules.  This  amount  is,  however,  inconsiderable  as  contrasted  with 
that  held  in  other  manners.  Water  is  also  found  as  a  vapor  in  the  air 
contained  in  the  respiratory  organs  of  animals. 

By  far  the  greater  part  of  the  water  found  in  the  animal  and  vege- 
table body  has  entered  from  without;  in  the  former  case  through  the 
food  and  drink,  and  in  the  latter  from  rain  or  from  the  absorption  of 
moisture  from  the  soil.  In  the  case  of  the  animal  body  a  certain  amount 
of  water  is  apparently  formed  within  the  animal  economy,  since  it  has 
been  found  that  under  certain  circumstances  the  amount  of  watery  vapor 
exhaled  through  the  lungs  and  skin,  and  that  passing  through  the  kid- 
neys and  intestines,  is  in  excess  of  the  amount  of  water  taken  internally, 
the  body  still  preserving  its  uniform  weight.  Again,  as  we  shall  find  in 
considering  the  subject  of  respiration,  the  volume  of  carbon  dioxide 
eliminated  through  the  lungs  is  smaller  than  the  amount  of  oxygen  taken 
into  the  blood  in  inspiration.  Ten  to  twent}7-five  per  cent,  of  oxygen 
disappears  in  this  manner,  and  must,  therefore,  have  formed  other  com- 
binations in  the  body  than  those  whose  end  product  is  C03.  Since  it  is 
readily  conceivable  that  the  hydrogen  of  hydrogen  compounds  is  set  free 
quite  as  readily  as  the  carbon  of  carbon  compounds,  a  certain  amount 
of  this  hydrogen  may  evidently  unite  with  oxygen  to  form  water,  not  by 
a  direct  oxidation  of  the  hydrogen,  but  through  the  gradual  union  of 
the  oxygen  with  a  long  series  of  oxidation  products  whose  terminal  is 
H20,  just  as  CO2  results  from  the  final  union  of  ox}'gen  and  carbon,  and 
not  by  a  direct  oxidation  of  carbon  in.  the  animal  body.  Such  an  origin 
of  water  in  the  economy  is  further  supported  by  the  fact  that  the  amount 
of  hydrogen  contained  in  organic  compounds  in  the  excretions  is  less 
than  that  which  is  contained  in  similar  combinations  in  the  food.  Thus, 
it  has  been  estimated  that  a  man  receives  daily  forty  grammes  of  hydrogen 
in  organic  combinations  with  the  food,  while  only  six  grammes  are  dis- 
charged in  such  combinations  in  the  excretions ;  hence,  thirty-four 
grammes,  or  about  85  per  cent,  of  the  hydrogen  so  introduced,  remains 
unaccounted  for.  Since  hydrogen  does  not  leave  the  body  as  a  vapor, 
nor  in  any  notable  amount  in  any  other  inorganic  compound  but  water, 
the  surplus  must  be  converted  into  water.  The  estimates  are  that  in 
man  about  three  hundred  grammes  of  water  are  formed  daily  in  this 
way, — probably  from  the  decomposition  of  carbo-hydrates  where  hydro- 
gen and  oxjrgen  are  present  in  the  proportion  to  form  water. 

Organisms  not  only  live  in  water,  but  they  may  be  said  to  live  in 
running  water  (Hoppe-Seyler) ;  for  they  are  continually  taking  in  water, 
which  may  contain  other  food-stuffs  in  solutions,  and  are  continually 
eliminating  water  which  contains  the  products  of  their  tissue-waste. 


INOKGANIC   CELL-CONSTITUENTS.  127 

Plants  get  rid  of  water  through  evaporation  from  their  entire  external 
surface,  while  water  is  absorbed  by  their  roots. 

Water  leaves  the  animal  body  through  the  kidneys,  skin,  lungs,  and 
intestines,  that  passing  daily  through  the  kidneys  being  about  half  of  the 
total  amount  of  water  eliminated.  The  relative  proportion  between  the 
amounts  eliminated  by  these  organs  is  subject  to  very  great  variation,  and 
depends  upon  numerous  external  and  internal  conditions,  which  will  sub- 
sequently be  alluded  to.  It  may,  however,  be  here  mentioned  that  of  the 
water  taken  as  food  but  a  small  amount  leaves  the  body  in  the  faeces ;  in 
m*n  the  amount  so  eliminated  is  only  4  per  cent.,  while  the  remaining  96 
per  cent,  leaves  the  body  through  the  kidne}^,  lungs,  and  skin.  Water, 
therefore,  does  not  simply  pass  through  the  alimentar}'  canal,  but  is  ab- 
sorbed by  its  mucous  membranes,  enters  the  blood,  and  thence  becomes 
a  constituent  of  the  different  tissues. 

Water  is  a  necessary  solvent  for  various  organic  and  inorganic  con- 
stituents of  the  body,  and  it  alone,  by  entering  into  the  condition  of  im- 
bibition in  the  tissues,  enables  the  various  physical  and  chemical  proc- 
esses which  constantly  occur  in  cells  to  take  place,  and  occasions  their 
semi-solid  state,  their  elasticit}',  flexibility,  and  transparency.  Through 
its  evaporation  from  the  external  surface  and  through  the  lungs  it  serves 
to  abstract  heat,  and  therefore  is,  to  a  certain  extent,  a  temperature  regu- 
lator. As  water  is  an  essential  constituent  of  organic  bodies,  its  loss, 
which  is  constantly  taking  place,  must  be  continually  replaced ;  in  the 
higher  animals  a  demand  for  an  increased  supply  of  water  is  indicated 
by  what  is  known  as  thirst.  This  will  subsequent^  demand  consideration. 

The  removal  of  water  from  lower  forms  of  cell  life  entirely  suspends 
all  evidences  of  vitalit}' ;  through  desiccation  life  in  such  forms  is  said 
to  be  rendered  latent.  A  renewed  supply  of  water  will  again  restore  all 
the  phenomena  of  cell  life.  None  of  the  higher  plants  or  animals  can 
support  loss  of  water  beyond  a  very  moderate  amount  without  causing 
permanent  loss  of  vitality  ;  seeds  and  infusoria  may  be  completely  dried 
and  recover  their  vital  properties  when  supplied  with  heat  and  moisture. 
Although  water  is  an  essential  constituent  of  all  cells,  it  may,  neverthe- 
less, act  as  a  poison  if  absorbed  in  too  great  amount. 

Protoplasm  of  all  kinds  is  killed  by  immersion  in  distilled  water ; 
this  fact  may  be  partly  due  to  the  diffusion  currents  which  are  thus  in- 
augurated,, the  essential  salts  being  removed  from  the  protoplasm,  and 
their  place  being  taken  by  water. 

Freezing  of  various  parts  of  plants  and  then  subjecting  them  to 
rapid  thawing  by  exposure  to  the  rays  of  the  sun  causes  their  death  by 
first  abstracting  water  from  the  solids  and  causing  its  aggregation  in  a 
crystalline  form,  and  then  by  sudden  melting  causes  drowning  out  of 
neighboring  parts  while  more  remote  portions  still  suffer  from  want  of 


128  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

water.  If  the  thawing  is  slowly  accomplished  the  water  has  time  to  dif- 
fuse and  restore  the  normal  condition  of  imbibition.  In  this  way  is  to 
be  explained  the  fact,  which  may  be  frequently  observed  in  cold  spring 
and  autumn  mornings,  that  of  the  parts  of  plants  which  are  frozen  those 
which  are  exposed  to  the  direct  rays  of  the  sun  are  killed,  while  those 
which  are  protected  from  the  sun's  heat  thaw  out  gradually  and  regain 
their  vitality.  So,  also,  red  blood-corpuscles  may  be  frozen  and  gradu- 
ally thawed  without  being  destroyed,  but  if  rapidly  thawed  are  dissolved. 
On  this  fact,  undoubtedly,  rests  the  practical  point  that  frozen  animal 
parts  must  not  be  rapidly  warmed,  but  have  their  circulation  only  gradu- 
ally restored  ;  hence,  the  common  practice  of  rubbing  with  snow. 

2.  SODIUM  CHLORIDE  (NaCl). — Of  the  saline  constituents  of  cells 
sodium  chloride  is  the  most  widely  distributed,  and  is  present  in  larger 
amount  than  any  other  salt  in  all  the  tissues  of  the  animal  body,  with 
the  exception  of  the  bones,  teeth,  red  blood-corpuscles  and  striated 
muscle-cell.  It  is  especialty  worthy  of  notice  that  the  amount  of  sodium 
chloride  in  most  organs,  especially  in  the  blood,  is  almost  constant  and 
is  independent  of  the  amount  of  this  salt  contained  in  the  food.  Its 
distribution  in  the  body  is  also  remarkable.  In  the  blood-plasma  it  is 
abundant,  while  it  is  almost  absent  from  the  blood-corpuscles  which  are 
suspended  in  the  plasma.  It  is  abundant  in  chyle,  lymph,  saliva,  gastric 
juice,  mucus,  and  pus,  and  is  present  in  only  small  quantity  in  muscle- 
juice  and  many  glands.  Sodium  chloride  is  present  in  the  form  of  a 
solution  in  water,  and  in  the  removal  of  the  fluids  from  the  semi-solid 
tissues  by  pressure  the  greater  part  of  the  salt  is  taken  away  with  the 
water.  The  relative  proportion  of  sodium  and  potassium  chlorides  in 
different  parts  of  the  animal  body  is  about  as  follows : — 

QUANTITY  OF  SODIUM  AND  POTASSIUM  CHLOBIDES  IN  1000  PARTS  IN  THE 


Bones, 
Blood,      . 
Bile, 

NaCl. 
7.02 
2.70 
5.58 

KC1. 

2.05 
0.28 
0.55 

2.13 

4.50 
0.02 

Gastric  juice, 
Sweat, 
Saliva, 
Milk 

1.45 
2.23 
1.53 

087 

Lymph,    5.67 
Sebaceous  matter,  .        .        .        .        .        .        .5.00 
Urine,      11.00 

Pancreatic  juice,     7.35 

All  the  sodium  chloride  found  in  the  animal  body  has  entered  it 
from  without.  It  leaves  the  body  in  the  urine  and  excrement,  perspira- 
tion, nasal  and  buccal  mucus.  By  far  the  greater  part  is  eliminated 
through  the  urine,  though  the  total  amount  eliminated  falls  short  of  that 
taken  in  the  food.  A  certain  amount  of  the  sodium  chloride  taken  in  as 


INORGANIC   CELL-CONSTITUENTS.  129 

food  undergoes  chemical  decomposition  in  the  bod}',  as  will  be  alluded 
to  in  the  subject  of  Nutrition.  Thus,  the  potassium  chloride  of  muscles 
and  red  blood-corpuscles  apparent!}^  originates  in  a  double  decomposition 
of  sodium  chloride  and  potassium  phosphate  into  sodium  phosphate  and 
potassium  chloride.  Possibly  the  hydrochloric  acid  of  the  gastric  juice 
and  the  sodium  salts  of  the  bile  have  similar  origins. 

Sodium  chloride  is  absolutely  essential  to  the  manifestation  of  life ; 
in  a  physical  sense,  it  is  of  great  importance,  from  the  influence  which  it 
exerts  over  diffusion,  particularly  in  the  degree  of  absorption  from  the 
alimentary  canal.  The  conditions  which  follow  the  deprivation  of 
sodium  chloride,  and  a  more  detailed  account  of  its  relations  to  the 
nutritive  processes  and  body  will  again  be  referred  to  more  at  length 
under  the  subject  of  Nutrition. 

3.  POTASSIUM   CHLORIDE    (KC1). — Potassium   chloride  is  usually  a 
companion  of  sodium  chloride,  although  in  certain  tissues,  such  as  the 
red  blood-corpuscles,  and  in  muscles,  it  occurs  in  greater  amount  than 
the  sodium  salt,  while  it  is  almost  absent  from  the  blood-plasma,  where 
a  slight  excess  of  potassium  salts  appears  to  act  as  a  poison  to  the  heart. 
A  similar  toxic  effect  is  also  exerted  by  potassium  chloride  on  muscles 
and  nerves. 

In  the  herbivora  potassium  chloride  is,  as  a  rule,  in  excess  over 
sodium  chloride.  The  salivary  glands  and  kidneys  appear  to  be  the 
special  organs  for  its  elimination. 

4.  SODIUM  AND  POTASSIUM  CARBONATES  (C08Naa,  CO,XaH,  3(CO,)- 
Na4H2,   CO8Ka,  CO8KH).— These  salts  are  found  in  the  ash  of  various 
organic   substances,   wrhere    they   have   probably   originated    from   the 
decomposition  of  various  organic  acid  compounds  of  sodium  and  potas- 
sium.    In  various  animal  juices,  however,  and  especially  in  the  blood 
and  urine  of  herbivorous  'animals,  and  in  the  blood  of  the  omnivora, 
sodium   and    potassium  carbonates    exist   already  formed.     When  car- 
nivorous  animals   are   fed    on   a   vegetable   diet   their   urine   contains 
considerable  quantities  of  carbonates  of  the  alkalies,  resembling  thus  the 
urine  of  herbivorous  animals  in  reaction  and  constitution  ;    it  will  be 
alkaline  in  reaction,  turbid,  and  deposit  a  calcareous  sediment,  instead  of 
being  acid  and  clear,  as  is  normally  the  case  in  the  urine  of  carnivora. 
It  is  also  interesting,  in  this  connection,  to  notice  that  the  urine  of  the 
suckling  calf  before  being  weaned  is  clear  and  acid, as  among  carnivora; 
when  the  calf  is  placed  on  a  vegetable  diet  the  urine  becomes  turbid 
and  alkaline.     Further,  if  herbivorous  animals  are  allowed  to  fast,  their 
urine  becomes  acid  and  clear,  for  they  are  then  living  at  the  expense 
of  their  own  tissues,  and  are  practically  carnivorous.     Sodium  carbonate 
is  also  found  in  the  lymph  and  the  parotid  saliva  of  the  horse. 

These  salts,  when  found  as  constituents  of  animal  cells  and  fluids, 


130  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

come  in  part  from  without,  and  are  in  part  formed  within  the  organism 
through  oxidation  processes  occurring  within  the  body.  Thus,  after  the 
ingestioh  of  various  vegetable  matters  containing  vegetable  acids  the 
urine  of  omnivorous  animals  becomes  alkaline  through  the  elimination 
of  carbonates  of  the  alkalies,  thus  explaining  the  alkaline  reaction  of 
the  urine  of  these  animals.  Carbonates  of  the  alkalies  so  formed  in  the 
animal  body,  or  when  taken  in  foods,  may  be  eliminated  in  this  manner 
through  the  urine,  or  they  may  themselves  undergo  decomposition,  and 
their  carbon  dioxide  be  eliminated  through  the  lungs.  When  present  in 
solution  they  seem  to  assist  in  the  various  processes  of  oxidation 
occurring  in  the  body;  they  appear  to  assist  in  the  emulsification  of  fats, 
and  in  the  blood  the  neutral  carbonates  of  the  alkalies  appear  to  serve 
in  part  as  carriers  of  the  carbon  dioxide  of  the  blood.  They  further 
may  modify  the  physical  processes  of  diffusion  occurring  within  the 
mism. 

5.  CALCIUM  CARBONATE  (C03Ca). — Calcium  carbonate  is  a  normal 
constituent  of  the  shell  of  birds'  eggs,  of  the  bones  and  teeth,  the  urine 
of  herbivorous  animals,  the  parotid  saliva  of  the  horse,  and  is  the  prin- 
cipal constituent  of  the  so-called  otoliths,  or  the  small,  inorganic  masses 
found  in  the  internal  auditoiy  organs  of  man  and  different  animals.     In 
the  animal  body  it  is  partly  in  a  state  of  solution  and  partly  deposited 
in  the  solid  form.     In  the  former  condition  it  is  found  in  the  urine  and 
saliva  of  the  herbivora,  where  its  solution  is  rendered  possible  by  carbon 
dioxide.     In  the  solid  form  it  is  deposited  either  in  amorphous  or 'crys- 
talline form,  as  in  deposits  of  sediment  in  the  parotid  saliva  of  the  dog 
and  in  the  urine  of  herbivora.     It  originates  from  without,  either  in  the 
water  taken  internally  or  as  a  carbonate  in  vegetable  food.     The  latter 
explains  its  abundance  in  the  urine  of  the  herbivora,  where  the  calcium 
salts  of  organic  acids  are  decomposed  into  carbonates.     Only  a  part  of 
the  calcium  carbonate  which  enters  the  organism  from  without  leaves  it 
as  such.     In  many  cases,  as  in  man,  it  undergoes  decomposition  into 
calcium  phosphate.     Its  importance  for  the  animal  economy  is  not  thor- 
oughly understood. 

6.  MAGNESIUM  CARBONATE  (C03Mg). — This  salt  is  frequently  a  com- 
panion of  calcium  carbonate,  particularly  in  the  urine  of  herbivora.    Its 
presence  in  bony  tissue  is  apparent!}'  doubtful.     It  has  been  found  in 
human  urinary  calculi,  but  only  in  small  amounts.    The  herbivorous  ani- 
mals in  their  food  nearly  alwa3rs  absorb  considerable  amounts  of  mag- 
nesium phospate,  and  since  this  salt  is  absent  from  their  urine  it  would 
appear  that  the  magnesium  carbonate  is  formed  in  the  animal  body  from 
the  magnesium  phosphate  of  vegetable  food. 

7.  ALKALINE   PHOSPHATES    (PO4Na8,   P04^a3H,   P04NaH2,   P04K8, 
P04KaII,  P04KHa). — Phosphates  of  sodium  and  potassium  are  constant 


IXOBGAXIC   CELL-CONSTITUEXTS.  131 

constituents  of  all  animal  fluids  and  tissues.  In  the  ash  of  the  blood  of 
the  herbivorous  animals  a  smaller  amount  of  the  alkaline  phosphates  is 
found  than  in  the  carnivora.  Grain-eating  animals  show  a  larger  amount 
of  phosphatic  salts  in  the  ash  of  their  blood.  Omnivora  occupy  a  mean 
between  the  two.  On  account  of  their  great  solubility  in  the  organism 
the  phosphates  must  nearly  always  exist  in  the  form  of  a  solution,  espe- 
cially in  the  acid  fluids,  as  in  urine,  muscle-juice,  and  the  parenchymatous 
fluids  of  certain  glands.  In  muscles,  together  with  lactic  acid,  they 
occasion  the  .acid  reaction  of  the  muscle-juice. 

Phosphates  are  taken  into  the  animal  body  with  food,  though  they 
may  also  doubtless  originate  in  the  blood  through  a  double  decom- 
position of  potassium  phosphate  and  sodium  chloride  into  sodium  phos- 
phate and  potassium  chloride.  The  alkaline  phosphates  leave  the  body 
through  the  kidneys  and  intestines.  The  former  is  the  case  especially  in 
the  urine  of  the  carnivora,  where  it  forms  twelve-thirteenths  of  the 
total  amount  of  these  substances  eliminated.  In  the  urine  of  the 
herbivora  but  small  amounts  of  phosphates  are  found,  in  spite  of  the 
fact  that  in  their  food  phosphates  of  the  alkalies  and  earthy  phosphates 
are  invariably  present.  This  is  to  be  explained  by  the  supposition  that 
the  salts  of  the  organic  acids,  with  the  alkaline  earths,  undergo  decompo- 
sition into  earthy  phosphates  and  carbonates  of  the  alkalies,  the  latter 
being  eliminated  through  the  urine.  From  their  great  abundance  and 
wide  distribution  in  the  animal  economy,  it  follows  that  they  must  be  of 
great  importance. 

The  phosphate  of  potassium  is  especially  abundant  in  the  blood- 
cells,  ovum,  and  in  muscular  tissue.  In  the  latter  case,  combined  with 
lactic  acid,  it  is  the  main  cause  of  their  acid  reaction,  while  phosphate 
of  sodium  is  found  in  blood-plasma.  These  salts  enter  the  organism  as 
constituents  of  food,  either  in  the  form  in  which  they  are  found  or  as 
the  result  of  decomposition  of  the  earthy  phosphates  and  other  alkaline 
salts.  This  is  especially  probable  on  account  of  the  great  abundance  of 
potassium  phosphates  and  potassium  chloride  in  the  fluids  of  muscle  and 
other  tissues,  while  sodium  chloride  and  sodium  phosphate,  being  found 
in  abundance  in  the  blood,  it  is  evident,  from  the  proportion  in  which 
these  different  substances  are  found  in  the  different  tissues,  that  they 
have  not  been  derived  directly  from  the  blood.  Again,  it  is  to  be 
remembered,  that  the  herbivorous  animals  in  their  food  receive  almost 
solely  potassium  salts,  and,  since  sodium  phosphate  is  necessary  for  the 
integrity  of  their  blood,  it  is  clear  that  this  must  be  formed  in  the  body 
through  the  decomposition  of  potassium  phosphate  and  sodium  chloride. 
In  the  blood  the  alkaline  phosphates  give  to  the  plasma  its  alkaline 
reaction,  to  which  its  great  capacity  for  dissolving  carbon  dioxide  is 
apparently  due,  since  it  has  been  found  that  water,  which  holds  only 


132  PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 

one  per  cent,  of  sodium  phosphate  in  solution,  is  able  to  retain  twice  the 
usual  amount  of  carbon  dioxide  in  solution. 

The  phosphates  of  the  alkalies  are  eliminated  from  the  animal  body 
through  the  kidneys,  intestines,  and  skin.  In  carnivorous  animals,  whose 
blood  is  rich  in  phosphates  of  the  alkalies,  the  urine  is  the  main  path  of 
elimination.  Through  the  production  of  acids,  such  as  uric,  hippuric, 
and  sulphuric,  the  latter  originating  from  the  sulphur  of  albuminoids 
and  their  derivatives,  a  part  of  the  base  is  withdrawn  from  the  alkaline 
phosphate,  and,  as  a  consequence,  the  alkaline  phosphate  now  becomes 
neutral  or  even  acid,  thus  explaining  the  production  of  an  acid  reaction 
in  urine  from  the  presence  of  dihydrate  sodium  phosphate  (P04NaH2). 
Since  phosphoric  acid,  or  acid  phosphates,  in  solution  give  to  fluids 
their  power  of  dissolving  calcium  and  magnesium  phosphates,  the  urine 
of  the  carnivora  and  omnivora  is  therefore  able  to  hold  in  solution  the 
earthy  phosphates  so  eliminated.  In  the  case  of  the  herbivora  the  state 
of  affairs  is  somewhat  different.  Here  but  small  amounts  of  phosphoric 
salts  are  found  in  the  urine,  although  alkaline  and  earthy  phosphates  are 
found  in  large  amount  in  their  food.  In  this  case  the  phosphates  of 
the  food  undergo  decomposition,  and  a  great  part  of  the  base  is  united 
with  carbonic  acid,  and  so  eliminated  as  alkaline  carbonates  in  the  urine, 
forming  thus  the  characteristic  of  the  urine  of  herbivorous  animals,  the 
earthy  carbonates  being  held  in  solution  by  the  free  carbon  dioxide.  The 
phosphoric  acid  of  the  phosphates  taken  in  the  food  of  herbivorous 
animals  in  greater  part  unites  with  calcium  and  magnesium,  and  is 
eliminated  through  the  intestine.  Wherever  free  acid  is  developed  in  the 
tissues  of  the  body  acid  phosphates  are  nearly  always  present  and  in 
part  contribute  to  the  formation  of  this  acid  reaction.  This  is  the  more 
remarkable  when  it  is  remembered  that  these* phosphates  have  originated 
from  the  blood,  where  they  always  exist  in  the  form  of  basic  or  neutral 
salts.  The  explanation  of  the  mode  in  which  this  alkaline  phosphate  is 
in  the  different  tissues  converted  into  an  acid  salt  is  to  be  explained 
through  the  development  in  the  tissues  of  organic  acids,  which,  as 
already  alluded  to  in  the  explanation  of  elimination  of  the  phosphates, 
takes  a  portion  of  the  base  from  the  alkaline  phosphate,  so  developing  an 
acid  salt. 

Phosphates  appear  to  be  absolutely  essential  to  the  development 
of  tissue.  This  is  indicated  in  the  first  place  by  their  great  abundance 
in  all  forming  tissues,  and  even  in  organizable  fluids,  and  in  the  fact  that 
the  tissues  of  herbivorous  mammals  are  quite  as  rich  in  the  phosphates  as 
that  of  the  carnivora,  although  in  the  former  case  they  are  nearly  absent 
from  the  blood,  and  in  the  latter  case  are  very  abundant.  In  special 
tissues,  such  as  the  muscles,  nerves,  blood-corpuscles,  and  ovum,  they 
appear,  from  their  exceptional  abundance,  to  have  some  special  functions 


INORGANIC   CELL-CONSTITUENTS.  133 

to  fulfill.  This  seems  indicated  by  the  fact  that  the  nervous  tissue  in 
solutions  of  alkaline  phosphates  may  preserve  its  irritability  much 
longer  than  when  in  contact  with  any  other  fluid.  In  the  tissues  the 
phosphates  of  the  alkalies  occur  as  acid  salts  ;  it  therefore  would  seem 
that  tissues  in  their  growth  require  the  presence  of  free  phosphoric  acid; 
In  the  case  of  the  blood,  on  the  other  hand,  an  alkaline  reaction  is 
essential  for  its  vital  phenomena,  and  it  appears  that,  provided  the 
alkaline  reaction  is  preserved,  the  salt  to  which  this  alkalinity  is  due  is 
of  minor  importance.  Thus,  in  the  carnivorous  animals  the  reaction  is 
attributable  to  the  excess  of  alkaline  phosphate,  in  the  herbivorous 
animals  to  the  carbonates.  In  omnivorous  animals  the  preponderance 
of  these  different  salts  varies  according  to  the  character  of  their  diet. 

8.  CALCIUM  PHOSPHATE  (2(PO4)Ca8,  2(P04)CaH4).— This  salt  is 
present,  without  exception,  in  all  tissues  and  fluids  of  the  animal  body ; 
in  bones  and  teeth  nearly  two  thirds  of  their  weight  is  due  to  the 
calcium  phosphate  present.  Of  all  the  inorganic  constituents  of  the 
body,  with  the  exception  of  water,  it  is  the  most  abundant.  In  most  of 
the  pathological  ossifications  and  concretions  calcium  phosphate  consti- 
tutes the  major  portion.  Thus,  nearly  all  the  urinary  calculi  in  the  ox 
are  formed  by  calcium  phosphate,  and  it  is  also  a  constituent  of  the 
mulberry  calculus  of  man.  So,  also,  calculi  which  develop  around  some 
foreign  nucleus  are  largely  calcium  phosphate.  Calcium  phosphate  also 
forms  the  greater  part  of  the  ash  of  albuminous  bodies,  with,  as  far  as  is 
3'et  known,  the  single  exception  of  elastin.  It  is  present  in  the  tissues 
of  the  human  body  in  the  following  proportions : — 

QUANTITY  OP  CALCIUM  PHOSPHATE  IN  1000  PARTS  IN  THE 

Enamel  of  teeth,  .        .        .        .        .        .        .        .  885. 

Dentine, '    .  643. 

Bones,    ..........  576. 

Cartilage, .        .        .40. 

Milk, '     .-    '   .        .        .        .  2.72 

Blood, -<       ....  0.30 

Bile, .        .        .        •  0.92 

Urine, 0.75 

The  greater  part  of  calcium  phosphate  in  the  organism  is  deposited 
in  the  form  of  a  solid  salt  in  the  bones  and  teeth,  in  the  form  of  the 
tricalcium  orthophosphate  (2(P04)Cas).  It  is  also  in  the  same  form 
present  in  nails,  hair,  and  hoofs.  When  it  is  found  in  solution,  as  is  the 
case  with  all  of  the  animal  fluids,  it  being  by  itself  perfectly  insoluble  in 
water,  its  presence  is  only  to  be  explained  as  chemically  united  with 
albuminoids,  although  possibly  it  may  be  in  minute  amount  in  solution 
in  fluids  which  contain  sodium  chloride  or  free  carbon  dioxide.  In  the 
urine  of  carnivora  and  omnivora  calcium  phosphate  is  present  as  an  acid 
salt  (2(P04)Ca"H4),  which  is  in  itself  soluble  in  water.  In  the  alkaline 


134  PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 

urine  of  the  herbivora  but  little  calcium  phosphate  is  present,  and  this  is 
not  dissolved,  but  merely  suspended,  and  readily  deposits  as  a  sediment. 
In  the  solid  tissues  the  lime  phosphate  appears  to  be  simply  deposited  in 
the  interstices  of  the  .organic  bases,  and  it  may  be  removed — as,  for 
example,  from  bone — by  prolonged  maceration  in  dilute  hydrochloric 
acid,  without  altering  the  form  of  the  bone.  As  Dalton  says  :  "  In  the 
bones,  teeth,  and  cartilage  the  lime  phosphate  exists  in  a  solid  form ; 
not,  however,  deposited  mechanically  in  the  osseous  or  cartilaginous 
substance  as  a  granular  powder,  but  intimately  united  with  the  animal 
matter  of  the  tissues,  like  coloring  matter  in  colored  glass,  the  union  of 
the  two  forming  a  homogeneous  material.  It  is  not,  on  the  other  hand, 
so  combined  with  the  animal  matter  as  to  lose  its  identity  and  constitute 
a  new  chemical  substance,  as  where  hydrogen  combines  with  oxygen  to 
form  water,  but  rather  as  salt  unites  with  water  in  a  saline  solution, both 
substances  retaining  their  original  character  and  composition,  though  so 
intimately  associated  that  they  cannot  be  separated  by  mechanical  means. ' 
The  lime  phosphate,  therefore,  may  be  extracted  from  a  bone  by  macer- 
ation in  dilute  muriatic  acid,  leaving  behind  the  animal  substance,  which 
still  retains  the  original  form  of  the  bone  or  cartilage."  The  bone  so 
treated  preserves  its  outline  perfectl}',  but  has  entirely  lost  all  rigidity, 
and  may  be  twisted  up,  and  the  long  bones  may  often  be  tied  into  a  knot. 
Calcium  phosphate,  therefore,  gives  to  bone-tissue  its  rigidit}^  Conse- 
quentl}T  when,  either  through  some  faulty  process  in  the  organism  or 
through  the  deprivation  of  calcium  salts  from  the  food,  this  substance  is 
not  deposited  in  normal  amounts  in  the  bones,  the  latter  become  soft, 
flexible,  and  deformed,  forming  the  affection  known  as  rachitis ;  or,  in 
adult  life,  a  similar  morbid  softening  of  bones  may  take  place  from 
a  defective  deposit  of  calcareous  matter,  and  a  progressive  yielding  of 
the  bony  skeleton  takes  place,  constituting  the  disease  known  as  osteo- 
malacia. 

The  greater  part  of  the  calcium  phosphate  enters  the  body  in  the 
food,  being  contained  in  both  animal  and  vegetable  articles  of  diet.  In 
suckling  animals  the  milk  contains,  in  its  normal  condition,  a  sufficient 
amount  of  calcium  phosphate  to  supply  the  growing  organism  with  its 
requisite  quantity.  When  taken  in  vegetable  food,  where,  of  course,  it 
is  ordinarily  present  as  a  union  of  calcium  with  one  or  more  of  the 
organic  acids,  in  the  animal  body,  as  already  referred  to,  it  undergoes 
decomposition  into  calcium  phosphate  and  carbonates  of  the  alkalies. 

9.  MAGNESIUM  PHOSPHATE  (2(P04)Mg8,  2(P04)MgH4). — Like  cal- 
cium phosphate,  magnesium  phosphate  is  found  in  all  the  tissues  and 
fluids  of  the  animal  body,  though  in  far  smaller  amount,  with  the  excep- 
tion of  muscle  and  the  thymus  gland,  where  the  magnesium  phosphate 
is  in  excess.  The  bones  of  the  herbivora  contain  more  magnesium  phos- 


INORGANIC   CELL-CONSTITUENTS.  135 

phate  than  those  of  the  carnivora.  The  combination  2(P04)Mg"H4  is 
often  found  in  the  urine  of  the  herbivora  when  fed  on  grain,  and  is 
occasional!}'  met  with  in  intestinal  concretions  under  the  same  conditions. 
Its  origin,  physiological  importance,  and  mode  of  disposition  in  the  body 
is  apparently  identical  with  that  of  the  alkaline  phosphates.  Occasion- 
ally magnesium  phosphate  undergoes  crystallization,  as  in  the  urine  of 
the  rabbit  and  in  suckling  calves. 

10.  SODIUM   AND   POTASSIUM   SULPHATES  (S04K2,    S04Na2). — These 
salts  are  to  be  regarded  as  normal  constituents  in  small  amount  of  most 
of  the  animal  fluids  and  tissues.     They  are  not,  however,  found  in  the 
milk,  bile,  or  gastric  juice,  their  presence  in  the  ash  being  without  impor- 
tance, since  in  incineration  of  sulphurous  organic  compounds  the  sul- 
phuric acid,  liberated  in  this  process,  unites  with  the  carbonates  and 
alkaline  bases.    A  certain  amount  of  these  salts  is  held  in  solution  in  the 
blood  and  in  the  urine,  though  the}'  are  less  abundant  than  either  the 
chlorides,  phosphates,  or  carbonates.     When  present  in  the  animal  body 
they  are  in  the  form  of  solution.     Only  part  of  the  sulphates  found  in 
the   animal   body  is   derived    from  without,  since   it   is   possible   that 
through  the  oxidation  of  sulphur  of  organic  compounds  sulphuric  acid  is 
formed,  which  leaves  the  body  united  with  alkaline  bases.     These  salts 
are  excreted  from  the  body  through  the  urine,  where  a  greater  part  of  the 
sulphuric  acid  is  not  derived  from  the  sulphates  contained  in  the  food, 
but  through  the  internal  oxidation  of  sulphur-holding  compounds.    This 
is  especially  shown  by  the  fact  that  an  abundant  animal  diet  increases 
the  amount  of  sulphates  in  the  urine  hand  in  hand  with  the  increase  of 
urea,  while  a  vegetable  diet  decreases  it.     The  sulphates  partly  con- 
tribute to  the  acid  reaction  of  the  urine  of  carnivora. 

The  entire  quantity  of  sulphur  in  the  body  of  an  adult  man  has  been 
estimated  at  about  one  hundred  and  ten  grammes,  and  to  keep  this 
amount  constant  at  least  one  gramme  must  be  taken  daily  in  the  food, 
where  it  is  combined  with  albuminoids.  A  part  of  this  sulphur  passes 
into  the  hair  and  nails,  part  is  consumed  in  the  manufacture  of  various 
complex,  sulphur-holding  compounds,  such  as  taurin,  taurocholic  acid, 
gelatin,  chondrin,  mucin,  etc.,  while  part  is  eliminated  in  the  form  of 
sulphates. 

11.  HYDROCHLORIC  ACID  (HC1). — The  presence  of  free  hydrochloric 
acid  has  as  yet  only  been  shown  to  exist  in  the  case  of  gastric  juice  of 
mammals.     Its  origin  and  importance  will  be  considered  under  the  sub- 
ject of  Gastric  Juice. 

Oxygen,  nitrogen,  and  carbon  dioxide  are  also  constant  constituents 
of  animal  fluids  and  tissues,  and  their  importance  will  be  discussed  under 
the  subject  of  Respiration. 

A  few  other  inorganic  substances  have  been  found  as  more  or  less 


136  PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 

constant  ingredients  of  animal  substances,  but  they  are  present  in  such 
small  amounts,  or  in  such  variable  quantities,  that  their  importance  has 
not  been  clearly  established.  These  are  magnesium  chloride,  calcium 
fluoride,  ammonium  carbonate,  magnesium-ammonium  phosphate,  calcium 
sulphate,  silicon,  iron,  manganese,  and  copper. 

In  vegetable  tissues  nearly  all  the  constituents  of  the  animal  cell  are 
found  deposited  or  in  solution.  They  serve  to  give  greater  solidity  to 
the  so-called  skeleton  of  plants,  and  are  also  without  doubt  of  importance 
in  the  vital  processes  of  vegetable  protoplasm.  Thus,  it  has  been  found 
that  the  amount  of  albumen  in  germinating  seeds  stands  in  direct  propor- 
tion to  the  amount  of  phosphate  which  the  plant  receives  as  food ;  also, 
that  without  potassium  salts  plants  cannot  grow.  Their  interest  to  us  as 
constituents  of  vegetable  organisms  is  simply  dependent  upon  their  ren- 
dering such  substances  suitable  for  animal  foods.  They  will  therefore 
receive  the  necessary  consideration  under  the  subject  of  Foods. 

II.  THE  CHEMICAL  PROCESSES   IN   CELLS.* 

The  great  mass  of  organized  bodies,  both  animal  and  vegetable,  are 
what  might  be  described  as  carbonic  acid  compounds,  associated  in  vari- 
able amounts  with  hydrogen,  oxygen,  and  nitrogen.  Plants  are  able, 
from  inorganic  substances,  such  as  CO2,  H20,  N03H,  NH,,  H2SO4,  P2O6, 
to  develop  organic  compounds,  the  difference  between  such  bodies  as 
entering  into  and  as  leaving  plants  depending  merely  upon  the  difference 
in  their  proportion  of  oxygen.  The  inorganic  bodies,  which  serve  as 
food  for  plants,  are  what  are  known  as  combustion  products ;  that  is, 
they  already  contain  the  maximum  quantity  of  oxygen  which  is  able  to 
enter  into  their  composition.  Organic  bodies,  on  the  other  hand,  contain 
in  all  cases  less  oxygen  than  will  satisfy  the  affinities  of  their  constituent 
elements.  They  therefore  are  capable  of  undergoing  further  oxidation, 
or,  in  other  words,  may  be  said  to  be  combustible.  The  plant-cell,  there- 
fore, must  be  able  to  deoxidize  the  inorganic  compounds  of  its  food  and 
set  free  oxygen ;  and  this  deoxidizing  force  must  evidently  be  greater 
than  the  affinity  exerted  by  the  oxygen  for  the  elements  with  which  it 
was  in  composition.  This  deoxidizing  power  possessed  by  plants  is  only 
capable  of  manifestation  in  the  sunlight,  and  is  a  function  of  the  green 
coloring  matter,  the  chlorophyll  of  plants.  The  animal  cell,  on  the  other 
hand,  in  its  nutritive  operations  exhibits  the  reverse  process  of  oxida- 
tion. The  inorganic  compounds  which  in  the  vegetable  cell  become 
organic,  that  is,  deoxidized,  in  the  animal  cell  become  again  oxidized  and 

*  For  the  preparation  of  this  section  special  acknowledgment  is  due  to  Wurtz, 
"  Chimie  Biologique  ;  "  Wundt,  "  Lehrbuch  der  Physiologic  ;  "  Gorup-Besanez,  "  Physi- 
ologische  Chemie  ;  "  Ranke,  "  Grundziige  der  Physiologic  ;  "  Hoppe-Seyler,  "  Physiolo- 
gische  Chemie ;  "  Schiitzenberger,  "  Fermentation  ;  "  Nageli,  "  Theorie  der  Garung." 


CHEMICAL   PEOCESSES   IN   CELLS.  137 

again  rendered  inorganic,  or  become  combustion  products.  They  are, 
therefore,  restored  to  the  mineral  world  by  the  animal  in  the  same  form 
in  which  they  were  originally  absorbed  by  the  vegetable. 

Vegetables  and  animals  are  the  depositories  and  agents  of  life  on  the 
surface  of  the  earth.  The  essential  characteristic  of  the  vital  operations 
of  the  former  is  their  power  of  elaborating  organic  from  inorganic  ma- 
terial. Animals  are  charged  to  destroy,  after  assimilation,  the  results  of 
the  vital  operations  of  the  vegetable.  The  animal  kingdom  is  thus  subor- 
dinate to  the  vegetable,  and  organic  life  represents  a  closed  circle  of 
metamorphosis  of  matter.  Plants  appropriate  inorganic  matter  out  of 
the  surrounding  inorganic  nature,  out  of  the  ground  and  air,  and  convert 
it  into  the  constituents  of  their  own  tissues.  They  then  become  food  for 
animals,  are  converted  into  animal  tissues,  and  are  again  returned  to  the 
ground  and  air  as  inorganic  compounds.  Thus,  the  carbon  of  the  carbon 
dioxide  of  the  air  becomes  the  carbon  of  cellulose  or  starch,  of  sugar,  of 
fat,  of  gum,  and  of  albumen  in  the  plant ;  as  food  of  animals  it  then 
becomes  the  carbon  of  various  animal  tissues.  In  the  vital  processes  of 
the  animal  the  carbon  of  the  tissues  undergoes  oxidation,  and  is  returned 
to  the  atmosphere  through  the  expelled  air  as  carbon  dioxide,  or,  in 
other  words,  in  the  form  in  which  it  originally  left  the  atmosphere.  An 
analogous  circle  might  also  be  traced  for  the  other  constituents  of  the 
animal  tissues. 

We  can  thus  understand  how  the  constituents  of  animal  and  vege- 
table cells  may  in  all  essential  points  be  analogous;  but,  while  this  is  so, 
the  chemical  processes  in  each  are  very  different.  Green  plants,  in  their 
capability  of  deoxidizing  inorganic  food  elements,  are  dependent  upon 
power  from  without — the  heat  and  light  from  the  sun.  They  therefore 
store  up  energy  in  their  tissues.  Animal  cells,  in  oxidizing  the  materials 
derived  from  the  vegetable  world,  liberate  a  force,  as  in  all  other  forms  of 
oxidation,  which  in  this  case  represents  an  equivalent  of  mechanical 
energy  precisely  equal  to  the  force  rendered  latent  in  the  nutritive  proc- 
esses in  the  vegetable.  In  the  animal  cell  this  energy  may  take  on  the 
form  of  heat,  electricity,  or  light,  as  in  certain  organisms,  or  mechanical 
movement. 

1.  The  Vegetable  Cell. — The  assimilative  processes  in  the  vegetable 
cell  are  dependent  upon  the  presence  of  protoplasm,  which  in  its  modir 
fied  form  as  chlorophyll  has  the  power  of  making  use  of  the  sunlight  for 
purposes  of  organic  deoxidation,  and  constitutes  the  most  powerful  re- 
ducing body  known.  The  properties  of  chlorophyll  are  not  exactly 
known,  as  it  has  probably  never  been  prepared  in  a  perfectly  pure  state. 
In  the  chlorophyll  granules  are  often  to  be  found,  the  results  of  its  organic 
activit}^,  such  as  starch-granules;  but  their  precise  mode  of  formation,  or 
the  precise  share  which  chlorophyll  has  in  producing  their  formation,  is 


138  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

not  well  known.  The  optical  properties  of  chlorophyll  are  very  remark- 
able. Fresh  alcoholic  solutions  in  ether,  even  when  very  dilute,  give  a 
broad  band  in  the  red  line  of  the  spectrum,  and  between  the  red  and  the 
orange.  The  most  luminous  portions  of  the  spectrum  are  the  red  and 
green  parts.  When  concentrated  ethereal  solutions  of  chlorophyll  are 
examined  in  the  spectroscope,  only  the  red  rays  pass.  Concentrated 
solutions  of  chlorophyll  give  a  red  fluorescence  with  reflected  light. 
When  subjected  to  the  action  of  light  solutions  of  chlorophyll  change  their 
color,  probably  in  a  manner  similar  to  that  which  accompanies  the  vital 
processes  of  the  vegetable  protoplasm  in  which  chlorophyll  is  contained. 

In  all  its  forms  protoplasm,  whether  animal  or  vegetable,  contains 
albuminous  bodies  in  a  state  of  solution  in  water,  and  associated  with 
compounds  of  an  inorganic  nature.  Carbo-hydrates,  hydro-carbons,  and 
ferments  are  also  nearty  invariably  present.  It  may  be  assumed  that  the 
albumen  is  the  highest  and  last  product  of  the  chemical  activit}^  of  vege- 
table cells,  while  starch  probably  constitutes  the  first  evidence  of  proto- 
plasm activit}r,  and  is  the  mother-substance  out  of  which  other  carbo- 
hydrates, such  as  cellulose  and  sugar,  as  well  as  fats,  are  manufactured. 

Plants  develop  various  modifications  of  albuminoids,  which  are 
apparently  identical  with  the  different  forms  of  albuminous  bodies  found 
as  constituents  of  animal  cells.  Thus,  in  growing  and  germinating 
plants  a  globulin-like  body  is  found  in  large  amount,  as  well  as  a  sub- 
stance similar  to  myosin  and  vitellin  in  combination  with  lecithin  and 
certain  inorganic  substances.  Albumen  is  found  in  especially  large 
quantities,  with  large  amounts  of  starch,  in  the  seeds  of  plants  ; 
hence,  the  undeveloped  plant  finds  in  these  two  substances,  albumen  and 
starch,  material  ready  prepared  for  building  up  its  tissues  until  it 
reaches  a  grade  of  development  in  which  it  is  able  to  manufacture  these 
organic  compounds  from  the  elements.  When  the  first  leaves  and  roots 
are  formed,  then  the  plant  commences  its  independent  existence.  The 
evidences  of  this,  as  we  have  already  seen,  consist  in  the  appropriation 
of  C02,  H20  and  NH8,  with  a  corresponding  liberation  of  oxygen. 

Since  all  vegetable  matters  contain  carbon  and  water,  their  con- 
stituents may  be  regarded  as  more  or  less  modified  C02  molecules. 
Thus,  sugar  may  be  regarded  as  CO,  in  which  one  equivalent  of  oxygen 
is  replaced  by  two  equivalents  of  hydrogen  (Liebig). 

Carbonic  Anhydride.  Grape-Sugar. 

'8  CH2 

or6(CO2(H20))  =  6(CH2O)  -f  6O2  =  C6H12O6  +6O2. 


Carbon  dioxide,  therefore,  in  the  formation  of  organic  matter,  may 
be  regarded  not  as  decomposed,  but  as  changing  the  arrangements  of  its 
molecules.  We  have  found  that  plants  in  their  nutritive  purposes  assimir 


CHEMICAL  PKOCESSES  IN   CELLS.  139 

late  carbon,  hydrogen,  nitrogen,  and  various  inorganic  substances.  We 
will  attempt  to  give  a  general  idea  as  to  the  processes  by  which  these 
substances  are  absorbed  by  plants,  and  the  way  in  which  in  their  tissues 
they  are  combined  to  form  organic  compounds. 

First,  as  regards  carbon.  The  carbon  of  plants  is  without  doubt 
derived  from  the  CO2  of  the  atmosphere,  or  in  solution  in  rain-water 
which  is  absorbed  b}'  the  leaves  and  roots,  which  under  the  influence  of 
the  sun  is  broken  up  in  the  body,  and  whose  oxygen  is  liberated.  The 
oxygen  given  off  in  the  day-time  by  plants  has  been  found  to  be  some- 
what less  than*  that  which  is  contained  in  the  C0a  which  has  been 
absorbed.  This  would  seem  to  indicate  that  COS  is  only  reduced  to  CO, 
since  it  is  known  that  part  of  the  oxygen  comes  from  the  decomposition 
of  water.  This  hypothesis  is  further  rendered  more  probable  by  the 
readiness  with  which  CO  combines  with  other  bodies.  Thus,  it  unites 
with  Cl  at  the  ordinary  temperature,  and  combines  directly  with  hydro- 
gen to  form  formic  acid.  Doubled,  —  that  is,  united  with  itself,  —  the 
radical  oxide  of  carbon,  or  carbonyl  CO,  constitutes  the  oxalic  radical 
C202,  or  oxatyl.  The  acid  which  contains  this  radical,  —  that  is,  oxalic 
acid,  —  can  be  formed  by  an  incomplete  reduction  of  COa  and  H2O  in  the 
presence  of  mineral  bases  ;  various  organic  acids  may  thus  originate  in 
vegetable  cells.  Taking  the  simplest  cases,  the  important  acids,  formic 
and  oxalic,  may  be  formed  in  this  way,  the  one  with  one  atom  of  carbon, 
the  other  with  two.  Thus,  with  one  molecule  of  water 

CO2  +  H2O  —  O  =  CH2O2  =  formic  acid. 
2  CO2  +  H2O  —  O  =  C2H2O4  =  oxalic  acid. 

Developing  this  idea,  Liebig  has  shown  that  the  organic  acids  once 
formed  may  give  rise  to  aldehydes  by  a  subsequent  reduction.  Formic 
aldehyde  represents  formic  acid  less  one  atom  of  ox^ygen  ;  oxalic  alde- 
hyde, or  glyonal,  oxalic  acid  less  two  atoms  of  oxygen,  thus  :  — 

CH  2  O2—  O  =  CH2O  =  formic  aldehyde. 
C2H204  —  O2  =  C2H202  =  glyonal. 

The  formation,  therefore,  of  aldehydes  in  vegetables  represents  a 
certain  stage  of  reduction  of  CO,  and  H2O.  Even  more  complex 
substances,  but  less  rich  in  oxygen,  will  result  from  further  decompo- 
sition. 

The  examples  above  given,  especially  in  the  case  of  formic  aldehyde, 
are  particularly  important,  as  there  is  scarcely  any  doubt  that  formic 
aldehyde  plays  an  important  role  in  vegetable  synthesis.  Thus,  six 
molecules  of  formic  aldehyde  will  form  one  molecule  of  glucose  :  — 


Again,  on  the  other  hand,  by  the  dehydration  of  aldehydes  resins  may 
be  formed,  as  it  is  well  known  how  readily  ordinary  aldehydes  become 


140  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

converted  into  resinous  bodies  by  losing  water;  while,  again,  ammonia 
through  its  combination  with  aldehydes  may  give  rise  to  nitrogenous 
bodies,  such  as  alkaloids.  We  therefore  see  that  in  the  appropriation  of 
the  carbon  and  the  carbon  dioxide  of  the  atmosphere  the  carbon  becomes 
fixed  to  form  these  various  bodies  synthetically  in  vegetable  protoplasm, 
while  the  oxygen  is  liberated. 

As  regards  the  assimilation  of  hydrogen  in  the  synthetical  processes 
occurring  in  vegetable  cells,  this  evidently  occurs  from  the  decomposition 
of  water,  as  is  proved  by  the  circumstance  that  the  oxygen  liberated, 
while  sometimes  less,  is  often  in  excess  of  that  which  is  contained  in  the 
C03  absorbed.  Thus,  in  the  vegetable  cell  the  carbo-hydrates,  such  as 
cellulose,  starch,  gum,  and  sugar,  are  made  by  the  simultaneous  reduction 
of  carbon  dioxide  and  water  under  the  influence  of  solar  radiation. 

For  nitrogen,  the  atmosphere  is  the  sole  source,  though  it  may 
possibly  to  a  certain  extent  be  derived  from  the  nitrates  in  the  soil. 
When  obtained  from  the  atmosphere  it  is  held  in  solution  in  the  form  of 
salts,  possibly  in  rain-water.  All  decomposing  organic  matters  set  free 
ammonia,  and  therefore  nitrates,  particularly  of  potassium,  are  powerful 
fertilizers,  and  increase  vegetation  b}^  supplying  the  nitrogen  which  is 
essential  in  the  development  of  albuminous  bodies  and  crystallized 
nitrogenous  vegetable  constituents. 

Of  the  minerals  which  are  essential  to  vegetable  life,  such  as 
phosphates,  silica,  salts  of  lime  and  magnesium,  and  alkaline  salts,  they 
are  obtained  partly  from  the  atmosphere  and  partly  from  the  soil.  They 
are  contained  in  large  amounts  in  all  parts  of  vegetable  matter,  and  will 
deserve  special  consideration  under  the  subject  of  the  vegetable  diet  of 
the  herbivora.  The  mineral  constituents  of  the  soil  and  atmosphere 
therefore  play  an  important  part  in  the  phenomena  of  the  development 
of  vegetable  life.  This  we  have  seen  to  be  essentially  one  of  reduction. 
In  separating  the  oxygen  from  carbon  and  hydrogen  a  portion  of  their 
affinity  for  ox}^gen  is  restored  to  these  latter  elements.  For  in  CO2  and 
H20  this  affinity  is  completely  satisfied ;  that  is,  the  energy  which  resides 
in  the  atoms  of  carbon  and  hydrogen  has  not  been  destroyed  by  combi- 
nation and  transformation,  and  when  these  atoms  unite  with  oxygen  this 
energy  is  dissipated  as  heat.  To  reduce  these  combinations,  therefore, 
the  energy  thus  latent  in  the  form  of  heat  must  be  restored  to  the  atoms 
of  carbon  and  hydrogen.  Thus  vegetables,  in  decomposing  water  and 
carbon  dioxide,  making  use  of  the  heat  of  the  sun,  not  only  convert  atoms 
of  carbon,  hydrogen,  and  nitrogen  into  organic  substances,  but  have  at 
the  same  time  accumulated  chemical  energy.  For  all  organic  compounds 
are  capable  of  uniting  with  oxygen ;  in  other  words,  are  combustible. 
The  energy  restored  under  the  name  of  affinity  to  the  atoms  is  hence 
derived  from  a  portion  of  the  solar  radiation  which  is  absorbed  by  plants 


CHEMICAL   PEOCESSES   IN   CELLS.  141 

and  is  converted  into  affinity.  This  is  the  indispensable  condition  of 
the  reduction  of  COa  and  H2O  and  the  elaboration  of  organic  compounds ; 
or,  in  other  words,  "  there  can  be  no  vegetation  without  the  sun." 

The  process  which  we  have  found  to  take  place  in  vegetable  cells 
only  holds  good  in  the  case  of  green  plants  under  the  influence  of  the 
sunlight,  for  there  is  in  all  cases  a  double  chemical  process  going  on  in 
plant-cells.  The  assimilation  through  deoxidation  of  organic  com- 
pounds under  the  influence  of  sunlight  has  already  been  described. 
This  process  is,  however,  limited  to  the  chlorophyll  plants,  and  in  them  to 
the  time  when  they  are  exposed  to  the  sun's  light  and  heat.  Another 
process,  however,  is  continual!}7  going  on  in  all  forms  of  vegetable  cells. 
The  products' of  assimilation  undergo  within  the  vegetable  cells  various 
chemical  changes  which  are  not  accompanied  by  a  liberation  of  oxygen, 
but  by  a  change  of  molecular  arrangement,  associated  with  the  absorption 
of  a  small  amount  of  oxygen  and  the  setting  free  of  carbon  dioxide. 
These  changes  are  independent  of  the  sunlight,  and  result  in  a  diminution 
of  the  mass  of  assimilated  materials.  That  a  plant  may  increase  in  size 
it  is  necessary  that  the  deoxidizing  activity  and  assimilation  produced  in 
the  sunlight  should  overbalance  the  loss  through  oxidation  which  is 
continually  going  on,  whether  in  darkness  or  light.  This  latter  process 
in  plants,  by  which  they  absorb  ox}Tgen  and  set  free  carbon  dioxide,  is 
clearly  analogous  to  the  processes  of  respiration  in  animals.  This  res- 
piration in  plants  is,  however,  very  feeble,  and  is  far  overbalanced  by  the 
processes  of  assimilation ;  therefore,  as  a  rule,  although  the  elaboration 
of  vegetable  products  is  accompanied  by  accumulation  of  force,  the 
vital  processes  in  plants  which  are  not  connected  with  assimilation  are, 
as  in  animals,  dependent  upon  oxidation  processes,  and  may  be  accom- 
panied by  the  liberation  of  heat  and  electrical  movement  of  protoplasm, 
and  the  formation  and  growth  of  cells.  In  the  case  of  the  non-chlorophyll- 
bearing  plants,  such  organisms  absorb  organic  matter  already  elaborated  ; 
the  parasitic  plants  may,  therefore,  be  regarded  as  a  connecting-link 
between  the  animal  and  vegetable  kingdoms,  especially  as  some  of  the 
lower  forms  of  the  former  are  also  possessed  of  chlorophyll,  by  which 
they  are  enabled  to  decompose  CO,  under  the  influence  of  the  sun.  A 
curious  exception  to  the  characteristics  of  the  vegetable  chemism  is  tlie 
power  which  certain  plants  possess  of  attracting,  seizing,  and  digesting 
insects.  The  so-called  insectivorous  plants  of  Darwin  and  Hooker,  such 
as  the  Drosera  rotundifolia,  Darlingtonia,  Nepenthes,  etc.,  are  supplied 
with  special  urn-like  vessels,  in  which  the  animals  are  trapped  and 
digested.  They  are  lined  with  glands  that  secrete  both  the  sugary  fluid 
to  attract  the  insects  and  a  true  digestive  juice,  containing  pepsin  and 
acid,  which  is  poured  out  when  the  plants  are  stimulated  by  contact  with 
digestible  substances.  This  secretion  will  turn  fibrin  into  -peptone,  but 


142  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS 

is  without  action  on  starches.  It  therefore  closely  resembles  animal 
gastric  juice. 

Still  another  analogy  may  be  traced  between  the  animal  and  vege- 
table kingdoms.  Under  certain  circumstances  plants  develop  heat,  as  in 
germinating  seeds,  or  in  flowers  during  fecundation.  Sugar  is  the  sub- 
stance in  such  cases  whose  combustion  sets  free  heat.  It  exists  in 
germinating  seeds,  and  disappears  during  germination,  from  the  action 
of  a  diastatic  ferment  analogous  to  the  glycogen  ferment  in  animals. 
The  analogy  is,  however,  not  perfectly  complete,  as  the  plants  manu- 
facture their  starchy  material  from  inorganic  materials ;  animals  must 
obtain  it  ready-made. 

In  the  dark  the  processes  of  assimilation  of  plants  are  entirely 
suspended.  Then  carbon  dioxide  is  given  off,  and  oxygen  is  absorbed, 
for  the  processes  of  respiration  or  oxidation  still  continue.  During  the 
day  the  carbon  dioxide,  which  is  constantly  absorbed  by  the  roots  and 
leaves,  is  in  the  leaves  broken  up  into  oxygen,  which  is  set  free,  while 
the  carbon  remains  tixed.  At  night  C02  is  also  absorbed  by  the  roots, 
but  is  exhaled  from  the  leaves  without  undergoing  change  :  for,  as  we 
have  found,  for  its  deoxidizing  purposes  chlorophyll  requires  the  assist- 
ance of  sunlight  and  heat.  It  is  also  possible  that  a  part  of  the  C02 
which  is  set  free  during  the  night  is  not  only  derived  from  C02  absorbed 
from  the  leaves  and  roots,  but  also  is  the  result  of  oxidation  by  a  part 
of  the  oxygen  which  is  absorbed. 

2.  The  Animal  Cell. — The  relationship  which  we  have  traced 
between  the  chemical  processes  of  plants  and  the  atmosphere  and  soil 
around  them  is  reversed  in  the  case  of  animal  cells ;  for,  while  green 
plants  absorb  the  inorganic  constituents  of  the  earth  and  atmosphere, 
and  from  them  build  up  complex,  inorganic  compounds,  the  oxygen  of 
the  atmosphere  in  the  animal  permits  of  the  reduction  of  its  complex  tis- 
sues and  constituents.  For  the  green  plants  the  atmosphere  forms  one  of 
their  chief  foods;  for  animals  it  is  the  great  agent  which  permits  their 
tissue  changes,  on  which  all  liberations  of  energy  depend.  In  green 
plants  the  chief  vital  phenomenon  is  the  liberation  of  oxygen  ;  in  ani- 
mals it  is  the  absorption  of  oxygen.  In  plants  the  liberation  of  oxygen 
is  an  index  of  increase  in  weight ;  in  animals  the  absorption  of  oxygen 
leads  to  a  loss  of  weight.  That  the  animal  cell  may  retain  its  com- 
position unaltered  it  must  be  supplied  with  its  tissue-constituents. 
Unlike  vegetable  cells,  the  animal  cell  is  incapable  of  manufacturing 
these  tissue-constituents  from  inorganic  elements.  The  most  that  the 
animal  cell  may  do  is  to  transform  a  member  of  one  class  of  its  con- 
stituents into  another  member  of  the  same  group.  Thus,  the  animal  cell 
may  transform  the  albuminoid  matters  contained  in  vegetable  cells  into 
albuminous  bodies  which  are  peculiar  to  animals.  It  may  transform  the 


CHEMICAL   PROCESSES   IN   CELLS.  143 

proteicls  of  one  class  into  those  of  another.  It  ma}'  transform  casein  of 
milk  into  the  proteids  of  blood  and  other  tissues.  Animal  cells  are,  how- 
ever, the  seat  also  of  certain  synthetical  processes,  such  as  the  formation 
of  haemoglobin  from  albumen  and  iron,  with  other  inorganic  matters,  the 
possible  reformation  of  albumen  from  peptone,  and  the  building  of  com- 
plex albuminoids,  such  as  mucin.  All  animal  foods,  nevertheless,  orig- 
inate in  the  vegetable  kingdom.  Even  carnivora  are  dependent  on  the 
vegetable  kingdom  for  their  sustenance ;  for  the  herbivora,  feeding  on 
vegetable  diet,  become  the  prey  of  carnivorous  animals,  which  are  there- 
fore dependent  on  the  vegetable  matters  which  serve  to  nourish  the  tissues 
of  the  animals  which  serve  as  their  food.  In  the  vegetable  cell  albumen 
is  the  end  product  of  its  chemical  processes;  in  the  animal  cell  it  is  the 
starting  point.  Albuminoids  represent  the  main  or  essential  tj'pe  of 
foods  which  must  be  supplied  to  the  animal  cell.  When  introduced  into 
the  interior  of  cells,  albuminoids  undergo  a  progressive  oxidation  and 
simplification,  by  which  lower  complex  substances  are  formed.  The 
mode  of  decomposition  of  albuminoids,  as  well  as  of  all  organic  bodies 
in  general,  is  different  in  different  cells.  This  difference  is  seen  in  the 
very  first  modification  of  the  albuminous  matters  of  food,  which  may  be 
converted  into  casein,  myosin,  etc..  according  as  the  resulting  albuminous 
body  is  destined  to  be  a  constituent  of  milk,  muscle-cell,  etc.  Then, 
again,  after  being  deposited  in  cells  the  subsequent  processes  differ  in 
different  cases,  according  to  the  nature  of  the  cell-membrane  or  inter- 
cellular substance,  or  the  function  of  the  special  cells  in  the  organism. 
Finally,  the  development  of  the  end  products  of  the  oxidation  of  the 
albumen  of  cells  differs  in  the  cells  of  different  tissues,  though  in  all 
cases  the  chemical  processes  in  cells  result  in  the  formation  of  carbon 
dioxide,  water,  and  ammoniacal  compounds. 

The  most  striking  example  of  the  products  resulting  from  the  oxi- 
dation of  proteids  is  the  formation  of  fat  from  albumen.  In  adipose 
tissue  and  in  fatt}^  degeneration  of  various  organs  the  protoplasmic  con- 
tents of  cells  become  replaced  by  oil,  formed  evidently  at  the  expense  of 
the  albuminoid  constituents  of  the  protoplasm.  So,  also,  carbo-hydrates, 
such  as  glycogen,  maybe  produced  from  a  splitting  of  the  albuminoid 
foods.  In  addition  to  the  carbo-hydrates  and  fats  thus  formed,  a  large 
number  of  nitrogenous  bodies  are  liberated  in  the  oxidation  of  the 
albuminous  molecule,  and  might  be  termed  ammonia  compounds,  such  as 
kreatin,  uric  acid,  urea,  etc.  Such  bodies  are,  as  a  rule,  richer  in  ox}Tgen 
than  albumen. 

The  carbo-hydrates  and  fats  are  also  subjected  to  progressive  oxida- 
tion in  the  animal  body,  and  result,  in  the  former  .case,  in  the  production 
of  organic  acids,  such  as  lactic,  formic,  and  oxalic,  and  in  the  latter  in 
the  formation  of  fatty  acids.  AS  already  several  times  mentioned,  the 


144  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

chemical  processes  in  the  animal  cell  result  in  the  formation  of  C03,  IT20, 
and  NH8  compounds,  and  hence  return  to  the  earth  and  air  the  matters 
originally  absorbed  by  the  plant-cell,  and  in  the  same  form.  These  end 
products  are,  however,  only  gradually  formed  as  the  result  of  a  long 
series  of  intermediary  oxidation  products,  which  are  formed  partly 
through  processes  of  splitting,  by  which  complex  molecules,  usually 
through  Irydration,  are  decomposed  into  two  or  more  simpler  compounds 
through  the  action  of  certain  ferments.  Through  these  means  the 
organic  cell-constituents  become  progressively  poorer  in  carbon  and 
richer  in  oxygen  and  nitrogen,  thus  losing  their  organic  characteristics 
and  becoming  gradually  more  nearly  allied  to  inorganic  bodies,  until 
finally  the  inorganic  end  products  are  reached. 

The  following  table,  based  on  hypothetical  formulae,  indicates  the 
manner  in  which  complex  albuminous  molecules  may  become  gradually 
reduced  to  simpler  forms  (Gorup-Besanez): — 

Haemoglobin,        .        .        .  C600  H960  N154  FeS3     O179 

Albumen,      .        .        .        .  C90  H139  N22  S           O30 

Lecithin,       ....  C42  H84  N  P           O9 

Taurocholic  Acid,        .         .  C26  H45  N  S           O7 

Glycocholic  Acid,        .         .  C26  H43  N  O6 

Hippuric  Acid,     .                 .  C9  H9  N  O3 

Tyrosin,        ...       .        .  C9  Hai  N  O3 

Leucin,         .        .        .        .  C6  H13  N  O2 

Asparagin,    .         .        .        .  C4  H8  N2  O3 

Asparaginic  Acid,        .        .  C4  H7  N  O4 

Glutanimic  Acid,                  .  C5  H9  N  O4 

Guanin,         ...        .  C5  H5  N5  O 

Hypoxantliin,                        .  C5  H4  N4  O 

Xanthin,       ...'..  C5  H4  N4  O2 

Uric  Acid,                              .  C5  H4  N4  O3 

Kreatin,        .        .        .        .  C4  H9  ]ST3  O2 

Allantoin,     ......  C4  H6  N4  O3 

Urea,     .....  C  H4  N2  O 

Urea  thus  forms  the  termination  of  the  decomposition  series  of  the 
organic  nitrogenous  molecules. 

A  similar  progressive  simplification  may  also  be  seen  in  the  non- 
nitrogenous  organic  constituents.  Thus,  according  to  Gorup-Besanez  : — 

Stearin,      ......  C57  H110  O6 

Palmitin,   .        ....        .        .  C51  H98  O6 

Olein,         .        ...        .         .  C57  H104  O6 

Stearic  Acid,     .....  C18  H36  O2 

Oleic  Acid, C18  H33  O2 

Palmitic  Acid, C16  H32  O2 

Butyric  Acid, C4  H8  O2 

Succinic  Acid, C4  H6  O4 

Grape-sugar,      .        .        .        .        .  C6  H12  O6 

Glycerin,  .......  C,  H8  O3 

Lactic  Acid C3  H6  O3 

Acetic  Acid, C2  H4  O2 

Oxalic  Acid C2  H2  O4 

Formic  Acid, C  H2  O2 


CHEMICAL  PROCESSES   IN   CELLS.  145 

Just  as  urea  is  readily  broken  up  into  ammonium  carbonate,  or 
S  and  CO2,  so  also  formic  and  oxalic  acids,  the  terminals  of  the  non- 
nitrogenous  organic  molecules,  readily  undergo  decomposition  into 
C0a  and  H,0. 

It  cannot  be  pretended  that  we  are  familiar  with  all  the  intermediary 
stages  of  these  retrogressive  metamorphoses,  yet  we  are  possessed  of 
numerous  facts,  gained  through  the  study  of  the  decomposition  of  albu- 
men by  various  chemical  agents,  which  go  far  to  fix  the  character  of 
these  changes.  Thus,  in  the  artificial  decomposition  of  albumen  by 
certain  chemical  reagents,  asparagin,  glutanimic  acid,  leucin,  and  tyrosin 
are  constantly  met  with ;  and  since  these  bodies  occur  in  the  process  of 
germination  in  seeds,  and  the  latter  two  often  in  the  animal  body  at  the 
seat  of  rapid  break  down  of  albuminoid  matter,  we  may  infer  that  a  simi- 
lar process  normally  occurs  in  animal  cells.  So,  also,  by  various  methods 
of  oxidation  uric  acid  is  readily  converted  outside  of  the  body  into  urea, 
allantoin,  oxalic  acid,  and  carbon  dioxide;  and  there  are  many  facts  for 
supposing  that  a  similar  conversion  occurs  in  the  animal  body.  Thus,  the 
administration  of  uric  acid  produces  not  an  increase  in  the  uric  acid 
eliminated,  but  in  the  urea  and  calcium  oxalate  ;  and  since  uric  acid  is 
normally  present  in  but  small  amount  in  the  urine  of  the  carnivora,  and 
is  absent  in  that  of  the  herbivora,  while  we  know  that  in  certain  organs 
of  both  classes  of  animals  it  is  formed  in  considerable  amount,  it  must 
undergo  oxidation  in  the  economy.  This  is  further  proved  by  the  fact 
that  a  reduction  in  the  supply  of  oxygen  leads  to  an  increase  in  the  uric 
acid  and  a  decrease  of  the  urea  in  the  urine.  In  a  similar  way  is  to  be 
explained  the  appearance  of  allantoin  in  the  urine  of  cats  and  dogs  when 
fed  on  abundant  animal  diet. 

A  similar  line  of  argument  ma}7  be  made  to  apply  to  the  decompo- 
sition of  the  non-nitrogenous  tissue-constituents. 

We  are  thus,  to  a  certain  extent,  familiar  with  the  starting  point  and 
terminals  of  the  series  of  decompositions  which  occur  in  the  animal 
bod}r,  and  with  a  few  of  the  intermediary  links  in  this  chain.  We  shall 
again  have  to  return  to  this  subject  in  the  study  of  Nutrition. 

3,  Fermentations. — The  word  fermentation  is  derived  from/ervere, 
to  boil,  and  owes  its  origin  to  the  appearance  presented  by  sugary  fluids 
when  placed  in  contact  with  ferments  ;  gas  is  liberated,  the  sugar  disap- 
pears, and  the  product  becomes  alcoholic.  While  the  term  fermentation 
was  originally  restricted  to  this  process,  it  is  now  applied  to  many  cases 
in  which  an  organic  body  when  dissolved  is  modified,  changed,  and  trans- 
formed under  the  action  of  formed  or  soluble  ferments.  As  regards  the 
action  of  fermentation  only  the  results  and  processes  of  the  soluble  fer- 
ments will  here  demand  consideration. 

The  soluble  ferments  act  on  a  large  number  of  organic  compounds, 

10 


146  PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 

their  mode  of  action  being  largely  the  same  in  all.  Water  is  always  essen- 
tial to  the  processes  of  fermentation,  and  the  result  is  acquired  by  a  more 
or  less  simple  splitting  up  of  the  organic  molecule  accompanied  by  hy- 
dration.  The  nature  of  this  splitting  up  is  governed  by  the  nature  of 
the  body  which  is  subjected  to  fermentation,  and  may  be  explained  in 
most  cases  by  chemical  processes  in  which  the  intervention  of  a  living 
organism  does  not  appear.  Ferments  have  been  classified  as  follows  in 
the  character  of  the  change  which  they  produce  (Hoppe-Seyler)  :  — 

CHANGE  OF   ANHYDRIDES   INTO   HYDRATES. 

A.  Ferments  that  Act  like  Dilute  Mineral  Acids  at  a  High  Temperature. 

a.  The  conversion  of  starch  into  sugar,  or  glycogen  into  dextrin 
and  grape-sugar,  as  b}T  the  action  of  ptyalin,  the  amylolytic  ferment  of 
the  pancreatic  or  intestinal  juices,  diastase,  or  the  liver-ferment.  Thus  :  —  - 


=  C6H1005+3(C6H1206). 
Glycogen.  Grape-Sugar. 

or,  in  the  case  of  starch  :  — 

C24H40020+3H20=:C6H1005  +3C6H1206. 
Starch.          Water.          Dextrin.  Glucose. 

b.  The  conversion  of  cane-  into  grape-sugar,  as  by  the  inversive 
ferment  :  — 

C^H^O^+H.O-CeH^Oe  +  CeH^Oe. 
Cane  Sugar.  Grape-Sugar.    Fruit-Sugar. 

This  reaction  also  gradually  occurs  through  the  action  of  water  at 
100°  C.,  while  starch  requires  a  temperature  of  170°,  the  resulting  sugar 
at  the  same  time  undergoing  decomposition. 

B.  Ferments  that  Act  like  Caustic  Alkalies  at  a  High  Temperature  — 
Fermentative  Saponification. 

a.  Splitting  up  of  fats  into  glycerin  and  fatty  acids,  as  by  the  action 
of  the  ferment  of  the  pancreatic  juice. 

b.  Splitting  up  of  amydo  compounds  by  hydration  through  decom- 
position products,  as 


Urea.  Ammonic  Carbonate. 


The  changes  in  albuminoids  produced  by  the  pancreatic  ferment  and 
in  decomposition  probably  fall  under  this  category. 


CHEMICAL  PROCESSES   IN   CELLS.  147 

FERMENTATION     PROCESSES,     WITH    TRANSFER     OF     OXYGEN     FROM 
THE   HYDROGEN   TO   THE   CARBON   ATOMS. 

a.  Lactic  Acid  Fermentation. — Under  the  action  of  various  ferments 
sugar  is  converted  into  lactic  acid.    This  occurs  in  the  milk,  and  also  very 
probably  in  sugary  solutions  within  the  intestine.     In  the  first  stage  of 
this  process  lactic  acid  is  produced  as  follows : — 

C6H1206=:2C3H603.  C12H22011  +  H20^4C3H603. 

In  the  later  stages  butyric  acid,  carbon  dioxide,  and  hydrogen  are 
formed.  Thus : — 

2(C3H603):=C4H802+2C02+2H2. 

b.  Alcoholic  Fermentation. — Under  the  influence  of  various  of  the 
formed  ferments,  such  as  yeast-plant,  grape-sugar  undergoes  fermentation 
and  results  in  the  formation  of  carbon  dioxide  and  alcohol. 

c.  Putrefactive  Fermentation. — Ferments  which  cause  putrefaction 
are  found  in  the  lowest  organisms,  micrococci,  bacteria,  etc.    Their  action 
is  destroyed  by  heating  above  53°  C. 

The  most  important  ferments  in  the  chemical  processes  occurring  in 
the  animal  body  are  the  diastatic  or  sugar-forming  ferments,  found  in 
the  saliva,  pancreatic  and  intestinal  juices,  liver,  and  blood ;  the  peptone- 
forming  ferments,  found  in  gastric,  pancreatic,  and,  perhaps,  intestinal 
secretions  ;  the  fat-ferment,  found  in  pancreatic  juice  ;  the  inversive  fer- 
ment, found  in  intestinal  juice  ;  and  the  milk-curdling  ferments,  found  in 
the  gastric  and  pancreatic  secretions.  All  the  above  ferments,  with  the 
exception,  possibly,  of  the  last,  are  so-called  hydrotytic  ferments  ;  that 
is,  their  action  is  accompanied  by  a  process  of  hydration.  Water  is 
essential  to  all  forms  of  fermentation  ;  hence,  ferments  become  inert  when 
dried.  For  the  action  of  the  proteolytic  ferment  of  the  gastric  secretion 
a  faintly  acid  reaction  is  essential,  as  is  also  the  case  for  the  pepsin-like 
ferment  of  the  insectivorous  plants,  such  as  the  Drosera  and  Dionsea, 
which  have  the  power  of  digesting  albuminous  bodies.  An  excess  of 
acid  will,  however,  interfere  with  the  action  of  the  proteolytic,  as  well  as 
of  the  diastatic,  ferments ;  the  same  holds  good  for  the  caustic  alkalies, 
although  an  alkaline  reaction  favors  the  action  of  the  proteolytic  ferment 
of  the  pancreatic  juice.  Salts  of  the  heavy  metals,  as  well  as  ether, 
chloroform,  and  all  the  so-called  antiseptics,  prevent  fermentation. 

Further  details  as  to  the  action  of  ferments  will  be  considered  under 
the  study  of  the  digestive  juices  and  the  putrefactive  changes  in  the 
alimentary  canal. 

4.  The  Consumption  and  Development  of  Force  in  Cells*. The 

development  of  force  in  cells  is  closely  dependent  on  the  chemical  inter- 

*  Wundt,  "  Lehrbuchder  Physiologie." 


148  PHYSIOLOGY   OF   THE  DOMESTIC  ANIMALS. 

changes  occurring  in  the  interior  of  cells.  The  constituents  of  all 
chemical  compounds  are  held  together  by  their  chemical  affinities,  and 
compound  atoms  hence  exhibit  a  lesser  tendency  to  form  new  combina- 
tions than  do  free,  uncombined  atoms.  When,  however,  a  combination 
is  broken  up,  as  by  some  external  force,  the  separated  atoms  again  tend 
to  unite.  There  is  again  a  difference  in  the  stability  of  chemical  com- 
pounds. In  other  words,  new  combinations  are  more  readily  formed  in 
some  instances  than  in  others.  Thus,  the  loosely -held  oxygen  atom  in 
hydrogen  peroxide  (H202)  is  much  more  readily  given  up  to  form  fresh 
combinations  than  the  closely-held  atom  of  oxygen  in  H20.  Thus,  forces 
which  only  exist  as  a  tendency  to  produce  motion  are  termed  potential 
forces;  those,  on  the  other  hand,  which  actually  manifest  themselves  in 
movements  are  actual  or  kinetic  forces.  The  tendency  to  combine  is, 
therefore,  a  potential  force,  which  varies  according  to  the  free  or  com- 
bined state  of  the  atoms,  and,  in  the  latter  case,  according  as  the  atoms 
are  held  in  loose  or  close  combination.  The  atom  released  from  chemical 
combination  acquires  an  increased  potential  force,  while  an  atom  which 
passes  from  the  free  to  the  combined  state  loses  in  potential.  In 
ever}''  chemical  decomposition,  or  the  passage  from  close  to  loose  com- 
pounds, the  potential  force  is  developed,  while  in  the  formation  of  other 
chemical  compounds,  or  the  passage  from  loose  to  close  compounds,  the 
potential  is  diminished.  The  separation  and  union  of  the  elements  and 
formation  of  chemical  compounds  are,  therefore,  movements  of  the 
elements ;  consequently,  in  their  decomposition  or  composition  actual 
forces  are  produced.  When  atoms  unite,  a  part  of  the  force  which  before 
existed  as  a  tendency  to  form  combination  (the  potential  force)  is 
converted  into  actual  or  kinetic  force,  and  the  combination  has  lost 
potential  to  that  extent  to  which  the  tendency  to  form  combinations  is 
satisfied.  In  decomposition  the  exact  opposite  holds.  In  order  to  break 
up  combinations  an  external  force  is  required,  and  the  amount  of  poten- 
tial acquired  by  the  atoms  is  precisely  equal  to  the  actual  force  employed. 
It  follows  from  this  that  in  the  act  of  every  chemical  composition  actual 
force  is  liberated,  and  in  every  chemical  decomposition  actual  force  is 
rendered  latent,  or  is  converted  into  potential.  In  the  first  case  the  force 
developed  is  equal  to  the  potential  lost  in  combination,  and  in  the  second 
case  the  actual  force  rendered  latent  equals  the  potential  force  developed. 
Where  a  loss  of  potential  occurs,  it  is  compensated  for  by  a  proportional 
development  of  actual  force,  and  vice  versa. 

The  same  rule  applies  to  all  forces  in  nature.  Every  development 
of  force  is  to  be  regarded  as  a  change  from  actual  to  potential  force  or  the 
reverse,  or  the  transformations  of  different  forms  of  actual  force.  This 
law  is  known  as  the  conservation  of  energy.  The  forms  of  actual  force 
that  we  are  familiar  with  are  movements  of  masses,  light,  heat,  and  elec- 


CHEMICAL   PROCESSES   IN   CELLS.  149 

tricity.  All  the  actual  forces  have  a  tendency  to  be  converted  into  a 
single  actual  force,  heat;  thus,  as  the  motions  of  bodies  decrease  through 
friction  and  the  resistance  of  the  atmosphere,  and  as  the  electric  current 
meets  with  resistance,  they  are  converted  into  heat.  So,  also,  the  form 
of  movement  which  appears  as  actual  force  in  the  formation  of  chemical 
compounds  is  usually  manifested  by  the  development  of  heat,  or  occa- 
sional light ;  and  the  actual  forces  which  disappear  in  chemical  decompo- 
sition are  again  usually  represented  by  heat  or  light.  Nearly  all  bodies 
are  chemical  compounds ;  that  is,  their  atoms  are  bound  together  by 
their  affinity  for  their  atoms.  This  also  applies  to  the  isolated  elements 
which,  in  their  free  state,  exist  as  molecules  of  like  atoms.  So  long  as 
no  external  force  is  brought  to  bear  upon  chemical  compounds,  there  is 
no  tendency  to  decomposition  or  formation  of  new  compounds. 

Heat  is  the  most  ordinary  external  force  which  produces  chemical 
change.  The  stability  of  chemical  compounds  may  therefore  be  meas- 
ured by  the  amount  of  heat  required  to  break  up  the  compound.  Every 
compound,  even  the  most  stable,  may  be  broken  up  if  the  heat  is  suf- 
ficient. While  C03  requires  enormous  heat  to  decompose  it,  the  organic 
compounds  of  carbon  are  decomposed  at  moderate  temperature.  Conse- 
quently, in  the  latter  case  the  atoms  are  loosely  combined  ;  that  is,  in  the 
formation  of  this  combination  not  all  the  potential  affinity  is  converted 
into  actual  energ}%but  a  considerable  degree  of  potential,  with  a  tendency 
to  form  compounds,  still  remains.  When  to  such  compounds  heat  is 
applied  in  a  degree  equal  to  the  amount  of  actual  energy  liberated  in  the 
formation  of  the  compound,  the  atoms  are  liberated  and  again  acquire 
their  original  potential  energy.  If  a  new  combination  is  now  formed, 
the  potential  is  again  converted  into  actual  energy,  and  the  latter,  in  the 
form  of  heat,  is  proportional  to  the  closeness  of  the  new  compound. 
This  is  the  process  which  is  concerned  in  the  burning  of  every  organic 
compound.  Thus,  by  the  artificial  application  of  heat  single  atoms  of  the 
combustible  body  and  .of  the  atmosphere  are  separated  and  their  combi- 
nation results  in  the  liberation  of  heat,  which  is  itself  sufficient  to 
decompose  other  atomic  combinations,  and  the  processes  of  combustion 
goes  on  by  itself.  The  entire  amount  of  heat  liberated  equals  the 
difference  between  the  amount  of  heat  required  to  break  up  the  organic 
compound  and  the  amount  liberated  in  the  formation  of  simpler,  closer 
compounds.  If,  on  the  other  hand,  atoms,  if  they  are  separated  by 
considerable  force,  do  not  enter  into  a  closer  but  into  a  looser  compound, 
more  actual  energy  is  lost  than  is  liberated,  and  a  decomposition  results 
in  which  a  certain  amount  of  heat  is  used  up,  which  in  the  new.  combi- 
nation is  present  as  potential  force  for  future  combustions.  The  amount 
of  potential  energy  is  therefore  dependent  on  the  closeness  of  the  chemical 
combination^  and  not  on  the  separation  of  the  affinities.  As  a  rule, 


150  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

the  closeness  of  the  combination  is  inversely  proportional  to  its  com- 
plexity. 

The  degree  of  potential  energy  of  a  combination  may  be  measured 
by  the  amount  of  heat  liberated  in  its  combustion  ;  thus,  a  heat  unit 
is  the  amount  of  heat  required  to  raise  one  gramme  of  water  one 
degree  C.  So  one  gramme  of  carbon  yields  8000  heat  units,  or  calorics  ; 
one  gramme  of  hydrogen  equals  34,000  heat  units.  These  numbers  are 
greatly  modified  when  the  carbon  and  hydrogen  are  combined  or  enter 
into  combination  with  other  elements.  Thus,  when  pure  carbon  is 
oxidized  to  CO2,  the  heat  developed  is  less  than  when,  with  an  equal 
quantity  of  0,  CO,  or  combinations  of  CH  and  O  and  H20  are  burned 
to  form  C02.  The  higher  the  atomic  weight  of  compounds,  the  greater 
the  amount  of  heat  given  off  in  combustion.  Thus,  fats  yield  more  heat 
than  sugar  and  alcohol ;  but  while  equal  weights  of  such  high  atomic 
bodies  yield  more  heat  in  proportion  to  their  weight,  when  compared 
with  equal  quantities  of  oxygen  consumed  they  yield  less  than  simpler 
bodies,  as  sugar  or  alcohol. 

The  elementary  compounds  which  are  found  in  animal  and  vegetable 
cells  in  no  way  differ  from  those  found  in  inorganic  nature.  Similar 
elementary  substances  are  found  in  the  earth  and  atmosphere,  and 
become  constituents  of  animal  and  vegetable  organisms.  In  organisms 
chemical  affinity  exerts  the  same  sway  as  in  inanimate  nature.  Acids 
unite  with  bases  to  form  salts  within  cells  just  as  without ;  no  one  of 
the  elementary  constituents  of  cells  has  lost  its  power  of  uniting  with 
oxygen,  and  the  products  so  formed  are  identical  with  similar  bodies 
formed  elsewhere. 

We  have  already  traced  the  processes  occurring  in  animal  and 
vegetable  cells,  by  which  these  bodies  are  converted  in  the  former  from 
simple  elementary  substances  to  complex  organic  bodies,  and  in  the 
latter  again  reduced  to  their  simple  elementary  form.  It  is  evident  that 
the  animal  and  vegetable  cells  differing  in  the  chemical  processes  which 
occur  within  them  will  also  differ  in  the  transformations  of  energy  which 
occur  within  them.  Thus,  we  have  seen  that  vegetable  cells  containing 
chlorophyll  convert  stable  oxygen  compounds  of  carbon  and  hydrogen, 
COa  and  H2O,  with  liberation  of  oxygen,  into  the  looser  organic  com- 
pounds, such  as  starch,  or,  less  frequently,  glucose  or  fat.  They  therefore 
return  to  atoms  of  these  combinations  a  portion  of  their  potential  energy, 
which  in  the  original  transformation  into  COa  and  HaO  they  had  lost  in 
actual  energy  in  the  form  of  heat.  To  accomplish  this,  plant-cells  require 
the  assistance  of  an  external  force,  namely,  the  heat  and  light  of  the  sun, 
which  they  convert  into  a  chemical  potential  force  in  the  resulting 
organic  compounds.  The  condition  is  more  complicated  in  cells  which 
possess  no  chlorophyll.  Here,  also,  the  reduction  processes  require  an 


CHEMICAL  PROCESSES   IN   CELLS.  151 

external  force ;  but  in  such  a  process  as  the  manufacture  of  fat  out  of 
carbo-hydrates,  or  the  synthesis  of  albuminoids  out  of  carbo-hydrates 
and  inorganic  nitrogenous  compounds,  or  the  formation  of  starch, 
cellulose,  etc.,  out  of  glucose,  the  potential  energy  developed  is  not 
derived  from  an  external  force,  as  the  light  in  chlorophyll  plants,  but 
from  a  force  inherent  in  the  cell  itself.  This  force  is  manifested  in  the 
oxidation  processes  occurring  in  colorless  protoplasm,  and  which  are 
evidenced  by  the  excretion  of  C02  and  H3O  as  combustion  products. 
Thus,  in  the  synthesis  of  higher  carbo-hydrates  from  glucose  a  combus- 
tion results,  in  which  H2O  is  formed,  and  in  it  the  two  atoms  H  and  O 
are  more  closely  united  with  one  another;  in  this  process  potential  energy 
is  transformed  into  actual  force.  In  order  to  comprehend  the  formation 
of  fat  or  albuminoids  out  of  oxygen  compounds  without  a  simultaneous 
liberation  of  oxygen  there  must  also  always  be  an  additional  combustion 
of  looser-combined  carbon  into  C02;  from  this  it  follows  that  pure 
oxidation  processes  occur  in  such  cells,  such  as  the  formation  of 
vegetable  acids  out  of  carbo-l^drates,  volatile  acids  from  fixed  fatty 
acids, — processes  which  yield  a  certain  amount  of  actual  energy  in  the 
form  of  heat,  of  which  a  part  is  again  rendered  latent  in  the  formation  of 
chemical  potential  energy.  As  a  whole,  in  cells  free  from  chlorophyll  the 
processes  accompanied  by  the  liberation  of  actual  forces  preponderate 
over  those  in  which  actual  energy  is  consumed.  In  every  such  cell, 
therefore,  there  is  an  actual  development  of  heat.  A  small  part  of  this 
actual  energy,  before  being  converted  into  heat,  may  be  transformed  into 
the  mechanical  movements  already  described.  Every  independent  organ- 
ism which  is  free  from  chlorophyll  manifests  changes  which  result  in  the 
same  transformation  of  force  as  described  above  ;  such  examples  are  seen 
in  the  case  of  the  organized  ferments. 

The  animal  cells,  on  the  other  hand,  directly  appropriate  highly 
complex  substances,  such  as  albumen,  fats,  and  carbo-hydrates,  in  which 
a  high  degree  of  potential  energy  is  contained.  In  the  act  of  forming  by 
oxidation  simpler  compounds,  such  as  C03,  H20,  and  NH8,  their  potential 
energy  is  transformed  into  actual  force,  partly  manifested  by  heat- 
production,  and  by  protoplasmic  contractile  movements.  In  animal  cells, 
therefore,  the  main  characteristic  is  the  conversion  of  the  potential 
energy  of  organic  compounds  into  the  actual  forces  of  heat  and 
mechanical  movements  ;  the  process  being  much  the  same  as  has  already 
been  referred  to  as  occurring  in  the  vegetable  cells  free  from  chlorophyll, 
differing  mainly  in  intensity.  A  reverse  process  may  be  also  present  by 
which  actual  force  may  be  consumed  and  potential  energy  stored  up,  as 
in  the  formation  of  complex  albuminoids,  such  as  haemoglobin,  or  in  tho 
re-formation  of  albumen  out  of  peptones. 


PART  II. 


SPECIAL  PHYSIOLOGY. 


(153) 


BOOK   I. 


THE  NUTRITIVE  FUNCTIONS. 


(155) 


SECTION    I. 
FOODS. 

IN  comparing  the  metamorphosis  of  matter  in  animal  and  vegetable 
organisms  it  has  been  found  that  in  both  cases  there  exists  a  certain 
relationship  between  such  changes  and  the  surrounding  media.  In  the  two 
classes  of  organisms,  however,  these  processes  are  diametrically  oppo- 
site ;  for,  while  we  found  that  the  higher  plants  remove  for  nutritive  pur- 
poses C02  from  the  atmosphere  and  returned  0  to  it,  the  animal  economy 
retains  a  portion  of  the  oxygen  of  the  atmosphere,  not  remaining  fixed 
as  such  in  the  body,  but  to  be  again  returned  to  the  atmosphere  as 
C02  and  H20.  For  plants,  consequently,  since  we  found  that  the  carbon 
of  the  CO2  and  a  portion  of  the  hydrogen  of  the  H2O  become  fixed  in 
their  tissues,  the  atmosphere  is  a  true  food ;  for  animals  it  merely  en- 
ables tissue  metabolism  to  take  place,  and  permits  of  the  maintenance 
of  animal  heat.  The  development  and  growth  of  plants  is  dependent  on 
the  liberation  of  ox}rgen  and  the  appropriation  of  the  inorganic  con- 
stituents of  their  foods.  In  animals  life  depends  upon  the  constant 
appropriation  of  oxygen,  its  union  with  the  different  constituents  of  the 
body,  and  final  elimination  through  the  lungs  and  skin  as  C02  and  HjO, 
and  through  the  bowels  and  kidneys  in  other  simple  compounds.  There- 
fore, through  the  absorption  of  oxygen  there  is  produced  no  increase  in 
bulk  of  the  animal  body,  but  rather  a  decrease.  To  meet  this  waste 
of  the  organism  there  must  be  a  constant  appropriation  of  tissue-con- 
stituents. Such  substances  are  called  foods. 

Nutrition  may  .be  defined  as  the  functions  which  are  concerned  in 
the  preservation  of  the  individual.  Foods  may,  therefore,  be  defined  as 
any  substances  which  may  serve  nutritive  purposes.  The  body  being  in 
a  constant  state  of  mutation,  the  constituents  of  the  organism  are  little 
by  little  eliminated  as  the  result  of  this  mutation,  and  to  preserve  the 
necessary  balance  must  be  replaced.  There  must,  therefore,  be  an  exact 
correlation  between  the  constituents  of  an  organism  and  the  aliments 
required  by  that  organism.  The  demand  for  aliment  is  governed  by  the 
waste ;  if  the  supply  is  not  as  great  as  the  waste,  the  body  loses  weight. 
If,  on  the  contrary,  as  in  youth,  the  supply  is  greater  than  the  waste, 
the  body  increases  in  weight.  When  the  losses  of  the  economy  reach 
a  certain  degree  without  a  sufficient  reparation  having  taken  place, 
when  the  disassimilation  exceeds  the  assimilation,  the  sense  of  hunger 

(157) 


158  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

reveals  the  wants  of  the  organism  and  creates  a  demand  for  food.  If 
these  demands  are  not  attended  to,  other  more  serious  phenomena 
result.  These,  as  well  as  the  sensations  of  hunger  and  thirst,  will  be 
described  at  a  later  point. 

Not  only  must  the  aliments  taken  to  repair  waste  have  a  certain 
weight,  but  they  must  also  have  a  definite  quality,  since  nitrogenous 
and  non-nitrogenous  material,  water  and  inorganic  substances,  all  escape 
through  the  various  excretions,  and  their  losses  must  be  supplied  by 
analogous  substances  in  quantities  in  proportion  to  the  amounts  lost 
by  excretion.  Under  all  circumstances  the  foods  of  animals  are  or- 
ganic, and  these  foods  for  the  most  part  contain  those  inorganic  sub- 
stances already  prepared  which  form  the  direct  constituents  of  the 
animal  body  ;  the}7  are  therefore  analogous  and  equivalent  to  what  they 
replace.  The  animal  economy  does  not,  as  does  the  plant,  supply  its 
nutritive  wants  by  synthesis  and  condensation  of  the  substances  con- 
tained in  its  food ;  but  it  requires  the  constituents  of  its  flesh  and 
blood  to  be  already  formed  in  its  food.  In  the  flesh  of  the  herbivora 
the  carnivora  consume  flesh  similar  to  their  own.  In  plants  the  her- 
bivora obtain  readj^-formed  constituents  of  their  flesh  and  blood.  The 
end  products  of  the  activity  of  plant  life,  vegetable  albumen,  and  other 
constituents  of  vegetable  tissue,  serve  directly  and  without  further  exten- 
sive chemical  modification  to  supply  the  waste  in  the  animal  economy ; 
consequently,  plants  act  as  the  food-preparing  organisms  in  the  general 
circle  of  life.  Vegetable  life  must,  therefore,  first  have  appeared  on  the 
earth,  for  it  is  a  necessary  condition  for  the  existence  of  animal  life ; 
both  herbivora  and  carnivora  are  dependent  upon  the  vegetable  kingdom 
for  food.  In  vegetable  matters  are  repeated  the  most  complex  ingre- 
dients of  animal  tissues.  Chemists  have  been  so  struck  by  the  similarity 
of  such  bodies  that  they  have  designated  them  by  the  same  names. 
Thus,  we  have  vegetable  albumen,  vegetable  fibrin,  vegetable  casein, 
representing  the  albuminous  group.  Among  the  carbo-hydrates  we 
have  starches  and  sugars,  and  it  is  well  known  that  fats  are  abundant 
in  the  vegetable  kingdom.  Animals,  therefore,  find  their  tissue-con- 
stituents ready-made  in  their  food,  whatever  be  its  nature. 

The  principles  of  food,  whether  derived  from  the  animal  or  vegetable 
kingdom,  and  whether  appropriated  by  the  herbivora  or  carnivora,  are 
not  retained  in  the  organism  in  the  form  in  which  they  are  taken  as  food. 
They  must  first  be  subjected  to  certain  modifications  before  they  can 
become  constituents  of  the  animal  tissue  or  juices  ;  in  other  words,  they 
cannot  fulfill  their  nutritive  purposes  until  they  have  been  subjected  to 
preparatory  modifications  in  the  digestive  tube.  These  modifications  are 
not  in  general  very  pr6found,  and  usually  consist  in  reducing  foods  to  a 
soluble  form,  if  not  already  so,  or  in  reducing  them  to  a  state  in  which 


FOODS.  159 

absorption  is  possible.  This  is  the  sole  end  of  digestion.  The  aliments 
are  in  the  digestive  tract  split  up  into  their  nutritive  elements,  which  are 
prepared  for  their  absorption,  while  the  non- nutritive  portions  are 
expelled.  Thus,  the  blood  of  animals  is  continually  receiving  additions 
from  the  food,  which  it  carries  to  different  organs  and  tissues.  Certain 
of  these  are  fixed  or  assimilated,  replacing  analogous  substances  rendered 
unfit  for  carrying  on  the  vital  functions  ;  the  others  are  modified  and 
destroyed.  There  is  thus  an  incessant  movement  in  the  animal  economy, 
a  continuous  interchange  of  material,  and  a  double  current  of  entering 
and  expelled  materials.  This  double  current  is  marked  by  two  series  of 
chemical  phenomena, — the  one  terminating  in  the  fixation  of  the  nutri- 
tive principles  in  the  economy,  in  their  assimilation  ;  the  other  in  their 
decomposition,  their  retrogressive  metamorphosis,  or  their  disassimila- 
tion.  The  ensemble  of  these  two  chemical  phenomena  constitutes 
nutrition. 

Foods  of  animals  are  destined  to  supply  the  waste  of  tissues.  They 
must,  therefore,  to  be  complete,  embrace  all  the  tissue-ingredients  which 
are  liable  to  waste.  The  statement,  therefore,  of  these  tissue-constituents 
will  be  also  a  statement  of  the  essential  food-stuffs.  The  chief  constitu- 
ents of  the  blood,  flesh,  and  other  tissues,  as  we  have  seen,  may  be  classi- 
fied as  follow : — 

ORGANIC. 
I 


Nitrogenous.  Non-nitrogenous. 

Albuminous  Bodies  and  Carbo-hydrates  and 

their  Derivatives.  Hydro-carbons. 

INORGANIC. 

Water,  Sodium  Chloride, 

Alkaline  Phosphates,  Sodium  Sulphate, 

Phosphatic  Earths  (Calcium,  Magnesium),  Potassium  Sulphate, 

Magnesium  and  Calcium  Carbonates,  Iron, 

Potassium  Chloride,  Silicon. 

It  is  rarely  the  case,  however,  that  these  simple  nutritive  substances 
are  taken  separate^  as  food.  Ordinarily  the  alimentaiy  substances  are 
formed  of  mixtures,  in  various  proportions,  of  the  simple  nutritive 
substances.  Thus,  water  that  we  drink  contains  mineral  salts  in  solution. 
Meat  contains  water,  albuminous  bodies,  salts,  and  fats,  while  milk 
contains  all  the  alimentary  principles.  We  must  therefore  distinguish 
between  simple  nutritive  substances  and  foods  which  contain  several  of 
these  bodies. 

In  addition  to  the  simple  food-stuffs,  there  are  other  substances  not 
belonging  to  any  of  the  above  classes  which  have  certain  nutritive  values, 
such  as  alcohol,  organic  acids,  tea,  coffee,  and  essential  oils.  These  are 


160  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

termed  accessory  foods,  and  have  but  little  bearing  on  the  study  of 
nutrition  in  the  domestic  animals. 

Blood  is  the  chief  nutritive  fluid  of  animals.  What,  therefore,  is  to 
be  converted  into  tissue  must  first  be  converted  into  blood;  consequently, 
the  substances  taken  in  food  must  be  converted  into  blood,  or,  at  least, 
pass  into  the  blood,  to  be  of  nutritive  value.  Blood  contains  about  80 
per  cent,  of  water  and  20  per  cent,  of  solids.  Of  the  latter,  1|  per  cent, 
is  organic,  consisting  of  albuminous  bodies,  fats,  and  carbo-hydrates,  the 
latter  being  represented  by  glucose  and  occurring  in  small  quantities. 
Blood,  therefore,  contains  all  the  constituents  of  the  tissues  and  the 
elements  for  their  formation,  so  arranged  as  to  require  but  slight  chem- 
ical modification  to  transform  them  into  tissue.  Blood  consequently 
contains,  in  suitable  form,  all  the  organic  elements  necessary  for  the 
formation  of  all  the  animal  tissues  and  fluids.  The  constituents  of  the 
blood  and  flesh  of  the  carnivora  are  absolutely  identical  with  the  constit- 
uents of  the  blood  and  flesh  of  those  animals  which  serve  as  their  food. 
The  nutritive  processes  of  the  carnivora  consist,  therefore,  in  a  simple 
nutritive  conversion  of  the  blood  and  flesh  of  herbivora.  Suckling 
animals,  whether  herbivorous  or  carnivorous,  obtain  in  milk  what  might 
be  regarded  as  the  equivalent  of  the  flesh  of  their  mother,  since  milk 
contains  representatives  of  all  the  constituents  of  blood,  casein  and 
albumen  representing  the  albuminous  group,  butter  the  fats,  and  milk- 
sugar  the  carbo-hydrates.  The  same  inorganic  salts  are  also  found  in  the 
milk  as  in  the  blood,  and  water  is  present  in  large  amount. 

In  the  herbivora  the  nutritive  processes  are  not  less  simple,  since  all 
parts  of  plants  which  serve  as  their  food  contain  representatives  of  albu- 
minous, carbo-hydrate,  and  fatty  tissue-constituents  which  are  similar,  or 
almost  identical,  to  those  found  in  the  animal  tissues.  Consequently,  the 
vegetable  bodies  which  serve  as  foods  for  animals  contain,  ready  formed, 
the  constituents  of  animal  tissues,  and  the  nutritive  value  of  vegetable 
foods  is  in  direct  relation  to  the  proportion  of  these  substances  present. 
It  may  therefore  be  said  that  animals  are  dependent  upon  the  inorganic 
matters  of  the  earth  and  air  for  their  food-stuffs ;  for  from  these  inor- 
ganic constituents  of  the  earth's  surface  plants  indirectly  create  the  blood 
and  flesh  of  herbivora,  and  in  the  blood  and  flesh  of  herbivora  the  car- 
nivora, in  a  strict  sense,  may  be  said  only  to  obtain  matter  of  vegetable 
origin  with  which  the  former  were  nourished.  Animals,  therefore,  through 
the  mediation  of  plants  are  built  up  out  of  C02,  H20,  NH3,  N03H,  and  a 
few  other  inorganic  compounds  (Gorup-Besanez). 

What  has  been  said  about  the  renewal  of  the  organic  tissue-elements 
might  be  repeated  for  the  inorganic  tissue-constituents  of  animals.  These 
are  also  obtained,  ready  prepared  and  reacty  for  assimilation,  by  both 
carnivora  and  herbivora.  The  inorganic  constituents  of  the  blood  of  the 


VEGETABLE  FOODS.  161 

! 

herbivorous  animals  are  precisely  similar  to  the  inorganic  constituents 
of  the  vegetable  matters  which  serve  as  their  food.  The  inorganic  con- 
stituents of  the  blood  are  the  same  as  the  inorganic  constituents  of 
tissues.  Herbivora  and  carnivora  therefore  find  in  their  foods  their 
necessary  inorganic  tissue-constituents.  The  statement  above  made  that 
animals  must  obtain  in  their  foods  constituents  of  their  blood  and  tissues 
ready  prepared  may  be  modified  in  the  case  of  the  fats ;  for  it  has  been 
found  that,  so  far  from  being  derived  from  fats  taken  as  food,  the  greater 
part  of  the  fats  stored  up  in  the  body  is  derived  from  the  breaking  up 
of  other  organic  bodies,  especially  the  albuminoids. 

I.    VEGETABLE  FOODS. 

The  nutritive  principles  of  vegetable  foods  are  disseminated 
in  various  proportions  in  different  parts  of  all  vegetables;  there  is 
therefore  no  vegetable  which  is  intrinsically  incapable  of  serving  as 
animal  food.  But  all  vegetables  do  not  contain  these  nutritive  principles 
in  equal  degrees,  or  in  such  a  state  as  to  permit  of  their  isolation 
and  appropriation  by  the  animal  digestive  apparatus ;  nor  are  they  in 
all  the  vegetables  free  from  noxious  principles.  Thus,  some  vegetables, 
as  the  herbaceous  plants,  contain  nutritive  principles  in  all  their  parts  ; 
others,  only  in  their  roots,  stem,  bark,  leaves,  fruit,  or  juices.  Some  may 
form  suitable  foods  for  a  large  number  of  different  species  of  animals ; 
others  are  only  capable  of  nourishing  a  single"  species ;  and  some  plants 
which  are  food  for  certain  groups  of  animals  are  poisons  to  others.  The 
parts  of  plants  above  the  ground — that  is,  their  stem,  leaves,  flowers,  and 
fruits — are  in  general  the  most  nutritious  from  the  time  when  vegetation 
is  well  commenced  to  the  time  of  flowering,  because  then  the  nutritive 
principles  are  not  yet  fixed  in  the  organs  of  fructification,  and  the  parts 
in  which  they  are  disseminated  are  soft  and  tender.  Earlier  than  this 
the  herbaceous  plants  are  too  watery  and  later  too  dry  to  prove  very 
nutritious.  The  stems  of  leguminous  plants  are  nutritive  while  young, 
while  their  leaves  are  suitable  for  food  in  all  varieties  of  vegetation.  The 
roots  of  plants,  when  soft  and  succulent,  serve  as  food  for  many  animals, 
such  as  the  hog  and  bear,  the  tapir  and  hippopotamus,  and  when  culti- 
vated form  valuable  food  for  man.  Soft  and  pulpy  fruits,  dried  fruits, 
nuts,  hulls,  and  seeds,  which  are  almost  invariably  rich  in  mucilaginous 
matters, — with  sugar,  starch,  oil,  and  nitrogenous  principles, — are  often 
food  for  many  animals.  Under  certain  circumstances,  parts  of  plants 
which  are  usually  but  slightly  nutritive,  such  as  the  bark,  stems,  and 
roots,  or  even  woody  tissue,  may  serve  as  foods,  especially  after  having 
undergone  partial  decomposition,  for  many  animals,  particularly  the 
beaver  and  other  rodents,  and  various  insects. 

11 


162  PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 

Vegetable  foods  differ  from  foods  of  animal  origin  in  the  respect 
that  the  nutritive  principles  are  not  present  in  as  concentrated  form  as 
in  animal  foods,  and  the  non-nitrogenous  food-stuffs  are  present  in  much 
greater  abundance  than  the  nitrogenous  ;  moreover,  vegetable  foods  are, 
as  a  rule,  very  much  less  readily  digestible  than  animal  foods,  from  the 
fact  that  the  nutritive  principles  are  inclosed  within  cellulose  capsules, 
which  offer  great  resistance  to  the  solvent  action  of  the  digestive  juices, 
and  which  necessitates  fine  comminution  before  being  capable  of  being 
digested  and  absorbed.  As  a  consequence  of  this  the  residue  from  the 
digestion  of  vegetable  matter  is  always  very  much  more  abundant  than 
from  an  animal  diet,  and  hence  the  intestinal  excreta  of  the  herbivora 
are  alwajrs  much  more  bulky  than  of  the  carnivora,  or  even  of  the  om- 
nivora.  Another  point  of  contrast  between  vegetable  and  animal  food 
is  found  in  the  difference  of  inorganic  constituents  of  the  ash.  Vege- 
table foods  are  especially  rich  in  potassium  and  magnesium  salts,  and 
comparatively  poor  in  sodium  salts,  while  chlorides  are  present  in 
extremely  small  amount,  and  phosphates  in  considerable  quantities. 
As  already  indicated,  in  vegetable  tissues  representatives  of  all 
the  different  food-stuffs  are  to  be  found ;  thus,  vegetable  albumen  is 
present,  and  in  its  characteristics  appears  identical  almost  with  the 
albumen  of  animal  origin.  So,  also,  are  carbo-hydrates,  oils,  and  inor- 
ganic salts.  The  relative  proportions  of  these  substances  vary  in  differ- 
,ent  plants.  The  usefulness,  therefore,  of  different  forms  of  vegetable 
food  for  different  nutritive  purposes  depends  upon  differences  in  the  rela- 
tive proportions  of  these  constituents.  The  vegetable  foods  may  be 
given  to  our  domestic  animals  in  the  fresh  state,  containing  their  natural 
juices,  when  they  are  termed  green  fodder,  or  after  having  been  dried 
by.the  sun,  when  they  are  called  dry  fodder. 

» Green  fodder  always  contains  a  large  amount  of  water  in  proportion 
to  the  solids  present,  the  proportion  often  being  75  per  cent,  water  to  25 
per  cent,  solids.  Of  the  solids  the  albuminous  bodies  may  amount  to  10 
or  20  per  cent.,  the  non-nitrogenous  extractive  matters  varying  between 
50  and  60  per  cent.,  while  cellulose  is  present  in  large  amount.  All  edible 
grasses  and  vegetable  tops  may  serve  as  green  fodder. 

Dry  fodder  consists  of  the  stems  and  leaves  of  various  grasses  and 
plants  after  the  major  part  of  their  water  has  been  removed  by  evapora- 
tion by  the  sun's  heat.  The  proportion  of  water  to  solids  in  dry 
fodder  is  reduced  to  15  per  cent,  of  the  former  to  85  per. cent,  of  the 
latter.  Of  the  solids  of  dry  fodder  cellulose  constitutes  from  20  to  40 
per  cent.,  a  moderate  amount  of  albuminoids  and  carbo  hydrates,  less 
fat,  and  a  maximum  of  inorganic  matter. 

Green  fodder,  as  a  rule,  is  more  readily  digestible  than  dry  fodder. 
Thus,  experiments  made  by  feeding  oxen  at  one  time  with  fresh  red  clover, 


VEGETABLE  FOODS.  163 

and  another  time  with  the  same  material  carefully  dried,  have  shown  the 
following  excess  of  matters  digested  in  favor  of 'the  green  fodder: — 

Solids,      .        .   •'.'-•     .  2.3  to    5.5  per  cent,  more  digested. 

Proteids,  .         .         .         .  2.7  to    3.2 

Carbo-hydrates,       .        .  4.1  to    5.6        "  " 

Fats,         ....  2.4  to  21.0 

Cellulose,        .        .        .  2.6  to    6.2 

The  attempt  has  been  made  to  attribute  these  results  to  the  reduc- 
tion in  digestibility  acquired  in  the  processes  of  drying.  This  is  not, 
however,  the  case,  since  there  is  an  actual  loss  of  digestible  matter  in 
the  processes  of  fermentation  which  occur  in  the  act  of  drying.  Green 
fodder  is  especially  adapted  for  all  ruminants,  and  for  young  horses  after 
the  completion  of  the  first  year.  Scarcely  any  single  green  fodder  is, 
however,  suited  for  forming  the  single  food  of  horses  or*  sheep.  The 
percentage  of  water  of  most  green  fodders  in  every  stage  of  growth 
amounts  to  from  70  to  90  per  cent.,  and  there  are  but  few  green  fodders 
which  contain  so  little  water  that  they  may  serve  without  the  mixture  of 
any  dry  fodder  for  feeding  sheep  or  horses.  Cattle,  on  the  other  hand, 
require  a  watery  food,  while  hogs,  on  account  of  the  arrangement  of 
their  digestive  apparatus,  are  only  capable  of  digesting  small  amounts 
of  the  youngest  and  most  tender  green  foods.  Green  fodder,  as  a  rule, 
is  the  more  nutritious  the  younger  and  more  tender  it  is,  since,  in  spite 
of  the  greater  amount  of  water  contained  in  this  period,  it  also  contains 
a  larger  amount  of  nitrogenous  nutritive  substances,  is  more  stimulating 
to  the  appetite,  and  is  more  readily  digested.  Thus,  it  has  been  found 
that  in  the  English  bay  grass  (Lolium  perenne)  the  composition  varies 
as  follows  (Pott)  : — 

Water.       Cellulose.    Proteids. 
On  the  6th  of  May,        .        .        .  81.2  17.7  27.9 


From  the  25th  to  the  27th  of  May, 

On  the  10th  of  June,      . 

On  the  24th  of  June,      . 

On  the  10th  of  July, 

On  the  22d  of  July, 

On  the  15th  of  August, 


83.5  21.4  16.0 

82.9  22.4  14.8 

82.4  23.6  12.8 

82.2  32.5  11.9 

76.9  28.6  12.5 

74.8  29.7  7.8 


Similar  results  have  been  obtained  in  the  case  of  clover  and  prairie 
hay.  From  the  fact  that  green  fodder  in  early  spring  is  so  rich  in  pro- 
teids  it  is  advisable  in  this  time  of  the  year  to  administer  it  mixed  with 
chopped  straw  that  the  fodder  be  not  too  rich  in  nitrogenous  compounds. 

The  following  represent  the  principal  vegetable  food-stuffs  :  the  seeds 
of  the  grains,  or  the  cereals ;  the  hulls  and  fruits  of  the  leguminous  plants  ; 
the  vegetables,  as  potatoes,  turnips,  and  beets ;  and  hay,  grasses  and 
straw,  of  the  green  and  dry  fodders  : — 

1.  THE  CEREALS. — Wheat,  barley,  corn,  rice,  and  oats  belong  to  this 
group,  and  are  valuable  food-stuffs.  Their  chemical  composition  is 


164  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

subject  to  variations  dependent  upon  the  mode  of  culture,  the  nature  of 
the  soil,  and  the  climate.  They  all  contain  a  small  amount  of  water  and 
cellulose  in  proportion  to  a  large  amount  of  solids  (over  80  per  cent.)  in 
which  non-nitrogenous  extractives  and  inorganic  matters  are  in  excess. 
The  following  table  gives  their  average  composition : — 

In  100  parts.  Wheat.       Rye.       Barley.       Oats.         Bice.       Corn. 

Water,      -   .<       .        .        .  13.6  15.3  13.8  13.5  13.2  13.9 

Albumen,    ....  12.4  11.4  11.2  11.9  7.8  10.1 

Fat, 1.7  1.7  2.1  5.8  0.7  48 

Carbo-hydrates    and    non- 
nitrogenous       extractive 

matters,    ....  67.9  67.8  65.5  57.5  76.4  66.8 

Cellulose,     ....  2.7  2.0  4.8  8.1  08  2.8 

Ash,     ...        .        .        .1.7  1.8  2.6  3.2  1.1  1.7 

The  cereal  grains,  of  which  wheat  may  be  taken  as  a  t}rpe,  consist 
of  a  number  of  layers  arranged  eccentrical^.  As  many  as  seven  different 
layers  have  been  recognized.  Externally  there  is  the  external  membrane 
or  epidermis;  within  that  the  epicarpium ;  3d,  the  endocarpium ;  4th,  the 
pigment-layer,  or  the  testa,  which  in  wheat  is  a  reddish-brown  membrane, 
and  gives  to  wheat-grains  their  characteristic  color;  5th,  the  tegmen,  or 
external  nuclear  membrane,  below  which  are  found  a  number  of  dice- 
shaped  cells  (the  perisperm),  which  were  formerly  spoken  of  as  gluten- 
cells,  in  which,  however,  the  contents  are  mainly  starch  ;  and  it  is  within 
the  endosperm  that  the  albuminous  contents  is  contained  between  the 
starchy  granules.  For,  if  a  granule  of  wheat  is  divided  and  touched 
with  a  drop  of  Millon's  solution,  it  will  be  seen  that  the  contents  of  the 
endosperm  only  stain  purple,  while  the  shells  and  the  so-called  gluten- - 
cells  remain  unchanged. 

When  wheat  is  subjected  to  the  action  of  a  digestive  fluid  the 
albuminous  bodies  of  the  endosperm  are  dissolved  and  the  starchy 
granules  become  separated,  while  the  hulls  and  so-called  gluten-cells 
remain  entirely  unaffected.  The  hulls  contain  a  certain  amount  of 
albuminous  bodies,  and  are  employed  in  bran  and  in  black  bread,  and 
have  considerable  nutritive  value.  In  the  so-called  gluten-cells  a  ferment 
seems  to  be  present  which  has  been  called  cereal  in,  and  which  seems  to 
interfere  in  some  way  with  digestion,  and  as  a  consequence,  although 
bran-bread  is  to  a  certain  extent  nutritious,  it  is  yet  difficult  to  digest. 
In  grinding,  the  external  hulls  or  capsules  are  bursted  and  the  contents 
reduced  to  a  fine  powder  in  the  mill,  and  thus  become  more  digestible. 
Hulls  which  are  separated  from  the  internal  contents  by  milling  always 
contain  a  certain  amount  of  albuminous  matter  and  starch  clinging  to 
them,  so  that  even  the  chaff,  or  the  hull  or  bran,  contains  considerable 
amounts  of  nutritive  matter,  and  may  be  used  as  fodder.  Bran  from 
wheat  has  been  found  to  contain  13  per  cent,  water,  14.5  per  cent. 


VEGETABLE  FOODS. 


165 


albumen,  2  per  cent,  fat,  53  per  cent.  carbo-h}'drates,  and  17.5  per  cent, 
cellulose. 

The  preparation  of  bread  depends  upon  the  fermentation  produced 
through  the  action  of  the  yeast-plant  in  rye-  or  wheat-meal  mixed  to  a 
thick  paste  with  water,  the  so-called  dough,  and  allowed  to  ferment  at 
about  30°  C.  Through  the  action  of  the  yeast  part  of  the  starch  is 
converted  into  dextrin  and  sugar,  of  which  a  part  again  undergoes 
further  decomposition  into  carbon  dioxide  and  alcohol.  The  bubbles  of 
the  former  serve  to  render  the  dough  light  and  porous.  In  baking  the 
gas-bubbles  expand  through  the  heat  and  render  the  bread  still  more 


FIG.  55.— SECTION  OF  A  WHEAT-GRAIN,  MAGNIFIED  610  DIAMETERS,  AFTER 

PEKAR.     (Thanhoffer.) 
1,  epidermis  ;  2,  epicarpium  ;  3,  endocarpium ;  4,  testa ;  5,  tegmen  ;  6,  perisperm  ;  1,  endosperm. 

porous,  and  therefore  more  permeable  to  the  digestive  juices  and  more 
readity  digestible,  while  in  the  action  of  the  heat  a  certain  amount  of 
starch  is  still  further  converted  into  dextrin  and  sugar.  The  nutritive 
properties  of  bread  depend  upon  the  starch,  dextrin,  sugar,  and 
albumen  which  are  contained  within  it.  Bread,  therefore,  contains  all 
the  nutritive  principles  in  some  amount,  as  a  certain  amount  of  oils  and 
inorganic  salts  are  also  present,  although  the  carbohydrates  are  present 
in  the  largest  proportion.  It  has  been  estimated  that  a  man,  to  obtain 
the  necessary  amount  of  albumen  required  for  his  daily  ration,  would 
have  to  consume  three  pounds  of  bread  daily. 

Oats,  rye,  and  corn  also  have  their  various  constituents  arranged 


166 


PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 


in  concentric  layers,  in  which  also  the  so-called  gluten-cells  are  to  be 
recognized,  as  well  as  numerous  free  starchy  granules.  The  relative 
proportions  of  the  different  constituents  vary  in  different  samples,  and 
hence  the  nutritive  value  of  these  grains  depends  upon  the  method  of 
cultivation,  etc.  Corn  and  rye  are  especially  rich  in  starch,  but  are 
poorer  than  wheat  in  albumen.  By  soaking  in  boiling  water, — the  only 
way  in  which  rice  is  used  as  a  food, — the  starch-granules  become  par- 
tially converted  into  soluble  starch,  through  the  rupture  of  the  cellulose 
membrane  and  solution  of  the  granulose  in  water.  So  prepared,  the 
starch  of  corn  and  rice  is  capable  of  being  entirely  absorbed,  while  only 
20  to  30  per  cent,  of  the  albuminous  matter  escapes.  Barley  and  oats 
are  food-constituents  which  are  especially  valuable  for  horses  when  a 
large  amount  of  nutritive  principles  in  a  concentrated  form  is  required. 
R}Te  is  poorer  in  albuminous  principles  than  wheat,  but  is,  nevertheless, 
a  valuable  food-stuff.  From  the  point  of  view  of  the  percentage  of 
albuminous  matter,  wheat  occupies  the  first  place  in  nutritive  value  of 
the  cereals.  In  1000  parts  135.58  parts  of  albuminous  matters  are 
present.  The  amount  of  starch  of  wheat  is  only  exceeded  by  the  carbo- 
hydrates found  in  corn  and  rice.  The  following  table,  after  Thanhoffer, 
shows  the  amounts  of  these  substances  present  in  1000  parts  of  the 
principal  cereals,  leguminous  plants,  and  tubers  : — 


In  1000  parts.      Wheat. 

Bye. 

Barley. 

Oats. 

Buckwheat- 
grits. 

Corn. 

Albumen,      135.37 

107.5 

122.5 

90.5 

78.0 

70.0 

Starch,           558.64 

555.0 

482.5 

503.5 

457.0 

637.0 

Dextrin,          46.5 

84.5 

. 

. 

. 

. 

Sugar,              48.5 
Cellulose,        32.5 

28.75 
49.5 

97.5 

116.5 

233.6 

Fats,                 .     . 

•     . 

'  ..'  *'• 

•     • 

5.9 

•      • 

In  1000  parts. 

Peas. 

Beans. 

Lentils. 

Potatoes. 

Albumen, 

223.5 

225.2 

265.0 

13.0 

Starch, 

. 

. 

. 

154.5 

From  the  above  table  it  is  seen  that  the  amount  of  starch  present 
in  rye  is  somewhat  less  than  that  of  wheat,  but  that  it  contains  nearly 
twice  as  much  dextrin ;  and  yet  the  cellulose,  which  is  almost  entirely  indi- 
gestible, is  in  larger  amount  than  in  wheat.  In  barley,  again,  there  is  usu- 
ally a  larger  amount  of  albuminous  matters  than  in  wheat,  but  also  three 
times  as  much  cellulose,  and  a  considerably  smaller  amount  of  starch. 
Barley  grown  in  Southern  latitudes  is  said  to  have  a  higher  percentage 
of  albuminous  matter  than  is  represented  above.  Oats,  again,  contain  a 
smaller  amount  of  albumen,  a  larger  amount  of  cellulose,  and  a  larger 
amount  of  starch  than  barle}^.  It  thus  falls  considerably  below  wheat 
in  albuminous  and  starchy  matters,  but  exceeds  wheat  in  the  amount 
of  cellulose  present.  Rape-seed,  again,  contains  twice  as  much  cellulose 
as  oats,  and  even  less  albumen  than  starch.  Corn  contains  the  smallest 


VEGETABLE  FOODS.  167 

amount  of  albuminous  matter  of  all  of  the  cereals,  but  a  larger  amount 
of  starch  than  any,  and  also  contains  a  considerable  quantity  of  oil,  and 
is  therefore  a  useful  food  for  fattening  purposes.  Rice  contains  only 
5  per  cent,  of  albuminous  matter  and  82  per  cent,  of  readily-digestible 
starch. 

The  nutritive  value  of  oats  is  very  largely  governed  by  the  character 
of  manure,  and  other  modes  of  cultivation.  The  composition  of  oat- 
grains,  according  to  Pott,  is  about  as  follows  :* 

Solids .  .  .86.3  per  cent. 

Proteids,  .         .         .         .        .        .  .  .12.0 

Fats,          .         .         .         .        .         .  .  .6.0 

Carbo-hydrates,        .        .        .        .  .  .56.6 

CeUulose,         .        .        ...  .  .      9.0 

Ash,          .        .        .        .        ,        .  .  .2.7 

The  nitrogenous  matters  of  oats  consist  in  part  of  albumen  (0.46 
to  2.3  per  cent.),  gliadin,  the  so-called  vegetable  casein,  the  latter  appear- 
ing to  be  almost  identical  with  gluten-casein  and  legumin.  In  addition, 
oats  appear  to  contain  a  nitrogenous  alkaloid,  the  so-called  avenine, 
which  possesses  the  property  of  acting  as  a  nerve  stimulant.  This  is 
more  abundant  in  darker  sorts  of  oats,  its  amount  depending  upon  con- 
ditions of  climate,  soil,  etc.  It  may  amount  to  0.9  per  cent.  It  also  has 
been  found  by  Ellenberger  and  Hofmeister  that  oats  contain  at  least  three 
ferments, — an  amylolytic,  a  proteolytic,  and  a  lactic  acid  ferment.  These 
ferments  are  destroyed  by  the  temperature  of  boiling  water,  but  in  the 
stomach  of  the  domestic  animals  exert  their  activity,  and  are  to  be 
regarded  as  important  factors  in  the  gastric  digestion  of  these  animals. 
The  most  active  of  these  ferments  is  the  starch  ferment.  It  has  been 
found  that  in  a  digestion  of  three  hours'  duration  with  water  2  per  cent, 
of  sugar  resulted  from  the  action  of  this  ferment  alone.  The  lactic  acid 
ferment  is  considerably  weaker,  and  it  is  stated  that  in  a  digestion  of 
three  hours'  duration  0.1  per  cent,  of  lactic  acid  was  formed,  while  0.2 
per  cent,  was  formed  in  seven  hours.  The  proteid  ferment  is  stated  to 
dissolve  from  0.5  in  three  hours  to  1  per  cent,  of  proteids  in  six  hours. 
These  results  were  obtained  by  the  simple  digestion  of  a  mixture  of  oats 
and  water,  kept  at  the  temperature  of  the  body.  They  have  a  practical 
application  to  the  subject  of  digestion  as  occurring  in  animals,  and  point 
to  the  fact  that  in  disturbances  of  digestion  in  domestic  animals  the 
administration  of  vegetable  food  in  a  raw  state  is  preferable  to  its  use 
after  boiling,  and  will  further,  perhaps,  explain  the  high  degree  of  digesti- 

*It  will  be  noticed,  in  comparing  the  different  tables  of  the  composition  of  vegetable 
fodders,  that  there  is  considerable  discrepancy  in  the  percentages  given  of  the  different 
nutritive  principles.  This  is  to  be  accounted  for  by  different  effects  of  cultivation,  etc., 
in  the  various  samples  analyzed. 


168 


PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 


bility  possessed  by  oats.     Wolff  has  found  the  following  amounts  to  be 
digested  of  the  different  constituents  of  oats : — 

Proteids.  Fats.  Carbo-hydrates. 

Ruminants,    .     77.3  per  cent.     82.4  per  cent.     73.7  per  cent. 
Horses,  .        .     86.0        "  77.6       "  76.3       " 

The  carbo-hydrate  constituents  of  oats  are  represented  principally 
by  starch,  although  from  3  to  6  per  cent,  of  sugar,  1.25  to  4.51  per  cent, 
of  gum  and  dextrin  have  been  found.  Oats  are,  above  all,  the  best  force- 
developing  food  for  horses, — a  fact  which  is  universally  recognized.  To 
foals  at  first  only  crushed  oats  should  be  given,  the  transition  to  whole 
oats  being  only  gradually  accomplished.  Oatmeal  is  also  a  good  addition 
to  the  food  of  milk  cattle,  and  is  said  to  increase  both  the  amount  of 
milk  and  the  amount  of  butter.  As  a  fattening  food  for  cattle  oats  are 
not  preferable  to  other  cereals.  In  the  natural  form  oat-grains  are  not, 
as  a  rule,  sufficiently  masticated  by  the  ruminants,  and  therefore  their 
maximum  nutritive  properties  are  not  appropriated.  It  is  therefore  the 
custom  to  feed  oats  to  these  animals  either  crushed  or  in  the  form  of  oat- 
meal. Sheep,  which  as  a  rule  masticate  their  food  better  than  other  rumi- 
nants, are  for  this  reason  capable  of  digesting  larger  amounts  of  oats. 
Oats  are  also  a  valuable  food  for  birds.  In  Pomerania  geese  are  fattened 
almost  solely  on  this  food.  It  has,  however,  the  disadvantage  of  causing 
a  thin  and  unpleasant  adipose  tissue  in  these  animals.  In  America  oats 
are  roasted  with  suet,  and  it  is  stated  that  hens  fed  on  this  food  are 
especially  prolific.  Oatmeal  is  richer  in  cellulose  than  the  other  meals, 
but  it  is  also  at  the  same  time  richer  in  proteids  and  fats.  The  average 
composition  of  oatmeal,  according  to  J.  Konig,  is  about  as  follows  : — 


Water, 

Proteids,   . 

Fats, 

Sugar, 

Gum  and  dextr  n, 

Starch, 

Cellulose, 

Ash,  . 


10.1  per  cent. 
14.3       •• 

5.7 

2.3 

3.1 
60.4 

2.2 

2.0 


Oatmeal  is  especially  valuable  as  an  accessory  food  in  the  nourish- 
ment of  young  animals,  especially  young  dogs,  when  it  may  be  mixed 
with  milk. 

Oat-straw  has  the  following  composition  (Pott)  : — 


Solids, 
Proteids, 
Fats, 
Carbo-hyd 
Cellulose, 
Ash,  . 

rates, 

? 

86.6  per  cent. 
3.3 
1.4 
42.5 
33.3 
6.2 

It  is  the  most  nutritious  of  the  cereal  straws.    Ruminants  digest  of 
the  proteid  matters  40.7,  fats  30.1,  carbo-hydrates  45.5  per  cent. 


VEGETABLE  FOODS.  169 

In  the  form  of  chopped  fodder  it  is  a  valuable  addition  to  the  food 
of  the  ruminants  and  horses.  Care  must  be  taken  that  the  straw  has  not 
been  kept  in  a  moist  place  ;  otherwise,  when  fed  to  milk  cattle,  an  unpleas- 
ant taste  will  be  given  to  the  milk. 

It  has  been  stated  that  of  all  the  cereals  oats  are  the  richest  in  oil 
and  albuminoids,  according  to  Mr.  Richardson  (Amer.  Chem.  Journ., 
October,  1886),  the  average  for  the  former  being  8.14,  and  for  the  latter 
14.31  per  cent.  The  composition  may  be  placed  as  follows,  in  its  dis- 
tribution in  the  kernel  and  hull : — 

Kernel.  Hull.       Whole  Grain. 


Water, 

.      4.85 

1.57 

6.42 

Ash,    .... 
Oil,      .... 
Carbo-hydrates, 
Crude  fibre, 
Albuminoids, 

.       1.50 
.      5.70 
.     46.96 
.      0.97 
.     10.02 

1.68 
0.24 
20.41 
5.36 
0.74 

3.18 
5.94 
67.37 
6.33 
10.76 

70.00  30.00          100.00 

It  is  thus  seen  that  Richardson's  analysis  of  American  oats  differs 
from  that  given  by  other  authorities.  He  places  the  percentage  of  water 
lower  than  that  of  other  aualysists,  whilst  'the  principal  increase  of 
solids  is  found  in  the  oil  and  inorganic  constituents,  his  estimation  of 
proteids  agreeing  with  that  of  others.  The  constituents  of  oats  are, 
however,  very  greatly  subject  to  the  climate  in  which  they  are  grown, 
and  Mr.  Richardson  has  found  the  average  albuminoids  in  the  grains 
distributed  as  follows  over  the  different  sections  of  the  United  States : — 

Northern  States, 10.96  per  cent. 

Southern  States, 10.66       " 

Pacific  Slope 9.60      " 

Atlantic  Slope, 10.76      " 

Western  States, 11.24      " 

These  figures  are,  however,  dependent  upon  the  percentage  of  husk, 
and  not  on  peculiarities  of  their  kernel,  and  therefore  the  proportion  of 
husk  to  kernel  and  the  compactness  of  the  grain  prove  to  be  the  most 
important  factors,  and  the  weight  per  bushel  the  best  means  of  judging 
of  the  value  of  the  grain.  Oats  having  the  husk  are  necessarily  heavier 
in  weight  per  one  hundred  grains.  The  heaviest  oats  are  from  the  Pacific 
Slope,  and  the  South  ranks  next,  owing  to  the  large  size  of  the  grain. 
In  weight  per  bushel,  however,  the  fluffy  husk  of  the  Southern  grain  makes 
it  the  lowest  in  the  country,  while  the  Pacific  Slope  contains  the  highest 
weight  per  bushel,  as  also  in  size  and  weight  per  hundred,  showing  the 
grain  to  be  plump  and  well-filled.  The  heaviest  weights  per  busliel 
determined  by  Mr.  Richardson  were  found  in  specimens  from  Colorado 
and  Dakota,  weighing  48.8  and  48.6  pounds.  The  lightest  were  from 
Alabama  and  Florida,  24.7  and  26.9  pounds,  respectively.  He  found  an 


170 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


average  of  37.2  pounds,  the  common  legal  weight  being  32  pounds  to  the 
bushel. 

Of  the  group  of  hordeum  (barley)  various  representatives  are  useful 
as  green  fodder,  but  more  especially  their  grains  and  straw.  The  com- 
position of  barley -grains  is  greatly  modified  by  the  locality  of  growth 
and  mode  of  cultivation.  The  following  represents  about  the  average 
composition : — 

Solids; .  86.2  per  cent. 

Nitrogenous  bodies,          .        .        .  .  11.2 

Fats, 2.1 

Non-nitrogenous  bodies, 65.5 

Cellulose, 5.2 

Ash, 2.2 

The  proteids  of  barley  consist  in  a  large  part  of  gluten-casein, 
gluten-fibrin,  mucedin,  and  albumen.  No  gluten  can  be  obtained  from 
barle3^-meal.  The  carbohydrates  consist  of  starch,  from  1  to  2^  per  cent, 
sugar,  and  1  to  7  per  cent,  dextrin.  The  digestibility  of  the  barley-grain 
is  placed  by  Wolff  as  follows : — 


Proteids,  . 

Fats, 

Carbo-hydrates, 


Ruminants. 
77  per  cent. 
100 

87       " 


Horses. 

80.3  per  cent. 

42.4  " 
87.3 


Hogs. 

78.2  per  cent. 
68.4       " 
90.0      " 


The  barley- grains  are,  therefore,  readily  digestible,  and  in  the  form 
of  meal  form  a  food  of  the  first  class  in  nutritive  properties  for  cattle, 
and  are  especially  valued  for  the  good  influence  which  they  exert  on  the 
quality  and  quantit}^  of  the  milk  and  butter.  For  horses  also  they  may 
be  used  to  a  certain  extent  as  a  substitute  for  oats,  given  in  the  entire 
form,  mixed  with  chopped  straw.  To  old  horses  or  foals,  on  the  other 
hand,  barley  should  be  given  as  meal,  or  after  being  crushed.  It  has 
been  .stated  that  if  the  barley-grains  are  swallowed  whole  they  swell  up 
in  the  stomach,  and  may  produce  serious  colic.  Therefore,  the  animals 
should  receive  water  about  half  an  hour  before  being  fed  with  barley- 
grains.  The  Arabs  make  Use  of  barley  almost  solely  as  food  for  their 
horses,  and  administer  it  in  the  entire  condition.  Barley-meal  has  the 
following  composition : — 


Solids, 
Proteids,    . 
Fats, 

Carbo-hydrates 
Cellulose, 
Ash,  . 


87.7  per  cent. 
11.6 

3.6 
52.0 
14.3 

6.2 


Barley-meal  is  frequently  adulterated  with  various  mineral  sub- 
stances, such  as  cla}^,  chalk,  or  plaster,  which  may  cause  it  to  prove 
hurtful.  Such  adulterations  may,  however,  be  readily  recognized  by 
microscopic  examination.  Barley-straw,  especially,  as  is  often  the  case, 


VEGETABLE  FOODS. 


171 


if  grown  with  clover,  forms  one  of  the  best  of  the  cereal  straws,  the 
straw  of  winter  barley  being,  however,  the  poorest  in  nutritive  substances 
of  any  form  of  straw.'  The  following  is  the  composition  of  barley-straw : — 


Solids,       ..        ; 

Nitrogenous  matters 

Fats, 

Non-nitrogenous  extractive  matter  , 

Cellulose,  . 

Ash,  . 


85.7  per  cent. 

3.4       " 

1.4 
34.7 
41.8 

4.4       <«     '- 


The  following  is  the  composition  of  barley-straw  when  grown  with 

clover : — 

Solids,        ...  .  85.7  per  cent. 

Nitrogenous  bodies,  .  6.5  " 

Fats,  ..;-...  .  2.0  " 

Non -nitrogenous  extractive  matters,  32  5  " 

Cellulose,  ...  .  38.0  " 

Ash,  ....  .  6.7  " 

Barley-straw,  therefore,  grown  with  clover,  almost  approaches  an 
average  hay  in  nutritive  value.  The  ruminants  digest  the  following 
amounts  of  the  different  constituents  of  barley-straw : — 


Proteids, 

Fats,     .        .  •     . 

Non -nitrogenous  extractive  matters, 


20  per  cent. 
41.6     " 
54.1     ". 


Barley-bran  agrees  in  its  general  properties  with  the  bran  of  the 
better  cereals.  It  contains — 

Solids, 85. 8  per  cent. 

Proteids, 3.1 

Fats, 1.5 

Carbo-hydrates, 38.5 

Cellulose, 30.3 

Ash, 12.4 

Barley-bran  frequently  contains  large  quantities  of  the  barlej'-bristles, 
and  should  then  only  be  given  to  animals  after  being  boiled  or  steamed. 
Given  dry,  the  bristles  stick  in  the  tongue,  and  produce  inflammatory 
reaction.  Steamed  barley  also  is  a  valuable  food.  By  malting,  the  barley 
undergoes  mechanical  and  chemical  alterations  which  lead  to  the 
increase  in  its  digestibility,  and,  although  the  starch  is  turned  into  sugar, 
there  is,  nevertheless,  in  the  process  of  malting  a  loss  in  nutritive  con- 
stituents of  the  total  solids,  especially  of  the  nitrogenous  bodies.  In 
sprouting  there  is  likewise  a  loss  of  proteids,  carbo-hydrates,  and  fats. 

Buckwheat  is  often  used  as  a  green  fodder,  and  its  grain  is  fre- 
quentty  administered  as  dry  food.  The  green  buckwheat  contains — 


Solids,          .        *        .        . 

Proteids 

Fats, 

Non -nitrogenous  extractive  matters, 

Cellulose, 

Ash, 


15.0  per  cent. 
2.4 
0.6 
6.4 
4.2 
1.4 


172 


PHYSIOLOGY   OF   THE  DOMESTIC  ANIMALS. 


In  digestibility  the  green  buckwheat  is  almost  comparable  to  clover, 
but  contains  a  much  larger  percentage  of  water,  and  is  not,  therefore, 
well  suited  to  constitute  the  sole  food  for  cattle.  When  given  to  cattle 
not  more  than  fifty  kilogrammes  per  thousand  kilogrammes  body  weight 
can  be  given,  the  remainder  of  the  food  consisting  of  dry  food.  On  feed- 
ing with  buckwheat  the  milk  and  the  butter  assume  a  beautiful  yellow 
color.  The  green  buckwheat  is  entirely  unsuitable  for  sheep  and  hogs, 
either  freshly  mown  or  for  grazing,  and  in  them  frequently  causes  serious 
disturbances.  On  account  of  its  large  percentage  of  water  it  is  only 
suitable  for  horses  as  an  accessory  food.  The  conversion  of  the  green 
buckwheat  into  hay  offers  great  difficulty  on  account  of  its  large  percent- 
age of  water.  The  grains  of  buckwheat  are  principally  used  as  food. 
They  contain — 

Solids, 
Proteids, 
Fats,  . 


Non-nitrogenous  extractive  matters 

Cellulose, 

Ash,   . 


86.8  per  cent. 
10.1 

1.5 
59.5 
15.0 

1.8 


They  are  thus  not  especially  rich  in  nitrogenous  matters  and  contain 
large  amounts  of  cellulose,  and  belong,  therefore,  to  the  more  indigestible 
cereals,  but  form  a  good  additional  food  for  draught  horses,  sheep,  milk 
cattle,  and  fattening  cattle.  When,  however,  given  in  large  amounts  to 
ruminants  and  hogs,  they  are  apt  to  produce  very  serious  disturbances, 
especially  in  summer.  In  winter,  on  the  other  hand,  the  buckwheat  is 
less  hurtful  a  food,  though  it  is  advisable  to  cease  its  administration  at 
least  two  weeks  before  grazing  commences.  Buckwheat-meal  contains — 


Solids,      .   .        . 

Proteids, 

Fats,    . 

Non -nitrogenous  exti active  matters 

Cellulose,    . 

Ash,    .        ... 


84.0  per  cent. 
15  0       " 

35  " 
43.0  " 
19.0  " 

3.4      " 


Buckwheat-meal  is,  therefore,  relatively  rich  in  proteids,  and  in  spite  of 
its  considerable  amount  of  cellulose  is  a  good  fattening  food  for  hogs.  It 
is  frequently  adulterated  with  the  seeds  of  various  weeds.  Buckwheat- 
straw  belongs  to  the  most  useful  of  this  class  of  fodders.  It  contains — • 


Solids, 

Proteids, 

Fats,  . 

^Non-nitrogenous  extractive  matters, 

Cellulose, 

Ash,  . 


89.9  per  cent. 

4.1 

1.4 
32.9 
44.3 

5.0 


It  contains  somewhat  more  cellulose  than  most  of  the  straws  of  the 
different  cereals,  and  is,  therefore,  perhaps  more  indigestible,  but  it  is 
also  richer  in  proteids. 


VEGETABLE  FOODS. 


173 


2.  The  LEGUMINOUS  PLANTS  stand  next  in  nutritive  value  to  the 
cereals.  They  are  composed  of  the  peas,  beans,  and  lentils.  By  boiling 
with  water  their  hulls  become  ruptured,  and  their  contents  readily  sub- 
jected to  the  action  of  the  digestive  juices.  The  leguminous  plants  are, 
therefore,  principally  used  in  the  form  of  soups  or  broths. 

The  hulled  fruits  contain  a  maximum  of  albuminous  matters,  and 
the  kernels  of  oily  fruits  more  fats  than  the  cereals. 

Beans  are  seldom  used  as  green  fodder,  or  as  the  principal  article  of 
diet,  since  they  are  too  rich  in  nitrogen ;  they  form,  however,  an  admi- 
rable addition  to  the  diet  of  cattle,  sheep,  and  horses. 

Peas,  both  as  a  green  fodder  and  as  grain,  form  highly  nutritive 
foods.  Green  peas  are  especially  good  as  a  food  for  milk  cattle,  and  give 
a  pleasant  taste  to  the  butter.  Dried  peas  are  also  highly  digestible 
and  nutritious.  They  contain — 


Solids, 
Proteids, 
Fats, 
Non-nitrog 
Cellulose, 
Ash,  . 

enou 

s  ext 

racti 

ve  mattei 

s, 

86.8  per  c 
22.4 
3.0 
52.6 
6.4 
2.4 

Of  these  nutritive  principles — 

Proteids. 


Fats. 


Non-nitrogenous 
Extractive  Matters. 


Ruminants  digest  88. 9  per  cent.     74.7  per  cent.     93. 3  per  cent. 
Horses  "        83.0       "  6.9      "  89.0       " 

Hogs  "        85.0  to  90  36.0  to  67  95.0  to  99 

The  grains  are  best  given  chopped  up  with  straw,  when  they  form  an 
excellent  food  for  draught  horses,  of  which  amounts  equivalent  to  half  of 
the  ordinary  corn  ration  may  be  given.  They  are  also  a  fattening  food 
of  the  first  rank  for  hogs,  and,  like  barley,  greatly  improve  the  character 
of  their  fat  and  flesh.  When  given  in  large  amounts  to  milk  cattle,  they 
are  apt  to  make  the  butter  too  hard.  The  straw  of  peas  is  also  readily 
digestible,  and  of  good  pea-straw  ruminants  digest  60.5  per  cent,  of  pro- 
teids,  45.9  per  cent,  of  fats,  and  64.4  per  cent,  of  non-nitrogenous  extract- 
ives. When  in  good  condition,  pea-straw  may  even  serve  as  a  substitute 
for  hay  for  j'oung  cattle.  For  milk  cattle  but  small  amounts  should  be 
given,  or  else  the  quantity  of  milk  will  be  reduced.  Unfortunately,  pea- 
straw  is  apt  to  be  contaminated  with  that  of  various  weeds  and  fungi. 

The  following  table  gives  the  average  composition  of  the  principal 
representatives  of  this  group,  as  contrasted  with  the  potato: — 


In  100  parts. 
Water,     . 
Albumen, 
Fats 

Lentils. 
.     12.5 
.     24.8 
.       1.9 

Peas. 
14.3 
22.6 

1.7 

Beans. 
14.8 
23.7 
1.6 

Potatoes. 
76.0 
2.5 
0.2 

Carbo-hydrates, 
Cellulose, 
Ash, 

.     54.8 
.      3.6 
.      2.4 

53.2 
5.5 

2.7 

49.3 
7.5 
3.1 

20.2 
0.4 
0.5 

174 


PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 


3.  BULBS  and  BOOTS,  represented  by  the  potato,  beets,  etc.,  constitute 
another  group  of  vegetable  foods. 

Potatoes  are  of  very  much  less  nutritive  value  than  either  of  the 
preceding  groups  of  foods,  from  the  fact  that  they  contain  but  a  small 
amount  of  albuminous  matters,  but  a  very  large  amount  of  starch.  Large 
amounts  of  water  are  present  in  bulbs  and  roots  which  serve  as  food,  with 
small  amounts  of  solids  (86  to  14).  Of  the  solids,  the  carbo-hydrates 
constitute  80  per  cent,  or  more,  while  the  other  nutritive  substances 
and  inorganic  salts  are  in  proportionately  small  amount.  Even  of  the 
amount  of  albumen  present  only  about  one-fourth  appears  to  be  capable 
of  digestion  in  the  alimentary  canal. 

In  the  vegetables,  such  as  beets,  asparagus,  and  cabbages,  there  is  a 
large  per  cent,  of  water, — from  80  to  90  per  cent., — but  only  2  per  cent,  of 
albuminous  matter,  2  to  4  per  cent,  of  starch  or  gumni}^  substances,  a 
small  amount  of  sugar,  and  1  to  1.5  per  cent,  of  cellulose.  Their  nutritive 
value  is  therefore  slight. 

Fodder-beets  (Beta  vulgaris,  mangold-beets),  of  which  a  large  variety 
is  met  with,  form  valuable  articles  of  fodder,  those  with  the  round  roots 
being  usually  more  rich  in  nutritive  constituents.  The  nutritive  qualities 
of  beets  are  further  increased  by  the  character  of  the  soil  and  climate, 
mode  of  culture  and  manuring,  and  are  especially  proportional  to  the 
slowness  with  which  they  are  grown.  Fodder-beets  have,  as  a  rule,  the 
following  constituents : — 


Solids, 
Proteids,     . 
Fats,  . 

Carbo-hydrates, 
Cellulose,  . 
Ash,   .        .       ", 

Sugar-beets  contain — 


12.0  per  cent. 
1.1 
0.1 
9.1 
0.9 
0.8 


Solids,        ... 18.5  per  cent. 

Proteids, 1.0 

Fats, 0.1 

Carbo-hydrates, 15.4 

Cellulose,  .        .        .    • 1.3 

Ash, 0.7 

The  principal  difference,  therefore,  between  fodder-beets  and  sugar- 
beets,  is  found  in  the  larger  percentage  of  solids  in  the  latter,  consisting 
principally  in  the  greater  amounts  of  sugar.  The  percentage  of  sugar 
is  further  increased  by  potassium  manures,  and  is  greater  in  beets  grown 
in  cold,  high  localities  than  in  warm  places.  It  also  is  in  proportion  to 
the  length  of  time,  after  growth  is  complete,  that  the  beets  are  kept  in 
the  ground,  especially  when  they  have  sprouted.  Nitrogenous  manures 
and  manures  rich  in  phosphates  increase  the  proteid  constituents  of  the 
beets,  although  all  the  nitrogen  in  the  beets  is  not  to  be  recorded  as 


VEGETABLE  FOODS.  175 

proteid.  Nitrate  of  potassium,  nitric  and  oxalic  acids,  magnesia  and 
other  alkalies  are  constituents  of  beets,  and  will  often  explain  the  pur- 
gative action  exerted  by  many  forms  of  beets.  As  regards  digestibility, 
Wolff  has  found  that  the  ruminants  digest  of  sugar-beets — proteids  62.0, 
carbo-hydrates  95.2  per  cent. ;  of  fodder-beets — proteids  75.6,  carbo- 
hydrates 95.3  per  cent. 

These  experiments  would  seem  to  show  that  sugar-beets  are  less 
digestible, — a  state  of  affairs  which  hardly  seems  probable.  On  account 
of  the  large  percentage  of  water  beets  contain  they  can  only  be  used  as  a 
fodder  with  certain  restrictions.  They  are  best  given  in  the  raw  state, 
chopped  up  into  pieces,  although  the  chopping  must  not  be  too  fine  ;  other- 
wise mastication  and  thorough  mixing  with  the  saliva  will  be,  to  a  large 
extent,  prevented.  They  are  especialty  suited  for  milk  cattle,  combined 
with  dry  foods,  twenty-five  kilogrammes  being  given  daily,  and  will  serve 
to  improve  the  amount  and  quality  of  the  butter  and  milk. 

Sugar-beets  cannot  be  given  in  as  large  an  amount  as  fodder-beets, 
on  account  of  their  higher  percentage  of  nutritive  principles.  For  young 
cattle,  as  well  as  sheep,  on  account  of  their  large  percentage  of  water, 
but  small  amounts  may  be  given.  Thus,  one-third  to  one-half  of  the  total 
food  for  these  animals  may  consist  of  chopped-up  raw  beets.  For  hogs 
the  beets  may  serve  as  the  principal  food,  especially  when  given  boiled, 
although  here  also  they  may  act  as  a  purgative,  and  it  is  better  that  the 
food  should  not  be  more  than  one-half  constituted  of  the  beets.  For 
horses,  beets,  on  account  of  their  high,  percentage  of  water,  are  only 
exceptional^  employed.  Beets  are  best  -preserved  by  placing  under  the 
ground  directly  after  harvesting,  care  being  taken  to  select  a  perfectly 
dr\T  localit}^.  Beet-top  leaves  are  also  v«ry  frequently  used  as  fodders. 
Fresh  beet-leaves  contain — 

Solids, 10.7  per  cent. 

Nitrogenous  matters, 2.2 

Proteids, 0.4 

Carbo-hydrates, 4.8 

Cellulose, 1.5 

Ash, 1.8 

On  account  of  the  large  percentage  of  water  and  oxalic  acid  con- 
tained within  them,  beet-tops  frequently  act  as  violent  purgatives.  They 
are,  however,  rich  in  proteids,  and  are  quite  as  digestible  as  the  best  fresh 
hay,  and  in  their  fresh  condition  are  suitable  in  small  amounts  for  feeding 
to  milk  cattle.  If,  however,  they  be  given  in  excessive  amounts,  or  con- 
stitute the  sole  food  of  milk  cattle,  the  percentage  of  fat  in  the  milk 
undergoes  a  rapid  decrease.  Not  more  than  one-third  of  the  total  amount 
of  food,  therefore,  should  be  constituted  of  beet-tops. 

4.  GRASSES. — In  addition  to  the  above  nutritive  substances,  domestic 
animals  may  be  nourished  on  the  various  grasses,  hays,  bran,  and  straw. 


176 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


The  following  table  gives  the  average  composition  of  different  members 
of  this  group: — 


In  100  parts.                                 Prairie  Hay. 

wy 
Best. 

e-»rraw. 
Ordinary. 

Grass. 

Water,          .        ...        .        .     130 

13.8 

18.6 

75.0 

Albumen,    .        ..           .                             9.5 

3.9 

1.5 

3.0 

Fats,     . 

3.1 

1.0 

1.5 

0.8 

Carbo-hydrates  and  n 
extractive  matters, 

on-n 

trog( 

nous 

40.9 

34.7 

32.4 

13.1 

Cellulose,     .        . 

26.7 

40.1 

43.0 

6.0 

Ash,              .        . 

6.8 

6.5 

3.0 

2.1 

Esparcet  (Onobrychis  saliva}  is  one  of  the  most  digestible  and  valu- 
able of  the  different  forms  of  clover,  and  may  be  regarded  as  a  type  of 
this  group.  Mowed  during  the  blossoming,  it  contains  in  the  green  state  : 


Solids,        .        .        . 

.     21.  5  DCI 

•  cent. 

Nitrogenous  substances,  . 
Fats  
Non-  nitrogenous  extractive  matters, 
Cellulose,  .        .        .        .        . 
Ash,  ..''... 

3.5 
0.7 

8.5 
7.6 
1.2 

According  to  Wolff,  its  digestibility  in  the  ruminants  is  as  follows  : — 


Proteids. 
72.5  per  cent. 

Esparcet-hay  contains — 


Fats. 
66.7  per  cent. 


Solids,        .        . 

Nitrogenous  matters, 

Fats,.         .      •  .  "••   .    • 

Non -nitrogenous  extractive  matters, 

Cellulose, . 

Ash,. 


Non-nitrogenous 
Extractive  Matters. 

78.3  per  cent. 


85.1  per  cent. 
13.3 
2.5 
34.5 

29.0 
5.8 


All  forms  of  fodder  undergo  in  time  considerable  deterioration  in 
the  amounts  of  their  nutritive  constituents,  especially  if  preserved  in 
localities  where  the}'  are  accessible  to  the  air,  moisture,  light,  and  warmth. 
Fermentative  processes  are  started  up  by  the  presence  of  various  forms 
of  the  lower  organisms  and  occasion  a  reduction  in  both  the  non-nitrogen- 
ous and  proteid  constituents  of  fodders.  Thus,  prairie  hay,  when  fresh, 
has  a  nitrogenous  percentage  of  1.81  per  cent.,  while,  if  kept  for  two 
years,  it  falls  to  1.68.  So  long  a  time  as  this  is,  however,  not  necessary 
for  the  evidence  of  considerable  loss  of  nutritive  principles.  Thus,  Wolff 
has  found  the  constituents  of  second-crop  hay  to  vary  as  follows : — 


Proteids,    ....        . 
Fats,.         .        ...     ,. 

Cellulose, 

Non-nitrogenous  extractive  matters, 


In  December. 

14.36 

.       4.01 

26.44 


XNon-niirogeiious  exiraciive  mailers,         .     40 
Inorganic  constituents,     ....      9 


45.71 

,48 


In  April. 

14.34 

4.24 

27.18 

44.80 

9.44 


VEGETABLE   FOODS.  177 

The  more  the  fodders  are  protected  from  the  air,  the  less  will  be  the 
loss.  Thus,  it  has  been  found  that  corn  kept  in  an  open  space  free  to  the 
air  will  form  in  a  given  time  twice  as  much  carbon  dioxide  as  if  kept  in  a 
closed  space, — of  course,  it  being  evident  that  the  greater  the  formation 
of  carbon  dioxide,  the  greater  will  be  the  loss.  The  moister  the  locality, 
also  the  greater  will  be  the  deterioration  in  nutritive  qualities.  Thus, 
oats  in  thirty  months  will  lose  7.2  per  cent,  more  of  their  solids  than  oats 
kept  in  closed  vessels.  Similar  facts  also  apply  to  the  preservation  of 
the  moist  fodders,  such  as  potatoes,  beets,  and  green  fodder.  Sprouting 
of  potatoes  and  beets  is  likewise  accompanied  by  great  loss  of  nutritive 
substance,  and  the  presence  of  solan ine  in  a  sprout  may  even  cause  it  to 
become  poisonous.  Thus,  Krammer  has  found  that  in  potatoes  with  the 
sprout  from  1  to  2  cm.  long  there  is  a  loss  of  3.18  per  cent,  of  starch, 
when  the  sprout  is  2  to  3  cm.  long  a  loss  of  5.26,  and  when  it  reaches  4  cm. 
in  length  there  has  been  a  loss  of  9.88.  Moulding,  likewise,  reduces  the 
amount  of  nutritive  substances,  in  addition  to  the  hurtful  action  of  the 
moulds  themselves.  Thus,  in  sound  potatoes  there  will  be  an  average 
amount  of  solids  of  23.8  per  cent.,  while  mouldy  potatoes  will  average 
only  20.6  per  cent.  Age  of  fodders  not  only  occasions  loss  in  absolute 
amounts  of  nutritive  \constituents,  but  also  diminishes  their  relative 
digestibility.  Thus,  Hofmeister  has  found  that  sheep  which  will  digest 
of  clover-hay,  when  half  a  year  old,  68.4  per  cent,  of  proteids  and  73.4  per 
cent,  of  carbo-hydrates,  when  one  year  old  will  digest  only  65.0  per  cent, 
of  proteids  and  63.1  per  cent,  of  carbo-hydrates,  and  when  four  years  old 
50.7  per  cent,  of  proteids  and  40.7  per  cent,  of  carbo-hydrates.  The  same 
facts  apply  likewise  to  other  forms  of  hay. 

The  preservation  of  grain  by  stowing  it  in  close  chambers  is  a  very 
ancient  one.  The  process  of  ensilage  as  at  .present  carried  out  is  per- 
formed simply  by  placing  green-fodder  crops,  such  as  grass,  clover, 
vetches,  etc.,  in  an  air-tight  chamber  of  almost  any  construction,  and, 
after  treading  the  mass  down,  covering  it  with  boards  on  which  pressure 
is  exerted,  either  by  dead  weights  or  mechanical  means.  The  grass  or 
other  substance  may  be  chopped  if  thought  desirable,  and  salt  may  also 
be  added.  When  preserved  in  this  manner  grass  may  be  kept  for  a  long 
time,  and  will  produce,  when  opened,  a  food  resembling  steamed  hay 
which  is  greedily  consumed  by  cattle.  The  whole  loss  occasioned  by 
this  process  is  but  small,  and  the  process  of  change  occurring  in  food  so 
preserved  has  been  carefully  studied  by  Mr.  A.  Smetham.  He  found  that 
fermentation  of  various  kinds  had  occurred,  and  he  was  able  to  detect  a 
small  quantity  of  alcohol,  as  well  as  various  acids,  of  which  acetic,  lactic, 
and  butyric  were  the  chief.  The  amount  of  the  acids  was  not  sufficiently 
great  to  render  the  silage  unfit  for  food,  and  the  practical  results  of 
feeding  with  it  were  decided!}7  satisfactory.  By  allowing  the  temperature 

12 


178  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

to-  rise  above  125°  F.  the  ferments  are  destroyed  and  the  production 
of  organic  acids  thus  largely  prevented,  and  a  sweet  silage  is  produced 
which  possesses  the  characteristics  of  old  hay  to  a  much  more  marked 
extent  than  by  the  old  or  "sour"  process.  This  process  is  especially 
valuable  in  wet  seasons  as  a  means  of  preserving  the  crop.  It  is  also 
invaluable  for  preserving  second  crops.  A  succulent  food  is  obtained  in 
place  of  a  dry  one  with  but  little  loss  in  nutritive  constituents ;  certainly 
less  than  occurs  during  hay-making  in  wet  weather,  although  there  is  but 
little  increase  in  the  digestibility  of  the  grass. 

Vegetable  matters  all  contain  from  two  to  eight  times  as  much  potas- 
sium as  sodium,  and,  as  we  shall  again  refer  to  under  the  subject  of 
Nutrition,  explains  the  fact  that  the  herbivorous  animals  need  an  extra 
ration  of  sodium  chloride. 

Straw  is  difficult  to  digest,  is  only  but  slightly  nutritive,  and  requires 
large  quantities  of  the  digestive  secretions  for  the  solution  of  its  nutri- 
tive constituents.  Straw  is  somewhat  more  readily  digested  by  the 
ruminants  than  by  the  horse.  Straw,  of  different  kinds,  has  about  the 
following  composition  : — 


Water, 
Albuminous  bodies,  . 
Fats,  .... 
Extractive  matter  and 
hydrates, 

Barley- 
Straw. 

.     14.3 
.       3.0 
.       1.4 
carbo- 
.     31.3 

Oat- 
Straw. 

14.3 
2.5 

2.0 

36.2 

Pea- 
Straw. 

14.3 
6.5 

2.0 

33.2 

Bean- 
Straw. 

17.3 

10.2 
1.0 

32.5 

Cellulose,  . 
Inorganic  matter, 

.     43.0 
.       7.0 

40.0 
5.0 

40.0 
4.0 

34.0 
5.0 

100.0      100.0      100.0      100.0 

Yery  frequently  various  forms  of  vegetable  food  will  produce  dis- 
turbances of  digestion  in  the  domestic  animals  from  the  mixing  with 
them  of  various  forms  of  adulteration,  or.  from  various  defects  in  the 
character  or  quality  of  the  food.  The  capability  of  recognizing  .this  in 
a  general  way  is,  therefore,  desirable.  Thus,  spoiled  hay  or  hay  which 
has  lost  its  inorganic  constituents  likewise  loses  its  normal  greenish  color, 
and  is  of  a  dirty-gray  or  brown  tint ;  while  acid  fermentation  or  putre- 
faction in  all  fodders  may  be  recognized  by  the  characteristic  odor  and 
taste.  Good  oats  must  be  clean  and  composed  of  perfectly-formed  mealy 
granules,  and  possess  a  certain  definite  specific  gravit}'.  Unripe  or 
frozen  oats  have  a  less  specific  gravity  and  a  less  nutritive  value,  while 
spoiled  oats  are  recognized  by  a  musty  smell  and  an  unpleasant,  burning 
taste.  The  quality  of  the  ha}^  will,  of  course,  depend  upon  the  quality 
of  the  ground  and  its  botanical  constituents,  the  time  of  cutting,  and 
the  mode  of  preservation.  In  order  to  judge  of  the  quality  and  nutri- 
tive value  of  hay  it  may  be  divided  into  three  different  groups.  In  the 
first  group  are  the  sweet  grasses  (graminese)',  in  the  second,  the  acid 


VEGETABLE  FOODS.  179 

grasses;  in  the  third,  all  other  grasses.  The  richer  the  hay  is  in  the 
sweet  grasses,  in  clovers,  and  leguminous  plants,  the  better  it  is.  The 
richer  it  is  in  acid,  marshy  grasses,  and  the  like,  the  poorer  it  is.  Hay 
cut  in.  summer  is  better  and  more  nutritious  than  that  cut  in  autumn,  and 
so  with  second  crop  or  after-cut.  In  the  latter  also  the  aromatic  hay- 
odor  is  wanting.  Hay  which  has  been  wet  by  the  rain,  so  losing  a  large 
part  of  its  inorganic  matters,  and  that  which  has  been  kept  for  several 
years,  has  but  little  more  nutritive  worth  than  straw.  Analysis  has  shown 
that  clover  and  prairie  ha3rs  which  have  been  exposed  to  the  rain  for  one 
or  two  weeks  may /lose  as  much  as  12  per  cent,  of  their  nutritive  matters. 
Hay  which  contains  poisonous  plants,  mud,  dust,  or  worms  or  cater- 
pillars, or  when  it  has  become  spoiled  by  putrefaction  or  fermentation, 
is  likewise  hurtful. 

In  the  manufacture  of  various  food-products  residues  are  often  left 
which  ma}'  be  of  considerable  nutritive  value  for  our  domestic  animals. 
Such  residues  have  a  somewhat  similar  composition,  usually,  to  that  of  the 
original  parts  of  plants  of  which  they  are  formed  ;  the  relative  proportions 
of  the  different  constituents  will,  however,  vary,  as  more  or  less  of  cer- 
tain substances  are  removed  in  the  process  of  manufacture.  Of  the  dry 
residues  the  various  milled  foods,  such  as  meals  and  flours  of  the  dif- 
ferent cereals,  are  the  most  important.  They  contain  usually  80  per 
cent,  of  solids.  The}^  are  especially  rich  in  albuminoids  (over  20  per 
cent.)  and  fats  (5.10  per  cent.),  and  are,  therefore,  valuable  adjuvants 
to  foods  which  are  poor  in  these  nutritive  principles. 

The  residue  from  beer-breweries  (beer-mash,  brewers'  grains)  is  also 
a  valuable  food.  It  contains  20.25  per  cent,  of  solids,  composed  largely 
of  albuminoids,  with  a  relatively  small  proportion  of  non-nitrogenous 
matters  (1:2),  somewhat  more  cellulose,  and  a  considerable  amount  of 
fat  and  inorganic  matter. 

Chemical  analysis  of  fresh  brewers'  grains  shows  the  following- 
average  composition  : — 

Solids,       .        .        .        ...        .        .  22  3  per  cent. 

Proteids, 4.6       " 

Fats,.         / 1.6       " 

Non-nitrogenous  extractives,  .        .         .  9.9       " 

Cellulose,          .         .        ...        .        .  5.0      " 

Assuming  that  73  per  cent,  of  the  proteids  is  digestible,  fat  84  per 
cent.,  extractives  64  per  cent.,  and  cellulose  39  per  cent.,  the  average 
amounts  of  digestible  matters  may  then  be  placed  as  follow : — 

Proteids,  .         .        .        •.        .        .        .        .      3.9  per  cent. 

Carbo-hydrates, 10  8 

Fats, 0.8      " 

The  proportion  of  nutritive  matter  may  thus  be  placed  as  1 : 3.4. 
The  fresh  residue  from  breweries  contains  a  large   percentage  of 


180 


PHYSIOLOGY  OF  THE   DOMESTIC  ANIMALS. 


water,  and  therefore  readil}'  decomposes  in  summer  in  a  few  hours, 
and  then  is  a  very  dangerous  fodder.  The  only  method  of  permanent 
preserving  is  by  drying,  and  this  necessitates  a  complicated  and  trouble- 
some process.  In  cool  weather  the  residue  may  be  preserved  for  one 
or  two  weeks  under  fresh  water.  Fresh  beer  residue  is  an  admirable 
fattening  food  for  both  cattle  and  hogs  and  for  milk  cows,  though  when 
sour  it  affects  both  the  quantity  and  quality  of  the  milk.  When  fresh  this 
food  is  not  so  well  suited  for  sheep  and  horses  as  when  dried ;  in  the 
latter  condition,  from  the  high  percentage  of  nitrogenous  constituents, 
it  is  comparable  to  the  cereals. 

The  residue  from  distilleries,  the  so-called  distillery  mash  or  swill, 
forms  a  valuable  article  of  fodder,  but  one  whose  composition  is  subject  to 
the  greatest  variations,  depending  upon  the  character  and  mode  of  treat- 
ment of  the  substance  manufactured.  All  such  residues  are,  in  their  natu- 
ral condition,  very  rich  in  water;  and  since  in  distillation  only  the  starch 
and  sugar  serve  for  the  production  of  the  spirits,  all  the  other  nutritive 
substances  remain,  with  slight  alteration,  in  the  residue  ;  so  that  the  solids 
of  the  latter  are  relatively  very  rich  in  nitrogen.  Most  of  these  residues 
in  their  fresh  condition  are  readil}7  devoured  by  the  domestic  animals, 
and  their  nutritive  effect  is  increased  by  administering  them  warm  and 
mixed  with  less  nutritive  substances,"  such  as  dry  fodders  rich  in  cellu- 
lose, which  are  less  readily  taken  by  cattle.  On  the  other  hand,  their  great 
richness  in  water  is  a  disadvantage  on  account  of  the  increased  demand 
for  nutritive  substances  so  occasioned.  The  high  percentage  of  water, 
soluble  proteids,  and  other  unstable  substances  in  distillery  residue 
leads  to  their  ready  decomposition,  or  souring,  in  which  condition  they 
are,  of  course,  not  suited  for  fodder,  on  account  of  the  disturbances  of 
digestion  and  alterations  of  milk  which  they  produce;  the  objection  to 
this  class  of  foods  is  largely  due  to  the  danger  of  using  a  spoiled  article. 
So  also  residues  from  which  the  spirit  has  not  been  entirely  removed  are 
likewise  hurtful  when  given  as  food.  The  most  common  of  these  resi- 
dues are  those  obtained  from  the  distillation  of  potatoes,  corn,  rye, 
beets,  and  malt. 

Potato  Residue. — The  residue  from  the  distillation  of  potatoes  will 
vary  greatly  in  the  percentage  of  nutritive  constituents  according  to 
the  more  or  less  complete  extraction  of  the  spirit, 
illustrates  this  : — 


The  following  table 


F 

Solids,       .    -     . 
Proteids,  .        .     '   . 
Fats, 
Non-nitrogenous  extract 
ive  matters,    . 
Cellulose, 
Ash, 

otato  Residue. 
3.8-8.7  ave 
0.8-1.9 
0.1-0.23 

1.1-5.6 
0.5-1.4 

rage  7.7 
1.1 
0.2 

4.6 
0.9 
07 

By  Hollef 
Proc 

6.05  pel 
1.14 
0.19 

3.56 
0.69 
0.70 

reund's 

ess. 

•  cent. 

VEGETABLE  FOODS.  181 

In  the  potato  residue  starch  has  been  largety  removed,  while  the 
other  constituents  remain  but  little  unchanged,  with  the  exception  that 
the  ferments  are,  of  course,  added  to  the  residue,  the  proteids  being  to  a 
certain  extent  changed  into  peptones.  Potato  residue  is  less  nutritive 
than  that  from  the  cereals,  and  is,  under  all  circumstances,  unsuitable  for 
constituting  the  sole  article  of  diet ;  since  it  is  not  only  too  watery  but 
too  poor  in  inorganic  materials,  especially  of  phosphates,- — an  objection 
which  does  not  apply  to  the  same  extent  to  the  residue  from  the  distilla- 
tion of  the  cereals.  Fresh  potato  residue,  in  which  condition  it  should 
alone  be  used,  sterns  to  assist  in  the  production  of  milk,  especially 
when  given  warm,  and  may  constitute  one-  or  two-thirds  of  the  total 
daily  ration,  the  remainder  being  composed  of  dry  fodder.  Fattening 
sheep  may  receive  from  two  to  ten  kilogrammes  per  one  hundred  kilo- 
grammes of  body  weight,  if  given  in  too  large  amounts,  seriously  affect- 
ing the  flesh  of  the  animal.  For  horses  potato  residue  is  in  general  too 
wratery,  and  only  animals  while  at  rest,  or  while  doing  light  work,  can 
stand  it.  In  using  this  article  of  food  care  should  be  taken  that  the 
potatoes  have  not  sprouted,  otherwise  they  will  contain  solanine,  and  in 
consequence  be  poisonous. 

Corn  Residue. — The  residue  remaining  after  the  distillation  of  corn 
is  richer  in  both  proteids  and  fats  than  that  from  potatoes.  It  contains — 

In  a  Fresh  Condition.  Pressed. 

Solids,    .        .        .                 .  9.4  per  cent.  28  4  per  cent. 

Proteids,        ....  2.0  8.6 

Fats,       .....  1.0  3.2 
Non  nitrogenous   extractive 

matters,       ....  4.9  12.7 

Cellulose,       ....  1.0  2.3 

Ash,       .....  0.4  1.5 

The  same  statements  apply  for  the  administration  of  these  sub- 
stances as  food  as  have  already  been  made  concerning  the  potato  residue. 
Milk  cattle  cannot,  however,  receive  more  than  thirty  kilogrammes  of 
this  daily,  since  it  will,  in  larger  amounts,  damage  the  character  of  the 
butter-fats;  while  they  ma}'  receive  as  high  as  fifty  kilogrammes  daily  of 
the  potato  residue. 

Eye  Residue. — The  residue  from  the  distillation  of  rye-whisk}-  is,  in 
consequence  of  the  higher  nitrogenous  and  lesser  oily  constituents  of 
the  rye-grains,  richer  in  proteids  and  poorer  in  fats  than  the  corn  residue. 
It  contains — 

Solids 9.9  per  cent. 

Proteids,      .        .        .      -.  .        .        .2.1 

Fats, 0.6 

Non-nitrogenous  extractive  matters,         .        .     5.9 

Cellulose, 0.9 

Ash,     .        . 0.5 


182  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

This  substance  is  one  of  the  most  useful  of  the  various  distillation 
residues,  unless,  as  is  often  the  case,  the  grain  which  has  undergone  the 
fermentation  has  contained  the  seeds  of  the  Agrostemma  yithago,  when 
it  will  possess  poisonous  properties. 

Beet  Residue. — The  residue  from  beet  distillation  contains  only  9 
per  cent,  of  solids,  0.9  per  cent,  proteids,  0.1  per  cent,  fats,  6.2  per 
cent,  non-nitrogenous  extractive  matters,  1.2  per  cent,  cellulose,  and  0.6 
per  cent,  of  ash.  It  is,  therefore,  the  poorest  in  nutritive  substances 
and  the  richest  in  water. 

For  preservation  of  the  distillery  residues,  either  they  may  be  dried, 
especially  when  mixed  with  various  forms  of  dry  fodder,  or  they  may  in 
the  fresh  condition  be  preserved  b\'  the  mixture  of  salic3'lic  acid,  one 
gramme  for  every  fift^-four  pounds.  A  process  of  preservation  which  is 
frequently  employed  depends  upon  the  souring  of  the  fresh  residue  in 
the  formation  of  lactic  acid  fermentation, — a  process  which  is  accompanied 
by  great  loss  of  non-nitrogenous  and  proteid  constituents.  In  spite, 
however,  of  this  loss  in  nutritive  constituents,  this  method  furnishes  a 
cheap  and  simple  mode  of  preserving  distillery  residues. 

The  residue  from  the  extraction  of  sugar  from  beets,  from  starch 
out  of  wheat  and  potatoes,  and  that  remaining  after  the  alcoholic  fer- 
mentation of  starchy  and  sugary  substances,  as  in  the  distillation  of 
spirits,  are  all  valuable  food  stuffs.  All  these  substances  contain  but 
small  amounts  of  solids,  and  the  proportion  of  nitrogenous  to  non- 
nitrogenous  matters  is  somewhat  lower  than  in  the  raw  material ;  but 
inorganic  matters  and  fats  are  present  in  considerable  amount  and 
render  them  important  accessory  foods  under  certain  circumstances. 

The  diffusion  residue  from  the  extraction  of  sugars  from  beet-roots 
furnishes  a  readily  digestible  form  of  food  which  is  richer  in  water  and 
poorer  in  inorganic  constituents  than  the  sugar-beets.  It  contains — 

Solids,        .        .  .        .  10.2  per  cent. 

Nitrogenous  matters         .        .  0.9 

Fats,  .         .         .  .         .  0.05 

Non-nitrogenous  extractive  matters,  6.3 

Cellulose,  ....  2.4 

Ash,  .        .        .  .        .        .  0.6 

For  cattle  and  hogs  as  much  as  one  hundred  kilogrammes  per  one 
thousand  kilogrammes  of  body  weight  of  this  fresh  residue  may  be  given 
as  food,  only  larger  amounts  may  be  given  to  animals  which  are  desired 
to  fatten  rapidly.  Larger  quantities  of  this  fodder  alter  both  the  char- 
acter and  quantity  of  the  meat  and  the  fat  of  animals  and  the  character 
of  the  milk.  For  draught  cattle  it  is  unsuitable,  as  is  also  the  case  for 
sheep,  with  the  exception  of  fattening  sheep,  which  may  stand  it  almost 
as  well  as  cattle.  Horses  can  only  receive  small  amounts, — ten  to  twenty 
kilogrammes  per  thousand  kilogrammes  of  body  weight, — and  then  only 


VEGETABLE  FOODS.  183 

when  not  worked.     This  residue  can  only  be  given  when  in  a  perfectly 
fresh  condition,  or  when  well  preserved. 

The  residue  after  the  extraction  of  oil  from  the  seeds  of  the 
various  members  of  the  cotton-plants  (Gossypium  herbaceum),  or  so- 
called  cotton-seed  cake,  furnishes  a  valuable  food  for  fattening  and  milk 
cattle.  The  seeds  are  inclosed  in  a  capsule,  which  bursts  as  the  fruit 
ripens,  and  which  are  covered  by  white  fibres  which  form  the  so-called 
cotton.  After  the  removal  of  the  cotton,  the  seeds,  which  have  a  hard 
shell,  contain  an  oily,  greenish-white  nucleus,  from  which  the  oil  is 
removed  by  pressure.  The  residue  from  this  process  of  extraction  of 
the  oil  is  by  no  means  constant  in  its  composition,  and  is  therefore  not 
always  suitable  for  a  food.  For  example,  many  of  the  cotton-seed 
cakes  contain  both  parts  of  the  indigestible  hull  of  the  seed  and  con- 
siderable cotton,  and  are  therefore  only  suitable  for  manures.  When 
such  an  article  is  given  to  cattle  serious  disturbance  of  digestion  is  pro- 
duced, and  may  even  prove  fatal  from  obstruction  and  inflammation  of  the 
alimentary  canal.  In  England  the  cake  produced  from  the  Eg3Tptian 
seeds  forms  a  favorite  article  of  fodder.  The  most  nutritious  and  most 
readily  digestible  are  the  cakes  from  the  hulled  seeds.  The  following- 
table  gives  their  composition  : — 


Cotton- 
Seeds. 

Oil-Cake  from 
Unhulled  Seeds. 

Oil-Cake  from 
Hulled  Seeds. 

Solids,  

91.1-92.3 

85.8-93.4 

85  7-92.3 

P  rote  ids,       .... 

22.7-22.8 

18.0-28.3 

19.7-49.2 

Fats?     

29.3-30.3 

4.8-  9.8 

5.4-19.7 

Non-nitrogenous  extractive 

matters,     .... 

7.6-15.4 

24.9-36.7 

10.5-29.3 

Cellulose,     .... 

16.0-24.7 

17.0-27.0 

3.5-11.4 

Ash. 

8.0 

6.6 

7.4 

The  oil-cake  from  the  hulled  seeds  constitutes  one  of  the  most 
nutritious  of  all  fodders.  From  digestion  experiments  on  ruminants 
Wolff  has  found  the  following  amounts  to  be  digested: — 

Protpuls  T^ata  Non-nitrogenous 

Fats'       Extractive  Matters. 

Hulled  cakes, 84.7  87.6  95.1 

Unhulled  cakes,       ....     73.4  90.8  46.2 

The  higher  digestibility  of  the  oil-cake  from  the  hulled  seeds  is  with- 
out doubt  to  be  attributed  to  the  large  amount  of  cellulose  in  the  hulls. 
The  oil-cake  from  the  unhulled  seeds  is  of  a  dark-brown  color,  while  that 
from  the  hulled  seeds  when  fresh  is  greenish, but  also  becomes  brownish 
with  age.  Both  of  these  forms  of  fodder  are  often  contaminated  by  the 
accidental  mixture  of  various  substances,  such  as  particles  of  iron  from 
the  presses,  and  when  kept  in  moist  places  with  various  forms  of  moulds 
which  lead  to  the  development  of  ptomaines  and  other  poisonous  alka- 
loids, and  so  may  explain  their  hurtful  action.  The  American  cotton-seed 


184 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


TABLE  I. 
AVERAGE  PERCENTAGE  COMPOSITION  OF  THE  ORDINARY  FOODS. 


According  to  Kuhn. 

According  to 
Wolff. 

| 

o 

o 

II 

'•£ 

o 

a 

"-'  53 

r£ 

C} 

•  a 

FOODS. 

1 

1 

a 
o 

If 

Sa 

K% 

iji 

w5 

1 

O 

a 
§><a 

|  a 
'3  a 

§ 

II 

o 

43   O 

1 

2 

1 

fil 

4 

3 

4 

u 

II 

. 

1 

1 

£r 
0 

g 

£* 

£ 

1 

s 

.2*  be 
Q 

£ 

I.  Green  Fodder. 

Prairie  grass,   .     .     . 

75.0 

25.0 

22.9 

3.0 

13.1 

0.8 

6.0 

2.1 

2.4 

9.9 

0.4 

Red  clover,       .    „   .. 

80.2 

19.8 

18.4 

3.6 

8.5 

0.7 

5.6    1.4 

1.7 

8.7 

0.4 

White  clover,  .     .     . 

80.2 

19.8 

18.45 

4.0 

8.0 

0.85 

5.6    1-4 

//.  Dry  Fodder. 

Prairie  hay,      .   '.     . 

14.3 

85.7 

79.2 

9.5 

40.3 

2.3 

27.1 

6.5 

5.4 

41.0 

1.0 

Clover-hay,      .     ...    . 

16.0 

84.0 

78.4 

13.4 

36.4 

3.2 

25.4 

5.6 

7.0 

38.1 

1.2 

Oat-straw,  .... 

14.3 

85.7 

81.3 

4.0 

35.6 

2.0 

39  .71  4.4 

1.4 

40.1 

0.7 

Bean  -straw,      .     .     . 

17.5 

82.5 

76.7 

9.9 

31.8 

1.5 

33  5 

5.8 

5.0 

35.2 

0.5 

Wheat-straw,  .     .     . 

14.3 

85.7 

81.8 

3.1 

37.5 

1.2 

40.0 

3.9 

Rye-straw,  .... 

14.3 

85.7 

81.6 

3.0 

33.3 

1.3 

44.0   4.1 

. 

. 

Barley-straw,  .     .     . 

14.3 

85.7 

81.3 

3.4 

34.7 

1.4 

41.8 

4.4 

///.  Roots  and  Bulbs. 

Potatoes,      .     .     .     . 

75.0 

25.0 

24.1 

2.0 

20.7 

0.3 

1.1 

0.9 

1.2 

21.8 

0.3 

Fodder-beets,   .     .     . 

88.0 

12.0 

11.2 

1.1 

9.1 

0.1 

0.9 

0.8 

0.5 

10.6 

0.1 

IV.  Grains  and  Fruits. 

Barley          .... 

13.8 

86.2 

84.0 

11.2 

65.5 

2.1 

5.2 

2.2 

8.0 

58.9 

1.7 

Oats         

13^7 

86.'  3 

83^6 

12^0 

56^6 

6.0 

9^0 

2.7 

9.0 

43^3 

4  0 

Corn        

12^7 

87^3 

85*6 

10^6 

65*7 

6.5 

2.8 

1.7 

8.4 

60.6     4  8 

Wheat,    

14.'  3 

85!  7 

84^0 

13^2 

66^2 

3.0 

1.7 

. 

Rice,  

13.7 

86.3 

86.0 

7.8 

74.5 

0.2 

3.5 

0.3 

. 

. 

Peas,  

13.2 

86.8 

83.4 

22.4 

52.6 

3.0 

6.4 

2.4 

_ 

< 

Beans,     

14.1 

85.9 

82.8 

25.1 

46.7 

1.6 

9.4 

3.1 

23.6 

50:2 

1.4 

V.  Food-  Products. 

Oat-meal,     .     . 

12  0 

88  0 

87.6 

17.7 

63.9 

6  0 

Corn-meal,  .... 

9.0'  91.0 

89.5 

is'.  2 

70.'  5 

3.8 

0.9 

Rve-rneal,    .... 

14  2    85  8 

84.2 

11.7 

69.3 

20 

1  2 

1.6 

11.7 

69.3 

2.6 

Rapeseed-cake,     .     . 

11.5 

885 

81.5 

31.6 

29.3 

9.6 

11.0 

7.0 

25.3 

23.8 

7  7 

Wheat-bran,     .     .     . 

13.0 

87.0 

81.0 

14.5 

53.6 

3.5 

9.4 

6.0 

11.8 

44.4 

3.9 

Malt,  

10.1 

89.9 

82.7 

24.2 

421 

2.1 

14.3 

7.2 

12.8 

51.6 

1.7 

Brewers'  grains,   .     . 

777 

22.3 

21.1 

46 

9.9 

1.6 

5.0 

1.2 

3.9 

11.8 

0.8 

Potato-mash,    .     .     . 

92.3 

7.7 

7.1 

1.4 

4.6 

0.2 

0.9 

0.6 

1.0 

4.0 

0.1 

VI.  Animal  Foods. 

Cows'  milk,      .     .     . 

88.0 

12.0 

11.3 

3.2 

45 

3.6 

. 

0.7 

3.2 

4.5 

3.6 

Skimmed  cows'  milk, 

90.0 

10.0 

9.2 

3.5 

5.0 

0.7 

. 

0.8 

3.5 

5.0 

0.7 

Goats'  milk,      .     .     . 

78.0 

12.0 

11.0 

3.4 

4.3    3.3 

. 

1.0 

. 

Flesh  

75.9 

24.1 

22.8 

20.0 

1.9 

0.9 

1.3 

. 

. 

Meat    residue    (from 

extracts),      .     .     . 

11.5 

88.5 

84.8 

72.8 

•    • 

12.0 

3.7 

69.2 

•    • 

11.2 

VEGETABLE   FOODS. 


185 


cake  is  of  a  bright-yellow  color.  If  dark  in  color  it  has  either  been 
subjected  to  pressure  while  too  hot,  or  has  spoiled  from  being  kept  in  too 
moist  a  place,  and  hence  is  of  poor  quality.  In  good  condition  it  should 
have  a  pleasant,  oily  smell  and  a  nutty  taste,  and  should  be  hard  and 
dr3'.  When  in  good  condition  such  a  fodder  is  readily  taken  by  domestic 
animals;  although,  especially  if  not  perfectly  fresh  and  of  the  first 
quality,  the  cattle  must  be  gradually  accustomed  to  it.  Under  all  cir- 
cumstances it  is  advisable  to  administer  it  dry,  mixed  up  with  other 
forms  of  fodder.  In  contact  with  hot  fluids  it  develops  an  extremely 
unpleasant  taste.  To  milk  cattle  from  three  to  five  pounds,  to  draught 
oxen  three  to  four  pounds,  and  to  beeves  six  pounds  for  every  thousand 
pounds  of  body  weight  may  be  given.  Sheep  and  cattle  may  receive 
from  one-half  to  one  pound,  and  horses  one  to  two  pounds.  An 
additional  advantage  of  this  substance  as  a  fodder  is  its  great  cheap- 
ness. 

The  table  on  the  preceding  page  gives,  in  the  first  eight  columns, 
the  percentage  composition  of  the  various  forms  of  food-stuffs  which  may 
be  employed  for  the  nutrition  of  the  herbivorous  domestic  animals.  The 
last  three  columns  give  the  average  degree  of  digestibility  of  their 


organic  constituents. 


TABLE  II. 


PERCENTAGE  CONSTITUENTS  OP  SOLIDS  IN  ORDINARY  FODDERS. 


FOODS. 

Nitrogen- 
ous Con- 
stituents. 

Non  nitro- 
genous 
Extractive 
Matters. 

Fats. 

Cellulose. 

Ash, 

Prairie  grass,        .... 
Red  clover,  

12.0 

18.4 
11.0 

52.4 

42.8 
46.9 

3.2 

3.8 

2.8 

24.0 

28.0 
31.6 

8.4 
7.0 

7.7 

15.7 

43.1 

3.7 

30.0 

7.5 

4.8 

41.5 

2,5 

46.0 

5.2 

Bean  -straw,          .... 

12.1 
8.0 

38.4 

82.8 

2.0 
1.2 

40.5 
4.4 

7.0 
3.6 

Fodder-beets,        .        .        . 
Barley,         ..... 
Oats 

9.3 
13.0 
14.0 

75.6 
76.0 
65.6 

0.9 
2.4 
7.0 

7.5 
.     6.1 
10.4 

6.7 
2.5 
3.0 

12.1 

75.0 

7.5 

3.4 

2.0 

29.2 

54.1 

2.1 

10.8 

3.8 

Rapeseed-cake,     .... 

35.7 
13.7 

33.2 

80.5 

10.8 
'2.4 

12.4 
1.5 

7.9 
1.9 

Wheat-bran,          .... 
Malt  
Beer-mash  (brewers'  grains), 
Potato-mash,         . 
Frpsh  milk 

15.8 
27.0 
20.7 
18.1 
26.6 

61.8 
46.8 
44.4 
59.8 
37.4 

4.3 
2.3 
7.1 
2.6 
30.0 

11.0 
15.9 
22.4 
11.7 

7.1 

8.0 

5.4 
7.8 
6.0 

Skimmed  milk,     .... 
Flesh,  
Meat  residue  (from  extracts), 

35.0 
83.0 
82.2 

50.0 

7.8 

7.0 
3.8 
13.6 

•     • 

8.0 
5.4 

4.2 

186 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


TABLE  III. 

THE  CONSTITUENTS  OP  FOODS,  ARRANGED  ACCORDING  TO  THEIR  PERCENTAGE 
COMPOSITION  IN  SOLIDS  AND  DIFFERENT  NUTRITIVE  PRINCIPLES. 


PERCENTAGE  OF 
SOLIDS  IN 
FOOD-STUFFS. 

PERCENTAGE  IN  THE  SOLIDS  OF 

Nitrogenous 
Constituents. 

Non-nitrogenous 
Extractive 
Matters. 

Fats 

Cellulose. 

Over  80  per  cent. 

Over  30  per  cent. 

Over  80  per  cent. 

Over  10  per  cent. 

Over  40  per  cent. 

Malt. 

Meat. 

Potatoes. 

Fresh  milk. 

Oat-straw. 

Meat  residue. 

Meat  residue. 

Rye-meal. 

Meat  residue. 

Bean-straw. 

Rapeseed-cake. 

Rapeseed-cake. 

Rapeseed-cake. 

Corn. 

Skimmed  milk. 

Bran. 

Between  70  and 

Oats. 

80  per  cent. 

Barley. 

Barley. 

Beans. 
Rye-meal. 

Over  20  per  cent. 

Beets. 
Corn. 

Oat-straw. 

Beans. 

Between  5  and 

Between  20  and 

Hay. 
Bean-straw. 

Malt. 
Fresh  milk. 
Beer-mash. 

Between  60  and 
70  per  cent. 
Oats. 

10  per  cent. 

Corn. 
Brewers'  grains. 
Oats. 

40  per  cent. 

Prairie  hay. 
Clover-hay. 
Red  clover. 

Bran. 

Skimmed  milk. 

Prairie  grass. 

Beer-mash. 

Between  15  and 

Between  50  and 

20  per  cent. 

60  per  cent. 

Clover. 

Beans. 

Potato  -mash. 

Grass. 

Bran. 

Skimmed  milk. 

Between  2  and 

Between  20  and 

Clover-hay. 

5  per  cent. 

30  per  cent. 

Grass. 
Potatoes. 

Between  40  and 
50  per  cent. 

Bran. 
Meat. 
Red  clover. 

Between  10  and 
20  per  cent. 

MaH- 

Flesh. 
Brewers'  grains. 

Between  10  and 
15  per  cent. 

Hay. 

Malt. 
Beer-mash. 

Clover-hay. 
Grass. 
Hay. 

iviai  u. 
Rapeseed-cake. 
Wheat-bran. 

Oats. 
Rye-meal. 

Clover-hay. 
Red  clover. 

Oat-straw. 
Barley. 

Beans. 
Oats. 

Barley. 

Oat-straw. 

Rye-meal. 

Bean-straw. 

Malt. 

Corn. 
Grass. 

Between  30  and 

Beans. 
Bean-straw. 

Hay. 

40  per  cent. 

Bean-straw. 

Milk. 
Oil-cake. 

Under  10  per  cent. 

Under  20  per  cent. 

Red  clover. 
Beets. 

Under  10  per  cent. 

Beets. 

Under  10  per  cent. 

Under  2  per  cent. 

Beets. 
Barley. 
Potatoes. 

Milk. 

Potatoes. 

Meat. 

Potatoes. 

Corn. 

Potato-mash. 

Straw. 

Meat  residue. 

Beets. 

Meal. 

VEGETABLE  FOODS.  187 

The  percentage  of  starch  and  sugars  in  fodders  has  been  recently 
investigated  by  Mr.  E.  F.  Ladd,  and  he  gives  the  following  tables  as 
representing  his  results  : — 


No. 

Substance. 

Invert 
Sugar. 

Sucrose. 

Per  cent,  of  Nitrogen- 
Starch,          free  Extract  as 
Sugars  and  Starch, 

1. 

Fodder-corn,     .        . 

900 

0.40 

13.87 

53.48 

2. 

Corn-  fodder,     . 

2.50 

1.43 

22.88 

53.32 

3. 

Sorghum,  .         .        . 

17.60 

3.40 

12.19 

64.21 

4. 

Alsike  clover,  .        fc  '• 

. 

. 

74.63 

33.81 

5. 

Red  clover,  average 

for  21,    . 

388 

2.48 

9.38 

35.40 

6. 

Timothy,  av.  for  21, 

2.23 

6.21 

19.72 

55.69 

7. 

Prickly  comfrey, 

6.22 

0.80 

8.14 

33.87 

8. 

Cactus,  top, 

5.92 

9.96 

30.00 

9. 

Cactus,  stump, 

2.80 

3.60 

17.10 

41.12 

10. 

Meadow  hay,    . 

m 

f 

24.32 

49.32 

11. 

Wheat-straw,    . 

22,42 

59.52 

12. 

Oat  -straw, 

23.18 

51.14 

13. 

Oats, 

53.20 

81.05 

14. 

Wheat,      . 

1.64 

2.36 

57.91 

76.37 

15. 

Wheat-flour,     . 

3.64 

8.36 

61.88 

86.77 

16. 

Wheat-middlings,     . 

3.20 

6.40 

41.44 

75.31 

17. 

Wheat-bran, 

1.60 

4.40 

45.60 

83.53 

18. 

Ship-stuff, 

2.08 

5.92 

41.46 

83.07 

In  red  clover  the  following  are  the  variations  : — 

Invert  sugar,         .        .     from  5  20  per  cent,  to  2.60  per  cent. 
Sucrose,         .        .        .        "    3.80          "  1.20 

Starch,  ..."  13.90  5.58 

For  timothy  the  following  represent  the  highest  and  lowest  per- 
centages : — 

Invert  sugar,         .        .     from  5.00  per  cent,  to  2.40  per  cent. 
Sucrose,         .        .         .        "7.60  "          4.68 

Starch,.          .        .        .         "2261  "        17.55 

The  percentage  of  sugars  and  starch  in  timothy  varies  according  as 
the  estimations  are  made :  while  in  full  bloom  or  after  the  seeds  are 
formed,  but  before  they  are  fully  matured.  This  is  shown  in  the  follow- 
ing  table : — 

Per  cent,  of  Nitrogen- 
Invert  Sugar.    Sucrose.     Starch.       free  Extract  as 

Sugar  and  Starch. 

Early-cut,     .        .        .     3.72  5.96        18.07  52.73 

Late-cut,        .        .        .     2.32  540        21.66  60.24 

It  thus  would  appear  that  as  hays  approach  ripeness  the  per  cent,  of 
sugar  is  diminished,  while  the  starch  is  increased.  Mr.  Ladd  was  unable 
to  trace  any  relation  between  the  per  cent,  of  sugars  and  starch  and  the 
kind  of  fertilizer  applied  to  the  soil,  and  was  unable  to  confirm  the  usual 
statement  that  a  potash  dressing  increased  the  starch-contents  of  the 
timothy. 


188  PHYSIOLOGY  OF  THE   DOMESTIC   ANIMALS. 


II.    ANIMAL   FOODS. 

The  most  important  of  the  foods  of  animal  origin  are  milk  and 
animal  flesh,  or  meat. 

1.  MILK  will  be  considered  more  at  length  under  the   Secretions, 
details  being  given  as  to  the  composition  and  characteristics  of  the  milk 
of  different  animals.     It  is  at  present  only  necessary  to  refer  in  outline 
to  its  composition  to  indicate  in  a  general  way  its  nutritive  value.     Milk 
contains  an  average,    in  100  parts,  of   85.7  parts  water,   5.4  parts  of 
albuminous  bodies,  4.3  parts  of  fats,  4  parts  of  sugar,  and  0.6  parts  of 
inorganic  salts.     Of  the  inorganic  salts,  potassium   phosphate,  calcium 
phosphate,  and    potassium   chloride    are  in    greatest   abundance,  while 
sodium  chloride  is  in  smaller  amount ;    iron    has   also   been    found    to 
be   present.      Milk,  therefore,  contains   examples   of    all   the  different 
nutritive  principles,  proteids,  carbo-hydrates,  fats,  and  salts,  and  these 
arranged  in  the  proportion  which  is  best  suited  for  nutritive  purposes. 
All   mammals,    in   the    earliest    period   of  their   extra-uterine   life,   are 
nourished  solely  on  milk,  and  their  rapid  growth  and  development  in 
this  period  is   without    doubt   largely  dependent  upon  the    manner   in 
which  the  different  food-principles  are  combined  in  milk.     Milk,  there- 
fore, may  be   regarded   as  a  tj^pical    food.      Buttermilk   is  the   name 
which   is   given  to  the  fluid  which   remains  after   the  fats  have  been 
removed  by  churning.     It  is  less  nutritious  than  milk  to  the  extent  to 
which  the  fats  have  been  removed,  but,  all  the  other  principles  remain- 
ing, it  may  serve   useful  nutritive   purposes.     It  has  an  acid  reaction, 
from    the   fermentation    of   the   milk-sugar   into   lactic   acid.      Cheese 
consists   of  the   casein   and  fats,   the   casein   being  coagulated,  either 
through  the   spontaneous   development  of  acidity,  when  it   is  termed 
a  curd,  or  by  the  addition  of  the  milk-curdling  ferment  from  the  stomach 
of  the  calf.     It  therefore  consists  principally  of  albuminous  bodies  and 
fats,  the  whey,  in  which  the  salts  and  sugar  remain  dissolved,  being 
largely  forced  out  by  pressure.      It  is  hence  well  suited  to  form  an 
addition  to  foods  which  are  poor  in  albuminoids  and  fats,  as  in  certain 
vegetables,  such  as  potatoes  and  rice.     The  whey  of  milk  contains  the 
sugar  and  lactic  acid,  which  is  developed  from  the  fermentation  of  the 
sugar,  salts,  and  a  certain  amount  of  milk-albumen.     It  also  has  con- 
siderable nutritive  value,  and  seems  especially  to  stimulate  intestinal 
peristalsis,  and  therefore  to  be,  to  a  certain  extent,  laxative. 

2.  MEAT. — Next  in  value  to  milk  as  food  comes  the  flesh  of  animals. 
The  nutritive  principles  of  meat  are  contained  within  the  muscle-fibre ; 
the  juice  obtained  by  subjecting  muscle  to  pressure  contains  myosin  and 
ordinary  albumen,  inosite  or  muscle-sugar,  and  glycogen,  as  representa- 
tives  of  the   carbo-hydrate   group,  while  within  the  connective  tissue 


ANIMAL  FOODS.  189 

around  the  muscular  fibres  fat  is  nearly  always  to  be  found.  Meat, 
therefore,  also  contains  members  of  the  proteid  group,  carbo-hydrate  and 
fatty  food-stuff's,  together  with  a  considerable  amount  of  inorganic  salts. 
Hence,  meat  is  also  an  excellent  food.  Albuminous  bodies  are  in  greatest 
amount ;  then  come  the  fats,  then  the  carbo-l^drates,  and  finally  the 
different  salts.  Ordinarily  lean  meat  may  be  said  to  c'ontain  an  average 
of  73.5  per  cent,  of  water,  26.5  per  cent,  of  solids  (of  which  21  per 
cent,  is  albuminous  and  1.5  per  cent,  gelatinous,  1.5  per  cent,  fats,  1 
per  cent,  carbo-hydrates,  and  1  per  cent,  inorganic  salts).  Of  the  latter, 
three-fourths  consist  of  acid  phosphate  of  potassium,  one- seventh  of  earthy 
phosphates  and  iron,  and  about  one-fifteenth  of  potassium  chloride.  The 
flesh  of  different  animals  differs  in  composition,  as  is  shown  by  the 
following  table : — 

In  100  parts  Flesh.        Ox.          Calf.         Pig.        Horse.    Chicken.   Fish  (Pike). 


Water, 
Solids, 
Albuminous  bodies,  . 
Fats,  .... 
Carbo-hydrates, 
Salts,      '    . 

76.7 
23.3 
20.0 
1.5 
0.6 
1  2 

75.6 
24.4 
19.4 
2.9 
0.8 
1.3 

72.6 
27.4 
19.9 
6.2 
0.6 
1.1 

74.3 
25  7 
21.7 
2.5 
0.6 
1.0 

70.8 
29.2 
22.7 
4.1 
.1.3 
1.1 

79.3 
20.7 
18.3 
0.7 
0.9 
0.8 

It  is  thus  seen  that  meat  is  especially  distinguished  by  its  high  albu- 
minoid constituents,  which  amount  to  four  times  that  contained  in  milk. 
Chicken-flesh  and  that  of  other  birds  is  richer  in  albuminoids  than  that 
of  mammals,  while  the  flesh  of  fish  is  poorer,  though  even  here  18  per 
cent,  of  albuminous  bodies  is  present.  Meat  alone  forms  the  food  of  the 
carnivora  onty,  and,  as  we  shall  find  that  carbo-hydrates  may  be  developed 
from  the  decomposition  of  albuminoids,  carnivorous  animals  will,  there- 
fore, require  an  immense  amount  of  albuminous  bodies,  and  therefore  a 
very  great  volume  of  meat.  If  carbo-hydrates  are  added  to  the  meat 
diet  of  the  carnivorous  animals  the  volume  of  the  latter  ma}T  be  very 
considerably  reduced  and  still  the  animal  preserve  its  nutritive  equilib- 
rium. In  a  diet  of  raw  meat  animals  always  run  a  risk  of  taking  entozoa 
or  parasites,  such  as  trichina,  into  their  interior.  The  preparation  of 
meat  by  prolonged  boiling  destroys  all  the  parasites,  and  therefore  serves 
to  render  even  infected  meat  harmless.  When  meat  is  placed  in  cold 
water  the  inorganic  salts  and  a  certain  part  of  the  albuminous  bodies 
(about  3  per  cent.),  together  with  the  so-called  extractives  of  meat, 
such  as  kreatin,  xanthin,  and  hippoxanthin,  pass  into  solution  along 
with  small  amounts  of  lactic  acid.  When  the  water  is  warmed  up  to 
45°  C.  a  certain  amount  of  soluble  albuminoids  undergo  coagulation  and 
form  coaguli,  Mrhich  float  on  the  surface  of  the  water.  As  the  tempera- 
ture of  the  water  is  increased  the  external  surfaces  of  the  meat  first  un- 
dergo coagulation,  and  so  prevent  further  escape  of  the  muscle-juices. 
Meat  which  has  been  subjected  to  prolonged  boiling  thus  preserves  a 


190  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

considerable  nutritive  value,  since  it  contains  still  16  or  18  per  cent,  of  the 
albuminous  bodies  and  a  small  quantity  of  nutritive  salts,  and  is  readily 
digestible  in  the  alimentary  canal.  If  meat  is  placed  in  water  which  is 
already  boiling  the  external  surfaces  are  at  once  coagulated  and  but  little 
of  the  nutritive  juices  escape,  so  that,  therefore,  meat  so  prepared  has  a 
greater  nutritive  value  than  meat  which  is  placed  in  cold  water  and  then 
graduall}T  subjected  to  boiling.  The  more  rapidly,  therefore,  the  exter- 
nal surfaces  of  the  meat  are  coagulated,  as,  for  example,  by  roasting,  the 
greater  will  be  the  proportion  of  nutritive  substances  retained.  In  roast- 
ing the  haemoglobin  of  the  blood  becomes  decomposed,  and  the  meat 
then  takes  the  characteristic  brown  color  of  roast  meat,  while  at  the  same 
time  a  number  of  aromatic  substances,  to  which  the  peculiar  odor  and 
taste  of  roast  meat  are  due,  are  developed.  By  soaking  meat  in  brine 
putrefaction  is  prevented,  but  meat  so  salted  loses  a  certain  degree  of 
nutritive  value  from  the  fact  that  a  considerable  quantity  of  albuminous 
bodies  and  extractive  matters  and  salts  pass  into  the  pickling  solution. 
Smoked  beef  is  protected  from  decomposition  by  the  development  of 
phenol  in  the  smoke ;  this  substance  is  an  energetic  preventive  of  decom- 
position. Beef  so  dried  preserves  nearly  all  of  its  nutritive  principles, 
only  having  lost  in  water.  Meat-broth  obtained  by  boiling  meat  with 
water  has  usually  an  acid  reaction,  from  the  lactic  acid  of  meat,  and  con- 
tains a  greater  part  of  salts  and  extractive  matters  of  meat,  together 
with  a  certain  amount  of  gelatinous  albuminoids  and  a  small  amount  of 
fat.  Meat-broth  will  contain  about  1.4  per  cent,  of  solids,  but  is  of  slight 
nutritive  value,  since  it  contains  scarcely  any  albuminoids  or  carbo- 
hydrates, and  but  an  extremely  small  amount  of  fats.  It  consists  almost 
solely  of  the  extractive  matters  and  salts,  and  is,  therefore,  simply  of 
value  as  a  means  of  supplying  the  inorganic  salts  of  meat.  From  the 
extractive  matters  and  the  potassium  salts  present  it  is  to  a  certain  ex- 
tent a  stimulant,  since  it  simply  in  this  way  produces  a  greater  secretion 
of  digestive  juices.  Beef-tea,  prepared  by  putting  meat  in  cold  .water 
and  gradually  raising  the  temperature,  has  a  higher  nutritive  value  than 
the  commercial  beef  extracts  from  the  fact  that  the  soluble  albuminoids 
have  time  to  pass  into  solution  in  the  water  before  their  temperature  of 
coagulation  has  been  reached.  The  composition  of  meat  will  be  given 
in  greater  extent  under  the  subject  of  Muscles. 

Eggs,  especially  those  of  the  hen,  are  also  valuable  nutritive  articles, 
containing  also  examples  of  all  the  different  food-stuffs ;  thus,  one  hun- 
dred parts  of  egg,  the  shells  having  been  removed,  consist  of  73.9  per 
cent,  water  and  26.1  per  cent,  solids.  Of  the  latter  14  percent,  is 
albuminoid,  10.8  per  cent,  fat,  a  small  amount  of  sugar,  and  1  per  cent, 
of  inorganic  salts,  especially  sodium  chloride,  potassium  phosphate,  and 
a  small  amount  of  oxide  of  iron. 


INORGANIC  FOODS.  191 

Eggs  are  also  frequently  used  as  food  for  calves  and  stallions  when 
rubbed  up  with  the  shells.  To  fattening  calves  three  eggs  ma}"  be  admin- 
istered daily,  rubbed  up,  shells  and  all,  with  their  daily  supply  of  milk, 
and  serve  to  give  an  especially  pleasant  flavor  to  their  flesh.  For  stallions, 
ten  to  fifteen  eggs  may  be  given  with  their  usual  food. 

III.      INORGANIC   FOODS. 

By  inorganic  foods  are  meant  those  inorganic  compounds  which 
are  found  in  the  different  tissues,  secretions,  and  excretions  of  the 
organism,  which,,  being  essential  to  the  vital  processes  of  the  organism 
and  being  continually  removed,  must  be  constantly  replaced.  Inorganic 
substances  are  indispensable  to  a  proper  nourishment  of  animals,  but 
they  are  not  usually  taken  in  their  simple  form,  but  as  constituents  of 
animal  or  vegetable  matter,  or  in  the  fluids  which  are  drunk.  Of  the 
inorganic  foods,  water,  common  salt,  salts  of  lime  and  potassium,  and 
iron  are  indispensable,  as  they  are  the  necessary  constituents  of  the 
blood,  lymph,  bones,  and  different  tissues,  and  are  continually  being 
removed  in  the  nutritive  processes  of  the  econom^y. 

1.  WATER. — Water,  as  an  alimentary  principle,  is  taken  into  the 
system,  either  alone  as  a  drink,  or  in  combination  with  articles  of  food; 
in  both  of  which  cases  it  is  also  associated  with  a  certain  amount  of 
inorganic  salts,  as  animals,  unless  pressed  by  great  thirst,  will  refuse  to 
drink  distilled  water.  For  certain  animals,  such  as  rabbits  and  kangaroos, 
which  seldom  or  never  apparent^  drink  water,  enough  fluid  for  their 
needs  is  contained  in  the  succulent  vegetables  which  serve  as  their 
food;  for  if  rabbits,  for  example,  are  fed  on  dry  food,  such  as  bran,  they 
will  then  require  water,  and  will  drink  it  like  other  animals.  So  also 
sheep,  which,  as  a  rule,  require  but  small  amounts  of  water  because 
of  the  succulent  character  of  their  food,  if  in  dry  localities,  or  if 
they  are  fed  on  dry  food,  will  also  hunt  for  water,  like  other  animals 
susceptible  of  thirst.  Water  not  only  carries  into  the  system  materials 
capable  of  solution,  but  it  holds  matters  in  suspension  which  in  some 
cases  may  be  nutritious,  in  others  poisonous.  The  purest  water  is  not 
necessarily  the  best  for  animals  or  man,  nor  is  dirty  water  necessarily 
injurious.  Drinking-water  must  possess  certain  qualities.  It  must  be 
fresh,  clear,  without  odor,  and  of  a  certain  taste.  It  should  always  con- 
tain gases  and  mineral  matter  in  solution,  but  be  free  from  organic 
substances.  The  presence  of  the  latter,  which  are  always  injurious,  may 
be  recognized  by  the  addition  of  a  small  amount  of  potassium  perman- 
ganate solution  to  the  suspected  water,  when,  if  organic  substances  are 
present,  the  bright-purple  solution  will  become  a  dirty  brown.  Drinkable 
water  should  contain  from  20  to  30  per  cent,  of  its  volume  of  air  in 


192  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

solution.  It  also  should  contain  a  considerable  amount  of  carbon 
dioxide,  to  which  the  flavor  of  water  is  due.  The  dispersion  of  these 
gases  by  boiling  gives  to  water  a  flat  and  disagreeable  taste.  The 
inorganic  salts  held  in  solution  in  natural  waters  may  vary  within  very 
wide  limits,  both  as  to  their  nature  and  quantity ;  ordinary  drinkable 
water  contains  about  twenty-five  to  one  hundred  centigrammes  of  solid 
residue  per  liter.  Of  this,  carbonates,  sulphates,  alkalies,  chlorides, 
and  earthy  matters  are  the  most  constant  constituents,  although  various 
other  substances,  such  as  sulphur,  iron,  and  lime,  are  contained  in 
waters  of  different  localities,  forming  the  so-called  mineral-spring  waters, 
whose  composition  is  subject  to  the  very  greatest  variation, 

2.  NUTRITIVE  SALTS. — Of  the  salts  which  are  essential  for  the  nutri- 
tion of  animals  the  most  important  is  sodium  chloride.  This  substance 
enters  largely  into  the  composition  of  all  animal  tissues  and  fluids,  and 
when  not  supplied  in  proper  amount  produces  great  disturbances  of  nutri- 
tion, and  a  morbid  craving  for  it  has  often  been  noticed.  The  effects  of 
the  deprivation  of  salts, -or  the  so-called  salt  hunger,  willbe  alluded  to 
under  the  subject  of  Nutrition.  Even  the  administration  of  an  extra 
ration  of  salt  is  sometimes  of  advantage;  thus,  the  experiment  has  been 
made  of  feeding  two  bullocks  on  food  which  in  one  case  contained  a 
daily  ration  of  five  hundred  grains  of  salt,  while  no  salt  was  supplied  to 
the  other.  For  five  months  no  very  evident  results  appeared ;  but  changes 
then  commenced  which  were  very  marked,  even  to  the  unpracticed  eye. 
In  the  bullock  to  which  the  salt  had  been  supplied  the  hair  was  smooth 
and  glistening,  and  in  the  other  rough  and  tarnished.  This  distribution 
Of  salt  in  the  diet  was  continued  for  a  year,  when  the  animal  which  had 
been  kept  without  salt  had  a  rough  and  tangled  hide,  with  patches  where 
the  skin  was  entirely  bare,  while  the  other,  to  whom  five  hundred  grains 
of  salt  had  been  supplied  daily,  had  all  the  appearance  of  a  healthy,  stall- 
fed  animal,  was  much  more  vivacious,  and  would  have  brought  a  much 
higher  price  in  the  market. 

In  addition  to  sodium  chloride,  phosphates,  carbo-hydrates,  and  sul- 
phates are  also  of  great  nutritive  value,  and  are  required  for  the  main- 
tenance of  a  proper  nutritive  condition  of  the  animal.  Carnivorous 
animals  receive  a  proper  supply  of  phosphates  in  the  animal  foods, 
especially  in  bones,  whereas  the  herbivora  derive  them  from  the  grasses 
on  which  they  feed.  Phosphatic  manures  owe  their  value  largely  to  the 
contribution  of  phosphates  which  they  make  to  the  soil,  and  hence  to 
the  grasses  grown  on  them.  The  lime  salts,  as  has  been  already  indi- 
cated, are  essential  for  the  development  of  the  solidity  of  bones,  and 
when  reduced  in  amount  lead  to  various  deformities  of  the  bony 
skeleton.  Even  suckling  animals  receive  in  the  milk  of  their  mothers 
when  normal  a  sufficiency  of  these  inorganic  matters ;  thus,  a  suckling 


DIET   OF   ANIMALS.  193 

calf  receives  daily  fifty-two  grammes  of  inorganic  matter  in  the  milk 
of  the  mother,  and  a  calf  six  months  old  appropriates  in  its  fodder 
an  amount  of  phosphoric  acid  corresponding  to  thirty-six  grammes  of 
calcium  phosphate ;  while  a  horse  fed  on  hay  and  oats  receives  daily 
about  one  hundred  and  sixty-eight  grammes  of  calcium  phosphate. 
Occasionally  animals  are  seen  to  eat  earth.  This,  with  the  exception  in 
the  case  of  birds,  where  gravel  is  required  to  assist  in  the  comminution 
of  the  food  in  the  gizzard,  is  to  be  explained  by  the  insufficiency  of  inor- 
ganic matter  in  the  food.  Thus,  the  earth-eating  Indians  in  South 
America  are  said  to  consume  earthy  matters  from  the  fact  that  their 
corn  is  poor  in  salts. 

IV.    THE   DIET   OF   ANIMALS. 

The  complexity  of  food-stuffs  is  essential  to  the  sustenance  of 
the  organism.  The  food  must  contain  albuminoids  for  the  recon- 
struction of  the  tissues,  carbo-hydrates  and  fats  for  calorification 
and  the  formation  of  adipose  tissue,  and  the  saline  matters  for  the 
different  secretions  and  tissues.  If  any  one  of  these  food-constit- 
uents is  not  represented  in  the  diet,  the  food,  even  although  in 
excessive  amount,  will  be  incapable  of  preserving  health.  Experi- 
mentation has  proved  that  single  alimentary  principles  will  not  sustain 
life.  Magendie  showed  long  ago  that  dogs  fed  exclusively  on  non- 
nitrogenous  substances,  such  as  sugar,  gum,  olive  oil  or  butter,  in  a  short 
time  died  of  marasmus,  the  appetite  soon  being  lost,  ulcerations  forming 
on  the  cornea,  and  death  occurring  with  all  the  symptoms  of  starvation 
after  about  four  weeks.  After  death  all  fat  was  found  to  have  disappeared 
from  the  body  ;  the  muscles  were  atrophied ;  the  urine  alkaline  and 
deprived  of  uric  acid  and  phosphates,  so  as  to  resemble  the  urine  of  her- 
bivora.  Similar  results  were  obtained  whether  the  animals  were  fed  with 
oil,  with  gum,  or  with  sugar  alone.  Any  one  of  these  substances  was 
found  to  be  incapable  of  sustaining  life.  Objection  might  naturally  be 
urged  against  these  experiments  that  the  dog  being  a  carnivorous 
animal,  a  diet  of  non-nitrogenous  food  was  not  adapted  to  his  nutritive 
needs ;  but  the  repetition  of  Magendie's  experiments  by  Tiedemann  and 
Grmelin  with  the  goose,  by  feeding  on  gum  arabic  and  water,  sugar  and 
water,  and  raw  or  uncooked  starch,  overcomes  the  force  of  this  argument. 
In  all  cases  death  occurred  in  from  two  to  three  weeks  with  all  the 
symptoms  of  starvation,  even  though  the  examination  of  the  excreta 
proved  that  the  substances  given  had  been  digested.  In  all  cases  the 
appetite  gradually  failed,  diarrhoea  set  in,  and  death  occurred  .from 
exhaustion  and  starvation.  It  thus  seems  clear  that,  even  though 
digested,  a  non-nitrogenous  diet  alone  will  not  sustain  life,  either  in  the 
carnivora  or  in  the  herbivora.  A  similar  state  of  affairs  holds  for 

13 


194  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

nitrogenous  diet.  Dogs  fed  exclusively  on  gelatin  soon  refuse  to  take 
it,  and  die  of  hunger.  Fibrin  alone  will  also  not  sustain  life,  death 
occurring  on  the  fortieth  to  the  eightieth  day,  while  albumen,  whether 
raw  or  cooked,  if  given  alone,  has  been  found  to  be  incapable  of  sustain- 
ing life  even  as  long  as  fibrin.  Gluten  alone  has  been  found  capable  of 
sustaining  life,  probably  because  it  is  not  a  pure  nitrogenous  matter  and 
always  contains  starch,  vegetable  albuminoids,  and  salts ;  so  that,  there- 
fore, the  experiments  made  with  gluten,  in  which  nutrition  seemed  to  be 
tolerably  well  preserved,  will  not  disprove  the  general  statement  that 
single  nutritive  principles  are  not  capable  of  sustaining  life.  Finally, 
again,  a  mixture  of  nitrogenous  matters,  such  as  fibrin,  albumen,  and 
gelatin,  although  more  nutritious  than  when  any  one  of  these  is  given 
alone,  is  always  incapable  of  supporting  life  for  more  than  about  four 
months. 

These  results  show  that  a  simple,  easily  -  digestible  substance, 
whether  nitrogenous  or  non-nitrogenous,  alone  is  incapable  of  supporting 
life.  An  aliment  must  contain  the  four  groups  of  nutritive  principles 
given  above.  Blood,  meat,  grasses,  and  grains  are  aliments,  any  one  of 
which,  when  taken  alone,  will  sustain  life.  Thus,  milk  contains  casein, 
an  albuminoid,  together  with  albuminous  bodies  allied  to  serum-albumen, 
which  supply  nitrogenous  elements  necessary  for  tissue  development.  It 
contains  sugar  and  fats  for  producing  heat,  and  it  contains  salts  in 
amounts  required  for  the  development  of  all  the  tissues.  Hay,  again, 
and  grasses  always  contain  a  mixture  of  several  kinds  of  plants,  their 
stems,  leaves,  and  seeds  always  containing  vegetable  albuminous  matters, 
sugar,  starch,  mineral  salts  and  fats.  Observation  has,  however,  shown 
that  the  association  of  different  alimentary  substances  already  complex  is 
favorable  to  nutrition,  not  only  by  the  different  degrees  of  stimulation 
which  they  exert  on  the  different  portions  of  the  digestive  tract,  but  by 
the  variety  of  nutritive  matters  which  they  render  for  absorption.  A 
number  of  apparent  exceptions  seem  to  offer  themselves  to  the  truth  of 
this  statement ;  thus,  where  we  find  birds  feeding  almost  solely  on  a 
single  article  of  food,  and  alwa}^s  maintaining  a  high  state  of  nutrition  ; 
and  yet  it  only  requires  a  little  reflection  to  show  that  such  foods  are 
invariably  themselves  highly  complex,  and  contain  within  them  examples 
of  all  the  different  food-stuffs.  So,  also,  the  larger  ruminants  will  thrive 
on  a  prolonged  diet  of  any  one  single  food;  and  yet  here,  also,  the  only 
foods  on  which  nutrition  may  be  so  preserved  must  be  those  which  con- 
tain examples  of  all  the  different  food-principles. 

It  is  not  only  necessary  that  an  aliment  should  contain  all  the  differ- 
ent food-principles,  but  that  they  should  be  present  in  considerable  quan- 
tities and  in  definite  proportions  ;  otherwise  nutritive  equilibrium  will  be 
destroyed.  The  essential  relations  between  the  relative  proportions  of 


DIET   OF   ANIMALS. 


195 


these  different  food-stuffs  will  be  discussed  when  we  consider  the  nutri- 
tive value  of  foods. 

We  may,  however,  here  call  attention  to  the  fact  that  in  an  animal 
in  whom  no  excessive  demands  for  work  are  made  a  proportion  of  one 
part  of  nitrogenous  to  eight  of  non-nitrogenous  food-stuffs  will  be  sufficient 
to  maintain  the  body  weight.  When,  however,  the  animal  is  worked, 
then  the  proportion  between  nitrogenous  and  non-nitrogenous  food  must 
be  increased  from  1:5  to  1:3.  The  following  table,  after  Liebig,  shows 
the  proportion  of  nitrogenous  to  non-nitrogenous  principles  in  some 
of  the  most  common  foods  : — 


Cows'  milk, 
Beans  and  peas,  . 
Ox-flesh,     . 
Pigs'  flesh, 

1 
1 
1 
1 
1 

2  to  1  :  4 
2 
1.7 
3 
1 

Potatoes,    . 
Oatmeal, 
Wheat-flour, 
Rve-  and  barlev-mea 

1 
1 
1 

10 
5 
4.6 
5.7 

The  aliment  which  is  well  adapted  to  nourish  one  species  of  animal 
is  not  necessarily  suitable  for  another.  Thus,  a  vegetable  food  which 
furnishes  the  maximum  of  its  nutritive  principles  to  a  ruminant,  which 
is  capable  of  perfectly  dividing  it  and  retaining  it  for  a  long  time  in  its 
complicated  gastro-intestinal  apparatus,  will  be  of  little  value  to  such  an 
animal  as  a  horse  for  the  directly  opposite  reasons.  Further,  the  food 
which  may  be  nutritive  for  an  animal  with  a  perfect  masticatory  appa- 
ratus will  be  useless  to  one  in  whom  the  teeth  have  not  appeared  or  have 
been  lost ;  or  it  may  serve  for  a  beast  of  burden  which  has  need  of  blood 
and  tissue  producers,  and  not  for  a  fattening  animal,  or  a  cow  kept 
entirely  for  milking.  The  alimentary  ration  must  correspond  to  the 
losses  of  the  organism,  and  must,  therefore,  be  proportionate  to  the  work 
done  and  the  animal's  size ;  thus,  a  man  under  ordinary  circumstances 
requires  20  grammes  of  nitrogen  and  330  grammes  of  carbon  daily,  rep- 
resented by  1000  grammes  of  bread  and  286  grammes  of  meat.  The 
horse  needs  7500  grammes  of  hay  and  2270  grammes  of  oats,  representing 
10  kilo  of  hay  and  2  kilo  of  oats  for  every  100  kilo  of  body  weight.  Loss 
of  weight  occurs  if  this  daily  ration  is  reduced  only  one-tenth.  For  the  dog 
40  grammes  of  meat  are  necessary  for  each  kilo  of  body  weight,  and  here 
also  the  animals  lose  flesh  if  these  rations  are  decreased  only  one-tenth. 
If  the  bodily  losses  are  increased  by  work  or  by  the  secretion  of  milk, 
or  if  the  animal  is  in  the  growing  period,  when  the  size  and  weight  of  the 
body  should  increase,  it  is  also  indispensable  that  these  rations  should 
increase.  In  cases  where  extraordinary  demands  are  made  on  the  forces 
of  the  animal,  as  in  beasts  of  burden,  the  supplementary  foods  are  then 
to  be  given,  in  small  volume,  and  should  then  be  of  extremely  nutritive 


196  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

nature  in  concentrated  form,  so  as  not  to  tax  the  digestive  organs.  Thus, 
for  workingmen  meat  shoulcl  represent  the  accessory  rations ;  for  horses 
oats  is  the  suitable  form.  For  if  the  extra  food  is  given  to  the  horse  in 
grasses  it  becomes  impossible  to  work  him  because  of  the  overdistension 
of  the  alimentary  canal  necessitated  by  the  greatly  increased  volume  of 
food  required.  Again,  in  fattening  animals  or  in  animals  kept  for  milk- 
ing purposes  the  diet  must  be  rich,  in  albumen,  in  fats  and  carbo-hydrates. 
Equivalent  values  of  different  amounts  of  different  foods  cannot  be  deter- 
mined by  chemical  analysis  alone,  as  will  be  shown  when  the  nutritive 
A^alues  of  the  different  foods  are  considered.  That  two  foods  should 
have  the  same  nutritive  value  they  should  contain  equal  proportions  of 
nitrogenous  matters,  carbo-hydrates,  salts,  etc.,  in  equal  volumes.  They 
should  possess  equal  stimulating  properties  to  the  digestive  tract,  and 
should  be  of  equal  digestibilitj^.  It  is  a  general  rule  that  animal  matters 
are  more  nutritive  than  vegetable  matters,  bulk  for  bulk.  They  are, 
further,  more  varied  in  composition,  and  are  more  readily  assimilated. 

The  mode  of  diet  suitable  for  different  animals,  the  character  of 
their  food  and  its  nature,  varies  very  widely  in  different  classes  of  ani- 
mals, whether  carnivorous,  herbivorous,  or  omnivorous.  Each  of  these 
classes  has  a  special  mode  of  alimentation,  as  especially  emphasized  by 
Colin,  which  is  governed  by  the  characteristics  of  its  digestive  organs. 
In  each  of  these  three  groups  of  animals  a  number  of  subdivisions  may 
be  established.  Thus,  among  the  carnivora  there  are  animals  which  only 
eat  living  prey  ;  others,  only  decomposing  animal  matter  ;  others,  again, 
only  insects. 

Among  the  herbivora,  some  only  eat  grasses;  others,  only  grains; 
others,  roots  and  leaves,  etc.  The  mode  of  alimentation  suitable  to  each 
of  these  species  is  closely  dependent  upon  the  digestive  organs  of  each, 
and  governs  its  habits,  instincts,  and  characters,  and  is  dependent  largely 
upon  the  modes  which  it  possesses  of  attack  and  defense. 

The  carnivora,  especially  those  belonging  to  the  group  of  mammals, 
have  a  strikingly  characteristic  organization.  Their  incisor  teeth  are  cut- 
ting, their  canine  teeth  long  and  pointed,  as  are  also  the  cusps  of  their 
molar  teeth.  Their  jaws  are  short ;  their  masseter  and  temporal  muscles 
enormously  developed,  lodged  in  deep  temporal  fossae,  and  attached 
to  highly-curved  zygomatic  arches ;  their  oesophagus  dilatable ;  their 
stomachs  large  ;  their  intestines  short  and  simple,  and  their  caeca  small 
or  absent.  Their  feet  are  divided  and  furnished  with  more  or  less  pointed 
claws.  They  are  admirably  organized  for  the  discovery  of  their  prey  by 
acute  sight  or  acute  sense  of  smell  or  hearing ;  their  agility  or  cunning 
enables  them  to  surprise  and  seize  their  prey,  and  their  strength  to  tear 
it  to  pieces;  while  their  jaws  are  powerful  enough  to  crush  the  bones, 
and  their  gastric  .juices  powerful  enough  to  dissolve  them.  Such  animals 


DIET   OF   ANIMALS.  197 

are  the  lion,  the  tiger,  the  jaguar,  and  all  cats.  The  carnivora  which 
feed  on  living  prey  are  always  ferocious.  Those  which  feed  on  dead 
nnimal  matter  are  usually  cowardly,  as  the  vulture,  hyena,  jackal,  etc. 
As  a  rule,  they  seek  their  prey  alone  and  seldom  hunt  in  flocks  or 
herds.  They  differ  in  their  manner  of  searching  for  food.  Some  lie  in 
wait  for  their  food  and  surprise  it,  others  chase  it ;  some  feed  almost 
solely  on  fish,  others  on  mammals.  The  general  rule,  however,  holds 
that  animals  seldom,  if  ever,  feed  on  their  own  species.  Carnivorous 
animals  invariably  devour  the  herbivorous.  There  are,  however,  many 
exceptions  to  this ;  thus,  swans  have  been  said  to  eat  their  own  kind ; 
ducks  and  ravens  are  said  to  have  eaten  birds  of  their  own  species ;  while 
it  seems  well  established  that  wolves  and  rats  both  destro}T  each  other 
for  food ;  so.  also,  the  sow  has  been  known  to  eat  her  young ;  but  all 
these  are  merely  exceptions  to  the  general  rule  that  animals,  even  when 
pressed  by  the  most  extreme  hunger,  refuse  to  devour  flesh  of  their  own 
species.  These  animals  differ  greatly  in  their  mode  of  devouring  their 
food.  Some  consume  their  prey  when  freshly  killed;  others  simply  con- 
sume the  blood  ;  some  wait  until  decomposition  has  commenced;  while 
many  bury  the  remains,  to  wait  until  again  pressed  by  hunger. 

Among  carnivorous  birds  we  always  find  a  mode  of  prehension  of 
food  suitable  to  the  character  of  their  diet.  Insect-eating  birds  have,  as 
a  rule,  long,  narrow  beaks,  with  prehensile  tongues.  Fish-eating  birds 
have  beaks  which  enable  them  to  seize  and  consume  their  prey. 

Herbivora  are  of  a  very  different  organism  from  carnivora.  Their 
molars  are  flat,  or  have  tuberculated  crowns  ;  their  jaws  are  longer,  more 
slender,  and  less  strong ;  their  stomachs  are  always  more  ample  from  the 
fact  that  in  vegetable  food  the  nutritive  principles  are  in  less  relative 
bulk  than  in  animal  food ;  their  intestines  are  larger,  longer,  and  more 
complicated,  and  often  have  special  diverticulse  for  the  retention  of  food  ; 
their  senses  are  not  as  delicate  as  those  of  the  carnivora.  The}",  as  a 
rule,  want  means  of  aggression,  while  the  instincts,  courage,  and  cunning 
of  the  carnivora  are  absent.  While  many  of  them  are  provided  with 
defensive  organs,  as  a  rule  they  depend  upon  their  speed  for  their  pro- 
tection. 

Herbivorous  animals  are  divided  into  the  grass-eaters,  the  herbivora 
proper;  the  granivora,OY  seed-eaters;  the  fructivora,  or  those  which  feed 
on  fruits.  Of  the  large  herbivora,  the  solipedes,  of  which  the  horse  and 
ass  are  examples,  and  the  ruminants,  are  the  most  prominent  examples. 
In  the  savage  state  they  live  exclusively  on  herbs  and  leaves,  and  never 
eat  roots  or  fruits.  Others,  such  as  the  hippopotamus,  rhinoceros,  and 
the  elephant,  prefer  roots,  but  eat  leaves  and  herbs,  and  in  the  domestic 
state  all  may^  live  on  dry  forage.  Others  belonging  to  this  same  group, 
such  as  the  castor  and  beaver,  and  the  rodents  generally,  will  eat  the  bark 


198  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

of  trees.  All  the  herbivora  are  possessed  of  instincts  which  enable  them 
to  select  the  vegetable  foods  which  are  most  suitable  for  them,  and  will 
reject  others.  Thus,  it  has  been  found,  as  mentioned  by  Colin,  who  has 
made  a  close  study  of  this  subject,  and  to  whom  the  author  is  largely 
indebted,  that  a  horse  will  eat  262  different  kinds  of  plants,  and  has  been 
seen  to  reject  212 ;  the  ox  will  eat  275  and  refuse  218 ;  the  sheep  will  eat 
387  and  refuse  141 ;  the  hare  will  eat  449  and  refuse  125  ;  and  the  pig, 
which  is  omnivorous,  and  yet  which  can  be  sustained  by  vegetable  food, 
has  been  found  to  devour  172  different  kinds  of  vegetable  matter  and 
reject  171.  Different  circumstances,  such  as  changing  seasons  or  migra- 
tion from  different  localities,  may  compel  them  to  feed  on  plants  which 
are  otherwise  ordinarily  refused.  Their  instinct  leads  them,  further,  to 
avoid  venomous  plants  when  mixed  with  other  plants,  or  unless  greatly 
pressed  by  hunger.  Different  plants  are  poisonous  articles  of  food  to 
some  animals,  while  other  plants  are  poisonous  to  others.  Here  it  is  only 
necessary  to  mention  that  the  ox  and  rabbit  may  eat  belladonna  with 
impunity,  the  goat  hemlock,  the  horse  aconite,  while  goats  and  sheep 
avoid  most  of  the  solanacese. 

The  omnivora  are  permitted,  by  their  organization  and  instinct,  to 
devour  both  kinds  of  food,  and,  as  a  consequence,  their  habits  are  not  so 
sharply  characterized  as  either  of  the  two  above-mentioned  groups.  They 
ma}r  live  either  on  exclusively  animal  or  exclusively  vegetable  diet,  accord- 
ing to  circumstances.  The  pig,  the  rat,  gallinaceous  fowls,  flat-footed 
birds,  the  raven  and  crow  are  all  omnivorous.  Many  animals  placed 
among  this  species  from  the  characteristics  of  their  organization  appar- 
ently belong  to  the  carnivora,  such  as  the  bear,  the  fox,  and  dog ;  and 
these  animals  are  also  omnivorous,  although  to  a  less-marked  degree  than 
the  preceding  examples.  The  hog  and  wild  boar  live  on  roots,  insects, 
and  reptiles.  Rats  and  mice,  strictly  speaking,  are.  omnivorous,  since 
they  devour  ever}Tthing  that  comes  within  their  reach. 

The  duck,  which  ordinarily  seeks  aquatic  regions,  where  it  can  feed 
on  tender  vegetable  shoots  and  small  aquatic  animals  and  insects,  may 
also  be  brought  to  live  on  a  purely  vegetable  or  even  a  purely  animal  diet. 
Also,  the  fox  will  live  on  fruits  when  animal  food  is  not  accessible.  Bears, 
while  distinctly  carnivorous  in  their  type  of  organization,  are  also  omniv- 
orous animals,  and  will  often  live  exclusively  on  roots,  honey,  etc.  So 
the  sea-otter  may  be  brought  to  live  011  vegetable  matter  when  fish  cannot 
be  obtained.  The  dog,  again,  is  strictly  carnivorous  in  its  organization, 
and  yet  can  live  on  purely  vegetable  matter,  and  in  its  state  of  domesti- 
cation this  diet  seems  to  suit  him  best.  A  great  number  of  animals 
belonging  to  these  species  have  distinct  tastes  for  certain  mineral  sub- 
stances, especially  common  salt;  and  this  is,  above  all,  marked  in  the 
herbivora,  which  perish  when  deprived  of  salt,  and,  as  is  well  known,  will 


DIET   OF  ANIMALS.  199 

seek  salt,  and  congregate  at  certain  periods  of  the  day  at  points  where 
salt  is  to  be  found,  and  will  eat  earth  when  sodium  chloride  is  not  to  be 
obtained.  This,  as  already  mentioned,  is  to  be  explained  by  the  fact  that 
vegetable  matters  are  poor  in  sodium  salts  and  rich  in  potassium  salts. 
So,  also,  the  granivorous  birds  will  devour  gravel,  stones,  and  sand  from 
an  instinct  which  leads  to  their  taking  such  substances  into  their  gizzard 
to  enable  them  to  properly  triturate  their  food  ;  for,  in  the  granivorous 
birds,  the  nutritive  principles  of  the  seeds  are  inclosed  within  dense  mem- 
branes. They  are  not  provided  with  teeth  for  the  mastication  of  food, 
and,  were  no  means  supplied  for  crushing  or  triturating  their  food, 
would  starve  to  death  with  their  stomachs  full  of  the  most  nutritious 
seeds. 

The  diet  most  in  harmony  with  the  organism,  teeth,  alimentary 
canal,  etc.,  of  animals  may  be  modified  if  the  force  required  of  animals 
is  increased  artificially.  Thus,  the  horse  in  a  state  of  nature  is  never 
granivorous  or  fructivorous,  but  only  eats  herbs  ;  when  in  the  service  of 
man  grains  are  necessary  to  reduce  the  bulk  of  food,  for  horses  cannot 
work  if  their  stomach  or  alimentary  canal  is  distended  with  forage.  By 
the  administration  of  oats  the  duration  of  the  feeding  time  and  of  the 
period  of  digestion  is  reduced.  There  is  economy  of  the  digestive  secre- 
tions, the  stomach  is  much  less  distended,  and  there  is  less  time  required 
for  digestion ;  hence,  herbivorous  animals  in  domestication  become 
largely  granivorous,  and  oats  form  a  large  portion  of  their  food,  for  oats 
are  always  nutritious  in  small  bulk  and  readily  digested.  They  eontain 
all  the  food-elements  in  suitable  proportions ;  the  large  amount  of  nitro- 
gen which  they  contain  render  them  particularly  suitable  for  repairing 
waste  in  the  muscular  system,  especially  when  work  is  demanded  of  them. 
Oats  nourish,  therefore,  without  fattening.  Since  the  process  of  diges- 
tion in  the  herbivora  and  carnivora,  and  the  ultimate  nature  of  their 
food-stuffs  is  identical,  it  is  natural  to  suppose  that  their  nutritive  habits 
may  be  changed  ;  thus,  the  herbivora  may  be  brought  to  feed  on  animal 
matter,  while  the  carnivora  may  be  led  to  feed  on  matters  of  purely  vege- 
table origin.  Numerous  facts  of  this  kind  have  been  over  and  over 
again  reported.  The  most  striking  of  all  is  seen  in  the  results  of  the 
domestication  of  the  common  cat.  Here  a  typical  carnivorous  animal 
by  education  and  habit  becomes  almost  herbivorous.  So,  also,  pigeons 
have  been  accustomed  to  eat  meat  to  such  a  point  that  they  will  after- 
ward refuse  seeds.  In  Iceland,  where  vegetation  is  sparse,  the  native 
horses  arid  oxen  have  been  seen  to  feed  upon  fish,  and  it  is  even  stated 
that  they  have  been  seen  to  enter  the  water  and  fish  for  themselves.  The 
starting  point  of  this  change  from  the  herbivorous  into  the  carnivorous 
t}rpe  is  found  in  the  fact  that  all  animals  after  their  birth  are  carnivo- 
rous ;  for  in  suckling  animals  there  is  but  little  if  any  difference  in  their 


200  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

organism  from  that  of  the  carnivora.  Even  in  such  a  typical  group  of 
herbivorous  animals  as  the  ruminants  we  find  that  in  them,  when  new- 
born, the  complex  stomach  is  rudimentary  and  their  alimentary  canal 
differs  but  little  from  that  of  the  carnivora,  simply  foreshadowing  what 
will  ultimately  be  developed  when  the  animals  are  placed  upon  a  purely 
herbivorous  diet.  Among  the  carnivora  the  most  typical  examples  will 
sometimes  refuse  vegetable  nourishment,  and  the  tiger  and  lion  and  the 
eagle  have  been  known  to  die  of  starvation  rather  than  touch  it ;  never- 
theless, an  eagle  has  been  educated  to  eat  and  digest  bread.  The  native 
repugnance  to  certain  foods  is  often  overcome  b}7  cooking,  and  it  is  with- 
out doubt  to  this  circumstance  that  man  is  omnivorous  in  character. 
Thus,  dogs  and  cats  do  not  eat  corn,  but  they  will  eat  bread.  This  is, 
however,  in  all  probability  to  be  explained  by  the  fact  that  the  uucrushed 
seeds  are  incapable  of  digestion  by  carnivorous  animals,  since  their 
organs  of  mastication  do  not  permit  of  the  liberation  of  the  nutritive 
principles  from  their  undigestible  envelopes.  Cooking,  nevertheless,  does 
lead  many  animals  to  eat  food  which  is  unnatural  to  their  species ;  thus, 
the  rabbit  will  refuse  raw  meat,  but  will  often  willingly  accept  and  digest 
boiled  meat.  Certain  animals  are  both  carnivorous  and  herbivorous. 
This  is  especially  illustrated  among  the  birds,  where  some  are  fructivorous 
in  winter  and  insectivorous  in  summer ;  so  the  small  fructivorous  monkey 
will  eat  insects  and  seek  for  eggs  and  little  birds  scarcely  hatched.  Even  in 
the  same  groups  of  animals  some  are  carnivorous  and  some  herbivorous ; 
thus,  among  plantigrades  and  the  cetaceans  we  have  examples  of  each. 
It  is  worthy  of  notice,  however,  that  when  forcing  the  diet  is  arrested 
and  animals  are  restored  to  their  native  state,  they  will  again  return  to 
their  natural  food.  The  herbivora  forming  the  food  of  the  carnivora, 
and  feeding  themselves  on  vegetable  matters  for  the  maintenance  of 
their  species,  must  consequently  be  in  excess  of  the  carnivora. 

We  thus  see  that  the  choice  of  food  is  controlled  by  the  animal's 
habits  and  appetites.  Herbivorous  quadrupeds  graze  and  consume 
grasses,  bulbs,  and  grains  suitable  to  the  organs  of  their  digestive 
apparatus,  while  the  carnivora  devour  the  flesh  of  the  herbivora,  and 
show  aversion  to  the  carcasses  of  animals  allied  to  themselves  in  their 
habits.  An  artificial  mode  of  existence  forces  on  animals  predilections 
which  in  a  state  of  nature  are  not  observed.  In  nature  they  are  essentially 
moderate  in  their  desires,  but  when  domesticated  will  eat  what  they 
would  in  a  state  of  nature  avoid,  and  never  appear  to  be  satisfied, 
devouring  much  more  than  when  in  the  field,  filling  themselves  to 
repletion.  In  their  natural  state  the  exercise  connected  with  the  selection 
of  food  is  of  great  importance  to  the  health  of  the  herbivora.  They 
cannot  fast  long,  like  the  carnivora,  nor  can  they  in  a  single  meal  con- 
sume enough  to  enable  them  to  pass  hours  or  days  in  a  state  of  torpor 


DIET   OF   ANIMALS.  201 

with  a  distended  alimentary  canal  before  again  called  upon  by  the 
demands  of  hunger.  The  domestic  animals  will  sometimes  kill  them- 
selves by  overeating  when  food  is  continually  placed  before  them,  but 
that  is  only  when  they  are  from  their  surrounding  circumstances  relieved 
from  traveling  for  food  and  water ;  where  their  time  is  not,  therefore, 
largely  occupied  in  exercise  and  in  watching  for  disturbing  causes.  So, 
if  treated  artificially,  animals  should  be  managed  according  to  their 
habits.  The  collection  of  food  further  varies  in  our  different  domestic 
animals :  one  bolts  flesh  and  coarsely-ground  bones,  to  be  deposited  in  a 
capacious  stomach ;  another  rapidly  swallows  large  volumes  of  food  and 
lodges  it  for  awhile  in  a  crop  or  paunch,  to  be  again  regurgitated  and 
masticated  at  leisure.  The  fowl  crushes  its  food  beyond  the  crop  or 
stomach  in  the  gizzard.  The  ox  swallows  large  volumes  of  food  which 
have  been  subjected  to  scarcely  any  mastication,  to  return  them  at  leisure 
to  the  mouth  to  be  remasticated.  The  horse  collects  and  at  once 
thoroughly  grinds  and  mixes  food  with  saliva,  and  rapidly  passes  it  from 
its  stomach  to  its  intestines  without  the  functions  of  rumination.  Habit, 
therefore,  materially  influences  the  collection  of  food,  its  retention,  and 
appropriation  to  the  wants  of  the  animal,  and  is  itself  governed  by  the 
type  of  the  organization  of  the  digestive  tract  (Gamgee). 

On  the  basis  of  the  above  considerations  we  may  indicate  in  a  general 
wa}r  the  fundamental  principles  which  must  underlie  a  rational  system  of 
feeding.  In  the  first  place,  it  is  evident  that  the  daily  ration  must  be 
appropriate  to  the  normal  mode  of  feeding  and  digestive  peculiarities  of 
the  species ;  further,  the  digestive  power  in  different  animals  varies  not 
only  in  different  species  for  the  same  food,  but  it  varies  in  different  indi- 
viduals of  the  same  species  of  different  ages.  The  capacity  of  the 
stomach  must  be  considered,  that  the  appetite  may  be  satisfied  without 
the  stomach  being  overloaded.  Experiment  has  proved  that  the  solipedes 
should  receive  daily  2  per  cent,  of  their  body  weight  in  solids,  and  rumi- 
nants 2J  per  cent,  of  their  weight. 

In  the  second  place,  the  food  must  be  adjusted  with  special  reference 
to  the  demands  which  are  made  upon  the  animal  economy,  whether  for 
work,  fat,  or  milk  production.  Special  directions  for  so  adjusting  the 
rations  will  be  given  after  the  composition  of  the  food-stuffs  and  the 
nutritive  changes  occurring  in  different  animals  in  various  conditions 
have  been  considered.  It  may  be  here  mentioned,  however,  that  good 
hay  is  taken  as  the  type  of  a  food  for  the  larger  herbivora,  and  that  it 
shows  a  nutritive  proportion  of  one  part  of  nitrogenous  matter  to  4.8 
parts  of  non-nitrogenous  constituents,  cellulose  being  disregarded.  This 
proportion,  therefore,  represents  the  normal  relation  between  the  nitroge- 
nous and  non-nitrogenous  matters  in  the  natural  diet  of  the  herbivora ; 
and  although  this  proportion  under  certain  circumstances  may  be  widened 


202  PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 

to  1  : 8  or  contracted  to  1  : 4,  the  digestibility,  and  therefore  the  nutri- 
tive value,  of  the  fodder  is  interfered  with  if  these  limits  be  passed. 

In  the  case  of  hay,  again,  the  amount  of  fatty  constituents  is  to  the 
nitrogenous  matters  as  1  :  3.7.  If  this  proportion  be  contracted  to  1  :  2.2 
the  horse  will  still  be  able  to  accomplish  its  normal  amounts  of  work  ;  but 
if  reduced  below  this  for  the  horse,  or  below  1 :  3  for  the  ox,  the  full 
nutritive  value  of  the  food  will  not  be  appropriated.  These  figures,  of 
course,  refer  to  the  digestible  percentages  of  the  fodders,  and  by  referring 
to  the  tables  of  the  composition  of  the  different  food-stuffs,  which  will  be 
subsequently  given,  it  will  be  found  possible  to  construct  dietary  tables 
according  to  the  demands  on  the  animal  economy. 

It  may  thus  be  added  to  the  general  statements  which  have  been 
made  in  the  early  parts  of  this  section  that  not  only  must  all  animals 
receive  representatives  of  the  different  food-constituents,  but  that  the 
herbivora  must  not  receive  more  than  eight  or  less  than  four  parts  of 
non-nitrogenous  matter  to  one  of  proteid,  and  not  less  than  two  parts 
of  proteid  to  one  of  fat. 


SECTION  II. 
DIGESTION. 

I.    GENERAL  CHARACTERISTICS   OF  THE  DIGESTIVE  APPARATUS. 

DIGESTION  is  the  preparation  of  food  for  absorption,  and  is  usually 
accomplished  by  the  introduction  of  the  food  into  a  special  cavity  com- 
municating with  the  exterior,  where  it  undergoes  such  changes  as  will 
enable  it  to  pass  through  the  walls  of  the  blood-vessels.  Foods  of 
animals,  as  alreacty  shown,  are  usually  solids  ;  that  they  may  be  ab- 
sorbed and  enter  into  the  blood  of  animals  they  must  first  be  reduced 
to  a  fluid  condition;  this  solution  is  the  object  of  digestion  and  is 
accomplished  by  means  of  the  different  secretions  poured  out  by  the 
alimentary  canal.  It  is  evident,  therefore,  that  the  alimentary  tract  must 
consist  of  a  cavity  to  contain  these  digestive  fluids ;  must  communicate 
with  the  exterior  to  permit  of  the  entrance  of  food  and  removal  of 
indigestible  residue ;  that  it  must  be  provided  with  motor  organs  for 
determining  the  entrance  of  food,  and  that  its  walls  must  be  capable 
of  elaborating  digestive  secretions  and  absorbing  the  results  of  the 
digestive  process.  Digestion,  therefore,  includes  a  number  of  complex 
processes :  the  prehension  of  food  and  in  many  cases  its  mechanical 
comminution  or  mastication  by  special  organs;  secretion,  or  the  mode 
of  production  of  the  digestive  fluids  ;  absorption,  or  the  means  of  con- 
veyance of  the  digestive  products  into  the  blood  stream;  and  finally 
defecation,  or  the  expulsion  of  the  non-nutritious  residue.  If  the 
digestive  tract  is  considered  from  the  point  of  view  of  these  different 
purposes,  it  will  be  found  to  be  very  differently  constituted  in  different 
members  of  the  animal  kingdom,  its  state  of  development  governing  the 
complexity  of  all  accessory  organs. 

In  the  higher  animals  it  consists  of  the  mouth,  the  pharynx,  gullet, 
stomach,  intestine,  and  anal  aperture.  In  its  development  it  is  found 
to  be  simply  a  continuation  of  the  external  surface  reflected  inward  as 
we  would  turn  in  the  finger  of  a  glove.  Consequently,  in  the  gradual 
evolution  of  the  alimentar}'  canal  from  its  simplest  to  its  most  com- 
plex form,  we  find  every  grade  of  such  reflection,  from  a  mere  depression 
in  the  external  surface,  as  in  the  amoeba,  to  the  long  and  complicated 
intestinal  tube  of  the  ruminant.  In  all  cases  this  is  the  mode  of  origin 
of  the  alimentary  canal ;  consequently,  food,  when  within  the  alimentary 

(203) 


204 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


canal,  is  still  practically  in  contact  with  the  external  surface,  and,  there- 
fore, still  outside  the  body.  To  enable  it  to  pass  through  the  walls  of 
the  digestive  cavity  into  the  circulatory  system  is  the  object  of  diges- 
tion, and  we  shall  find  that  this  is  accomplished  by  the  production  of 
more  or  less  profound  chemical  changes  in  the  food-constituents. 

The  length,  capacity,  and  complexity  of  the  digestive  canal  are 
governed  by  the  complexity  of  the  food.  Yegetable  feeders,  therefore, 
of  all  classes  of  animals,  have  a  more  highly  developed  alimentary  canal 
than  animals  of  the  same  class  which  feed  on  animal  food.  With  this 
modification,  the  statement  may  be  made  that  there  is  a  gradual  in- 
crease in  complexity  of  the  digestive  organs  as  the  animal  scale  is 
ascended. 

In  the  amoeba  we  find  the  simplest  possible  representative  of  a 
digestive  function.  When  alimentary  substances  come  in  contact  with 
i 


FIG.  56.—  PARAMCECITTM  BITRSARIA,  AFTER  STEIN.    (Huxley.) 

1.  The  animal  viewed  from  the  dorsal  side.     A,  cortical  layer  of  the  body  ;  B,  nucleus  ;  C,  contractile 
chamber:  D  D',  matters  taken  in  as  food :  E,  chlorophyll  grannies. 

2.  The  animal  viewed  from  the  ventral  side.     A,  depression  leading  to  B,  mouth :  C,  gullet :  D, 
nucleus;  D',  nucleolus:    E.  central  sarcode.    In  both  these  figures  the  arrows  indicate  the  direction  of 
the  circulation  of  the  sarcode. 

,  3.    Paramoecium  dividing  transversely.       A  A',   contractile   spaces;      B  B',    nucleus    dividing; 
C  C',  nucleolus. 

the  soft  external  surface  of  the  amoeba  a  temporary  depression  or 
pocket  forms  around  them,  and  b}r  the  gradual  deepening  of  this  de- 
pression and  closing  of  a  wall  around  it  a  cavity  is  formed  and  the 
alimentary  substances  gradually  brought  to  the  interior  of  the  mass. 
Within  this  temporary  chamber  the  alimentary  substances  are  removed 
and  appropriated,  while  the  undigestible  residue  is  removed  by  a  process 
the  reverse  of  that  concerned  in  its  introduction.  The  amoeba  there- 
fore has,  strictly  speaking,  no  digestive  organs,  but  it  temporarily  de- 
velops a  cavity  at  the  point  of  contact  with  the  food. 

In  certain  of  the  infusoria,  such  as  the  paramcecium,  we  have  a 
single  portion  of  the  external  body  surface  specialized  as  the  orifice  of 
entrance  for  the  food-stuffs.  An  oral  aperture  (which  in  this  illustration 


CHAEACTEKISTICS  OF  THE  DIGESTIVE  APPAKATUS. 


205 


is  bordered  by  cilia)  is,  therefore,  the  first  point  of  specialization  of 
the  digestive  tract.  No  digestive  tube  is,  however,  yet  present,  but  the 
orifice  in  the  walls  of  such  an  animalcule  communicates  directly  with  a 
central  body-cavity,  and  the  orifice  of  entrance  and  exit  of  the  food  is 
the  same  (Fig.  56). 

In  the  hydra  there  is  a  definite  oral  aperture,  or  mouth,  leading  to 
a  permanent  body  cavity,  and  this  opening  serves  also  for  the  inlet  of 
food  and  the  outlet  of  the  undigestible  residue.  The  hydra  has,  how- 
ever, advanced  a  step  in  specialization,  since  it  is  provided  with  definite 
prehensile  organs  (tentacles)  for  the  seizure  of  food  (Fig.  57). 

There  are  apparently,  however,  no  true  digestive  secreting  organs  in 
the  hydra,  since  the  internal  body  cavity  appears  to  be  strictly  the  same 
as  the  external  surface.  Hydrse  have  even  been  everted,  so  as  to  make 


FIG.  57.— HYDROZO  A.     (Jeffrey-Bell. ) 
A,  hydra  viridis  attached  to  duck-weed ;  B,  a  single  specimen 

magnified;  C,  hydra  in  diagrammatic  section. 

E  C,   ectoderm  :    E  N,  endoderm ;    M,    mouth  ;    B  C,   enteric 

cavity ;  T,  tentacles. 


FIG.  58.— FLTTSTRA.  DIAGRAMMATIC 
SECTION  OF  A  SINGLE  CELL,  OF 
FLUSTRA,  OR  "SEA-MAT"  (GREATLY 

MAGNIFIED).      {  Wilson.) 

A  A,  ciliated  tentacles ;  B,  mouth  ;  C,  gullet ; 
D,  stomach;  E,  intestine:  F,  anus;  G.  nervous 
ganglion :  H  H,  general  body  cavity  ;  I,  testis ;  K, 
ovary ;  L«,  ectocyst,  or  outer  membrane  of  body ; 
M,  endocyst.  or  inner  membrane  of  body ;  N.  re- 
tractor muscle,  by  the  action  of  which  the  animal 
can  withdraw  the  ciliated  tentacles. 


the  original  outside  surface  the  lining  surface  of  the  digestive  cavity,  and 
digestion  was  still  quite  as  efficiently  performed.  Similar  types  of  digest- 
ive organs  are  seen  in  sponges  and  in  the  jelly-fish.  In  the  latter, 
however,  a  step  still  further  has  been  made  in  the  development  of  chan- 
nels for  the  distribution  of  the  nutritive  substances. 

A  true  alimentary  canal  should  have  two  openings,  one  for  the 
ingress  of  food,  the  other  for  the  egress  of  excreta.  The  simplest  form 
of  such  an  .organ  is  seen  in  the  flustra,  or  sea-mat,  and  in  the  sea-urchins 
(Fig.  58.)  In  these  organisms  both  the  mouth  and  the  vent  develop  con- 
stricting muscles.  In  the  animals  of  which  the  worm  is  the  type  (Figs. 
59  and  60),  the  digestive  tract  is  either  a  straight  tube  running  from  one 
end  of  the  bod}r  to  the  other,  or  it  ma}T  be  divided  into  little  pouches  or 
saccules.  as  in  the  leech  (Fig.  61). 


206 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


•M 


In  the  myriapods  and  larvae  the  same  general  plan  is  continued,  the 
alimentary  canal  still  being  a  simple  tube  passing  from  one  extremity 
of  the  body  to  the  other,  with  an  oral  orifice  and  vent,  but  in  these 
animals  showing  a  division  into  gullet,  stomach,  and  intestines  (Fig.  62). 
A  difference  is  also  met  with  according  as  the  animals  are  carnivorous  or 
vegetable-feeders.  In  the  former  the  canal  is  narrow  and  nearly  straight, 
with  a  slight  dilatation  representing  the  stomach, 
while  in  the  herbivorous  species  it  is  complicated 
by  saccular  pouches  to  delay  the  onward  progress 
of  the  food.  In  the  tunicata  the  division  of  the 
alimentary  canal  into  gullet,  stomach,  and  intestines 
is  more  marked,  since  we  have  in  them  a  distinct 
O3sophagus,  stomach,  small  and  large  intestines.  In 
the  crustaceans  there  exists  a  definite  digestive 
apparatus,  with  the  first  appearance  of  distinct 
glands  having  for  their  function  the  secretion  of 
digestive  juices,  crustaceans  especially  having  a 
voluminous  liver  which  secretes  a  yellowish-green 

fluid   of  the   nature   of  bile.      In  the  crustaceans 
•CG 


OES 


CP 


FIG.  59.  —  DIAGRAM  OF 
THE  ALIMENTARY  CA- 
NAL, OF  AN  EARTH- 
WORM, AFTER  BAY 
LANKESTER. 

M,  mouth;  PH.  pharynx; 
OES,  oesophagus;  CG,  calcare- 
>us  glands;  CP,  crop;  G,  giz- 
zard ;  I,  intestine. 


FIG.  60.— TRANSVERSE  SECTION  OF  EARTH-WORM  TO  SHOW 
POSITION  AND  RELATIONS  OF  THE  INTESTINES,  AFTER 
CLAPAREDE.  (Jeffrey- Bell.) 

A,  cuticle;  B,  hypodermis;  C,  layer  of  circular  muscles:  D,  layer  of  longitudinal 
muscles;  I,  enteric  cavity;  M,  "green  layer;  "  N,  dorsal  vessel;  O,  liver. 


the  liver  has  become  a  symmetrical,  lobulated  organ,  instead  of  the 
numerous  small  folliculi  which  are  found  in  earlier  forms  around  the 
alimentar}^  canal,  and  which  pours  its  secretion  into  the  upper  part  of 
the  intestine.  In  the  higher  crustaceans,  such  as  the  crabs  and  lobsters, 
there  is  a  short,  wide  sac,  provided  with  internal  hard,  calcareous  dent- 
icles, which  serves  the  purpose  of  a  gullet,  stomach,  and  gizzard.  The 


CHAKACTEKISTICS   OF  THE  DIGESTIVE  APPAKATUS. 


207 


intestine  is  short,  nearty  straight,  and  simple ;  sometimes  it  is  also  pro- 
vided with  caeca.  In  insects  there  is  a  great  variation  in  the  form  and 
length  of  the  canal,  depending  on  the  stage  of  metamorphosis  ;  nearly 


FIG.  61.— DIGESTIVE 
CANAL  OF  THE 
LEECH  (Sanguisuga 
medicinalis),  AFTER 

NUHN. 

oe,    oesophagus:    v,  stom- 


FIG. 62.— VISCERA  OF  A  CATERPILLAR.    (Rymer  Jones.) 
GH.   oesophagus:    HI,  stomach;    IM,  intestine:  K,  biliary  vessels:  QR,  salivary 


ach;  vt,  cascal  appendages;      glands:   P.  salivary  ducts;   ABC,  trachea;  D  E  E  E  E,' air-tubes ;    FFF,  epiploon,  or 
r.  rectum ;  a,  anus.  fat-mass ;  V  X  Y,  cjeca. 


208 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


always,  however,  a  gullet,  craw,  gizzard,  large  and  small  intestines,  and 
numerous  glandular  appendages  may  be  recognized  (Fig.  63). 

In  the  vermiform  larvae  the  alimentary  canal  is  a  straight  tube  passing 
from  one  end  of  the  body  to  the  other,  the  dilatations  which  represent 
the  stomach  and  crop  appearing  later.  Caeca  are  also  then  present,  and 
there  is  hence  a  division  into  small  and  large  intestines.  In  mandibulate 

insects,  as  in  the  wasps  and  beetles, 
the  crop  and  stomach  are  glandular, 
and  the  gizzard,  unlike  that  of  birds, 
is  placed  above  the  stomach,  and 
has  muscular  walls  and  a  chitinous 
lining-membrane.  In  insects  the 
form  of  the  liver  has  again  returned 
to  that  of  long,  slender  tubes,  pouring 
their  secretion  into  the  intestine, 
and  which  are  believed  to  represent 
biliary  canals  (Fig.  63).  In  carniv- 
orous insects  the  crop  and  gizzard 
and  large  intestine  are  less  developed 
than  in  those  which  feed  on  vege- 


Fio.  63.— DIGESTIVE  APPARATUS  OF  HONEY- 
BEE (Apis  mellifica),  AFTER  LEON  Du- 
FOUR. 

rjl,  salivary  gland;  rjlv,  poison-gland:  »(,  sting;  oe, 
oesophagus ;  vm,  vasa  malpjghii ;  c,  colon ;  r,  rectum ; 
ingl,  crop. 


FIG.  64.— ANATOMY  OF  THE  OYSTER. 

(Perrier). 

F,  moxith  ;    E.  stomach :    I.  intestine ;    A.  anus ; 
GG',  nervous  ganglia;  MT,  mantle;  B,  branchiae. 


table  food,  thus  indicating  in  them  the  first  appearance  of  the  distinction 
between  the  herbivorous  and  carnivorous  animals,  showing  that  the  com- 
plexit}'"  of  the  alimentary  canal  is  in  direct  proportion  to  the  complexity 
of  the  food.  The  intestine  is  narrow,  convoluted,  and  but  seldom  has  a 
mesentery;  distinctions  between  small  and  large  intestines  are  but  imper- 


CHARACTERISTICS   OF   THE   DIGESTIVE   APPARATUS. 


209 


fectly  indicated.     The  intestine  terminates  in  an  expansion,  the  cloaca, 
into  which  the  reproductive  organs  open. 

In  bivalved  mollusks  like  the  oyster  (Fig.  64)  the  gullet  and 
pharynx  are  absent  and  the  mouth  communicates  directly  with  the 
stomach,  which  is  imbedded  in  a  large  glandular  organ,  the  liver,  and  the 
intestine  after  making  a  few  turns  passes  directly  through  the  heart.  In 
univalved  mollusks  like  the  snail  the 
gullet  is  long,  the  crop  is  frequently 
present,  and  the  stomach  is  some- 
times double,  the  anterior  portion 
provided  with  teeth  and  serving  as 
an  organ  of  mastication  or  as  a  giz- 
zard (Fig.  65).  A  lobulated  liver  is 
also  here  present;  the  intestine  is 
convoluted,  passes  through  the  liver, 
and  usually  terminates  in  the  an- 
terior part  of  the  body.  The  highest 
mollusks,  such  as  the  cuttle-fish 
(Fig.  66),  show  a  marked  advance 
in  complexity,  the  highest  stage  of 
development  of  the  alimentary  canal 


s  v 


FIG.  65.— DIAGRAMMATIC  SECTION  OF  SNAIL. 
(Wilson.) 

A,  foot ;  B.  operculum :  C,  tentacles :  D.  mouth  ;  E,  sali- 
vary glands:  F,  stomach:  G  G,  intestines:  H.  amis;  I,  liver; 
L.  aperture  of  gill-chamber:  M.  oviduct:  N.  gill-chamber; 
<).  floor  of  gill-chamber:  P,  gill  of  breathing  organ;  ST.  heart; 
W,  cephalic,  X,  pedal,  and  Y,  branchial  ganglia. 


FIG.  66.— DIAGRAMMATIC  SECTION  OF  A 
FEMALE  CEPHALOPOD  (Sepia  offid- 
nalis).  (Huxley.) 

A,  buccal  mass  surrounded  by  the  lips,  and  showing 
the  horny  jaws  and  tongue :  B,  oesophagus ;  C,  salivary 
gland  ;  D,  stomach  ;  E,  pyloric  caecum  ;  F,  the  funnel ; 
G,  the  intestine ;  H,  the  anus ;  I,  the  ink-bag ;  K,  the 


duct  of  the  left  side:  O,  the  ovary;  P,  the  oviduct;  Q, 
one  of  the  apertures  by  which  the  atrial  system,  or  water 
chambers,  are  placed  in  communication  with  the  ex- 
terior; R,  one  of  the  branchiae;  S,  the  principal  ganglia 
around  the  oesophagus ;  M,  the  mantle  ;  SH,  the  internal 
shell,  or  cuttle-bone :  1,  2,  3,  4, 5,  the  margins  of  the  foot, 
constituting  the  so-called  arms  of  the  sepia. 


being  accompanied  by  the  appearance  of  definite  organs  of  circulation 
and  of  the  nervous  system. 

In  vertebrates  the  complexity  and  perfection  of  the  alimenta^  canal 
has  advanced  still  further,  and  we  find  in  them  that  the  buccal  cavity, 
which  in  fish  and  amphibians  is  single,  in  the  reptiles  is  divided  into  two 
divisions, — a  nasal  or  respiratory  portion  and  a  buccal  or  digestive 

14 


210 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


portion.  The  teeth  here  also  commence  to  be  especially  developed. 
Fishes  have  a  short,  simple,  wide  alimentary  canal  and  stomach,  separated 
by  a  marked  constriction  from  the  small  intestine,  but  the  separation  of 
the  stomach  from  the  gullet  is  less  marked,  being  indicated  often  only  by 
the  difference  in  structure  of  the  mucous  membrane ;  hence,  in  these 
animals  regurgitation  of  food  is  easy,  and  is  the  method  which  is  often 
employed  for  the  removal  of  indigestible  residue.  A  form  of  rumination 
is  also  said  to  occur  in  certain  fishes,  the  food  being  regurgitated  to  the 
mouth  and  remasticated  by  the  teeth  or  pharyngeal 
bones,  as  in  the  carp.  In  fishes  (Figs.  67  and  68) 
the  stomach  is  usually  bent  like  a  siphon,  the 
intestine  is  straight  and  short,  with  but  in  rare 
cases  any  distinction  betwreen  large  and  small 
intestines.  There  is  no  distinct  ileo-caecal  valve, 
but  sometimes  a  caecum  is  present.  The  intestine 
is  rarely  supported  on  a  mesentery. 

In  the  amphibious  reptile  the  type  of  the 
alimentary  canal  is  somewhat  similar  to  that  of 
the  fish,  though  the  distinction  between  the  large 
and  small  intestines  is  better  marked.  The  oesoph- 
agus is  short,  dilatable,  and  muscular,  and  the 
stomach  is  tubular  and  may  be  bent  upon  itself. 
A  distinction  between  large  and  small  intestines 


FIG.  67.— INTESTINAL  CANAL, 
OP  THE  STURGEON. 
(Cam*.) 

BB,  pharynx  and  cul-de-sac  of 
the  stomach  ;  A,  pylorus :  C,  pancre- 
atic appendices  of  the  pylorus ;  below 
are  seen  the  convolutions  of  the  small 
intestine  terminating  in  the  spiral 
large  intestine. 


FIG.  68.— STOMACH  OF  THE  SALMON-TROUT  (Carus), 
SHOWING  THE  PANCREATIC  APPENDICES  OF  THE 
PYLORUS  AT  A. 


is  readily  made.  The  influence  of  the  food  on  the  development  of  the 
alimentary  canal  is  seen  in  the  long,  coiled  intestine  of  the  vegetable- 
feeding  tadpole,  as  contrasted  with  the  short  intestine,  of  the  insectivo- 
rous frog  and  toad.  The  crocodile  (Fig.  69)  has  a  more  complex  stomach 
than  any  animal  lower  in  the  scale.  It  is  a  sort  of  blending  of  the 
digestive  organ  of  the  cuttle-fish  and  the  bird,  having  powerful  muscular 
walls,  with  muscular  fibres  radiating  from  a  central  tendon  in  a  manner 
very  closely  similar  to  that  seen  in  the  gizzard  of  the  bird.  The 


CHARACTERISTICS  OF  THE  DIGESTIVE  APPARATUS. 


211 


crocodile,  therefore,  forms  the  connective  link  in  the  development  of  the 
digestive  tube  between  reptiles  and  birds.  In  this  animal  the  duodenum 
is  also  first  seen,  the  liver  and  pancreas  emptying  into  it,  and  the  mesen- 
tery first  makes  its  appearance  as  a  constant  organ.  The  alimentary 
canal  of  reptiles  is  simpler  than  that  of  birds,  but  resembles  the  bird 
more  than  the  fish.  The  oesophagus  varies  with  the  length  of  the  neck,  and 
is  wide  and  dilatable  in  the  ophidia.  It  joins  the  stomach  without  any 
constriction,  its  mucous  membrane  becom- 
ing glandular.  In  the  serpents  the  cardiac 
portion  of  the  stomach  is  long,  saccular, 
and  dilatable,  while  the  pylorus  is  narrow 
and  muscular.  The  intestines  are  short 
and  wide  in  the  carnivorous  species,  but 
long  and  furnished  with  caeca  in  vegetable 
feeders. 


tomach 

L 


B 


FIG.  70.— DIGESTIVE  APPARATUS  OF 
BIRDS. 

FIG.  69.-STOMACH  OF  CROCODILE.      (Rymer  Jones.)    D    Ajp^^^-Njj^^dg^ 

C.  oesophagus :  A.  muscular  fibres  of  stomach  radiating  from  B,  creas:  H,  duodenum;  I,  small  intestine;  K, 
the  central  tendon,  as  in  the  gizzard  of  the  bird  ;  D,  commencement  of  Caeca. :  L,  large  intestine  •  M  M  ureters  •  N 
duodenum.  oviduct;  O,  cloaca. 

In  bir.ds  there  is  a  most  marked  difference  in  the  length  and  develop- 
ment of  their  alimentaiy  canal,  dependent  upon  the  nature  of  their  food, 
the  granivorous  and  fructivorous  birds  having  intestinal  tubes  of  greater 
length  and  complexity  than  those  which  live  on  animal  diet  (Fig.  70). 
In  all  cases  the  stomach  is  well  separated  from  the  oesophagus,  the 
length  of  the  latter  being,  of  course,  dependent  upon  the  length  of  the 


212 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


neck  of  the  bird,  while  its  width  and  dilatability  depend  upon  the  nature 
of  the  food.  In  granivorous  birds  we  meet  with  the  first  indication  of 
the  development  of  the  cesophageal  pouches  for  the  retention  and  macer- 
ation of  food, — organs  which  are  identical  in  function  with  the  first  three 
pouches  of  the  mammalian  ruminant  stomach.  The  locality  and  character 
of  these  pouches  vary  in  different  birds. 

In  the  granivorous  birds  this  organ,  which  is  termed  the  crop,  is 
located  at  the  lower  part  of  the  gullet.  It  may  be  double,  as  in  the  case 
of  the  pigeon,  and  distinctly  arrests  the  food  and  retains  it  in  contact 
with  fluids  to  enable  it  to  become  macerated  before  being  passed  down 
to  the  digestive  organs  proper.  In  flesh-eating  birds,  such  as  the  pelican, 


FIG.  71.— HORIZONTAL  SECTION  OF  GIZZARD  OF  GOOSE,  AFTER  GARROD. 

A,  in  contraction ;  B,  in  relaxation. 

the  pouch  is  located  higher  up  in  the  digestive  canal,  ordinarily  below 
the  lower  jaw,  and  here  seems  to  be  more  of  a  reservoir  for  storing  food 
than  as  a  distinct  commencement  of  the  digestive  apparatus.  Fruit-  and 
insect-eating  birds  are  not  supplied  with  any  such  reservoirs,  while  the 
turkey,  ostrich,  goose,  swan,  and  most  of  the  waders,  have  a  highly- 
developed  crop  ;  the  pigeon,  as  before  stated,  having  two,  one  on  each 
side  of  the  oesophagus.  The  stomach  in  birds  differs  according  as  their 
diet  is  vegetable  or  animal.  Granivorous  birds  have  a  small,  straight, 
dilatable  stomach,  called  the  proventriculus.  communicating  above  with 
the  gullet  and  below  with  a  highly  muscular  organ,  the  gizzard  (Fig. 
71),  lined  with  horny  epithelium,  usually  containing  gravel  or  sand, 


CHAKACTEKISTICS   OF   THE  DIGESTIVE   APPARATUS.  213 

and  which  has  for  its  function  the  crushing  and  mastication  of  food.  The 
proventriculus,  ventriculus  succenturiatus,  or  true  glandular  stomach, 
varies  in  form  and  size  in  different  birds,  being  sometimes  wide  and 
straight  and  sometimes  round.  In  the  rasorial  birds  it  is  wider  than  the 
gullet  and  smaller  than  the  gizzard.  Its  mucous  membrane  is  thicker 
than  that  of  the  oesophagus,  and  furnished  with  tubular  glands  which 
secrete  an  acid  digestive  secretion.  In  the  grain-eaters  these  glands  are 
sacculated,  or  expanded  into  compound  follicles,  the  disposition  of  the 
glands  varying  in  different  species.  The  gizzard,  ventriculus  bulbosus,  the 
third  or  muscular  stomach,  is  a  more  or  less  flattened,  ovoid  organ,  hav- 
ing two  apertures  at  its  upper  part,  one  communicating  with  the  proven- 
triculus, the  other  with  the  small  intestine.  The  gizzard  is  feebly  devel- 
oped, or  may  be  even  absent  in  carnivorous  birds,  such  as  the  crow  and 
the  raven,  and  is  there  simply  a  membranous  expansion  of  the  stomach, 
free  from  secreting  membrane,  and  bearing  close  analogy  and  function 
with  the  membranous  cardiac  extremity  of  the  stomach  of  the  horse. 
The  intestines  of  birds  are,  as  a  rule,  relatively  to  the  size  of  the  body, 
shorter  than  those  of  mammalia,  but  longer  than  those  of  reptiles.  In 
birds  of  prey,  as  a  rule,  they  are  not  more  than  twice  as  long  as  the  body, 
including  the  bill,  but  in  the  osprey  they  are  eight  times  as  long.  In 
fructivorous  and  granivorous  birds  they  are  much  longer.  The  duodenum 
forms  a  loop,  embracing  the  pancreas.  The  division  between  small  and 
large  intestines  is  not  clearly  marked,  as  villi  are  found  in  both.  The 
point  of  entrance  of  the  caeca,  which  are  most  developed  in  birds  feed- 
ing on  vegetable  food,  marks  the  union  of  small  and  large  intestines. 

In  all  the  groups  of  animals  already  referred  to  the  stomach  occupies 
a  position  in  the  long  axis  of  the  body.  It  is  only  in  mammals  that  its 
position  becomes  transverse  (Fig.  72),  and  we  notice  that  even  in  these 
animals  this  transverse  position  becomes  more  accentuated  during  its 
state  of  functional  activity.  Thus,  when  fasting  the  pyloric  orifice  of 
the  stomach  sinks  and  the  organ  tends  to  assume  a  longitudinal  position ; 
when  filled  with  food  it  undergoes  a  partial  rotation  on  its  own  axis,  the 
pyloric  orifice  ascends,  and  it  now  becomes  transverse. 

In  mammals  the  oesophagus  is  only  destined  to  convey  food  to  the 
stomach ;  it  has  contractile  walls,  but  few  or  no  glands,  and  the  pouches 
which  we  have  recognized  in  the  birds  are  represented  in  but  a  single 
group  of  mammals, — the  ruminants, — and  here  they  are  situated  so  low 
down  in  the  oesophagus  as  to  be  ordinarity  described  as  divisions  of  the 
stomach.  Their  function  and  structure  prove  that  they  maybe  regarded, 
nevertheless,  as  oesophageal  pouches.  The  diameter  of  the  oesophagus 
varies  according  to  the  food  which  serves  as  the  normal  diet  for  these 
animals.  It  is  large  and  readily  dilatable  in  carnivora,  which  bolt  their 
food  entire ;  it  is  narrow  in  the  herbivora ;  and  in  those  animals  which 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


thoroughly  masticate  their  food,  as  in  solipecles,  it  is  narrow  and  less 
distensible  than  in  ruminants,  where  the  preliminary  mastication  is  less 
complete. 


B'- 


FIG.  72.— DIGESTIVE  TRACT  OF  THE  DOG,  AFTER  BERNARD. 


P,  parotid    gland;     G,  -submaxillary  gland :    G",  sublingual    gland;    OE,  oesophagus,  or  gullet; 
ht  carotid  ;  C,  jugular  vein  ;  PP.  lungs,  that  on  the  left  opened  to  show  the  bronchial  tubes,  arteries, 

"I,  right  auricle  of  the  heart;  H',  left  auricle:  F',  right 
ventricle ;  O,  left  ventricle ;  P',  pulmonary  artery ;  T  T,  thoracic  duct ;  F,  liver ;  B,  gall-bladder,  enter- 


ed, right  carotid  ;  C,  jugular 
and  veins;  VC',  superior  ve 


na  cava ;  K,  aorta ;    H,  rip 


ing  the  intestine  by  the  duct,  B';  E,  stomach;  R,  spleen;  S,  Pecquet's  reservoir:  J,  lymphatics;  M, 
mesenteric  ganglia;  VP,  trunk  of  portal  vein;  V  V,  origins  of  portal  vein ;  W,  pancreas;  VC.  inferior 
vena  cava ;  D,  duodenum ;  VL,  lacteals ;  I,  small  intestine ;  Q,  caecum ;  R,  colon,  or  large  intestine. 


CHAKACTEKISTICS   OF   THE   DIGESTIVE   APPARATUS.  215 

The  stomach  is  charged  to  contain  the  food  until  it  has  undergone 
the  chemical  modifications  which  are  essential  to  its  absorption.  It  forms 
a  reservoir  which  is  in  mammals  clearly  separated  from  the  oesophagus 
and  the  intestine,  and  which,  as  already  stated,  occupies  a  transverse 
position  in  mammals,  longitudinal  in  reptiles  and  the  oviparous  verte- 
brates, while  its  transverse  position  commences  to  be  indicated  in  birds. 
The  stomach  may  be  either  simple  or  complex.  In  carnivora,  whose 
lood  is  eas}'  of  solution,  it  is  a  single  cavity  lined  with  a  uniform  mucous 
membrane  abundantly  supplied  with  glands  which  secrete  an  acid  fluid, 
the  gastric  juice,  which  has  for  its  function  the  conversion  of  albuminous 


FIG.  73.— STOMACH  OF  DIFFERENT  MAMMALS  AND  OF  A  TURTLE.    (Thanhoffer.) 

1,  stomach  of  seal ;  2,  stomach  of  hyena :  3,  stomach  of  cricetns  :  4,  stomach  of  manate ;  5,  stomach 
of  camel;  6,  stomach  of  sheep;  7,  stomach  of  lion;  8,  stomach  of  horse. 

c,  cardia ;  p,  pylorus ;  1, 2,  3, 4, 1st,  2d,  3d,  and  4th  stomachs ;  v,  ventriculus ;  /,  fundus  ventriculi. 

foods  into  peptones.  The  complication  of  the  stomach  in  mammals 
progresses  in  insensible  degrees,  and  in  a  general  way  is  in  proportion  to 
the  indigestibility  of  the  food  (Fig.  73).  At  first^the  division  of  the 
stomach  into  pouches  is  only  indicated  by  a  difference  in  structure  and 
properties  of  the  mucous  membrane  of  the  cardiac  and  pyloric  portions 
of  this  vis'cus.  This  difference  is,  to  a  certain  extent,  present  in  all 
animals,  even  in  the  carnivora,  where  it  is  confined  simply  to  a  histologi- 
cal  difference  in  the  nature  of  the  glands  of  these  two  portions  of  the 
stomach.  No  difference  is,  however,  evident  to  the  naked  eye  in  these 
animals.  In  the  horse  the  separation  into  a  cardiac  and  pyloric  pouch  is 


216  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

indicated  by  a  groove  seen  on  the  external  surface  of  this  organ  and  in- 
ternall}T  b}T  a  sharp  demarcation  between  the  glandular  mucous  membrane 


FIG.  74.— POSTERIOR  SURFACE  OF  STOMACH  OF  HORSE.     (Strangeways.) 

A,  left  cul-de-sac;  B,  right  cul-de-sac;  C,  greater  curvature:  D,  lesser  curvature;  E,  oesophagus;  F,  duodenum. 

of  the  pyloric  portion  and  the  membranous  portion  of  the  cardiac  end. 
In  the  solipedes  (Fig.  74),  therefore,  the  general  appearance  and  char- 
acters of  the  stomach  correspond  with  those  of  the  carnivorous  birds, 


FIG.  75.— STOMACH  OF  HOG,  INFLATED.    (Strangeways.) 

A,  cardiac  portion ;    B,  its  accessory  cul-<1e-sar, ;    C.  pyloric  portion ;    D,  lesser  curvature ;    E,  greater  curvature ; 
F,  oesophagus ;   G,  pyloric  orifice. 

where  we  have  a  separation  into  a  glandular  and  membranous  portion; 
the  difference  between  these  animals  consisting  in  the  fact  that  in  such 
birds  it  is  the  cardiac  extremity  which  is  glandular,  and  the  pyloric 


CHARACTERISTICS  OF  THE  DIGESTIVE  APPARATUS.     217 

extremity,  or  the  rudiment  of  the  gizzard,  membranous,  while  in  the  horse 
the  reverse  holds.  In  the  hog  (Fig.  75)  the  division  into  pouches  is 
more  marked  by  the  appearance  of  a  distinct,  curved,  conical  diverticulum 
at  the  cardiac  extremity  of  the  stomach.  In  the  porcupine  three  or  four 
contractions  are  marked,  and  in  the  kangaroo,  porpoise  and  other  ceta- 
ceans, and  many  rodents  a  large  number  of  dilatations,  separated  by 
marked  constrictions,  are  to  be  noticed  (Fig.  76).  In  other  animals  this 
complication  is  not  only  in  external  form,  but  also  in  internal  structure, 
the  highest  degree  of  complexity  being  found  in  the  ruminant,  where 
the  stomach,  so  called,  is  divided  into  four  distinct  gastric  sacs,  com- 
municating with  each  other  only  by  small  orifices,  whose  function  and 
structure  will  occupy  us  later  (Fig.  77).  This  complication  is  found  not 


FIG.  76.— STOMACH  OF  THE  DUGONG,  AFTER  SIR  EVERARD  HOME. 

rloric  portion :    C,  constriction  between  the  1 
the  stomach ;  F,  oesophagus ;  G,  intestine. 


A,  cardiac  portion  of  stomach ;  B.  pyloric  portion :    C,  constriction  between  the  two ;    D  D,  tubular  prolongations 
of  T 


only  in  mammals,  but  also  in  birds ;  but,  whatever  may  be  the  external 
form  of  the  organ,  the  function  is  always  the  same, — to  supply  an  acid 
secretion  for  the  solution  and  digestion  of  certain  constituents  of  the 
food, — and  where  reservoirs  are  present  their  function  is  simply  to 
retain  food  until,  as  in  the  case  of  the  ruminant,  it  may  be  again  masti- 
cated ;  or  in  all  cases  to  enable  the  food  to  undergo  preparatory  changes 
before  being  subjected  to  the  action  of  the  gastric  secretion. 

The  intestine  is  the  prolongation  of  the  stomach,  and  its  shape  as  a 
canal  is  again  regained.  In  its  simplest  form  in  the  lowest  animals  it  is 
a  short  tube  of  uniform  size,  with  the  same  structure  and  properties  from 
one  end  to  the  other,  as  seen  in  invertebrates,  in  most  reptiles  and  fishes, 
and,  among  the  mammals,  in  the  hedgehog  and  the  bat.  In  the  higher 


218 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


classes  it  is  divided  into  two  forms,  the  small  and  large  intestines.  The 
small  intestine  is  destined  for  the  absorption  of  food-products,  and  for 
the  elaboration  of  the  digestive  secretions  for  the  solution  of  food-stuffs 
which  have  escaped  the  action  of  the  gastric  juice.  We  find  its  walls, 
therefore,  supplied  with  tubular  glands  secreting  the  so-called  intestinal 
fluid ;  and  emptying  into  the  small  intestine  we  find  in  all  cases  two  large 
glandular  organs,  the  liver  and  pancreas,  secreting  alkaline  fluids  which 
have  a  greater  or  less  importance  in  digestion.  In  the  small  intestine  of 
mammals  are  also  to  be  found  special  organs  for  assisting  the  absorption 


FIG.  77.— STOMACH  OF  ADULT  SHEEP,  DRIED  AND  INFLATED  ;  ONE-FIFTH 

THE  NATURAL  SIZE.     (TlianJi offer.) 

B,  rumen ;  R,  reticulum ;  S,  omasum  ;  O,  abomasum :  c,  cardia :  p,  pylorus ;  br,  oesophagus :  cb, 
cardiac  valve;  be,  oesophageal  gutter;  r,  pillars  of  the  rumen;  rn,  opening  of  the  reticulum;  on,  open- 
ing of  the  abomasum,  or  fourth  stomach ;  b,  valve  between  reticulum  and  omasum ;  e,  duodenum. 

of  food,  the  so-called  villi,  which  are  simply  conical  expansions  covered 
by  mucous  membrane,  whose  function,  together  with  that  of  the  folds  of 
the  mucous  membrane,  is  simply  to  give  increased  surface  for  absorption. 
In  the  higher  animals  the  small  intestine  is  divided  arbitrarily  into  three 
divisions,  the  duodenum,  or  the  portion  of  bowel  directty  in  communica- 
tion with  the  stomach,  which  is  always  curved  and  usually  free  from 
mesentery.  Following  this  we  have  the  jejunum,  so-called  because  ordi- 
narily found  empty,  and  following  that  the  ileum. 

The   intestinal   canal   is   supplied   with   muscular   fibres,   arranged 
longitudinally  and  in  concentric  rings,  being  red-striped  muscular  fibres 


CHAEACTEKISTICS  OF  THE  DIGESTIVE  APPAKATUS.     219 

in  the  mouth,  pharynx,  and  anus,  and  pale,  unstriped,  involuntary  fibres 
elsewhere.  The  contractions  of  these  muscular  fibres  in  the  small  and 
large  intestines  serve  to  cause  the  onward  progression  of  the  food  or  the 
so-called  peristaltic  movement  of  the  intestines.  The  mucous  membrane 
of  the  alimentary  canal  is  epithelial  in  nature  in  the  mouth,  pharynx, 
and  gullet,  and  in  the  first  three  pouches  of  the  ruminant  stomach,  and 
in  the  cardiac  half  of  the  stomach  of  the  horse.  It  is  free  from  glands, 
and  is  simply  protective  in  nature.  In  the  entire  stomach  of  carnivorous 
animals,  the  fourth  stomach  of  ruminants,  and  the  pyloric  half  of  the 
stomach  of  solipedes,  as  well  as  through  the  entire  extent  of  the  in- 
testines of  all  mammals,  it  is  glandular,  and  furnishes  a  more  or  less 
active  digestive  secretion. 

Sensory  nerves  are  supplied  to  the  two  extremities  of  the  digestive 
tube,  while  the  intermediary  portions  are  supplied  with  nerves  whose 
stimulation  seems  to  lead  to  secretion,  and  not,  as  a  rule,  to  individual 
sensations. 

The  extent  of  mucous  membrane  varies  natural!}'  with  the  length, 
diameter,  and  complexity  of  the  alimentary  canal.  It  is,  therefore,  less 
in  carnivora,  greater  in  omnivora,  and  immense  in  herbivora.  The  extent 
of  surface,  therefore,  depends  upon  the  complexity  of  the  food.  The 
more  concentrated  the  food,  as  in  carnivora,  the  less  surface  is  required 
for  producing  secretion,  and  the  less  for  its  absorption.  In  animals 
living  on  a  vegetable  diet,  where  the  nutritive  principles  of  the  food  are 
mixed  writh  a  larger  amount  of  non-nutritious  residue,  a  greater  surface  is 
required  for  secretion,  greater  time  is  required  for  digestion,  and  a 
greater  surface  must  be  supplied  for  the  absorption  of  digestive  matters  ; 
we  find,  therefore,  that  in  herbivorous  animals  the  intestinal  tube  is 
always  longer,  more  complicated,  and  supplied  with  a  larger  extent 
of  mucous  membrane  than  in  the  carnivora.  Even  in  the  herbivora 
we  find  a  difference  in  the  distribution  of  the  mucous  surfaces ;  thus, 
the  horse  and  ox  are  both  herbivorous  animals :  the  former  is  a 
monogastric  animal,  the  latter  a  pol}*gastric,  or  ruminant.  The  former 
digests  little  by  its  stomach,  and  much  by  its  intestinal  tube;  the 
latter  readily  digests  more  by  its  vast  and  complex  stomach  than  by  its 
narrow  and  small  intestinal  tube.  Both,  however,  from  the  fact  that 
they  are  herbivorous  animals,  have  a  great  extent  of  mucous  mem- 
brane, which  may  be  twice  or  three  times  as  extensive  as  their  ex- 
ternal body  surface.  Thus,  the  cutaneous  surface  of  the  horse  is  about 
five  or  six  square  meters,  while  its  mucous  gastro-intestinal  surface 
may  be  as  much  as  twelve  square  meters,  of  which  one-thirtieth  is 
represented  by  the  stomach  and  the  rest  by  the  intestines.  An  ox,  on 
the  other  hand,  of  about  the  same  size,  has  a  mucous  membrane  of  about 
seventeen  square  meters,  of  which  nine  square  meters  represent  the 


220  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

membrane  of  the  stomach.  Consequently,  the  solipede  has  a  mucous 
membrane  about  twice,  and  the  ruminant  about  three  times,  as  extensive 
as  its  cutaneous  surface,  while  the  mucous  membrane  of  the  stomach 
alone  of  the  ox  is  one  and  one-half  times  as  extensive  as  the  skin  sur- 
face. In  the  carnivora — the  dog  or  the  cat,  for  example — the  mucous 
membrane,  from  the  simple  character  of  their  food,  is  very  much  less 
extensive  in  proportion  to  their  external  body  surface,  being  only  about 
two-thirds  as  large  as  their  skin  surface.  The  omnivora,  again,  occupy  a 
mean  between  the  carnivora  and  the  herbivora. 

The  length  of  the  alimentary  canal,  in  a  less  strict  degree,  however, 
is  also  subordinate  to  the  character  of  the  alimentation.  In  the  herbiv- 
ora the  intestinal  tube  may  be  as  much  as  twenty-eight  times  the  length 
of  the  body,  while  the  intestinal  canal  of  the  carnivora  is  only  three  or 
four  times  as  long  as  the  body.  There  are,  however,  many  exceptions 
to  this  rule.  Thus,  the  dromedary  has  an  intestinal  tube  only  five  times 
as  long  as  its  body ;  the  ram  twenty-eight  times  as  long  ;  the  deer  twelve 
times ;  the  rabbit  nine ;  elephant  seven ;  the  hyena  eight,  and  the  seal 
twenty-eight  times  as  long  as  its  body  length.  In  these  apparent  excep- 
tions, as,  for  example,  in  the  case  of  the  seal,  a  carnivorous  animal , 
though  there  is  an  intestinal  tube  twenty-eight  times  as  long  as  its  body, 
we  have  the  proportion  of  mucous  membrane  still  preserved  ;  for,  where 
in  herbivorous  animals  we  have  a  comparatively  short  tube,  its  diameter 
is  always  proportionately  great,  while  in  the  case  of  carnivorous  ani- 
mals, where  the  tube  is  long,  its  diameter  is  accordingly  small.  Thus, 
the  alimentary  canal  of  the  horse  is  shorter  than  that  of  the  ox,  the 
former  being  about  ninety  feet ;  but  it  is  very  much  more  capacious. 

Change  in  the  normal  diet  of  animals  leads  to  changes  in  the  rela- 
tive dimensions  of  their  intestinal  canals.  Thus,  the  alimentary  tube  of 
the  wild  boar  is  shorter  than  that  of  the  domestic  hog,  since  its  habit  in  a 
state  of  nature  is  more  carnivorous  than  in  domestication.  The  domes- 
ticated cat,  living  on  a  mixed  diet,  has  an  intestinal  tube  which  is  longer 
than  the  cat  in  a  state  of  nature,  and  the  same  difference  also  applies  to 
the  domestic  ox  as  contrasted  with  the  buffalo. 

The  relative  capacity  of  the  alimentary  canal  is  even  more  strictl}' 
definable  in  different  species  according  to  their  alimentation.  The  herbiv- 
ora always  have  a  greater  capacity  of  intestinal  tube  than  the  carnivora. 
In  all  cases  the  volume  of  the  stomach  is  in  inverse  proportion  to  that  of 
the  capacit}'  of  the  intestine.  Thus,  in  the  horse  the  stomach  is  capable 
of  containing  from  about  sixteen  to  eighteen  litres,  while  the  capacity  of 
the  horse's  intestine  varies  from  one  hundred  and  twenty-five  to  three 
hundred  litres.  In  the  ox  the  stomach  contains  two  hundred  litres,  the 
intestine  one  hundred  litres.  The  value  of  these  differences  will  be 
studied  later.  They  serve  simply  to  indicate  the  immense  expanse  in 


CHARACTERISTICS  OF  THE  DIGESTIVE  APPARATUS.     221 

the  alimentary  canal  of  the  herbivora.  The  extent  of  surface  for  absorp- 
tion in  the  intestinal  tube  is  still  further  increased  by  the  formation  of 
plicie,  or  folds  of  mucous  membrane,  and  from  what  has  been  said  above 
we  would  naturally  expect  that  these  are  more  extensive  and  more  highly 
developed  in  the  herbivora  than  in  the  carnivora.  This  is  well  exem- 
plified in  the  case  of  the  ox,  whose  stomach,  which  is  capable  of  contain- 
ing two  hundred  litres,  has  onhr  two  square  meters  of  external  surface, 
and  yet  whose  internal  mucous  surface  amounts  to  nine  square  meters. 
Such  an  immense  increase  of  internal  over  external  surface  could  only 
be  accomplished  by  the  throwing  up  of  the  mucous 'membrane  into  folds. 
In  the  intestine,  again,  which  is  capable  of  holding  about  sevent37-five 
litres,  the  square  surface  externally  amounts  to  fifteen  or  sixteen  meters, 
showing,  therefore,  that  in  the  ox  the  mucous  coating  of  the  intestine 
is  more  simple. 

The  carnivora  are  distinguished  by  a  large,  voluminous   stomach, 
coated  throughout  with  a  secreting  mucous  membrane,  and  the  intestine 


FIG.  78.— C^CUM  OF  A  DOG,  INFLATED.    (Strangeways.) 

A,  ileum ;  B,  caecum ;  C,  colon. 

is  simple  and  deprived  of  folds.  With  the  exception  of  the  cetacea  and 
a  few  edentata,  the  subdivision  into  a  small  and  large  intestine  prevails 
throughout  the  entire  group  of  mammals.  The  greater  the  length  of 
the  small  intestine,  the  more  is  it  convoluted.  Yilli  are  always  absent 
from  the  large  intestine.  A  well-marked  ileo-caecal  valve,  with  but  few 
exceptions,  is  situated  at  the  junction  of  the  small  and  large  intestines. 

At  this  point,  also,  is  almost  invariably  found  a  diverticulum, 
called  the  caecum,  which  varies  very  greatly  in  size  and  functional  impor- 
tance in  different  animals,  these  differences  also  being  dependent  upon 
differences  in  regimen.  In  the  carnivora  the  caecum  is  only  a  spiral 
appendix,  as  seen  in  the  dog  (Fig.  78),  and  the  large  intestine  is  divided 
into  the  ascending,  transverse,  and  descending  portions,  as  in  man ;  there 


222 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


is  no  floating  colon,  and,  while  the  mucous  membrane  is  sacculated  to  a 
certain  extent,  the  folds  are  by  no  means  as  extensive  as  in  the  herbivora. 
In  the  omnivora  the  caecum  resembles  that  of  the  horse  in  having  three 
longitudinal  bands  and  transverse  constrictions,  and  has  increased  in 
complexity  from  that  of  the  carnivorous  animal.  It  is  absent  in  the 
bear  and  weasel.  The  caecum  reaches  its  highest  degree  of  complexity  in 
the  monogastric  herbivora.  In  these  animals,  as  in  the  horse  (Fig.  79),  it 
becomes  greatly  enlarged,  convoluted,  condensed  into  folds,  has  special 


Fro.  79.— CAECUM  AND  GKEAT  COTTON  OK  HORSE.    (Strangeways.) 

A,  caecum;  B  C,  its  muscular  bands;  D,  termination  of  ilenm:  E,  first,  E'.  second,  F,  third,  and 
F',  fourth  divisions  of  colon ;  G,  pelvic  flexure;  H,  origin  of  floating  colon.  The  arrows  indicate  the 
course  of  the  food  through  the  colon. 

valves  and  glands,  and  in  the  horse  may  contain  six  gallons  of  fluid, 
being  three  times  as  large  as  the  stomach.  In  the  solipede  and  rodent 
the  caecum  therefore  reaches  its  highest  stage  of  development,  and  has 
special  digestive  functions  to  fulfill.  In  the  ox,  whose  small  intestine 
differs  but  little  from  that  of  the  horse,  although  it  is  smaller  in  calibre 


CHARACTERISTICS  OF  THE  DIGESTIVE  APPARATUS.     223 

and  twice  as  long,  from  the  fact  that  the  increased  complexity  of  the 
stomach  furnishes  the  necessary  differences  for  the  digesting  of  the 
food  the  caecum  is  smooth  and  devoid  of  longitudinal  and  transverse 
bands  (Fig.  80).  Its  free  extremity  is  blunt,  rounded,  and  directed  back- 
ward, and  floats  free  in  the  abdomen,  while  its  other  extremit3r,  having 
received  the  insertion  of  the  ileum,  is  continuous  with  the  colon,  which 
also  is  free  from  bands,  and  soon  becomes  constricted,  and  then,  preserv- 
ing about  the  same  diameter  throughout,  is  arranged  in  an  elliptical 
coil  between  the  folds  of  the  mesentery.  In  the  ox  there  is  no  distinction 
between  the  great  and  floating  colon,  as  in  the  horse.  The  total  length  of 
the  large  intestine  in  the  ox,  from  the  caecum  to  the  rectum,  is  about 
thirty-six  feet,  but  its  capacity  is  much  less  than  in  the  horse. 

Further  details  as  to  the  functions  and  structure  of  the  different 
parts  of  the  alimentary  canal  in  the  various  domestic  animals  wilt  be 


FIG.  80.  C.ECUM  AND  ORIGIN  OF  COLON  OF  AN  Ox,  INFLATED.    (Strangeways.) 

A,  terminal  portion  of  the  ileum  ;  B,  caecum ;  C,  origin  of  colon. 

given  during  the  consideration  of  the  subject  of  digestion.  So  far  the 
aim  has  been  merely  to  indicate,  in  a  general  wa}r,  the  adaptability  of 
the  digestive  organs  to  the  character  of  the  food. 

The  following  tables,  compiled  by  Colin,  represent  the  different 
comparative  dimensions  and  capacities  of  different  parts  of  the  ali- 
mentary canal  in  the  domestic  animals.  They  offer  confirmation  of  the 
statement  already  made  that  the  functional  activity  of  the  stomach  and 
digestive  tube  being  in  inverse  ratio,  in  those  herbivora  with  capacious, 
complex  stomachs  the  intestinal  tube  will  always  be  less  developed  than 
in  the  monogastric  herbivora,  where  the  role  of  the  stomach  in  digestion 
is  secondary  to  that  of  the  intestine. 


224 


PHYSIOLOGY   OF   THE    DOMESTIC   ANIMALS. 


LENGTH  OF  DIFFERENT  PORTIONS  OF  THE  INTESTINE  COMPARED  WITH  THAT 

OF  THE  BODY. 


ANIMAL. 

Parts  of  Intestine. 

i 

S 

8 

.s 

S3 

1 

Minimum  in 
Meters. 

Maximum  in 
Meters. 

Ratio  between 
Body  Length 
and  that  of 
Intestine. 

Horse,    . 

Small  intestine,      .        . 
Caecum,          .        .        . 

Fixed  colon,        .  „•' 
Floating  colon, 

0.75 
0.04 
0.11 
0.10 

22.44 
1.00 
3.39 
3.08 

16.00 
0.81 
2.91 
2.35 

31.60 
1.28 
4.00 
3.44 

1:12 

Total  length,  .      .  . 

1.00 

29.91 

22.07 

40.32 

Ass,       .        . 

Small  intestine,      . 
Caecum, 
Fixed  colon, 
Floating  colon,      .         . 

0.67 
0.06 
0.17 
0.10 

12.00 
1.02 
3.00 
1.85 

1:11 

Total  length,  . 

1.00 

17.87 

Mule,     . 

Small  intestine,      .     '  . 
Caecum, 
Fixed  colon, 
Floating  colon,      .        * 

0.70 
0.05 
0.13 
0.12 

18.56 
1.21 
3.50 
3.23 

1:11 

Total  length,  .        .  ' 

1.00 

26.50 

Small  intestine,      .      •  ...'.' 
Caecum  .        .        «        . 

0.81 
0.02 

46.00 

0.88 

41.00 
0.78 

51.00 
1.00 

1:20 

Ox, 

Colon,    .        .      •;-..    ;. 

0.17 

10.18 

9.25 

11.00 

Total  length,  . 

1.00 

57.06 

51.03 

63.00 

Dromedary,  . 

Small  intestine, 
Caecum,  .         .    "     . 
Colon,    ... 

0.63 
0.01 
0.36 

31.20 
0.40 
17.72 

1:15 

Total  length,  .    •    . 

1.00 

49.32 

Sheep  and  Goat, 

Small  intestine, 
Caecum,  .        .  .      •.     -.  y 
Colon,    . 

0.80 
0.01 
0.19 

26.20 
0.36 
6.17 

15.32 
0.21 
4.10 

33.00 
0.45 
'  8.49 

1:27 

Total  length,  . 

1.00 

32.73 

19.63 

41.94 

Hog,      .        i 

Small  intestine, 
Caecum,  .... 

Colon,    .         .        -,.      '  • 

0.78 
0.01 
0.21 

18.29 
0.23 
4.99 

14.79 
0.20 
4.32 

20.14 
0.25 
5.55 

1:14 

Total  length,  . 

1.00 

23.51 

19.31 

25.94 

Dog,    ^        . 

Small  intestine, 
Caecum,  .... 

Colon,    .        ;       V        . 

0.85 
0.02 
0.13 

4.14 
0.08 
0.60 

2.00 
0.03 
0.23 

6.10 
0.16 
1.05 

1:    6 

Total  length,  . 

1.00 

4.82 

2.26 

7.31 

Cat,        . 

Small  intestine, 
Large  intestine, 

0.83 
0.17 

1.72 
0.35 

1.27 
0.30 

1.94 
0.40 

1:    4 

Total  length,  . 

1.00 

2.07 

1.57 

2.34 

Rabbit,.     •   .. 

Small  intestine, 
Caecum,  .... 
Colon,    .... 

0.61 
0.11 

0.28 

3.56 
0.61 
1.65 

3.30 
0.50 
1.41 

3.90 
0.76 
1.85 

1:10 

Total  length,  . 

1.00 

5.82 

5.21 

6.51 

CHAKACTEKISTICS   OF  THE  DIGESTIVE  APPARATUS. 


225 


ABSOLUTE   AND    RELATIVE   CAPACITY   OP    THE   STOMACH  AND  INTESTINE  OP 
THE  DOMESTIC  ANIMALS. 


ANIMAL. 

Parts  of  Intestine. 

Ratio. 

Mean  in 
Litres. 

Minimum 
in  .Litres. 

Maximum 
in  Litres. 

Horse, 

Stomach,  .... 
Small  intestine, 
Caecum,      .... 
Fixed  colon, 
Floating  colon  and  rectum, 

0.085 
0.302 
0.159 
0.384 
0.070 

17.96 
63.82 
33.54 
81.25 
14.77 

10.00 
38.30 
16.20 
55.00 
10.00 

37.50 

105.00 
68.00 
128.00 
19.00 

Total  capacity,  . 

1.000 

211.34 

129.50 

357.50 

Ass,.        .        . 

Stomach,  .... 
Small  intestine, 
Caecum,      .... 
Fixed  colon, 
Floating  colon  and  rectum, 

0.097 
0.229 
0.201 
0.397 
0.076 

10.00 
24.00 
21.00 
41.50 
8.00 

Total  capacity,  . 

1.000 

104.50 

Ox,  . 

Stomach,   .... 
Small  intestine, 
Caecum,      .... 
Colon  and  rectum,     . 

0.708 
0.185 
0.028 
0.079 

252.50 
66.00 
9.90 

28.00 

215.00 
56.00 
8.80 
26.00 

290.00 
76.00 
11.00 
30.00 

Total  capacity,  . 

1.000 

356.40 

305.80 

407.00 

Dromedary, 

Stomach,   .... 
Small  intestine, 
Caecum,      .         . 
Colon,        .... 

0.810 
0.131 
0.011 
0.048 

245.00 
39.50 
3.40 
14.60 

Total  capacity,  . 

1.000 

302.50 

Sheep  and  Goat, 

Rumen,     .... 
Reticulum,         .         . 
Manyplies, 
Abomasum, 
Small  intestine, 
Caecum,      .... 
Colon  and  rectum,     . 

0.529 
0.045 
0.020 
0.075 
0.204 
0.023 
0.104 

23.40 
2.00 
0.90 
3.30 
9.00 
1.00 
4.60 

Total  capacity,  . 

1.000 

44.20 

Hog,         .        . 

Stomach,   .... 
Small  intestine,      -   .        .. 
Caecum,      .... 
Colon  and  rectum,     . 

0.292 
0.335 
0.056 
0.317 

8.00 
9.20 
1.55 

8.70 

7.50 
8.60 
1.50 
6.10 

8.50 
9.80 
1.60 
11.30 

Total  capacity,  . 

1.000 

27.45 

23.70 

31.20 

Cat,  . 

Stomach,   .... 
Small  intestine, 
Large  intestine,     "-    . 

0.695 
0.146 
0.159 

0.341 
0.114 
0.124 

0.287 
0.095 
0.118 

0.378 
0.127 
0.130- 

Total  capacity,  . 

1.000 

0.579 

0.500 

0.635 

Dog, 

Stomach,  .... 
Small  intestine, 
Caecum,      .... 
Colon  and  rectum,     . 

0.623 
0.233 
0.013 
0.131 

4.33 
1.62 
0.09 
0.91 

0.65 
0.25 
0.01 
0.07 

8.00 
3.00 
0.20 

2.20 

Total  capacity,  . 

1.000 

6.95 

0.98 

13.40 

15 


226 


PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 


COMPARISON  OF  THE  GASTRO-INTESTINAL   Mucous  SURFACES  WITH   THAT  OF 

THE  SKIN. 


ANIMAL. 

Organ. 

Partial 
Mucous 
Surface 
in  Square 
Meters. 

Total 
Mucous 
Surface 
in 
Square 
Meters. 

Skin 
Surface 
in 
Square 
Meters. 

Ratio 
between 
Mucous 
Surface 
of 
Stomach 
and 
Intestine. 

Ratio 
between 
Skin  and 
Gastro- 
intestinal 
Mucous 
Surfaces. 

Stomach  

0.40 

Small  intestine,          . 

4.39 

Horse, 

Caecum,      .... 

1.50 

14.95 

5.50 

1  :  29.87 

1  :  2.18 

Fixed  colon,      .        . 

4.29 

Floating  colon,  .  -  .    . 

1.37 

Rumen,     . 

2.00 

Reticulum, 

0.43 

Ox,     .        . 

Manyplies, 
Abomasum, 

5.56 
1.18 

17.23 

5.80 

1  :  7.61 

1  :  2.97 

Small  intestine, 

5.60 

Caecum,      .        .        . 

0.46 

Colon,        ... 

2.00 

Stomach,   .... 

0.19 

Hog,  .        . 

Small  intestine, 
Caecum,     .... 

1.66 
0.11 

2.81 

1  :  13.22 

Colon,        .... 

0.83 

Stomach,  .         .         . 

0.12 

r>og)  . 

Small  intestine, 
Caecum,      .... 

0.32 
0.005 

0.52 

0.88 

1  :  3.36 

1  :  0.59 

Colon,        .... 

0.06 

. 

Stomach,   .... 

0.02 

Cat,    . 

Small  intestine, 

0.07 

0.12 

0.21 

1  :  4.15 

1  :  0.58 

Large  intestine, 

0.02 

II.    PREHENSION   OF  FOOD. 

1.  PREHENSION  OF  SOLIDS. — By  the  term  prehension  of  food  is  meant 
the  different  methods  emplo3Ted  by  animals  in  seizing  their  food  and 
conveying  it  to  the  oral  aperture  of  their  alimentary  canal.  Man}T  aquatic 
animals,  whose  food  consists  of  small  particles  diffused  through  water, 
are  supplied  with  an  apparatus  for  producing  currents  so  as  to  bring 
such  substances  within  their  reach.  This  is  especial^  true  in  the  case 
of  fixed  forms  of  life  which  are  unable  to  go  in  search  of  their  food. 
Thus,  the  sponge  and  sea-mat,  and  various  other  of  the  lower  forms  of 
life,  obtain  their  nourishment  by  the  production  of  currents  in  the  water 
through  the  vibration  of  cilia  lining  or  surrounding  the  opening  of  their 
alimentary  canal.  In  infusoria,  also,  we  find  similar  arrangements, 


PEEHENSION   OF  FOOD.  227 

either  in  the  form  of  cilia  or  even  in  tentacles.  In  the  lowly-organized 
rhizopods  and  amoebae,  their  soft,  jelly-like  body  is  simply  applied  to 
the  food,  which  then  and  there  enters  their  body  substance.  The  most 
marked  illustration  of  the  mode  of  seizing  food  by  means  of  prehensile 
tentacles  is  found  in  the  case  of  the  hj'dra  or  polyp, — small  organisms 
whose  bodies  are  not  usually  longer  than  one  centimeter,  and  which,  as 
already  described,  are  supplied  with  a  single  body  cavity,  around  the 
single  opening  of  which  are  long,  slender,  retractile  tentacles,  themselves 
often  provided  with  cilia,  and  which  are  capable  of  grasping  small  sub- 
stances which  may  serve  as  their  food  and  conveying  them  to  their 
digestive  sac ;  the  adhesive  power  of  these  tentacles  is  increased  by  a 
number  of  minute  spiral  filaments,  the  so-called  "urticating  cysts," 
which  by  some  observers  are  supposed  to  be  offensive  weapons,  and  are 
used  to  paralyze  the  small  organisms  that  serve  as  their  food.  The  jell}-- 
fish  furnishes  another  example  of  a  similar  method  of  seizing  food. 
These  prehensile  tentacles  may  be  few  and  simple,  as  in  the  hydra;  very 
numerous,  as  in  the  sea-anemone;  and  often  of  great  length  and  irregular 
form,  as  in  the  medusae. 

Bivalve  mollusks,  like  the  oyster  and  the  clam,  employ  the  vibration 
of  cilia  for  creating  currents  to  bring  the  nutritive  matters  suspended  in 
water  within  their  reach.  When  the  food  is  solid  permanent  prehensile 
organs  are  usually  present,  though  they  may  be  extemporized,  as  in  the 
case  of  the  amoeba,  where  any  portion  of  the  body  surface  which  is 
accidentally  in  contact  with  food  may  serve  as  a  prehensile  organ  to 
draw  matter  into  the  interior  of  its  body.  In  a  higher  stage  of  develop- 
ment we  find  that  tentacles  are  absent,  but  that  their  function  is  assumed 
by  flexible  portions  of  their  body,  commonly  called  arms,  which  are 
provided  with  a  number  of  minute  adhesive  organs,  which  serve  to  seize 
their  food,  and  whose  flexibility  enables  them  to  convey  it  to  their  oral 
aperture.  This  form  of  prehension  of  food  is  seen  in  the  star-fish.  In 
the  sea-urchin  a  considerable  advance  is  seen  in  the  method  of  prehension 
of  food.  The  mouth  itself  is  there  the  prehensive  organ,  and  is  provided 
with  five  sharp  teeth,  each  standing  in  a  single  jaw,  and  capable  of  being 
projected  so  as  to  seize  as  well  as  masticate  the  prey.  Univalve  mollusks, 
such  as  the  snail,  have  again  another  organ,  the  tongue  serving  as  an 
organ  of  prehension.  In  this  case  the  tongue  is  long  and  covered  with 
minute  recurved  teeth  or  spines,  by  which  the  food  is  seized  and  drawn 
into  the  mouth,  the  upper  part  of  which  is  armed  with  a  sharp,  horny 
plate.  In  the  cuttle-fish,  again,  the  organs  of  prehension  of  food  have 
advanced  still  further  in  their  development.  The  tongue  is  still  present 
as  a  prehensile  organ;  the  jaws,  represented  by  a  pair  of  hard  mandibles 
like  the  beak  of  the  parrot,  and  working  vertically ;  and  in  addition  to 
these  several  powerful  prehensile  tentacles,  provided  with  powerful 


228  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

suckers,  or  adhesive  organs,  which  serve  to  grasp  its  food  and  to  bring 
it  within  the  mouth. 

In  the  articulates,  in  addition  to  the  suctorial  contrivance  already 
mentioned,  innumerable  modifications  of  the  mouth  are  seen,  that  being 
the  organ  which  in  this  group  constitutes  the  main  prehensile  organ,  its 
modifications  corresponding  to  the  character  of  the  food;  thus,  the  earth- 
worm has  a  muscular  upper  lip,  by  which  it  secures  the  earth  which  con- 
tains its  food,  and  which  serves  to  bring  it  within  the  mouth.  In  other 
worms,  again,  the  gullet  is  so  constructed  that  it  can  be  turned  inside 
out  to  form  a  proboscis  for  seizing  prey.  In  such  instances  it  is  nearly 
invariably  supplied  with  horny  teeth.  Millipedes  and  caterpillars  have 
powerful  horny  jaws,  working  horizontal^ ,  while  the  centipedes  have  a 
second  pair,  which  are  really  modified  feet,  terminating  in  curved  fangs 
containing  a  poison-duct.  In  the  crab,  the  legs  and  feet  serve  not  only 
for  progression,  but  also  for  the  mastication  of  food,  as  is  also  the  case 
in  the  lobster,  where  the  seventh  pair  of  feet  are  enormously  developed 
and  furnished  with  powerful,  crushing  pinchers,  those  on  one  side  of  the 
body  being  smooth,  the  other  knobbed.  Scorpions  have,  again,  a  small 
pair  of  claws  for  prehension  of  food,  and  a  smaller  pair  of  forceps  for 
holding  the  food  in  contact  with  the  mouth.  In  the  spider  the  claws  are 
wanting,  and  the  forceps  ends  in  a  fang  or  hook,  which  is  perforated  to 
convey  venom.  Biting  insects,  such  as  the  beetle,  have  distinct  buccal 
appendages,  consisting  of  two  pairs  of  horny  jaws,  which  open  one  above, 
the  other  below,  the  oral  aperture;  the  upper  are  called  mandibles  or 
pinchers,  the  lower  the  maxillae,  which  support  the  palpi.  The  former 
are  armed  with  sharp  teeth.  The  maxillae  are  similar,  but  smaller,  and  in 
some  insects  have  appendages  which  are  called  palpi  or  feelers,  which  not 
only  select  but  hold  the  food  steady  while  it  is  crushed  .by  the  mandibles 
and  maxillae.  Such  appendages  represent  a  free  pair  of  jaws.  All 
invertebrates  Vnove  their  jaws  horizontally. 

In  all  vertebrates  the  jaws  move  vertically,  and  are  in  many  instances 
the  main  or  sole  organ  for  the  prehension  of  food.  In  fishes  the  jaws  are 
always  prehensile  and  often  provided  with  teeth,  which,  being  sharp  and 
curved  inward,  are  prehensile  organs ;  where  teeth  are  absent,  as  in  the 
sturgeon,  the  food  is  drawn  in  by  suction.  The  hog-fish  has  a  single 
tooth,  which  it  plunges  into  its  prey  and  then  bores  a  hole  with  its  saw- 
like  tongue.  The  fins  or  tongues  of  fish  are  not  prehensile. 

In  reptiles  the  jaws,  teeth,  or  tongues  may  serve  as  prehensile  organs, 
while  in  reptiles  prehensile  lips  are  never  present.  Thus,  the  turtle  has 
a  mouth  provided  with  horny  jaws,  the  crocodile  sharp,  curved  teeth,  and 
the  frog,  toad,  and  chameleon,  glutinous  tongues  for  seizing  their  food. 
In  chelonians  the  jaws  are  horny,  and  are  supplied  with  small  teeth  in 
ophidians;  in  the  larger  saurian s  the  teeth  are  powerful,  while  they  are 


FREHEXSION   OF   FOOD.  229 

delicate  and  complex  in  the  insectivorous  species.     Serpents  crush  their 
prey  in  their  coils  before  swallowing  it. 

All  birds  use  their  toothless  beaks  in  procuring  food.  Birds  of  prey 
also  seize  with  their  claws,  while  certain  birds,  such  as  parrots  and  wood- 
peckers, also  employ  their  beaks  as  prehensile  organs.  The  beak  in  birds 
varies  in  shape  according  to  their  food.  Thus,  it  is  short  and  strong  in 
graniverous  birds ;  long  and  slender  in  insectivorous  birds.  In  birds 
which  catch  their  prey  on  the  wing,  as  the  swallows,  it  is  short  and 
gaping ;  strong  and  curved  in  birds  of  prey  which  tear  their  food ;  long, 
conical,  and  of  great  strength  in  borers,  as  in  the  woodpecker  ;  short  and 
curved  in  the  parrot  tribe  to  enable  them  to  crush  nuts ;  delicate  and 
tapering  in  humming-birds  to  allow  them  to  penetrate  the  corollas  of 
flowers ;  long,  strong,  and  pointed  in  most  fish-eaters,  as  the  heron,  stork, 
and  king-fisher  ;  shovel-shaped  in  many  aquatic  birds,  such  as  the  duck 
and  goose ;  or  it  may  be  fashioned  to  hold  fish,  as  in  the  pelican,  albatross, 
penguins,  etc.  In  the  cross-bills  the  mandibles  when  closed  overlap, — 
a  conformation  which  enables  them  to  extract  the  seeds  from  fir-cones. 
Finally,  in  the  young  pigeon,  which  feeds  by  placing  its  bill  in  the  mouth 
of  the  mother-bird,  the  lower  mandible  is  elongated  and  boat-shaped,  and 
of  greater  size  than  the  upper.  Hence,  it  acts  as  a  spoon,  and  becomes 
relatively  smaller  as  the  pigeon  grows.  In  parrots  and  woodpeckers  the 
tongue  is  also  prehensile. 

The  tongue  in  birds  and  reptiles,  besides  being  the  seat  of  the  sense 
of  taste  and  an  organ  of  deglutition,  is  often  the  sole  organ  for  the  pre- 
hension of  food,  the  mechanisms  concerned  in  this  operation,  that  is,  the 
extension  and  retraction  of  the  tongue,  differing  in  birds,  reptiles,  and 
mammals.  In  birds  the  forward  and  backward  movements  of  the  tongue 
depend  upon  the  muscles  which  move  the  hyoid  bone.  The  horns  of  this 
bone  in  birds  are  arched  and  extend  up  behind  the  occiput,  and  give 
attachment  to  a  muscle  which  is  wrapped  around  them,  and  is  then  in- 
serted in  the  inferior  and  posterior  surfaces  of  the  rami  of  the  lower  jaw. 
This  muscle,  which  is  termed  the  conic  muscle  of  the  hyoid  bone  (Vicq 
d'Azyr),  by  its  contraction  advances  the  tongue  by  bending  the  arches 
of  the  hyoid  bone,  at  the  same  time  drawing  them  forward.  Retraction 
of  the  tongue  is  accomplished  by  the  recoil  of  the  elasticity  of  the 
hyoid  arches,  when  these  muscles  relax,  aided  by  the  serpo-hyoid  muscles 
(Duvernoy).  These  arches  are  much  larger  in  the  woodpeckers  than  in 
other  birds. 

The  mechanism  of  movement  of  the  tongue  in  reptiles  is  much  more 
complicated,  and  differs  somewhat  in  the  four  orders  of  this  class.  In 
general  it  may  be  said  the  movements  of  the  tongue  in  reptiles  depend 
on  the  two  principal  means  employed  separately  in  birds  and  mammals ; 
that  is,  the  intrinsic  muscles  of  the  tongue  and  the  hyoid  muscles. 


230  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

In  the  chelonians  the  hyoid  cartilage  is  of  variable  shape,  but  in  the 
main  resembles  somewhat  the  hyoid  bone  of  the  bird,  and  is  moved  by  a 
somewhat  similar  mechanism,  excepting  that  the  conic-hyoid  muscles  are 
not  wrapped  around  the  hyoid  arches.  The  tongue  in  this  species  is 
muscular  and  glandular,  but  not  extensible. 

In  the  saurians  (especially  in  the  crocodiles)  the  tongue  resembles 
that  of  the  chelonians  in  its  slight  degree  of  mobility,  and  the  hyoid 
bone  has  a  somewhat  similar  shape.  In  some  saurians  the  tongue  is 
glandular,  in  others  very  muscular  and  quite  extensible. 

Most  of  the  ophidians  have  the  tongue  hidden  in  a  sac,  non-glandu- 
lar, and  composed  of  the  union  of  two  muscular  cylinders  which  become 
separate  at  the  tip,  forming  the  well-known  forked  tongue  of  serpents. 
The  tongue  is  proportionately  long  and  extends  some  distance  down 
beneath  the  trachea.  The  posterior  extremity  of  the  sac  terminates  in 
two  cartilaginous  plates,  which  unite  anteriorly  and  constitute  the  hyoid 
arch.  By  means  of  muscles  which  originate  from  the  lower  jaw  and  first 
ribs,  and  which  are  inserted  in  the  hyoid  arch,  the  tongue  is  extruded 
from  the  mouth. 

The  tongue  of  the  batradiians,  with  the  exception  of  the  salamanders, 
differs  greatly  from  that  of  other  reptiles.  Its  anterior  extremHy  is 
convex  and  is  fixed  to  the  arch  of  the  chin,  while  its  posterior  extremity 
is  free.  To  be  extended  from  the  mouth  it  must  be  reversed,  and  it  is 
the  posterior  tip  which  is  extruded,  while  it  is  withdrawn  by  a  reversal 
of  this  motion.  These  movements  are  accomplished  by  the  contraction 
of  the  genio-glossus  and  hyo-glossus  muscles, — the  only  ones  which  have 
any  connection  with  the  tongue. 

In  quadrupeds,  although  in  some  cases  we  find  a  special  contrivance 
for  the  seizing  of  food,  as  in  the  trunk  of  the  elephant,  the  snout  of  the 
tapir,  the  long  tongue  of  the  giraffe,  and  the  extensible,  viscid  tongue 
of  the  ant-eater,  the  teeth  are  the  chief  organs  of  prehension,  aided  by 
the  lips  and,  in  some  cases,  the  tongue.  Such  animals  as  may  stand 
erect  on  their  hind  legs,  as  the  squirrel,  bear,  and  kangaroo,  use  their 
fore  legs  for  holding  food  and  bringing  it  to  the  mouth,  but  never  use 
one  of  them  alone.  Clawed  animals  make  use  of  their  feet  in  securing 
prey,  but  the  food  is  conveyed  to  the  mouth  by  movements  of  the  head 
and  jaws.  In  the  rhinoceros  the  upper  lip  is  prolonged  into  a  finger-like 
point,  which  in  these  animals,  as  well  as  in  the  dromedary,  is  the  prin- 
cipal organ  of  prehension  of  food, 

In  man  and  monkeys  the  distinguishing  prehensile  organs  are 
found  in  the  hand,  and  we  find  that  the  first  office  that  the  hand  instinct- 
ively performs  in  both  species  is  to  carry  food  to  the  mouth. 

Therefore,  according  to  the  mode  of  life  for  which  an  animal  has 
been  formed,  we  observe  a  variety  in  the  arrangement  of  parts  destined  to 


PKEHENSIOX   OF  FOOD.  231 

gather  food.  In  the  higher  animals  we  find  prehensile  organs  represented 
in  lower  animals  by  special  organs  which  in  different  species  form  a 
single  type  of  prehensile  organ.  Thus:  in  lower  forms  of  life  we  have 
tentacles,  or  the  lip  may  serve  as  the  chief  organ  of  prehension,  or  the 
tongue  or  the  jaws ;  while  in  the  higher  mammals  we  find  all  these 
organs  together  serving  the  purpose  of  conveying  food  to  the  mouth. 

In  the  latter,  which  are  of  the  same  prehensile  type  as  man,  the 
radius  and  ulna  are  isolated  and  movable,  one  on  the  other,  and  there 
are  distinct  fingers,  nails,  or  claws,  as  in  monkeys,  carnivora,  and  most 
rodents.  In  all  animals  which  use  the  fore  limbs  as  prehensile  organs, 
this  separation  of  the  radius  and  ulna  is  invariabty  to  be  found.  In 
the  large  mammals  the  anterior  limbs  are  only  for  support,  and  such 
animals  are  usually  herbivorous.  In  them  the  radius  constitutes  the 
principal  bone  of  the  forearm,  while  the  ulna  is  very  small  and  almost 
always  fused  with  the  radius  ;  so  no  motion  between  the  two  is  possible. 
There  are,  however,  numerous  exceptions  to  this,  and  in  animals  where 
it  would  be  least  expected.  For  instance :  in  the  elephant  the  volume  of 
the  ulna  is  superior  to  that  of  the  radius,  and  its  carpal  extremity  is 
greater  than  that  of  the  radius,  and  both  are  distinct.  This  also  is  the 
case  in  the  rhinoceros  ;  but  in  both  these  animals  the  motions  of  pro- 
nation  and  supination  are  impossible.  Most  of  the  herbivora  have  a 
forearm  terminating  in  one  or  two  single  fingers  or  phalanges  surrounded 
by  a  hoof,  and  in  these  the  radius  constitutes  the  main  or  sole  bone  of 
the  fore  extremit}'.  The  development  of  the  ulna  and  the  fingers  are  in 
direct  ratio. 

In  the  domestic  animals  the  prehension  of  food  is  accomplished  by 
different  organs,  which  have  different  degrees  of  usefulness  and  develop- 
ment in  different  types.  In  the  dog  and  cat  the  fore  limbs  have  inde- 
pendent radii  and  ulnae,  a  certain  amount  of  pronation  and  supination  is 
possible,  and  they  indicate,  to  a  certain  extent,  the  prehensile  power  of 
the  hand  as  seen  in  man  and  monkeys.  Where,  as  in  the  herbivorous 
quadrupeds,  the  fore  limbs  are  destined  solely  for  support  and  progression, 
a  long  neck  and  peculiarly  shaped  head  favor  the  use  of  the  tongue,  lips, 
and  teeth,  which  in  these  animals  are  the  sole  prehensile  organs.  The 
tongue  and  lips  are  supplied  with  muscular  tissue :  hence  the  power  of 
motion. 

In  the  horse  the  upper  lip  is  the  principal  organ  of  prehension. 
This  organ  is  supplied  with  circular  muscular  fibres,  as  well  as  ele- 
vator and  depressor  muscles,  the  elevator  being  especially  efficient  in 
curling  and  elevating  the  upper  lip  so  as  to  grasp  food.  The  elevator 
of  the  upper  lip  terminates  in  a  broad  Y-shaped  tendon,  which  is  inserted 
in  the  free  part  of  the  upper  lip  (Fig.  81).  The  tongue  has  extrinsic 
and  intrinsic  muscles,  which  favor  its  protrusion  and  enable  it  to  grasp 


232 


PHYSIOLOGY   OF   THE   DOMESTIC  ANIMALS. 


the  food  and  draw  it  within  the  mouth.  The  extrinsic  muscles  are 
connected  with  the  hyoid  bone  and  chin,  and  render  possible  the  pro- 
trusion and  retraction  of  the  tongue ;  the  intrinsic  muscles  permit  of 


FIG.  81.— AFTER  GAMGEE  AND  CHAITVEATT. 

1  and  2,  attricnlar  muscles ;  3,  scutiform  cartilage:  4,  external  scuto-auricular  muscle;  A  A, 
ular  branches  of  first  pair  of  cervical  nerves ;  B  B.  anterior  auricular  nerves  ;  C,  terminal  fibres  of  the 
supraorbital  nerve;  D,  superficial  branch  of  the  lachrymal  nerve;  Y,  tendon  of  muscle  to  elevate  upper 
lip ;  Z,  naso-transversalis  muscle. 

the  change  of  shape  of  the  tongue  required  in  mastication  and  deglu- 
tition. The  tongue  is,  further,  covered  with  a  mucous  membrane,  on 
the  dorsal  surface  of  which  are  numerous  more  or  less  horny  papillae, 


PREHENSION   OF   FOOD. 


233 


which  in  the  cat  tribe  acquire  especial  hardness.  The  arrangement 
of  these  papillae  is  characteristic  of  the  different  animals.  Four  kinds 
of  papillae  have  been  recognized, — the  filiform,  or  thread-like;  the 
mushroom-shape,  or  fungiform ;  the  conical ;  and  the  so-called  circum- 
vallate  papillae,  which  are  in  shape  similar  to  the  fungiform  papillae, 


FIG.  82.— TONGUE  OF  HORSE.    (Gamgee.) 


FIG.  83.— TONGUE  OF  Ox.    (Gamgee.) 


but  which  are  surrounded  by  a  circular  groove.  By  the  distribution 
of  these  papillae  the  tongue  of  the  horse  can  readily  be  distinguished 
from  that  of  the  ox, — a  point  of  some  consequence,  since  horses'  tongues 
are  sometimes  sold  in  the  market  as  beef-tongues.  The  tongue  of  the 
horse  is  long,  with  a  well-marked  middle  depression,  or  raphe,  with  a 


234 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


broad,  flattened  spatula-shaped  tip.  At  either  side  of  the  middle  line 
toward  the  root  of  the  tongue  is  a  very  large  compound  circumvallate 
papilla  (Figs.  82  and  83).  In  the  ox  the  tongue  is  pointed,  thicker,  and 


FIG.  84.— THE  "  PARROT-MOUTH"  MALFORMATION  OF  THE  HORSE'S  MOUTH.  (Gamgee.) 

deeper,  and  with  two  diverging  rows  of  papillae,  each  containing  from 
eleven  to  thirteen  papillae,  at  the  base  of  the  tongue. 

In  the  horse  the  sensitive  and  mobile  upper  lip  is  the  main  organ  in 
the  collection  of  food.  The  nose,  aided  by  the  sense  of  touch,  serves  to 
indicate  the  substances  suitable  for  food;  the  upper  lip  serves  to  carry  the 
food  between  the  incisor  teeth,  so  that  it  may  be  firmly  held,  while  by  an 

active  jerk  and  twisting  motion  of  the 
head  the  grass  is  cut,  hay  pulled  from 
the  rick,  or  branches  severed.  In  stall- 
fed  animals  loose  food  is  taken  from 
the  manger  by  the  lips,  aided  by  the 
tongue.  If  the  incisor  teeth  are  badly 
formed,  as  in  the  projection  of  the  upper 
incisor  teeth  over  the  lower,  as  in  the 
malformation  termed  "parrot-mouth," 
grazing  will  be  prevented  (Fig.  84).  So 
also  swelling  of  the  gums  or  of  the 
palate,  as  in  dentition,  may  act  as  a 
mechanical  impediment  to  the  action  of 
the  incisor  teeth  and  prevent  grazing 
(Fig.  85).  The  position  assumed  by 
the  grazing  horse  is  characteristic.  The  fore  legs  are  separated,  one 
fore  leg  usually  being  advanced,  or  may  be  flexed,  since  the  neck  is  not 


FIG.  85.— PREHENSILE  EXTREMITY  OF 

THE  JAWS  OF  THE  HORSE.      (Colin.) 


PREHENSION   OF  FOOD.  235 

long  enough  to  reach  the  ground :  the  lips  then  carry  the  grass  between 
the  teeth.  A  horse  cannot  live  on  very  bare  pasture,  since  the  grass  must 
be  long  enough  to  be  grasped  by  his  prehensile  upper  lip ;  and  he  there- 
fore cannot  enter  into  competition  with  close-biting  animals,  such  as 
sheep,  since  they  will  deprive  a  field  of  the  best  and  youngest  plants  as 
fast  as  they  come  through  the  ground. 

In  the  ox  the  tongue  is  the  main  organ  of  prehension  of  food,  since 
the  upper  lip  is  short,  has  but  slight  power  of  motion,  and  is  blended 
with  the  cartilaginous,  solid  muzzle,  which  is  covered  by  a  thick,  secret- 
ing membrane.  The  tongue  of  the  ox  is,  however,  provided  with  great 
mobile  power;  it  may  project  far  from  the  mouth,  and,  curving  like  a 
sickle,  the  animal  may  seize  and  draw  food  into  the  mouth.  It  is  rough; 
pointed,  covered  with  recurved,  sharply -pointed  papillae  so  as  to  strengthen 
its  grasp  on  bodies  with  which  it  comes  in  contact.  In  grazing,  the 
tongue  is  protruded,  curved  around  the  grass,  which  is  thus  drawn  into 
the  mouth  and  then  cut  by  the  pressure  of  the  lower  chisel-like  incisors 
against  the  elastic  pad  which  occupies  the  position  of  the  upper  incisors. 
The  ox  also  is  unable  to  feed  on  very  short  grass. 

In  the  sheep  and  goat  the  upper  lip  has  a  certain  degree  of  mobile 
power,  more  than  that  possessed  by  the  ox,  but  not  as  great  as  that  of 
the  horse.  It,  however,  is  unable  to  grasp  food.,  and  merely  aids  the 
incisors  and  tongue  in  grazing.  The  tongue  is  also  more  freely  mova- 
ble than  in  the  horse,  and  the  combination  of  the  mobile  lip  and  prehen- 
sile tongue  enables  it  to  feed  close  to  the  ground.  Here  also  the  upper 
incisors  are  absent,  and  grass  is  cut  by  the  pressure  of  the  lower  incisors 
against  the  cartilaginous  elastic  pad  of  the  upper  jaw. 

The  pig  in  its  native  state  feeds  by  rooting  out  plants,  roots,  and 
nuts  from  the  ground,  and  is  provided  with  a  strong  and  mobile  snout, 
having  a  bony  and  cartilaginous  basis,  and  moved  by  powerful  muscles. 
It  acts  like  a  spade  in  digging  up  the  ground,  while  the  lower  lip  is  short 
and  pointed,  and  is  enabled  to  gather  food  loosened  by  the  digging  action 
of  the  snout.  The  passing  of  a  ring  through  the  snout  of  a  hog  entirely 
destroys  its  natural  methods  of  collecting  food,  and  animals  so  treated 
are  dependent  upon  artificial  feeding,  and  if  left  to  their  own  efforts 
would  starve.  Pigs  are  omnivorous,  but  yet  their  incisor  teeth  are  so 
shaped  as  to  prevent  them  from  grazing. 

Carnivorous  animals,  such  as  the  dog  and  cat,  feeding  principally  on 
meat  and  animal  matters,  fix  their  food  with  the  forelegs,  grasp  it  between 
their  powerful  jaws,  using  here  mainly  the  canine  teeth,  and  lacerate  it 
by  a  backward  jerk  of  the  head.  They  are  biting  animals,  and  as  a  con- 
sequence their  cheeks  are  loose  and  ample,  their  mouths  open  widely, 
and  their  teeth  are  pointed  and  curved  back.  The  lower  jaw  only  is  used; 
and  it  is  said  that  when  the  lower  jaw  is  fixed  carnivorous  animals, 


236  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

with  the   single   doubtful   exception   of  the   dog,  are   unable   to    close 
the  mouth. 

2.  PREHENSION  OP  LIQUIDS.— In  the  lower  forms  of  animal  life  pre- 
hension of  liquid  is  accomplished  by  absorption  through  the  general 
external  body  surface,  and  in  many  cases,  as,  for  instance,  in  the  tape- 
worm, where  neither  mouth  nor  stomach  are  present,  the  fluids  so 
absorbed  carry  also  the  nutritive  matters  in  solution  into  its  interior. 
Many  other  animals  which  live  on  liquid  food  are  provided  with  special 
organs  for  absorption ;  thus,  in  the  leech  there  is  a  mouth  or  sucker, 
provided  with  minute  teeth  for  piercing  the  skin  of  other  animals,  while 
in  the  mosquito  there  is  a  sharp,  bristle-like  tube  for  piercing  the  skin, 
and  in  the  louse  there  is  a  sharp  suc'ker,  armed  with  barbs  to  fix  it 
securely  during  the  act  of  sucking.  In  certain  insects  which  live  on 
viscid  or  fluid  food,  as  the  butterflies  and  moths,  the  mandibular  append- 
ages are  modified  from  their  usual  form  described  in  the  preceding 
section,  and  take  on  the  form  of  a  long,  spiral  tube,  the  proboscis,  which 
can  be  unfolded  and  protruded  into  flowers.  A  sucking  proboscis  also 
is  found  in  many  flies  and  gnats.  In  fleas  and  bugs  the  mandibles  are 
penetrating  and  suctorial.  In  the  higher  animals  no  special  prehensile 
organs  for  the  absorption  of  liquids  are  present,  it  being  accomplished 
by  means  of  the  apparatus  already  described  for  the  prehension  of 
solids.  Four  methods  for  the  prehension  of  liquids  have,  however,  been 
described  by  Colin: —  • 

a.  Suction,  as  in  the  drawing  of  milk  by  young  animals. 

b.  Pumping,  by  the  immersion  of  the  lips  and  the  piston-like  action 
of  the  tongue  within  the  mouth,  on  the  principle  of  the  common  pump. 

c.  Aspiration,  where   the  vacuum  is  produced   by  an  inspiratory 
movement,  as  well  as  by  the  motion  of  the  tongue. 

d.  By  lapping  or  ladling  the  fluid  by  the  tongue  into  the  mouth. 

a.  Suction. — In  suckling,  the  teat  is  grasped  by  the  lips,  or,  it  may 
be,  even  by  the  teeth,  and  the  mouth  closed  around  it.  The  tongue  is 
then  pressed  against  the  teat  and  withdrawn  into  the  mouth,  producing  a 
vacuum,  and  from  the  atmospheric  pressure  on  the  exterior  of  the  breast 
the  milk  then  enters  the  mouth.  There  is,  therefore,  no  danger  of  milk 
entering  the  windpipe,  since  inspiration  is  not  at  all  concerned  in  the 
process  of  suckling ;  hence,  aquatic  animals,  like  the  cetaceans,  may 
suckle  under  water.  In  solipedes  and  ruminants,  during  suckling,  the 
tip  of  the  tongue  is  often  fixed  between  the  teeth  and  the  nipple ;  the 
vacuum  is  then  made  by  the  reduction  in  volume  of  the  anterior  part  of 
the  tongue,  while  the  base  becomes  applied  to  the  roof  of  the  mouth. 

During  the  act  of  suckling,  the  sterno-thyroid  and  the  sterno-,  omo-, 
and  thyro-hyoicl  muscles  contract  together,  and  so  depress  the  larynx 
and  hyoid  bone,  while  at  the  same  time  the  hyoid  bone  is  advanced  by 


PREHENSION   OF   FOOD.  237 

the  contraction  of  the  genio-hyoid  muscle,  the  root  of  the  tongue  being, 
therefore,  likewise  depressed  and  drawn  forward.  At  the  same  time 
the  genio-glossi  muscles,  contracting  with  their  antagonists,  the  hyo- 
glossi,  have  the  effect  of  drawing  the  body  of  the  tongue  directly  back- 
ward, while  the  organ  itself  becomes  flattened.  The  cheek-muscles  are 
entirely  inactive  in  the  act  of  suckling. 

b.  Pumping. — The  process  of  drinking  by  means  of  pumping  with 
the  tongue  is  employed  by  the  horse  and  ruminants  and  most  herbivora. 
The  lips  are  immersed  below  the  surface  of  the  water,  which  seldom  or 
never  rises  above  the  level  of  the  nose  ;  a  small  space  is  opened  between 
the  lips,  and  the  tongue  is  withdrawn  in  the  mouth  by  a  mechanism 
similar  to  that  employed  in  suckling  ;  the  tongue  thus  acting  as  a  piston, 
the  pressure  of  the  atmosphere  on  the  water  without  serves  to  force  it 
into  the  mouth,  and  it  is  then  carried  by  a  motion  of  deglutition  to  the 
phaiynx  and  gullet. 

That  drinking  in  the  horse  is  not  due  to  the  production  of  a  vacuum 
in  the  mouth  by  inspiration  has  been  proved  by  performing  tracheotomy 
on  a  horse,  when,  of  course,  the  production  of  a  vacuum  by  inspiration 
would  be  impossible,  and  yet  it  was  found  that  this  operation  did  not  in- 
terfere with  suction  and  drinking.  So  also  a  case  has  been  reported  of  a 
horse  who  was  unable  to  drink,  in  whom,  on  examination,  it  was  found 
that  a  second  molar  tooth  of  the  upper  jaw  had  been  lost,  and  a  fistulous 
tract  led  through  to  the  nasal  cavit}r.  The  tongue,  therefore,  was  unable 
to  produce  a  vacuum,  even  when  the  nose  was  immersed  below  the  surface 
of  the  water,  from  the  large  nasal  chambers  and  pharynx  being  in  direct 
communication  through  the  fistula  with  the  fore  part  of  the  mouth.  Here 
evidently  was  sufficient  proof  of  the  fact  that  drinking  in  these  animals 
was  not  due  to  any  inspiratory  effort.  In  the  case  reported,  plugging  the 
fistula  served  to  restore  the  power  of  drinking.  Even  without  this  proof, 
however,  the  anatomical  relation  between  the  mouth  and  pharynx  in  the 
horse  is  sufficient  to  show  that  in  these  animals  breathing  cannot  occur 
through  the  mouth  in  drinking,  or  in  any  other  natural  action  of  the  or- 
gans situated  in  the  oral  chamber;  for.  the  soft  palate  forms  a  complete 
partition  between  the  mouth  and  the  throat,  and  can  only  be  elevated  to 
allow  the  passage  of  fluid  or  solids  backward  by  compression,  such  as 
that  which  occurs  in  swallowing. 

c.  Aspiration. — In  this  method  of  drinking  the  vacuum  is  produced 
by  the  respiratory  apparatus  ;  the  mouth,  then,  is  not  entirely  closed,  and 
air  is  also  drawn  in,  the  water  and  air  together  causing  a  rushing  sound, 
the  palate  is  raised,  and  both  the  air  and  water  enter  the  pharynx, 
the  water  being  swallowed  with  a  part  of  the  air.  This  method  of 
drinking  is  jerky,  since  H  must  be  interrupted  for  respiration,  as  the 
nose  may  be  immersed  in  water ;  and  although  it  has  been  said  to  occur 


238  PHYSIOLOGY   OF   THE    DOMESTIC   ANIMALS. 

in  the  pig,  and  often  has  been  noticed  in  the  horse,  there  is  considerable 
reason  for  doubting  that  this  is  ever  a  normal  method  for  the  prehension 
of  liquids. 

d.  Lapping. — This  method  of  the  prehension  of  liquids  is  seen  in 
the  carnivora,  as  in  the  dog  and  cat;  since  their  mouths  are  relatively 
much  larger  than  the  herbivora,  they  cannot  be  immersed  in  water  up  to' 
the  commissure  of  the  lips  without  also  immersing  the  nose.  Such  ani- 
mals, therefore,  spoon  up  water  with  the  tongue,  like  taking  water  to  the 
mouth  with  the  hand.  The  tongue  is  protruded,  its  tip  rendered  cup- 
shaped  by  the  action  of  its  intrinsic  muscles,  and  a  small  amount  of 
water  lifted  up  and  carried  by  the  repeated  protrusion  and  retraction  of 
the  tongue  to  the  mouth.  The  process  is  a  very  slow  one,  and  is  seen' 
only  in  caruivora. 

Various  other  animals  have  different  modes  for  the  prehension 
of  liquids.  Thus,  in  the  elephant  the  trunk  is  a  combined  force-pump 
and  suction-pump.  The  trunk  being  immersed  in  water,  by  inspiratory 
efforts  it  is  filled  with  fluid;  the  tip  is  then  directed  toward  the  mouth 
and  the  water  is  forced  through  it  into  the  mouth.  Birds  drink  by 
filling  their  lower  beak  with  water,  elevating  their  heads  and  allowing  the 
water  to  flow  back  into  their  pharynx  without  the  production  of  any 
motion  of  deglutition.  The  single  exception  to  this  manner  of  drinking 
seen  in  the  birds  is  in  the  case  of  doves  and  pigeons. 


III.  MASTICATION. 

The  term  mastication  is  given  to  the  purely  mechanical  operations  by 
which  the  alimentary  matters,  through  the  action  of  jaws  furnished  with 
teeth,  are  comminuted  in  the  mouth,. and  is,  in  most  animals,  a  necessary 
preparation  for  the  submission  of  food  to  the  action  of  the  gastric  juice. 
Its  importance  and  completeness  differ  in  different  animals,  depending 
upon  the.  nature  of  their  food.  Animals,  such  as  the  carnivora,  which 
feed  on  readily  digestible  matters,  do  not  need  this  preliminary  prepara- 
tion, and  as  a  consequence  the  food  of  carnivora  is  swallowed  in  bulk 
without  having  been  subjected  to  any,  or,  at  best,  to  but  slight  division 
in  the  mouth.  This  applies  also  to  all  animals  which  feed  on  liquid  or 
soft  foods,  where  a  masticatory  apparatus  is  not  needed.  All  animals 
which  feed  on  grain  and  other  vegetable  matters  require  the  process  of 
mastication  to  render  the  food  susceptible  to  the  action  of  the  digestive 
juices  ;  for,  as  we  have  found  in  these  animals,  the  food-constituents  are 
inclosed  in  unjdelding  envelopes  which  resist  the  action  of  the  digestive 
juices.  To  enable  the  nutritive  matter  to  be  released  from  these  sub- 
stances, such  foods  require  mechanical  subdivision  before  they  can  prove 
of  nutritive  value. 


MASTICATION.  239 

In  the  bird,  which  is  not  supplied  with  a  masticatory  apparatus  as 
ordinarily  understood, — that  is,  in  whom  mastication  does  not  occur  in 
the  mouth, — we  have  a  supplementary  organ,  the  gizzard,  which  serves  the 
same  purpose  in  comminuting  the  food.  In  these  animals,  therefore,  the 
operation  of  mastication  is  performed  in  the  abdominal  organs  and  is 
involuntary.  Voluntary  mastication  performed  in  the  mouth  only  occurs 
in  mammals,  and  is  seen  in  its  typical  form  in  the  herbivora,  in  a  less  per- 
fect degree  in  the  carnivora,  while  the  omnivora  occupy  a  mean  between 
the  two. 

Mastication  is  a  complex  act,  and  requires  the  action  of  active  and 
passive  organs ;  that  is,  the  muscles  of  mastication,  the  jaws  and  teeth, 
while  it  is  aided  by  the  tongue,  lips,  and  cheek.  In  all  vertebrates  the 
jaws  move  vertically,  the  nature  and  degree  of  the  movement  varying 
with  the  nature  of  the  food.  In  the  carnivora  the  lower  jaw  is  alone 
usually  movable,  and  its  extent  of  motion  is  very  much  greater  than  in 
the  herbivora.  The  lower  jaw  is  moved  by  five  muscles  on  each  side,  the 
temporal,  the  masseters,the  two  pterygoids,  and  digastric  muscles,  while 
in  the  solipedes  the  stylo-maxillary  muscle  constitutes  an  auxiliary 
muscle  of  mastication.  The  action  which  a  muscle  exerts  is  dependent 
not  only  on  the  bulk  of  the  muscle,  but  on  the  angle  of  insertion  of  the 
muscle  in  the  bone.  The  more  acute  the  angle,  and  the  nearer  the  point 
of  insertion  to  the  articulation,  the  more  extensive  will  be  the  excursion 
of  the  movable  part  in  the  contraction  of  the  muscle,  and  the  greater 
will  be  its  velocity  of  movement.  The  more  perpendicular  the  insertion 
of  the  muscle,  and  the  greater  the  distance  between  the  point  of  insertion 
and  the  articulation,  the  greater  will  be  the  power  developed  in  the  con- 
traction of  the  muscle.  The  latter  is  the  arrangement  which  generally 
characterizes  the  muscles  of  mastication ;  they  are  inserted  perpendicu- 
larly in  the  lower  jaw,  and  at  a  considerable  distance  from  the  maxillary 
articulation.  The  arrangement  of  the  parts  and  the  motions  in  mastica- 
tion differ  in  different  animals. 

In  the  carnivora  the  articulation  of  the  lower  with  the  upper  jaw  is 
by  a  transverse  cond3rle  fitting  into  a  canal-like  groove  in  the  temporal 
bone,  the  canine  teeth  and  molars  overlap,  and,  the  lower  jaw  being  nar- 
rower than  the  upper,  the  only  motion  therefore  possible  is  a  simple  up 
and  down  movement  (Figs.  86  and  87). 

In  herbivora  the  articulation  of  the  lower  with  the  upper  jaw  is  above 
the  level  of  the  molar  teeth,  and  permits  of  a  forward,  backward,  and 
lateral,  as  well  as  an  up  and  down,  motion*.  Three  distinct  t}rpes  of  her- 
bivora, with  reference  to  their  mode  of  mastication,  may  be  recognized. 

First,  the  rodents,  which  have  only  two  kinds  of  teeth,  two  highty 
developed  incisors  in  each  jaw  ;  the  canine  teeth  are  absent,  while  the 
molars,  which  are  compound  teeth,  have  a  flat  crown  and  transverse  rows  of 


240 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


enamel.  The  temporal  fossae  are  small,  their  zj'gomatic  arches  are  slight, 
and  the  maxillary  condyle,  instead  of  being  transverse,  as  in  the  carnivora, 
is  antero-posterior,  and  articulates  with  the  glenoid  cavity  in  the  same 
direction,  the  articulating  surface  in  these  animals  being  a  sort  of 
eanal  or  gutter  running  from  before  backward  (Figs.  88  and  89).  The 
arrangement  of  the  articulation  ^^\  /? 

of  the  upper  and  lower  jaw,  as 
well  as  the  mode  of  insertion 
of  the  muscles,  favor  a  backward 


FIG.  86.— 


HEAD  OF  CARNIVORA— DOG. 
(Beclard. ) 


FIG.   87.— INFERIOR     MAXILLARY    BONE    OF 
CARNIVORA — POLAK  BEAK.    (B&clard.) 

c,  profile  view  of  articular  condyle  of  lower  jaw  (condyle  of 
right  side) ;  ct,  front  view  of  same  condyle. 


and  forward  motion  of  the  lower  jaw,  which  is,  therefore,  the  character- 
istic motion  of  rodents. 

Second. — In  the  ruminants  the  jaws  are  long  and  feeble,  the  canine 
and  upper  incisor  teeth  are  absent,  while  the  molars  are  compound  teeth 
with  a  flat  crown,  with  the  enamel  arranged  in  antero-posterior  layers. 
The  condyle  of  the  lower  jaw  articulates  with  a  plane  or  almost  convex 
glenoid  surface  of  the  temporal  bone,  and  this  mode  of  articulation, 


FIG.  88.— HEAD  OF  RODENT— MARMOT. 
(Beclard.) 


FIG.  89.— INFERIOR  MAXILLARY  BONE    OF 
RODENT— CAPYBAKA.    (Beclard.) 

b,  right  articular  condyle  of  lower  jaw. 


together  again  with  the  arrangement  of  muscles,  permits  of  a  rotatory 
motion  of  the  lower  jaw,  which  is  therefore  a  characteristic  trait  in  the 
mastication  of  the  ruminants  (Figs.  90  and  91). 

Third. — In  the  solipedes  and  pachydermata  three  kinds  of  teeth  are 
present,  and  both  of  the  above  kinds  of  movement ;  that  is,  rotation  and 


MASTICATION. 


241 


forward  and  backward  motions  are  possible,  but  are  not  present  in  as 
great  a  degree  in  this  case  as  in  the  two  preceding  types  of  herbivora. 
These  animals,  therefore,  occupy  a  mean  between  the  rodents  and 
ruminants  (Fig.  92). 

1.  THE  MOVEMENTS  OF  THE  JAWS. — The  mouth  is  opened  by  depres- 
sion of  the  lower  jaw,  which  is 
effected  in  all  animals  by  the 
digastric  muscles,  aided,  in  the 
horse,  by  the  stylo-maxillary 
muscle,  which  is  in  reality  a 
short  branch  of  the  former.  The 
lower  jaw  is  depressed  very 
largely  by  gravity ;  hence,  in  all 
animals  we  find  such  a  slight 
muscular  power  acting  as  de- 
pressor of  the  lower  jaw  as  con- 
trasted with  the  large  number 
of  powerful  muscles  which  pro- 
duce its  elevation.  When  the 
mouth  is  opened  the  maxillary 
condyle  turns  on  its  axis  and 
its  posterior  part,  which,  when 
the  jaws  are  closed,  is  in  con- 
tact, as  in  the  horse,  with  the 
subcondyloid  apophysis,  leaves  this  surface  and  moves  anteriorly. 
In  carnivorous  animals  the  condyle  being  fixed  in  a  gutter-like  glenoid 
cavity,  rotation  on  its  axis  is  the  only  motion  which  is  noticed. 


FIG.  90.— HEAD  OF  HORNED  RUMINANT— Ox. 
(Btclard.) 


FIG.  91.— HEAD  OF  HORNLESS  RUMINANT— CAMEL.     (Btclard.) 

In  all  animals  the  finger  placed  below  the  zygomatic  fossa  will 
distinguish  the  forward  and  backward  motion  of  the  coronary  process 
as  the  mouth  is  opened  and  closed.  In  carnivora  the  extent  to  which 

16 


242  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


the  lower  jaw  may  be  depressed  is  ve^  much  greater  than  in  the 
lierbivora  ;  in  the  latter,  as  in  the  horse,  eight  to  ten  centimeters  being 
the  extent  of  separation  of  the  lower  from  the  upper  incisors.  The 
digastric  muscle  is  comparatively  feeble,  and  would  appear  to  pull  the 
jaw  back,  but  really  it  tends  to  advance  it,  since  it  is  a  lever  of  the 
third  class.  In  the  hare,  rabbit,  and  ox  the  digastric  muscle  has  only  one 
bell}7,  and  in  the  ox  is  joined  to  the  same  muscle  of  the  opposite  side 
by  transverse  muscular  fibres  ;  in  the  dog  there  is  no  intermediary 
tendon  in  the  digastric  muscle.  The  development  of  the  digastric  de- 
pends upon  the  character  of  the  food  of  animals.  In  the  horse,  sheep, 
and  ox,  where  it  is  small,  it  is  a  double  muscle,  and  is  inserted  more 
anteriorly  in  the  lower  jaw  than  in  carnivorous  animals,  where  it  is 
large.  The  conditions,  therefore,  are  most  favorable  for  its  action  in 
lierbivora  on  account  of  its  different  insertion.  This  muscle  antagonizes 
the  temporals,  masseters,  and  pterygoid  muscles. 


FIG.  92.— HEAD  OF  SOLJPEDE— HORSE.    (B&clard.) 

The  representative  of  the  digastric  in  the  lower  vertebrates,  as  in 
reptilia,  according  to  Mr.  G.  E.  Dobson,  is  a  bundle  of  muscular  fibres 
arising  from  the  occiput  and  inserted  into  the  posterior  extremity  of 
the  mandibular  ramus,  its  functions  being  simply  those  of  drawing  the 
angle  of  the  mandible  backward  and  upward,  and  so  separating  the 
jaws  in  front.  This  is  also  its  form  and  function  in  birds  and  most 
mammals,  though  in  man,  monke^ys,  and  rodents  the  muscle  is  made  up 
of  two  bellies  with  an  intermediate  tendon,  which  is  often  connected 
by  ligament  with  the  hyoid  bone.  Mr.  Dobson  has  traced  an  interesting, 
connection  between  the  mode  of  feeding  and  the  type  of  the  digastric 
muscle.  In  the  group  of  animals  in  which  this  muscle  is  connected 
with  the  hyoid  bone,  the  species  swallow  their  food  while  in  the  erect  po- 
sition, with  the  head  bent  forward  on  the  chest  and  the  long  axis  of  the 
cavity  of  the  mouth  at  right  angles  with  the  oesophagus ;  in  the  other 
this  muscle  is  free,  and  all  the  species  feed  while  resting  on  their 


MASTICATION.  243 

anterior  extremities,  having  the  long  axis  of  the  mouth  in  a  line  with 
the  oesophagus.  Thus,  among  certain  rodents  and  arboreal  insectivora, 
which  habitually  sit  erect  while  feeding,  holding  their  food  between  their 
fore  feet,  the  anterior  bellies  of  the  digastrics  are  large  and  united,  and 
the  intermediate  tendons  well  developed  and  connected  by  fascial  bands 
with  the  hyoid  bone,  and  by  their  deep  surfaces  with  the  mylo-hyoitf 
muscles,  as  in  the  rat  and  the  common  dormouse.  In  the  water-vole 
(Arvicola  amphibius),  however,  the  digastrics  are  connected  together  in 
front  by  fascia  alone,  and  the  upper  margin  only  of  their  middle  part 
is  tendinous,  and  not  connected  with  the  hyoid  bone.  These  animals 
live  on  vegetable  substances  obtained  while  swimming,  and  habitually 
hold  the  head  stretched  out  in  a  line  with  the  body. 

The  mouth  is  closed  by  elevation  of  the  lower  jaw,  and  is  the 
reversal  of  the  previous  motion.  Here  powerful  muscular  action  is  re- 
quired, since  in  the  closure  of  the  jaws,  in  many  cases,  great  force  is 
needed.  It  is  accomplished  by  the  temporals,  the  masseter,  and  pterj*- 
goid  muscles.  In  carnivora  the  temporal  is  the  principal  elevator  of  the 
lower  jaw.  Its  volume  is  proportionately  enormous,  the  temporal  fossa* 
occupying  the  entire  surface  of  the  parietal  bones  back  to  the  occipital 
spine.  In  herbivora  and  rodents  the  masseter  muscles  are  the  most 
highly  developed;  their  origin  being  from  the  zygomatic  arch  and  a 
portion  of  the  superior  maxillary  bone,  and  being  inserted  in  the  lower 
jaw,  in  the  solipedes  on  both  faces  of  the  coronoid  processes,  as  far 
back  as  the  last  molars.  Both  of  these  muscles  act  as  levers  of  the 
third  class,  as  is  very  evident  in  the  rabbit,  where  the  coronoid  processes 
are  much  lower  than  the  articulation  of  the  lower  and  upper  jaw.  In. 
the  carnivora,  the  coronoid  processes  being  separated  b}'  a  considerable 
space  from  the  condyle,  the  conditions  are  most  favorable  for  the  action 
of  the  temporal  muscle.  From  the  oblique  direction  of  its  fibres  it  tends 
to  produce  drawing  back  of  the  lower  jaw,  where,  as  in  the  herbivora, 
this  is  possible. 

The  masseter  muscle  is  developed  in  inverse  proportion  to  the  tem- 
poral. It  is,  therefore,  the  principal  elevator  of  the  jaw  in  the  herbivora 
and  in  the  rodents.  It  rises  from  the  zygomatic  spine  in  solipedes,  the 
maxillary  tubercle  in  ruminants,  to  be  inserted  in  the  lower  jaw.  It  is 
also  a  lever  of  the  third  class ;  its  fibres  are  directed  backward  and 
downward  in  the  herbivora,  and  it  may^  serve,  therefore,  as  in  the  rodents, 
to  assist  in  the  forward  motion  of  the  lower  jaw ;  its  greatest  power  is  de- 
veloped when  the  resistance  to  the  elevation  of  the  lower  jaw  is  between 
the  molar  teeth,  while  its  origin,  being  on  a  plane  external  to  its  insertion 
in  the  lower  jaw,  as  in  the  horse  and  rabbit,  it  may  aid  in  lateral  motion 
of  the  jaw  in  animals  where  this  motion  is  not  rendered  impossible  by 
the  mode  of  articulation  of  the  jaws,  or  by  the  overlapping  of  the  teeth. 


244  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

The  pteiygoid  muscles,  especially  the  internal,  which  is  usually  the 
largest,  are  also  elevators  of  the  lower  jaw,  and  are  most  developed  in 
herbivorous  animals ;  they  are  also  levers  of  the  third  class,  and  are,  to 
a  certain  extent,  concerned  in  the  production  of  lateral  and  antero- 
posterior  motion  of  the  lower  jaw  in  animals  where  these  motions  are 
possible.  Propulsion  of  the  lower  jaw,  or  antero-posterior  motion,  is 
most  marked  in  the  rodents,  although  it  is  also  present  to  a  less  degree 
in  solipedes  and  ruminants,  but  is  impossible  in  carnivora  on  account  of 
the  shape  of  the  articulation  of  the  jaws.  In  this  motion  the  maxillary 
condyles  slide  forward  on  the  glenoid  fossae  of  the  temporal  bone  in  ani- 
mals where  there  may  be  a  subcondyloid  apophysis  posteriorly  and  no 
restricting  surface  anteriorly.  This  motion  is  quite  marked  in  the  pig, 
which  has  a  triangular  condyle,  but  attains  its  maximum  development  in 
the  rodent.  This  motion  is  accomplished  by  means  of  the  masseter 
muscle,  aided  by  the  external  pterygoids ;  for  in  the  rodents,  and  in  a  less 
degree  in  ruminants,  the  origin  of  the  most  posterior  fibres  of  the  mas- 
seter muscle  are  in  advance  of  their  insertion  in  the  lower  jaw.  This 
obliquity  in  direction  of  the  masseter  fibres,  in  contraction  of  this  muscle, 
therefore  serves  to  move  the  jaw  forward. 

The  retraction  of  the  lower  jaw,  which  of  course  occurs  only  in  ani- 
mals in  which  forward  motion  is  possible,  is  accomplished  by  means  of 
the  temporal  muscle,  the  digastric  being  not  concerned  in  the  process, 
since  backward  motion  of  the  jaws  only  occurs  in  closing  the  mouth, 
while  the  digastric  in  its  contraction  opens  the  mouth  and  even  tends  to 
advance  the  lower  jaw  somewhat. 

Lateral  movement  of  the  lower  jaws  is  more  or  less  pronounced  in 
all  herbivora,  but  is  most  marked  in  the  ruminants  ;  it  never  occurs  in 
the  carnivora,  as  already  explained,  on  account  of  the  shape  of  the  con- 
dyles and  overlapping  molars,  and  the  crossing  of  the  canine  teeth.  The 
lateral  motion  of  the  lower  jaw  is  not  a  simple  lateral  displacement 
parallel  to  the  axis  of  the  lower  jaw;  that  is,  it  is  not  equal  at  both  ex- 
tremities of  the  jaw,  but  is  an  angular  deviation  very  marked  at  the  in- 
cisor teeth,  and  is  a  rotation  of  the  lower  jaw  around  one  condyle  of  the 
inferior  maxillary  bone,  the  incisor  teeth  describing  an  arc  of  a  circle, 
whose  centre  is  one  condyle,  which  thus  moves  very  little,  while  the  oppo- 
site condyle  advances  and  partly  leaves  the  articular  surface,  as  may  be 
determined  by  placing  the  finger  in  the  temporal  fossa,  when  the  coronoid 
process  on  the  side  opposite  to  that  toward  which  rotation  is  taking  place 
may  be  felt  to  move  forward.  In  this  lateral  motion  of  the  lower  jaw 
the  axes  of  the  molar  teeth  cease  to  be  parallel,  the  incisor  arch  passing 
one-third  to  one-half  its  extent  to  one  side  of  the  upper  arch  or  pad 
which  represents  it  in  the  ruminants  ;  the  molar  teeth  of  the  upper  and 
lower  jaw  are  in  contact  on  the  side  toward  which  rotation  is  occurring, 


MASTICATION.  245 

while  they  cease  to  correspond  on  the  opposite  side.  It  is,  therefore,  to 
a  certain  extent,  a  circular  motion,  in  which  the  axis  of  the  lower  jaw 
crosses  that  of  the  upper.  A  further  peculiarity  of  this  lateral  motion 
of  the  lower  jaw  is  that  it  is  alternative;  that  is,  there  is  not  a  deviation 
first  to  the  right  and  then  to  the  left,  but  if  the  motion  is  first  a  deviation 
to  the  right  in  the  process  of  mastication  it  returns  again  to  its  central 
position  and  again  rotates  to  the  right.  This  may  occur  for  half  an  hour 
or  more  in  solipedes,  and  in  ruminants  in  both  first  mastication  and  in  rumi- 
nation ;  then  the  motion  may  be  reversed,  and  may  occur  as  a  left  lateral 
deviation  for  a  similar  length  of  time.  The  camel  is  the  only  animal 
which  furnishes  an  exception  to  this  method  of  mastication.  In  it  the 
lateral  motion  is  alternative ;  the  deviation  occurring  first  to  the  right 
and  then  to  the  left  of  the  central  position.  In  solipedes  this  motion  is 
apparently  not  as  marked  as  in  the  ruminants,  but  this  difference  is 
merely  apparent,  it  being  to  a  certain  extent  concealed  b}r  the  long  lips 
of  these  animals.  It  is,  therefore,  more  evident  but  not  actually  greater 
in  the  ruminants  than  in  solipedes.  Lateral  motion  of  the  lower  jaw  is 
produced  by  alternate  contractions  of  the  pterygoids,  especially  the  in- 
ternal, the  external  being  very  small  in  ruminants,  and  by  the  nmsseters  ; 
when  the  deviation  occurs  to  the  right  the  motion  is  produced  by  con- 
traction of  the  right  masseter  and  left  internal  pterygold  muscles.  When 
the  deviation  occurs  to  the  left  it  is  produced  by  contractions  of  the  left 
masseter  and  right  internal  pterygoids,  the  action  of  the  pterygoids  being 
more  marked  in  ruminants  than  in  solipedes  from  the  fact  that  in  the 
former  animals  the  palatine  ridges  are  nearer  together ;  therefore,  the 
lateral  power  of  the  pterygoid  muscles  is  more  marked. 

2.  THE  ACTION  OF  THE  TEETH  IN  MASTICATION. — The  teeth  are  passive 
organs  of  mastication,  which  are  imbedded  in  the  alveoli  of  the  jaws. 
Teeth  may  be  divided  into  three  different  parts  :  the  crown,  or  the  part 
which  projects  into  the  mouth  above  the  gum;  the  neck  of  the  tooth,  where 
it  passes  through  the  gum ;  and  the  root,  which  is  imbedded  in  the  alveolus. 
Teeth  may  be  of  two  different  kinds, — either  simple,  where  the  entire 
external  surface  of  the  tooth  is  covered  by  enamel;  or  compound,  where 
two  different  substances,  enamel  and  dentine,  compose  the  free  surface. 
When  a  tooth  is  divided  longitudinally  it  is  found  to  consist  of  three 
different  substances  ;  the  hardest,  and  that  which  in  simple  teeth  covers 
the  crown,  is  termed  the  enamel,  and  passes  over  the  neck  of  the  tooth, 
becoming  gradually  thinner,  and  only  partially  covering  the  fang.  The 
enamel  (Fig.  93)  is  composed  of  pentagonal  or  hexagonal  prisms,  or 
enamel  fibres,  of  about  one  five-thousandth  of  an  inch  in  diameter, 
closety  packed  together  and  arranged  in  a  radiating  manner  from  the 
surface  of  dentine  below.  The  enamel  contains  no  nutrient  vessels,  and 
when  destroyed  is  not  renewed.  The  bulk  of  both  crown  and  fang  of 


246 


PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 


a  tootli  is  constituted  of  what  is  known  us  dentine,  a  section  of  which 
reveals  it  to  be  formed  of  a  densely  packed  mass  of  curving  tubes  with 
distinct  walls,  imbedded  in  a  dense,  bone-like  matrix,  which  run  from  the 
pulp-cavity  to  the  outer  surface  of  the  dentine  near  which  they  ramify. 
The  material  between  the  tubules  or  the  matrix  of  the  dentine  is  a  per- 
fectly homogeneous  substance,  containing  nearly  the  whole  of  the  earthy 
matter  contained  in  the  tooth,  arranged  in  all  animals  in  superimposed 
layers.  The  tubules  are  the  one  four-thousandth  of  an  inch  in  diameter, 
and  when  fresh  contain  nerve  and  vascular  processes  from  the  pulp. 
The  third  substance  found  in  teeth  is  known  as  the  cement,  or  crusta 
petrosa,  and  in  the  simple  tooth  merety  covers  the  fang,  whereas  it  dips 
in  between  the  layers  of  enamel  in  com- 
pound teeth  on  the  crown,  and  when  the 
tooth  is  wholly  inclosed  within  its  cavity 
also  covers  the  crown  (Fig.  94).  In 
carnivora  the  teeth,  as  already  remarked, 
are  simple  ;  in  other  words,  their  crowns 
are  permanently  covered  with  enamel,  and 
when  in  extremely  old  subjects  the  incisor 


FIG.  93.— ENAMEL  PRISMS,  AFTEK  KOLLIKER. 

(Klein.) 
A,  in  longitudinal  view;  B,  in  cross-section. 


...c 


FIG.  94.— SECTION  THROUGH  A 
CANINE  TOOTH  OF  MAN,  AFTER 
WAL.DEYER.  (Klein.) 

A,  crusta  petrosa,  with  large  bone-cor- 
puscles; B,  interglobular  substance;  C,  den- 
tinal  tubules. 


teeth  and  canine  teeth  wear  down, — then  only  does  the  dentine  of  the 
teeth  become  exposed.  In  herbivora  compound  teeth  are  invariably  met 
with.  In  other  words,  on  the  free  surface  of  the  teeth  of  herbivora 
different  substances  of  varying  degrees  of  density  and  hardness  are 
always  met  with,  the  function  of  which  is  to  insure  a  constantly  rough 
surface  for  the  purposes  of  grinding;  for  a  good  mill-stone  is  composed  of 
materials  which  wear  with  different  degrees  of  rapidity,  and  thus,  always 
remaining  rough,  most  effectually  grinds  the  substances  over  which  it 
passes.  In  the  compound  tooth,  as  found  in  the  herbivora,  the  cement  has 
originally  covered  the  entire  crown,  but  as  the  tooth  is  erupted  simply 
remains  on  the  biting  or  grinding  surface  of  the  tooth.  Thus,  in  the 


MASTICATION. 


247 


incisors  of  a  horse,  the  free  surface,  with  the  exception  of  the  crown,  is 
covered  with  enamel  alone  (Figs.  95  and  96).  On  the  biting  surface  of 
the  incisor  tooth,  when  freshly  erupted,  is  always  found  a  central  spot 
composed  of  cement,  the  enamel  dipping  in  to  form  a  cavity  or  depres- 
sion on  the  free  biting  surface  of  these  teeth.  By  the  change  in  shape 


FIG. 95 —DIAGRAM  OF  FRESHLY-ERUPTED 
INCISOR  OF  LOWER  JAW  OF  HORSE. 
(Nuhn.) 

c,  depression  in  table  of  tooth :  *,  cement,  which  rapidly 
disappears  except  from  infundibuluin ;  z,  enamel ;  c«, 
dentine. 


— X 


FIG.    96.— LOWER    INCISOR     TOOTH     OP 
HORSE.     (Nuhn.) 

c,  worn-down  surface  of  table  of  tooth,  showing  the 
alternate  layers  of  enamel,  s :  z,  dentine ;  and  x,  dis- 
colored cement  filling  infundibulum. 


Cl 


of  this  central  depression  in  the  incisor  teeth  of  the  horse,  through  the 
gradual  wearing  down  of  the  surface,  an  index  is  furnished  of  the  age 
of  the  horse, — a  matter  which  will  subsequently  be  alluded  to. 

The  molar  teeth  of  herbivorous  animals  are  chiefly  compound  teeth, — 
that  is,  the  enamel  dips  down  below  the  surface  of  the  crown,  and  in 
some  animals,  as  in  the  elephant,  the  com- 
pound teeth"  may  be  regarded  as  a  series 
of  flattened  teeth  arranged  side  by  side  in 
the  jaw,  and  connected  only  by  the 
cement,  or  crusta  petrosa  (Figs.  97  and 
98).  This  substance  is  like  that  invari- 
ably found  covering  the  fangs  of  teeth, 
but  which  only  in  compound  teeth  appears 
upon  the  crown.  The  pointed  fang  or 
fangs  of  teeth  are  pierced  by  an  opening 
which  communicates  with  a  cavity  in  the 
centre  of  the  body  of  the  tooth,  called 
the  pulp-cavity,  which  contains  blood- 
vessels and  nerves  which  enter  through 
the  opening  in  the  fang,  and  in  the  pulp- 
cavity  ramify  over  a  delicate  fibro-cellular 
structure  constituting  the  pulp  (Fig.  99). 

The  pulp  is  continuous  over  its  surface  with  an  infinite  number  of  small 
projections  which  extend  into  the  tubes  of  dentine  in  the  inner  structure 
of  the  tooth. 

These  three  different  substances,  which  constitute  the  substances  of 


FIG.  97.— SECOND  UPPER  MOLAR  OF 
HORSE,  SHOWING  WEAR  OF 
TABLE.  (Nuhn.) 

<•»',  depression  on  table;  pi,  depression  on 
side;  s,  enamel ;  2,  dentine;  Cae,  cement;  a,  ex- 
ternal or  buccal  surface;  t,  internal  or  oral 


248  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

the  teeth,  var}^  in  their  chemical  composition,  and,  as  a  consequence,  in 
their  different  degrees  of  hardness,  dependent  upon  the  varying  amount 
of  inorganic  matter  found  within  them,  thus  : — 

Dentine.         Enamel.         Cement. 

Organic  matter,  .        .        .        .28.01  3.59  32.24 

Inorganic  matter,        .         .        .     71.99  96.41  67.76 

The  sharp  angles  and  prominences  on  the  crown  of  the  compound 
tooth  are  formed  of  enamel,  as  is  the  entire  free  surface  of  the  simple 
tooth.  The  deeper  hollows  in  the  crown  of  compound  teeth  are  formed 
by  the  wearing  of  the  cement,  while  the  substances  varying  in  hardness 
between  these  two  are  formed  by  the  dentine.  The  fang  of  the  tooth, 
where  inserted  in  the  alveolus,  is  further  covered  by  a  membranous 
lining,  the  periosteum,  which  is  soft  and  contains  vessels  and  nerves,  and 
which  is  reflected  into  the  pulp-cavity  through  the  opening  in  the  fang 
of  the  tooth.  When  ossified,  this  membrane  forms  osteo-dentine. 


cae 


FIG.  98.— HALF  OF  A  FOSSIL,  TOOTH  OF  ELEPHANT  (Dens  lamellosus).    (Nuhn.)   . 
I,  the  single  segments,  or  secondary  teeth ;  s,  enamel ;  z,  dentine;  cae,  cement. 

Teeth  are  entirely  absent  in  birds,  but  are  generally  present  in 
fishes,  amphibia,  reptiles,  and  mammalia.  In  the  latter  class  alone  are 
two  sets  of  teeth  met  with :  the  first,  the  deciduous  or  milk-teeth,  which 
are  only  temporary,  fall  out  and  give  place  to  the  permanent  teeth.  With 
the  exception  of  a  few  fishes,  such  as  the  sheep's-head,  and  certain  her- 
bivorous reptiles,  the  teeth  in  fishes,  amphibia,  and  reptiles  as  a  class,  are 
solely  prehensile ;  they  serve  simply  for  seizing  and  dividing  their  prey 
into  portions  small  enough  to  be  swallowed.  It  is  only  in  the  mammals 
that  the  teeth  serve  actually  as  organs  of  mastication. 

The  teeth  of  fishes  present  greater  varieties  than  those  found  in  any 
other  class.  They  may  be  almost  innumerable  or  they  may  be  reduced  to 
a  single  tooth,  as  in  the  lepidosiren,  which  has  only  a  single  dental  plate 


MASTICATION. 


249 


in  each  jaw  and  a  small  tooth  on  the  nasal  bones;  or,  in  many  fishes, as  in 
the  sturgeon  and  amphyoxus,  they  may  be  entirely  absent.  Their  shape 
is  also  subject  to  great  variation.  In  the  lowest  forms  of  fish  they  are 
short  and  blunt,  and  well  fitted  for  grinding  sea-weed  and  crushing  shell- 
fish ;  such  teeth  are  seen  in  the  ray -fish.  But  in  most  fish  the  teeth  are 


FIG.  99.— DIAGRAM  OF  PREMOLAR  TOOTH  OF  CAT,  WITH  ALVEOLUS,  AFTER 
WALDEYER  (MAGNIFIED  THIRTY  DIAMETERS).     (Thanhoffer.) 

A,  bony  wall  of  alveolus  :  zo.  enamel  prisms  :  zh,  enamel  coating:  h,  spaces  in  the  base  of  the  enamel 
prisms;  D,  dentine:  d<-,  dentinal  tubules:  fh,  gum,  with  alveolar  periosteum  below  it;  C,  cement;  ch, 
cement  spaces;  fb,  tooth-pulp;  i,  nerve  entering  pulp ;  and  c,  pulp  blood-vessels. 

usually  small  and  conical,  generally  cylindrical,  but  sometimes  flattened, 
straight,  curved,  bent  side  wise,  or  even  barbed  ;  or  their  edge  may  be  ser- 
rated, as  in  sharks  generally ;  or  the  base  may  be  broader  than  the  apex, 
as  in  the  sharks.  The  teeth  of  fishes  are  by  no  means  limited  to  the  free 


250  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

maxillary  and  free  mandibular  bones,  or  the  lower  and  upper  jaws.  In 
some  fishes,  as  in  the  carp,  all  the  teeth  are  in  the  back  of  the  mouth, 
while  in  most  fishes  there  are  teeth  not  only  on  the  maxillary  and  man- 
dibular  bones,  but  also  on  the  bones  around  the  middle  part  of  the  mouth; 
even,  sometimes,  being  found  on  the  median  line  of  the  palate.  In  cer- 
tain cartilaginous  fishes  the  teeth  depart  from  the  usual  rule,  in  conse- 
quence of  which  they  are  mostly  inclosed  in  the  bone  on  which  they  rest, 
but  are  attached  by  ligaments,  so  as  to  allow  the  teeth  to  be  bent  back- 
ward in  the  mouth  by  pressure.  In  most  fishes  the  enamel  and  cement 
substances  are  absent,  the  body  of  the  teeth  being  composed  simply  of 
dentine,  which  on  its  external  surface  is  more  compact  than  when  found 
in  mammals.  The  teeth  of  fishes  are,  as  a  rule,  replaced  several  times 
during  life,  especially  in  the  cartilaginous  fishes. 

In  amphibia,  fine,  prehensile  teeth  are  found  on  the  upper  jaw  and 
palate-bones  of  the  frogs  and  salamanders;  more  seldom  on  the  lower  jaw 
also.  In  toads  only  palatal  teeth  are  present. 

In  reptiles  the  jaws  may  be  either  covered  with  a  thick,  dense  horn, 
which  assists  in  dividing  the  food,  or  they  may  exhibit  the  most  perfect 
dentition,  as  in  the  saurians. 

The  number  of  teeth  is  always  very  large,  and  while  in  crocodiles  and 
many  lizards  they  are  limited  to  the  jaw-bones,  they  also  exist  on  the  ptery- 
goid  or  palatine  bones,  and  on  the  roof  of  the  mouth  of  most  ophidians. 
The  t^ypical  form  of  the  teeth  of  reptiles  is  conical,  and  they  vary  greatly 
in  size,  from  the  minute  tooth  of  the  blind-worm  to  the  powerful  canine- 
like  teeth  of  the  crocodile.  They  are  sometimes  c}'lindrical,  but  may  be 
flattened,  or  even  have  serrated  margins.  Their  surface  is  smooth,  or  is 
notched.  In  serpents  they  are  relatively  longest,  and  present  a  remark- 
able structure  in  the  case  of  the  poison-teeth  or  fangs,  which  are  strongly 
curved  and  contain  a  canal  opening  at  both  ends  of  the  tooth :  on  the 
anterior  or  convex  aspect  of  the  teeth  above,  close  to  the  gums,  and 
below  on  the  concave  surface,  a  short  distance  from  the  point  of  the 
tooth.  These  teeth  are  usually  confined  to  the  upper  jaw,  and  the  canal 
serves  to  convey  the  secretion  of  the  poison-glands,  by  the  duct,  to  the 
substances  in  which  the  tooth  is  imbedded,  the  poison  being  forced  out 
by  muscles  which  join  the  gland-capsule  and  compress  the  gland.  The 
poison-fangs  are  fixed  to  the  superior  maxillary  bones,  but,  since  these 
in  poisonous  serpents  are  movable,  the  teeth  can  when  at  rest  either  lie 
flat  upon  the  gum,  or  they  can  be  brought  into  a  vertical  position  in  the 
act  of  striking.  Reptilian  teeth  always  contain  dentine  and  cement,  and 
sometimes,  also,  enamel  and  true  bone,  the  dentine  differing  slightly  from 
that  of  mammals,  its  substance  being  traversed  by  canals  which  commu- 
nicate with  the  pulp-cavity.  As  the  teeth  of  the  reptile  wear  away  they 
fall  out,  and  are  replaced  by  an  almost  unlimited  succession  of  new  ones. 


MASTICATION.  251 

In  birds  teeth  are  never  present  as  organs  of  mastication,  their 
place  being  taken  by  the  muscular  gizzard;  but  the  horny  coating  of  the 
jaws  is  developed  in  successive  laminae,  especially  seen  in  the  parrot, 
which  forms  the  beak,  and  which  serves,  in  the  prehension  of  food,  the 
same  purpose  as  the  prehensile  tooth  of  other  animals. 

In  the  mammal  the  greatest  variety^  is  met  with  in  the  number, 
the  shape,  and  external  characteristics  of  teeth.  They  may  vary  in 
number  from  one  in  the  narwhal  to  as  many  as  one  hundred  and  ninety 
in  the  dolphins.  In  the  elephant  there  are  at  most  ten,  but  usually  only 
six,  namely,  one  entire  molar,  or  sometimes  parts  of  two  on  each  side 
of  both  jaws,  together  with  the  two  tusks  of  the  upper  jaw.  In  the 
rodents  the  ordinary  number  is  twenty,  but  there  are  sometimes  only 
twelve,  while  in  the  hare  aud  rabbit  there  are  twenty-eight.  In  rumi- 
nants and  commonly  among  the  mammalia  there  are  thirty-two  ;  but 
forty-four  (as  in  the  hog  and  mole)  is  said  by  Owen  to  be  the  typical 
number.  When  more  than  forty-four  teeth  are  present,  as  is  occasion- 
ally the  case  in  the  lowest  groups,  the%y  are  of  the  reptilian  type,  as  in 
the  porpoise. 

Three  kinds  of  teeth,  as  already  mentioned,  are  met  with  :  the  in- 
cisors, which  are  chisel-shaped  for  cutting  and  gnawing ;  the  canines, 
which  are  longer  and  conical  for  tearing  food ;  and  the  premolars  and 
molars,  which  are  variously  cusped  and  tuberculated,  and  either  flat- 
tened at  the  sides  for  cutting  or  broad  at  the  summits  for  grinding. 
The  incisors  are  smallest  in  the  insectivora,  larger  in  the  carnivora,  of 
great  strength  in  the  herbivora,  and  especially  strong  in  the  rodents. 
These  vary  in  number :  the  lion  has  six  in  each  jaw ;  the  squirrel  two 
highly-developed  incisors  in  each  jaw  ;  the  ruminants  none  in  the  upper 
jaw;  the  elephant  none  in  the  lower  jaw;  wThile  the  sloth  has  none  at  all. 
The  canine  teeth  are  prominent,  conical,  and  larger  than  the  other  teeth 
in  the  dog  and  cat  tribes ;  but  not  so  in  man.*  They  are  also  large  in 
many  non-carnivorous  animals,  as  in  the  ape,  bear,  musk-deer,  and  others 
where  they  are  used  as  weapons  of  offense  and  defense.  There  are 
never  more  than  four,  and  are  wanting  in  rodents  and  most  herbivora. 
The  carnivorous  molars  are  generally  flat,  ridged,  or  tuberculated,  the 
anterior  ones  being,  as  a  rule,  very  small ;  they  overlap  like  the  blades 
of  a  scissors,  and  are,  therefore,  cutting  and  not  grinding  teeth  in  these 
animals.  The  more  purely  carnivorous  the  species,  the  fewer  the  number 
of  molars.  The  herbivorous  molars  are  provided  with  tubercles,  as  in 
the  quadrumana,  man,  and  most  omnivora,  or  are  marked  with  trans- 
verse ridges  of  enamel  and  dentine  in  the  ruminants,  solipedes,  pachy- 
dermata,  and  rodents.  The  premolar  teeth  are  preceded  by  milk-teeth ; 
the  true  molars  have  no  predecessors.  In  mammals  the  teeth  are  con- 
fined to  the  jaw-bones,  fit  closely  in  the  sockets,  may  have  one  or  more 


252  PHYSIOLOGY   OF   THE   DOMESTIC  ANIMALS. 

fangs,  each  of  which  has  its  own  socket  lined  with  periosteum.  Mam- 
mals have,  as  a  rule,  two  sets  of  teeth,  —  the  deciduous  and  permanent 
teeth  ;  and  when  the  latter  are  worn  down  they  usually  loosen  and  fall 
out,  since  they  undergo  little  or  no  repair.  An  exception  to  this  state- 
ment is  found  in  the  case  of  the  rodents,  where  the  teeth  continue  to 
grow  from  the  fact  that  the  fang  remains  open  and  the  hollow  at  the 
base  into  which  the  pulp  extends  —  the  so-called  enamel  organ  —  is  per- 
sistent, and  fresh  dentine  is  constantly  being  formed  within  the  pulp 
and  fresh  enamel  upon  the  anterior  surface.  The  unequal  wear  of  the 
hard  coating  of  the  enamel  in  front  and  the  dentine  behind  preserves 
throughout  the  whole  life  of  the  tooth  its  chisel-like  edge.  In  many 
animals  sex  exercises  a  remarkable  influence  on  the  development  of  the 
teeth.  Thus,  in  the  anthropoid  apes  the  upper  canine  teeth  in  the  male 
are  more  than  twice  the  size  of  the  analogous  teeth  in  the  female  ;  while 
the  tusks  of  the  bear  and  of  the  male  elephant  and  musk-deer  are 
larger  than  those  of  the  female.  So  also  in  the  solipedes  the  canine 
teeth  are  absent  in  the  female,  while  in  the  ox  tribe,  although  temporary 
incisors  appear  aboAre  the  gum  in  both  jaws,  the  permanent  incisors  are 
not  developed  in  the  upper  jaw,  but  remain  in  a  rudimentary  condition 
within  the  bone. 

By  the  formula  of  dentition,  or  the  dental  formula,  is  meant  the  con- 
venient method  of  reproducing  in  numerals  the  number  and  nature  of 
teeth  found  in  different  animals.  To  distinguish  these  teeth  the  letter 
i  is  used  to  indicate  the  incisors,  the  letter  c  the  canines,  pm  the  pre- 
molars,  and  m  the  molars.  The  upper  rows  of  figures  represent  the  teeth 
of  the  upper  jaw  and  the  lower  those  of  the  inferior  jaw,  the  formula 
usually  simply  representing  the  teeth  on  one  side  of  the  mouth;  doubling 
the  numbers  given  therefore  represents  the  total  amount  of  teeth.  In 
the  dog  the  formula  is  as  follows  :  — 

' 


That  of  the  cat  is  :— 


Man: — 

1  2-2  '  C  l-\  '  Pm  2^2  '  m  3^3  ' 

In  herbivora  the  incisor  teeth  vary  in  importance  in  our  grass-feed- 
ing  animals,  and  are  absent  in  the  upper  jaw  of  ruminants,  where  their 
place  is  occupied  by  the  nbro-elastic  pad  already  referred  to. .  Ruminants 
have  thirty-two  teeth, — eight  incisors  and  twenty-four  molars.  In  the 
horse  there  are  two  pairs  of  tushes,  or  canine  teeth,  and  twelve  large 


MASTICATION.  253 

molars  in  the  upper  and  lower  jaws.  In  front  of  the  molar  teeth  there 
are  sometimes  rudimentary  teeth,  which  are  called  wolf-teeth.  In  the 
horse  the  molar  teeth  have  their  grooves  produced  by  the  cement  ar- 
ranged longitudinally  on  the  crown.  In  the  stallion  there  are  twelve 
incisors, — six  in  each  jaw,  of  which  the  upper  are  the  longest,  while  the 
central  are  the  largest  and  the  corner  teeth  the  smallest, — four  canine 
teeth, and  twenty-four  molars;  in  all  forty.  In  the  mare  there  are  thirty- 
six  teeth,  the  canine  teeth  being  wanting.  The  free  surface  of  the  incisor 
teeth,  with  the  exception  of  the  table,  is  covered  with  enamel,  while  the 
fang  is  covered  with  cement.  As  the  incisor  tooth  comes  through  the 
jaw  the  cement  which  originally  covered  the  entire  body  of  the  tooth 
remains  on  the  table  of  the  tooth  in  a  depression  which  is  called  the 
infundibulum.  As  the  enamel  of  the  table  of  the  tooth  wears  away 
around  this  central  infundibulum  the  dentine  of  the  bod}^  of  the  tooth 
within  is  gradually  exposed.  We,  therefore,  have  three  different  substances 
composing  the  table  of  the  incisor  teeth  of  the  horse  (see  Figs.  95  and 
96), — the  outer  ring  of  enamel;  within  that,  concentrically,  the  exposed 
dentine ;  and  within  that  again  the  more  or 
less  triangular  ring  of  enamel  which  com- 
posed  originally  the  wall  of  the  infundibulum, 
and  which  was  continuous  with  the  enamel 
covering  the  crown  of  the  tooth.  Within 
this,  again,  is  a  more  or  less  circular  or  tri- 
angular portion  of  cement  by  which  the 
infundibulum  was  originally  filled.  Occa- 
sionally in  front  of  the  infundibulum  a  still 
denser  substance  than  the  dentine  will  be  FIG.  100.— INCISOR  TOOTH  oy 

RUMINANT.    (Nuhn.) 

met  with,  which  is  called  osteodentme,  and       8,enamel;  Z)dentine;  cd,pu]p.cavity. 
which  is  due  to  the  exposure  of  the  ossified 

covering  of  the  pulp-sac.  This  is  also  called  the  dental  star.  Two  sets 
of  teeth  are  found  in  the  horse,  of  which  the  first,  or  milk-teeth,  are 
wider  and  have  distinct  necks,  are  convex  and  are  grooved  posterior^. 
The  incisors  at  first  are  almost  perpendicular,  but  become  more  and  more 
horizontal  as  the  teeth  wear  down ;  the  lower  permanent  incisors  have 
one  groove,  the  upper  two. 

In  ruminants  thirty-two  teeth  are  met  with,  the  incisors  being  found 
only  in  the  lower  jaw.  Eight  incisors  and  twenty-four  molars  are  met 
with.  The  incisor  teeth  in  the  ruminant  are  always  somewhat  loose,  their 
table  is  always  inclined,  and  the  anterior  border  sharp  (Fig.  100).  The 
molars  are  compound  teeth  which  wear  down  and  continue  to  grow  even 
to  an  advanced  age  of  the  animal.  The  inferior  molars  have  their  tables 
inclining  outwardly,  the  upper  incline  inwardly,  while,  as  in  the  solipedes, 
the  molars  of  both  sides  cannot  be  in  apposition  at  the  same  time,  since 


254  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

the  molar  arches  of  the  upper  jaw  are  wider  apart  than  those  of  the  lower 
jaw :  and  when  the  molars  are  in  contact  the  incisors  do  not  touch,  thus 
saving  unnecessary  wearing. 

In  the  omnivora,  as  represented  by  the  hog,  there  are  forty-four 
teeth, — twelve  incisors,  four  canine  or  eye  teeth,  twenty-four  grinders,  and 
four  so-called  wolf-teeth. 

In  the  carnivora  three  kinds  of  teeth  are  met  with.  They  are  the 
incisors,  which  are  twelve  in  number,  are  sharp  and  cutting,  and  when 
first  erupted  have  three  cusps  on  their  free  extremity,  the  lateral  cusps 
being  on  a  lower  plane  than  the  central  cusp.  They  thus,  therefore, 
resemble  a  fleur-de-lis.  In  carnivorous  animals  the  two  central  incisors 
are  smaller  than  the  next  two,  and  these  smaller  than  the  next  teeth.  The 
canine  teeth  are  four  in  number,  two  in  each  jaw,  and  attain  considerable 
length,  being  larger  in  the  upper  jaw  than  in  the  lower,  are  pointed  and 
curved  backward.  The  molars  are  variable  in  number,  augmented .  in 
volume  from  the  first  to  the  penultimate,  which  has  large  cusps  and  is 
termed  the  dens  sectorius.  The  teeth  of  carnivorous  animals,  with  the 
exception  of  the  incisors,  preserve  their  pointed  form  unaltered. 

In  the  dog  the  first  three  molars  of  the  upper  jaw  do  not  come  in 
contact  with  the  first  four  molars  of  the  lower  jaw,  which  correspond  to 
them,  even  when  the  mouth  is  closed.  The  highest  cusp  of  the  dens 
sectorius,  however,  rests  on  the  posterior  surface  of  the  first  tuberculated 
molar  of  the  upper  jaw.  The  incisors  are  cutting  teeth,  the  canines  tear- 
ing, and  the  molars  crushing  or  cutting,  like  scissors,  but  not  grinding 
in  function. 

The  character  and  shape  of  the  teeth  vary  in  the  different  members 
of  the  carnivorous  group ;  in  the  bear,  which  is  essentially  in  type  car- 
nivorous, but  which  is  an  omnivorous  animal,  the  molars  are  less  pointed 
than  those  of  the  pure  carnivora,  and  approach  in  nature  the  shape 
of  the  teeth  of  omnivora,  of  which  man  may  be  taken  as  a  type.  "  In 
the  cat  tribe  all  the  teeth  are  very  pointed. 

The  teeth  are  mechanical  instruments  without  sensation,  but  serve 
as  conducting  organs  of  sensibility,  like  the  hair;  since  in  man  they  are 
sensitive  to  cold,  therefore  they  are  also  probably  sensitive  in  other 
animals.  They  transmit  sensations  of  resistance,  which  must  be  less 
acute  in  animals,  such  as  the  carnivora,  which  are  accustomed  to 
crush  bones,  and  thus  convey  information  as  to  the  solidity  of  matters 
between  the  teeth  and  regulate  the  degree  of  muscular  effort  required  in 
mastication.  The  articulation  of  the  teeth  with  the  alveoli  is  in  the  form 
of  a  pyramid  whose  base  is  external.  In  mastication,  therefore,  pressure 
is  transmitted  to  the  bony  walls  of  the  alveoli,  and  the  sensitive  pulp  is 
protected,  unless  the  teeth  are  loose  in  their  sockets,  when  mastication 
becomes  painful. 


MASTICATION.  255 


TO  DETERMINE  THE  AGE  OF  THE  DOMESTIC  ANIMALS  BY  THE  TEETH.* 

It  is  chiefly  by  the  incisor  teeth  that  we  can  tell  how  old  a  horse 
is,  and  it  is  important  to  consider  the  change  in  shape  and  general 
appearance  which  these  teeth  undergo.  There  are  temporary  and  per- 
manent incisors.  The  first  have  a  broad  crown,  flattened  somewhat 
from  before  back,  with  a  wearing  surface  far  wider  from  side  to  side 
than  from  behind  forward.  They  have  a  distinct  neck,  and  a  narrow, 
sharp  fang.  The  appearance  of  the  temporary  teeth  is  shelly,  and  there 
is  a  well-marked  depression  or  iufundibulum  on  the  upper  aspect.  The 
front  of  the  tooth  is  of  a  pearly  white,  and  is  grooved  or  fluted.  The 
permanent  incisor  is  much  larger  than  the  tempora^  tooth ;  its  crown 
thicker,  of  a  duller  color,  and  the  cavity  or  infundibulum  is  deeper.  The 
neck  of  the  tooth  is  not  so  well  defined,  and  as  the  animal  acquires  age 
we  find  a  ver}T  remarkable  change  in  the  shape.  This  is  seen  in  Fig.  101,  B, 
which  represents  different  sections  of  the  permanent  incisor,  as  its  surface 
appears  from  progressive  wear.  It  is  from  birth  to  the  age  of  eight 
years  that  from  the  condition  of  the  "  marks"  or  dark  cavities  in  the 
table  of  the  incisors  we  can  determine  the  age  of  the  horse.  There  are, 
however,  deceptive  cases. 

The  molar  teeth  are  rarely  looked  at  in  determining  the  age  of  the 
horse,  but  they  furnish  valuable  corroborative  evidence,  especially  in 
young  animals.  They  are  not  easily  examined,  but  it  is  their  number 
which  in  the  colt  confirms  or  negatives  the  opinion  expressed  as  to  the 
animal's  age.  The  recentl}'-formed  molar  has  a  shelly  character  (Fig. 
101 ,  C)  and  prominent  tubercles  of  enamel,  which  soon  wear  down  to  form 
a  broad,  grinding  surface,  and  then  the  young  and  old  teeth  are  not 
easily  distinguished. 

The  horse  has  six  incisors  above  and  six  below.  They  are  compound 
teeth,  as  shown  in  Fig.  101  at  A,  and  the  cavity  extends  downward, 
having  beyond  and  a  little  in  front  of  it  the  pulp-cavity,  which  in  old 
horses  as  the  teeth  wear  down  is  indicated  by  a  dark,  hard  structure, 
which  then  fills  it,  and  which  is  called  osteodentine. 

The  temporary  incisors  are  in  perfect  apposition  as  the  colt 
approaches  two  years,  and  not  seldom  an  animal,  especially  a  pony,  has 
been  bought  for  five  years  of  age  from  the  temporary  teeth  being  mis- 
taken for  the  permanent  incisors.  The  temporary  incisor  is  gradually 
displaced  by  pressure  from  the  permanent.  The  latter  advances,  and  has 
a  shelly  aspect,  seen  in  a,  Fig.  101,  at  B.  At  b  the  incisor  tooth  indicates 
two  years'  wear;  at  c  five  years',  at  d  nine  years',  and  at  e  about 


Disease. 


*This  chapter  is  taken  from  Gamgee,  "  Our  Domestic  Animals  in  Health  and  in 

•  i^..    " 


256 


PHYSIOLOGY  OF   THE   DOMESTIC   ANIMALS. 


seventeen  years'  friction.  The  shape  of  the  wearing  surface  of  the  tooth 
is  of  great  importance  in  determining  approxi- 
mately the  age  of  the  horse.  Before  eight 
years  the  eruptive  changes  and  periodic  appear- 
ances of  the  teeth  are  very  regular  and  valuable  in 
indicating  age.  The  foal  at  birth  indicates  the 
fast  approaching  eruption  of  the  two  central 
incisors.  Sometimes  these  are  through  the  gum 
when  the  animal  is  foaled  ;  if  not  they  appear 
within  the  first  month.  Three  molar  teeth  on 
each  side  of  both  upper  and  lower  jaws  are  prom- 
inent, and  in  apposition  for  wear  at  the  same  time. 
One  incisor  on  each  side  of  the  two  central  ap- 
pears at  six  weeks,  and  then  time  is  allowed  for 
the  jaw  to  grow.  The  cavities  of  reserve  with 
teeth  forming  in  them  grow  behind  the  teeth  first 
formed,  and  by  nine  months  the  corner  incisors 
appear,  and  gradually  grow  until  the  animal  is  a 
year  old,  when  all  the  colt's  incisors  are  in  full 
use.  Within  one  and  two  years  of  age  little  can 
be  seen  beyond  a  gradual  wearing  down  of  the 
temporary  teeth,  and  the  protrusions  through  the 
gums  of  the  fourth  molar  on  each  side  of  the  two 
jaws.  At  two  years  the  worn  aspect  of  the 
incisors  indicates  the  approaching  displacement 
of  the  central  ones,  and  the  fifth  molar  protrudes 
through  the  gums. 

Between  two  and  three  years  the  central  per- 
manent incisors  displace  the  temporary,  and  are 
readily  recognized  by  their  size,  yellowish  color 
of  enamel,  and  dark  infundibulum.  At  this  age 
the  middle  incisors  are  often  knocked  out  to  make 
the  horse  look  "three  off"  or  "coming  four." 
This  often  retards  their  eruption,  which  is  always 
complete  at  four  years,  when  the  sixth  molar  tooth 
on  either  side  of  both  jaws  is  also  advanced 
sections  of  per-  through  the  gum.  B\'  this  time  the  three  tempo- 

rhHay  ihetbie°fbeco°mee3  triZgu!  ™y  molars,  or  grinders,  which  are  noticed  shortly 

lar  from  wear,    a,  on  eruption;  6,        «,  -,.     ,,        , 

at  two  years ;  c,  at  five  years :  d,  at  after  birth,  have  given  way  to   permanent  teeth. 

nine  years;   e,  at  about  seventeen    „          .  . 

The  lower  tushes  are  felt  through  the  membrane 

le  of  molar  tooth  of  horse, 

^gSoves1  arrangement  between  the  corner,  and   first   molar   as   early  as 
three  years  of  age,  but  they  only  appear  above  it 
between  four  and  five.     It  is  at  this  age  that  the  horse's  mouth  becomes 


FIG.    101.— TEETH     OF 
HORSE.    (Gamgee.) 

A.  Longitudinal  section  of  per- 
manent    incisor   of    horse    shortly 


15  Years.  18  Years.  24  Years. 

FIG.  102.— CHANGES  FROM  AGE  IN  THE  INCISOR  TEETH  OF  THE  HORSE.    ( Wilckens.) 

17  (257) 


258 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


fully  furnished,  and  by  five  the  whole  of  the  incisors  are  in  full  wear, 
and  indicate  the  extent  to  which  they  have  been  worn  proportionate  to 
the  period  since  their  eruption.  The  central  incisors  then  appear  as 
shown  in  6,  Fig.  101,  B,  whereas  the  corner  teeth,  having  just  protruded, 
are  shelly,  as  shown  in  a. 

At  six  the  central  incisors  lose  their  mark ;  at  seven  this  occurs 
with  the  middle  one,  and  at  eight  all  the  infundibula  are  worn  out,  and 
the  plate  of  the  tooth  is  clean  and  only  very  slightly  marked  in  the 
corner  teeth.  Beyond  this  period  the  horse  is  stated  to  be  aged.  The 
incisors  protrude  straighter  from  the  receding  jaw;  the  teeth  become 

narrower,  and  their  wearing  surface  becomes 
triangular,  as  seen  at  c,  d,  and  e,  Fig.  101,  B. 
This  distinguishes  the  old  animal. 

The  table  on  the  preceding  page,  taken 
from  the  "  Encyclopadie  der  gessammten 
Thierheilkunde,"  indicates  the  wear  of  the  in- 
cisors of  the  horse  at  different  ages  (Fig.  102). 
Dentition  in  the  Ox. — The  incisor  teeth  of 
the  lower  jaw  of  the  ox  are  simple,  and  eight 
in  number  (Fig.  103).  From  the  periods  of 
eruption  of  both  temporary  and  permanent 
teeth  being  regular,  the  latter  being  much 
the  broader,  the  age  of  the  animal  is  readily 
determined.  Further,  the  sharp  teeth  become 
more  and  more  blunt  and  narrow,  until  in  old 
cattle  they  are  reduced  to  very  small  stumps. 
The  wear  of  the  incisors  commences  on  the  free  border,  both  in  the  decid- 
uous and  permanent  teeth,  the  enamel  being  worn  gradually  from  .the 
table  of  the  tooth,  from  the  anterior  border  posteriorly,  the  dentine  being 
exposed  in  zigzag  lines,  which  at  the  sides  extend  further  toward  the 
neck  of  the  teeth  than  in  the  middle.  When  the  enamel  is  all  gone  from 
the  table  of  the  incisors  (after  the  tenth  year),  the  entire  crowns  of  the 
teeth  wear  down  until,  in  extreme  age,  only  the  necks  are  left.  The 
following  table  gives  the  succession  of  changes  in  the  ox  : — 


FIG.  103.— LONGITUDINAL  SEC- 
TION OF  INCISOK  TOOTH  OF 
RUMINANT.  (Ellenberger.) 

C,  tooth-cavity ;  G,  enamel ;  E,  pulp-canal ; 
D,  dentine. 


SlMONDS. 

SlMONDS. 

GlRARD. 

TABLE  OF  EARLY  AVERAGE 

TABLE  OF  LATE  AVERAGE 

TABLE  OF  LATE  AVERAGE 

(IMPROVED  BREEDS). 

(IMPROVED  BREEDS). 

(UNIMPROVED  BREEDS). 

t 

1 

No.  of  Teeth. 

£ 

1 

No.  of  Teeth. 

2* 

1 

No.  of  Teeth. 

1 

9 

2  permanent  incisors 

2 

3 

2  permanent  incisors 

2 

3 

2  permanent  incisors 

2 

3 

4 

2 

y 

4 

3 

0 

4 

2 

9 

6 

3 

3 

6 

4 

0 

6 

3 

3 

8 

3 

9 

8 

5 

0 

8 

MASTICATION. 


259 


The  following  figures,  from  the  "  Encyclopedic  der  gessammten 
Thierheilkunde,"  indicate  the  changes  occurring  with  age  in  the  incisor 
teeth  of  cattle  (Fig.  104). 


Newborn.         8  Days.  4  Weeks. 


12  Years.  14  Years.  16  Years.  18  Years.  20  Years. 

FIG.  104.— CHANGES  FROM  AGE  IN  THE  INCISOR  TEETH  OF  THE  Ox.    (Wilckens.) 


Dentition  of  Sheep. — In  the  sheep  it  is  by  the  displacement  of  tem- 
porary and  eruption  of  the  permanent  teeth  that  the  age  of  the  animal 
is  determined. 


TABLE  OF  EARLY  DENTITION. 


TABLE  OF  LATE  DENTITION. 


Years. 

Mos. 

No.  of  Teeth. 

Years. 

Mos. 

No.  of  Teeth. 

1 

0 

Central  pair    of    temporary 

1 

4 

Two  permanent  incisors. 

incisors  replaced  by  per- 

manent. 

1 

6 

Second 

2 

0 

Four        "    • 

2 

3 

Third 

2 

9 

Six 

3 

0 

Fourth             "              " 

3 

6 

Eight       " 

260 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


These  changes  are  also  indicated  in  the  following  diagrams  from  the 
"  Encyclopadie  der  gessammten  Thierheilkunde  "  (Fig.  105). 


2  Months. 
(Milk-Teeth.) 


Years. 
(2  Broad  Incisors) 


%  Years. 
(4  Broad  Incisors.) 


2M  Years. 
(6  Broad  Incisors.) 


4  Years. 
(8  Broad  Incisors. ) 


Over  7  Years. 
(8  Broad  Incisors.) 


FIG.  105.— CHANGES  FROM  AGE  IN  THE  INCISOR  TEETH  OF  THE  SHEEP.    ( Wilckcns. ) 

Teeth  of  Carnivora. — All  the  carnivora  have  simple  teeth ;  i.e., 
covered  entirely  over  the  crown  by  white  enamel.  There  are  three  pairs 
of  incisors,  one  pair  of  canines,  and  a  certain  number  of  molars.  It  is 
the  last  premolars,  or  the  first  true  molars,  which  are  emplo^yed  in  chew- 
ing flesh;  they  are  prominent  and  sharp.  Behind  these,  especially  in  the 
dog,  the  teeth  are  armed  with  round  tubercles  on  their  surface,  destined 
for  crushing  or  grinding  action,  and  in  breaking  bones  or  gnawing  long- 
grass  the  dog  may  be  seen  -to  push  the  substance  between  these  back 
molar  teeth. 

Dentition  in  Dog. — 

6  1-1  6-6 

Incisors  -  ;  canines  —  ;  molars =  42. 

6  1-1  7-7 

The  dog  is  born  with  his  eyes  shut ;  they  open  on  the  tenth  or  fifteenth 
day  after  birth.  The  whole  of  the  milk-teeth  are  usually  cut  then,  or 
very  shortly  after.  Between  two  and  four  months  the  central  incisors 
and  often  even  the  middle  ones  of  both  upper  and  lower  jaws  drop  out, 
and  speedily  the  whole  of  the  permanent  teeth  are  fully  developed,  so 
as  to  complete  the  mouth  by  eight  months. 

The  inferior  incisors  begin  to  wear  by  fifteen  months.  Fig.  106 
shows  the  milk-teeth  in  a  puppy  two  or  three  months  old  ;  Fig.  107  in  a 
year-old  dog.  At  eighteen  months,  or  two  3rears,  the  inferior  central 
incisors  are  much  worn,  and  between  two  and  three  years  the  middle 
ones  also  (Fig.  108)  ;  the  worn  incisors  bear  a  striking  contrast  to  the 


MASTICATION. 


261 


young  teeth,  as  seen  in  Fig-.  107,  where  the  edge  or  border  of  the  tooth 
is  divided  into  three  lobes,  of  which  the  most  prominent  constitutes  the 
point  of  the  tooth.  Between  three  and  four  3* ears  the  upper  central 
incisors  are  worn,  and  between  four  and  five  the  whole  give  indications 
of  much  use  (Figs.  109  and  110).  Beyond  this  age  the  teeth  are  very 
uncertain.  The  bluntness  and  yellow  color  of  the  tusks  and  other 
teeth  offer  the  best  signs  of  increasing  age. 


FIG.  106.— MII.K-TEETH  IN   A  PLTPPY 
2  OK  3  MONTHS  OLD.    (Gamgee.) 


FIG.  107.— DENTITION  IN  A  YEAR-OLD  DOG. 
(Gamgee.) 


FIG.  108.— DENTITION  IN  A  TWO-YEAR-OBD  DOG.    (Gamgee.) 


FIG.  109.— DEXTITIOX  IN  DOG  BETWEEN 
3  AND  4  YE  A  us  OF  AGE.     (Gamgee.) 


FIG.  110.— DENTITION  IN  DOG  4  OR  5  YEARS  OF 
AGE.    (Gamgee.) 


Dentition  in  the  Pig. — The  pig  is  born  with  eight  teeth,  which  are 
foetal  incisors  and  foetal  tusks.  At  one  month  four  incisors  are  cut, 
besides  three  temporanr  molars  on  either  side  of  each  jaw.  Two  more 
temporary  incisors  are  added  to  each  jaw  at  three  months,  and  all  the 
milk-teeth  are  then  in  position.  The  jaws  and  teeth  grow,  and  at  six 
months  in  most  animals,  but  not  .in  all,  a  small  tooth  comes  up  on  either 
side  of  the  lower  jaw,  behind  the  temporary  tusks,  between  them  and  the 
molars,  and  in  the  upper  jaw  directly  in  front  of  the  molars.  These 
teeth  have  been  mistaken  for  tusks.  The  fourth  molar  in  position 


262 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


appears  through  the  gum  also  at  six  months.  The  corner  incisors  are 
displaced  and  permanent  ones  cut  at  nine  months.  The  permanent  tusks 
are  also  cut  at  this  period,  as  well  as  the  fifth  molar  on  either  side  of 
each  jaw.  At  one  year  the  middle  incisors  are  changed  and  the  tusks 
appear  of  considerable  size.  The  deciduous  molars  are  likewise  shed  at 
one  year  and  succeeded  by  permanent.  At  eighteen  months  the  denti- 
tion of  the  pig  is  completed  by  the  cutting  of  the  lateral  incisors  and  the 
last  or  sixth  molar.  The  succession  of  teeth  in  the  pig  is  shown  in  the 
following  table : — 


At 
Birth. 

One  Month. 

Three 
Months. 

Nine 
Months. 

Twelve 
Months. 

Eighteen 
Months. 

-n    ,   i  <  Incisors. 
Foetal  \  Tusks,    .     . 

4 
4 

4 
4 

4 
4 

.  •  -' 

Temporary  incisors, 

4  central. 

8   central 
and  lateral. 

8    central 
and  lateral. 

4  lateral. 

•       •-"? 

Permanent  incisors, 

4  corner. 

8   central 

12  central, 

and  corner. 

lateral.and 

corner. 

Permanent  tusks,    . 

".•> 

. 

• 

4  (cutting}. 

4 

4 

Total  in  both  jaws, 

8 

12 

16 

16 

16 

16 

Other  Signs  of  Age  in  Domestic  Animals. — In  horned  animals  the 
horns  grow  annually  a  certain  length,  and  this  is  shown  by  the  appear- 
ance of  an  extra  ring  every  year  at  the  root  of  the  horn.  .For  the  first 
two  years  the  rings  are  so  indistinct  that,  in  calculating  the  age  in  an 
animal  five  or  six  years  old,  the  first  ring  indicates  a  three-years' growth, 
so  that  an  animal  with  six  rings  must  be  regarded  as  eight  years  old. 

Fraud  may  be  practiced  to  destroy  the  marks  of  age.  Angularity  of 
form,  sharpness  of  bones  and  gray  hair  are  not  easily  disguised,  but  teeth 
can  be  filed  and  marked  and  horns  scraped.  Making  false  marks  on  teeth 
is  called  "  bishoping."  Gray  hairs  may  be  painted,  called  "gypping." 
In  old  horses  the  remarkable  depressions  behind  the  orbits  are  some- 
times pricked  and  blown  up  with  air;  this  is  called  "puffing  the  glym." 

Some  of  the  abnormal  conditions  of  the  teeth  are  the  persistence  of 
temporary  teeth,  so  that  twelve  incisors  may  be  present  in  the  lower  jaw, 
or  the  permanent  teeth  may  fail  to  develop.  One  or  more  teeth  may  be 
absent,  from  removal  or  from  faulty  development. 

In  the  following  table  the  order  of  dentition  of  the  domestic  animals 
is  recapitulated : — 


MASTICATION. 


263 


1..-  -  *  5  !  P  i 

* 

t2j 

^> 

=    =  S 

&     ^             & 

\ 

cr 

5       .*              -°  ^ 

Ca 

o 

^CS       4^           ^    2        ^<f" 

-    "1 

^^                ™    5*                      S"         0                 g-uD    g» 
O    O    O                  ^    ^                                        ro                        5^    *"* 

I 

r 

01  ^  to    "    '  ^  o                v-        3             3?  % 

» 

£cgH 

**ff  9          E^p              £      §      •£.5t?D 

g 

a  T  ^ 

"^§                   e^-   2*                         P3?                  £^.S* 

w 

5'"°  -® 

•    '            r"  "^                       •"*               P"  ^ 

0 

P 

• 

6 

K 

K' 

CO                ^3                                      ^                 CO          tO 

c 

_ 

*^                                                           "** 

8* 

W 

• 

P       "           o>                                          J>                                   ® 

§ 

H 

"^               p                                 p                 :        p 
.     .     .      °°               s                                 ^ 

<n 

d 

• 

3                        3                    3 

• 

H 
N 

w 

^ 

.      .      . 

_                    CL...                                                                            0-,—, 

iftfc      '°*            SB  03                             t^                  p   OT 

oT 

^-                CrJ     CT>                                                          H^-        C-     CT> 

8 

H 

•      • 

CJK-*    ^^                  i.    ^                                   •       CO  •-  •  P            |.     cp 

^ 

tt 

^  |  3    :  :  »  s                   ^  S.^    "  §"  g 

S 

t< 

W 

.  .  . 

•   I  ?  g.         ^p             '       %  r  E,     S!p 

p 

g 

0 

•S       «*          B1!'                        .**      §*      i^ 

^ 

•^ 

CC  CO  ^JS 

g 

^ 

to  Oi  ^s 

B 

Q 

w 
^ 

co  to      >-»                         ^      co  to      ^ 

o 

» 

Hj 

V!                                                             Wj 

p* 

3 

"     ~        p                                   "           "     -        S 

o 

•    •    •    •                3               •                            3 

M 

izj 

e 

i_»      en                                      p"  td                    co 

H 

S 

*    ~  3 

If 
s, 

_      -  O 

-    -  o 

'    §       |                                  |f                  1 

Eruption. 

S 

E  DOMESTK 

f|i 

to 

HH 
tO                                   H-         05                             ^ 

-^                    ^      3                  °. 

Q 
P 

Q 

tj 
t> 

H 

21-*                                   »<; 

6 

>• 

e* 

*                         E? 

OB 

.  .  . 

c^ot*.         *.     ca                                       *- 

''^  o"  o"           o"      o"                                              ? 
o  05  cn           CT      ^                                *             o 

! 

^      3     :    ^       3                                               j 

. 

. 

r     -^  r                       -^ 

g 

en                           en       en                      co 

? 

oto£ 

o"                          o"       3                      o" 

0                                 0        §                             ^ 

"3                      3      ?                 3 

o 

B" 

i 

o                           05°                      o 

•   •   •          2.     *              2-            *          2- 

¥"              ?"                ? 

264  PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 

3.  The  TONGUE,  LIPS,  and  CHEEKS  are  accessory  organs  of  mastication, 
and  act  by  maintaining  the  food  in  its  position  between  the  teeth.  In 
many  animals,  particularly  the  horse,  as  already  mentioned,  the  lips  have 
a  high  degree  of  prehensile  power,  and  when  the  upper  lip  is  paralyzed, 
as  by  section  of  its  motor  nerve,  prehension  of  food  in  the  horse  is 
impossible.  When  the  lips  and  cheeks  are  paralyzed,  again,  even  in 
animals  in  which  these  organs  do  not  serve  for  prehensile  purposes,  mas- 
tication is  impossible,  or  at  least  rendered  extremely  difficult,  from  the 
fact  that  their  loss  of  motor  power  prevents  their  keeping  the  food 
between  the  teeth ;  their  loss  of  sensibility  prevents  the  determination 
as  to  when  the  food  has  acquired  the  proper  degree  of  comminution,  and 
their  insensibility  prevents  these  organs  avoiding  being  themselves 
lacerated  by  the  teeth.  This  especially  applies  to  the  occurrence  of  mas- 
tication between  the  molar  teeth.  Here,  when  the  buccinator  muscles 
are  paralyzed,  through  paralysis  of  the  facial  nerve  (seventh  pair),  the 
food  collects  in  the  pouches  formed  by  the  relaxed  cheeks,  and  cannot  be 
properly  masticated.  The  sensibility  of  the  lips  and  cheek  is  derived 
from  the  fifth  pair  of  nerves. 

The  tongue  is  also  an  important  organ  of  mastication  ;  it  serves  in 
a  large  group  of  animals  for  the  prehension  of  solids  and  liquids ;  it  is 
of  great  importance  in  starting  the  process  of  deglutition,  and  in  man  it 
is  one  of  the  principal  organs  of  articulation.  By  its  high  degree  of 
sensibility  it  aids  in  mastication  in  determining  the  degree  of  comminu- 
tion of  the  food,  and  in  keeping  the  particles  of  food  between  the  teeth 
during  their  mastication;  its  mobility  enables  it  to  act  as  a  sort  of  hand 
in  the  necessary  movements  of  the  bolus  of  food  in  the  mouth.  Its 
muscles  are  striped  and  voluntary  in  nature  and  arranged  in  four  different 
layers ;  an  upper  and  lower  layer,  passing  from  the  root  to  the  tip  of  the 
tongue,  and  an  upper  and  lower  oblique  layer.  These  muscles  form  a 
complicated  net-work  of  fibres  which,  b}^  varying  degrees  of  partial  con- 
traction, permit  not  only  changes  in  the  shape  of  the  tongue,  but  also  in 
its  position  within  and  without  the  mouth.  The  extension  of  the  tongue 
is  accomplished  by  the  muscles  passing  from  the  chin  to  the  body  of  the 
organ,  the  genio-giossus  muscles.  The  retraction  of  the  tongue  is  accom- 
plished by  means  of  the  muscles  arising  from  the  hyoid  bone  and  styloid 
process, — the  hyo-  and  stylo-glossus  muscles, — and  by  the  longitudinal 
fibres  in  the  body  of  the  tongue.  The  different  alterations  in  shape  of 
the  tongue  are  accomplished  by  the  contraction  of  its  intrinsic  muscles. 
Thus,  when  the  upper  longitudinal  fibres  of  the  tongue  contract  the  tip 
of  the  tongue  is  elevated.  When  those  of  the  inferior  layer  contract  the 
tip  of  the  tongue  is  depressed,  and  by  contraction  of  the  upper  oblique 
layers  the  tip  of  the  tongue  is  formed  into  the  spoon  shape  which  is  so 
useful  in  the  prehension  of  liquids  in  the  cat  tribe.  The  motor  power 


MASTICATION.  265 

of  the  tongue  is  derived  from  the  Ii3'poglossal  nerve ;  its  sensation  is 
derived  from  the  lingual  branch  of  the  fifth  nerve  and  the  glosso-pharyn- 
geal,  both  of  these  nerves  being  also  concerned  in  the  special  sense  of 
taste. 

We  see  from  the  above  that  the  act  of  mastication  differs  very  decid- 
edly in  nature  according  to  the  type  of  organization  of  the  animal,  and 
its  characters  result  from  the  configuration  of  the  jaws,  the  play  of  the 
muscles,  and  the  form  of  the  teeth.  Thus,  we  find  that  the  movements 
of  mastication  in  carnivorous  animals  are  restricted  to  a  simple  eleva- 
tion and  depression  of  the  lower  jaw,  this  mode  of  mastication  being 
dependent  upon  the  mode  of  articulation  of  the  lower  with  the  upper  jaw 
and  the  overlapping  of  the  upper  molar  and  canine  teeth.  Mastication, 
therefore,  in  these  animals  is  reduced  simply  to  a  process  of  section, 
laceration,  and  crushing.  The  incisor  teeth  have  but  slight  functional  im- 
portance, and  are  confined  in  their  action  to  cutting.  The  canine  teeth 
are  the  principal  organs  of  mastication,  and  exert  a  lacerating  or  tearing 
function,  while  the  molars  are  crushing  in  function  and,  from  the  fact 
that  they  are  highly  tuberculated  on  their  free  crown  surface,  no  process 
at  all  analogous  to  grinding  can  occur  between  them.  When  in  these 
animals  bones  are  crushed,  such  an  operation  only  occurs  on  one  side  at 
a  time.  In  animals  of  the  cat  tribe,  from  the  highly  pointed  character 
of  their  molar  teeth,  crushing  of  hard  articles  of  food  is  performed  with 
greater  difficulty  than  in  animals  in  whom  the  molar  teeth  have  a  more 
blunt,  tuberculated  crown.  Thus,  animals  allied  to  the  dog  can  more 
readily  crush  bones  than  the  cat  tribe.  When  the  molar  teeth  are 
brought  into  play,  as  in  crushing  a  bone,  the  substance  is  usually  fixed 
by  the  fore  paws,  while  the  flesh  is  torn  from  the  bones  l>y  the  canine 
teeth,  and  then  the  bones  are  drawn  between  the  molar  teeth  by  the  action 
of  the  tongue,  the  lips  being  loose  and  pendulous  and  enabling  the  mou'h 
to  be  opened  back  bc}rond  the  level  of  the  molar  teeth:  so  that,  therefore, 
even  large  bones  may  partly  be  placed  between  the  molar  teeth,  while  the 
remainder  remains  without  the  mouth.  Crushing  is  then  accomplished 
by  powerful  contractions  of  the  temporal  and  masseter  muscles  on  one 
side  of  the  jaw  at  a  time,  and  are  accompanied  by  motions  of  the  head 
on  the  side  on  which  mastication  is  taking  place,  and  usually  by  the 
closure  of  the  eye  on  the  side  in  which  this  operation  occurs. 

In  the  herbivora  the  movements  of  mastication  are  much  more  com- 
plicated, and,  as  we  find,  differ  in  nature,  the  most  marked  extremes 
being  found  in  the  rodents  and  the  ruminants.  In  all  herbivora  the 
lower  jaw  is  always  the  narrower,  and  therefore  both  sides  cannot  act  at 
once.  The  jaw  is  longer,  less  powerful,  and  we  find  among  the  her- 
bivora differences  in  the  series  of  movements  for  the  necessary  com- 
plete comminution  of  the  food  with  which  these  animals  are  sustained. 


266  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

A  cutting  motion  is  required,  fulfilled  by  the  incisor  teeth,  which  are 
consequently  most  highly  developed  in  the  rodents;  and  a  grinding 
motion,  accomplished  by  the  molars.  As  we  have  already  found,  the 
lower  jaw  is  capable  not  only  of  elevation  and  depression,  but  also  of 
advancement,  retraction,  and  rotation,  and  all  these  motions  are  required 
in  the  mastication  of  food  by  the  herbivora.  This  motion  is  unilateral, 
and  may  occur  continuously  on  one  side  for  fifteen  minutes,  and  then 
alternate  to  the  opposite  molars,  and  we  shall  find  that  the  secretion  of 
the  parotid  salivary  gland  coincides  with  the  side  on  which  mastication 
is  taking  place.  This  peculiarity  of  secretion  is  seen  in  all  ruminants 
and  most  herbivora,  and  has  been  even  claimed  to  take  place  in  man. 

The  duration  of  mastication  depends  upon  the  natural  group  to 
which  the  animal  belongs,  on  its  age,  and  therefore  the  condition  of  its 
teeth,  and  the  character  of  its  food.  Carnivora  require  but  slight  mas- 
tication of  their  food,  and,  in  fact,  mastication,  as  seen  in  the  herbivora, 
may  in  them  be  said  to  be  entirely  absent,  the  movements  of  mastication 
in  carnivora  being  simply  confined  to  tearing  the  food  into  pieces  small 
enough  to  be  swallowed.  The  herbivora,  from  the  nature  of  their  food, 
need  a  longer  time  for  reducing  it  to  a  condition  of  fine  comminution, 
and  we  find  among  the  herbivora  differences  in  the  duration  of  mastica- 
tion, according  as  the  animals  are  ruminant  or  non-ruminant.  The  non- 
ruminant  animals,  such  as  the  horse,  chew  their  food  thoroughly  and 
once  for  all.  It  has  been  estimated  by  Colin  that  a  horse  will  require  one 
and  one-fourth  hours  for  the  mastication  of  four  pounds  of  dry  hay,  and 
of  this  amount  will  make  sixty  to  sixty-five  boluses,  and,  accordingly, 
sixty  to  sixty-five  motions  of  deglutition,  while  the  rate  of  mastication 
will  be  about  seventy  to  eighty  strokes  of  the  teeth  per  minute.  If  any- 
thing interferes  with  the  secretion  of  saliva  the  duration  of  mastication 
will  be  very  much  prolonged.  One  of  the  main  objects  of  mastication 
in  the  herbivora  is  to  aid  in  the  maceration  of  the  food.  Where,  as  in 
the  solipede,  the  food  must  be  thoroughly  macerated  and  comminuted 
before  reaching  the  stomach,  the  duration  of  mastication  will  naturally 
l)e  much  longer  than  in  the  ruminant,  where  the  food  is  simply  subjected 
to  a  few  strokes  of  the  teeth  and  then  swallowed,  to  then  undergo  pro- 
longed maceration  in  the  rumen  of  these  animals,  and  to  be  again 
subjected  to  a  second  mastication  in  the  mouth.  In  both  animals, 
although  in  a  more  marked  degree  in  the  horse,  suppression  or  inter- 
ference with  the  flow  of  saliva  will  prolong  mastication;  again,  the  drier 
the  food  the  greater  will  be  the  amount  of  mastication  necessary  before 
the  food  can  be  comminuted  and  macerated  sufficiently  to  be  swallowed. 
Therefore,  grazing  animals  will  require  a  less  degree  of  mastication  of 
their  food  than  those  which  are  fed  on  grains  or  dry  fodder.  In  the 
ruminant  the  first  mastication  is  three  times  as  fast  as  the  mastication 


MASTICATION. 


267 


in  the  horse  for  the  same  amount  of  food,  while  the  second  mastication 
is  proportionately  lengthened.  As  the  teeth  become  worn  away,  masti- 
cation becomes  more  and  more  difficult,  and  proportionately  more  and 
more  prolonged.  In  the  horse  the  molar  teeth  are  used  up  faster  than 
the  incisors,  and  if  it  were  not  for  the  fact  that  the  incisors  become  more 
and  more  horizontal,  the  molar  teeth  could  no  longer  come  in  appo- 
sition. The  influence  of  the  secretion  of  saliva  on  mastication  has  been 
determined  by  Colin  experimentally,  by  making  a  fistula  of  the  duct  of 
the  parotid  glands  and  allowing  the  saliva  to  escape  externally  from  the 
mouth.  His  results  are  shown  in  the  following  table : — 


ALL  THE  SALIVA 

SALIVA  OF  ONE 

SALIVA  OF  BOTH 

POURED  INTO  MOUTH. 

PAROTID  ESCAPING. 

PAROTIDS  ESCAPING. 

No.  of 
Boluses. 

Duration  of 
Mastication 
of  One 
Bolus. 

No.  of 
Strokes  of 
Teeth. 

Duration  of 
Mastication. 

No.  of 
Strokes  of 
Teeth. 

Duration  of 
Mastication. 

No.  of 
Strokes  of 
Teeth. 

1 

35  Seconds. 

39 

30  Seconds. 

33 

45  Seconds. 

38 

2 

33 

42 

29 

30 

43 

47 

3 

25 

31 

37 

44 

35 

35 

4 

27 

36 

33 

36 

80 

79 

5 

30 

39 

47 

42 

115 

114 

6 

35 

41 

45 

38 

60 

63 

7 

25 

37 

23 

33 

110 

101 

8 

25 

34 

33 

35 

95 

95 

9 

42 

47 

40 

45 

100 

101 

10 

40 

40 

25 

30 

65 

68 

As  regards  the  importance  of  thorough  mastication,  it  is  hardly 
necessary  to  add  anything  further.  We  have  found  that  its  importance, 
of  course,  varies  in  accordance  with  the  nature  of  the  food.  Carnivora, 
as  has  been  mentioned,  require  mastication  simpty  to  be  perfect  enough 
to  tear  their  food  into  pieces  small  enough  to  be  swallowed,  and  in  the 
herbivora  we  reach  the  opposite  extreme,  and  find  there  the  group  of 
animals  in  whom  a  thorough  mastication  is  of  the  utmost  necessit}7. 
From  our  considerations  of  the  nature  of  vegetable  foods  w^e  know  that 
the  nutritive  principles  of  these  foods  are  contained  within  resisting, 
tenacious  envelopes.  To  enable  these  substances  to  be  acted  upon  by 
the  digestive  juices,  and  therefore  to  be  absorbed,  these  envelopes  must 
be  first  mechanically  ruptured,  and  this  in  the  herbivora  is  the  main 
object  of  mastication. 

Where  we  find  mastication  imperfectly  performed,  we  have,  as  an 
invariable  sequence,  imperfect  digestion,  and  we  find  that  the  grasses  and 
seeds,  and  so  on,  which  escape  mastication  pass  through  the  intestinal 
canal  entirely  unaltered  and  are  found  in  the  excreta  unchanged,  and,  in 
the  case  of  seeds,  without  even  having  lost  their  power  of  germination. 


268  PHYSIOLOGY  OF   THE   DOMESTIC   ANIMALS. 

They  are,  therefore,  perfectly  inert  as  regards  any  action  to  which  they 
may  be  subjected  by  the  digestive  juices.  In  the  omnivora  we  find 
mastication  occupying  a  mean  as  regards  importance  between  the  her- 
bivora  and  the  carnivora.  Where  an  omnivorous  animal  feeds  on  vegetable 
diet  the  performance  of  mastication  is  as  important  as  in  the  herbivora ; 
while  when  on  a  meat  or  animal  diet  its  importance  becomes  reduced  to 
the  secondary  degree  in  which  it  is  seen  in  animals  of  a  purely  carnivo- 
rous type. 

IV.  DIGESTION  IN  THE  MOUTH. 

THE  SALIVARY  SECRETION. — The  salivary  glands  appear  in  most  verte- 
brates as  tubular  glands,  as  in  insects,  but  in  the  mollusks  they  take  on 
the  lobular  form  which  characterizes  them  in  the  vertebrates.  In  birds 
the  salivary  glands  are  small  in  the  species  which  live  on  soft  animal  food 
(waders  and  web-footed  species),  while  they  are  larger  in  the  graniverous 
birds.  In  birds  the  saliva  is  mainly  to  assist  in  deglutition  by  lubricating 
the  food,  as  buccal  mastication  does  not  occur  in  these  animals.  In 
certain  birds,  as  the  woodpecker,  the  salivary  secretion  assists  in  the 
prehension  of  food.  In  the  fishes,  from  the  nature  of  their  food,  which 
requires  no  mastication,  we  find  the  salivary  glands  almost  entirely  absent, 
even  in  such  groups  as  the  cetaceans  which  belong  to  the  general  di- 
vision of  mammals.  Here,  also,  we  find  that  their  food  requires  no  pre- 
liminary subdivision  before  being  swallowed.  As  has  been  already 
mentioned,  one  of  the  uses  of  the  saliva  is  to  assist  in  mastication  ;  where, 
therefore,  mastication  is  not  performed  we  have  in  such  animals  a  corre- 
spondingly rudimentary  condition  of  the  salivary  glands.  On  the  other 
hand,  in  nearly  all  animals  which  possess  buccal  or  pharyngeal  teeth 
there  is  usually  a  glandular  apparatus  whose  secretion,  by  macerating  the 
food,  is  destined  to  facilitate  mastication  and  deglutition.  In  a  general 
way  it  may  be  said  that  in  most  cases  where  there  are  permanent  prehen- 
sile organs  salivary  glands  are  also  present  (Letourneau).  Thus,  the  fly 
emits  on  the  particles  it  is  about  to  draw  in  a  brown  liquid  which  dilutes 
them.  In  reptiles  the  salivaiy  glands  become  very  highly  developed,  and 
in  certain  of  them  their  secretion  acquires  a  poisonous  character.  In 
chelonians  and  saurians  the  salivaiy  apparatus  consists  principally  of 
lingual  glands.  In  the  chameleon  they  are  located  in  the  tongue  and 
secrete  the  sticky  fluid  which  is  of  importance  in  their  mode  of  prehen- 
sion of  food.  Their  maximum  development  is,  however,  reached  in 
mammals,  with  the  exception  of  the  cetaceans,  as  already  alluded  to, 
where  the  lacrymal  glands  are  also  absent,  and  is  especially  marked  in 
the  herbivora,  whose  food  requires  the  finest  comminution  in  the  mouth. 
In  the  ant-eater  the  salivary  apparatus  is  enormously  developed,  the 
glands  covering  the  fore  part  of  the  neck  and  even  extending  to  the  chest, 


DIGESTION   IN   THE   MOUTH.  289 

and  a  special  reservoir,  or  salivary  bladder,  exists  beneath  the  mouth.  In 
these  animals  also  the  saliva,  through  its  viscidity,  assists  in  the  prehen- 
sion of  food.  In  the  carnivora  mastication  is  incomplete  ;  since  the  food 
of  carnivorous  animals  contains  a  large  quantity  of  water,  the  salivary 
glands  of  these  animals  are  therefore  relatively  small,  and  their  function 
is  confined  to  the  production  of  a  secretion  which  may  act  simply  as  a 
lubricant  and  assist  in  deglutition.  In  the  herbivora,  on  the  other  hand, 
from  the  necessity  for  perfect  subdivision  required  by  their  food,  they 
are  relatively  very  large.  The  salivary  glands  thus  reach  their  highest 
development  in  the  rodents,  the  pachyderms,  solipedes,  and  ruminants. 

Colin  has  divided  the  salivary  glands  into  two  different  types.  The 
anterior  system,  or  the  mucous  type,  which  empty  their  secretions  into 
the  mouth  in  the  neighborhood  of  the  incisor  teeth,  comprise  the 
submaxillary  and  sublingual  glands ;  these  glands  are  most  developed 
in  carnivora  and  in  aquatic  animals,  whose  food  must  be  lubricated  for 
deglutition,  but  not  masticated.  The  posterior  system,  or  serous  type, 
which  empty  their  secretions  into  the  mouth  near  the  molar  teeth,  are 
most  developed  in  animals  whose  food  requires  thorough  mastication,  as 
in  the  herbivora,  and  especially  in  non-ruminants.  The  parotid  is  the 
type  of  this  system.  The  glands  which  form  these  two  systems  are  not 
all  developed  in  the  same  proportion.  Thus,  in  the  anterior  system, 
composed  of  the  submaxillary,  sublingual,  and  the  gland  of  Nuck,  the  sub- 
lingual  maybe  very  small  and  the  submaxillary  very  large,  the  former 
being  rudimentary  in  the  dog.  Again,  they  are  rudimentary  in  the 
dromedary,  and  are  extremely  highly  developed  in  the  ox.  Again,  as 
regards  the  posterior  system,  in  the  horse  the  parotids  are  enormous, 
while  the  submaxillary  glands  are  rudimentary.  In  the  ox  the  reverse  is 
the  case.  In  herbivorous  animals  these  glands  have  their  largest  volume, 
but  there  is  no  relative  proportion  between  the  volume  of  the  glands  and 
the  volume  of  the  secretion  which  the}r  produce.  Thus,  in  the  ox  the 
weight  of  the  salivary  glands  will  amount  on  an  average  to  six  hundred 
and  twenty-four  grammes ;  the  horse  to  five  hundred  and  nine  grammes ; 
the  pig,  three  hundred  and  five ;  sheep,  eighty-three;  dog,  twenty -five; 
and  the  cat,  ten.  The  parotid  is  the  largest  salivary  gland  in  all  animals 
with  the  exception  of  the  dog,  and  here  the  submaxillary  gland  is  the 
largest.  In  the  pig,  ox,  and  sheep  the  sublingual  glands  are  sometimes 
double,  the  one  part  emptying  its  secretion  by  a  long  duct  opening  at 
the  papilla  at  the  side  of  the  fraenum  of  the  tongue,  the  other  by  a  num- 
ber of  coiled  ducts  at  the  side  of  the  floor  of  the  mouth. 

In  addition  to  these  large  salivary  glands  the  fluid  in  the  mouth  is 
also  poured  out  by  glands  located  in  its  mucous  membrane,  forming 
the  so-called  buccal,  lingual,  palatine,  and  pharyngeal  glands.  The 
secretion  formed  by  all  these  glands  combined  is  termed  mixed  saliva. 


270  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

It  is  evident  from  the  varied  sources  of  the  buccal  fluid  that  the 
saliva  is  by  no  means  a  homogeneous  fluid.  If  collected  from  the 
mouth  by  expectoration,  or  in  the  lower  animals  by, holding  the  mouth 
open  and  stimulating  the  surface  of  the  tongue  and  the  cheeks  by  any 
sapid  substance,  as  by  the  vapor  of  ether  or  acetic  acid,  or  even  me- 
chanically, the  fluid  poured  out  will  be  found  to  be  opalescent  or  more 
or  less  turbulent,  with  a  decided  froth  on  its  surface,  from  the  air- 
bubbles  retained  through  its  viscidity,  and  when  allowed  to  stand  in  a 
glass  will  deposit  a  sediment  of  epithelial  cells  and  the  so-called  salivary 
corpuscles.  It  will,  therefore,  form  three  different  layers  :  the  lower 
one  composed  of  this  deposited  sediment ;  the  middle,  of  a  clear,  though 
opalescent,  watery  fluid ;  while  the  uppermost  layer  will  be  more  or  less 
frothy.  Where  a  specimen  of  saliva  remains  standing  for  two  or  three 
daj's  exposed  to  the  air  the  froth  will  disappear,  and  its  place  be  taken 
by  a  thin  pellicle  of  carbonate  of  lime.  When  filtered,  saliva  forms  a 
watery  fluid  with  alkaline  reaction.  Occasionally,  where  it  appears  to 
have  an  acid  reaction,  the  acidity  is  due  to  the  fermentation  of  some 
retained  fragments  of  food  in  the  mouth,  as  occurs  after  prolonged  fast- 
ing in  diabetes  and  other  pathological  conditions;  the  secretion  of  the 
salivary  gland  is  invariably  alkaline.  Frerichs  states  that  0.15  gramme 
sulphuric  acid  is  necessary  to  neutralize  the  alkalinity  of  human  saliva 
collected  during  smoking. 

The  specific  gravity  of  mixed  saliva  varies  somewhat  in  different 
animals.  It  has  been  placed  at  1004.5  in  the  horse;  1010.2  in  the  pig; 
1010  in  the  cow;  1007.1  in  the  dog;  and  from  1002  to  1006  in  man. 
D-eprivation  of  water  is  said  to  cause  the  saliva  to  acquire  a  higher 
specific  gravity  ;  thus,  in  the  horse  the  normal  specific  gravity  of  1004.5 
or  1005,  may  be  raised  to  1007.4  after  the  animals  have  been  deprived 
of  water  for  twelve  hours. 

The  amount  of  saliva  varies  ve^  largely  according  to  a  number  of 
different  conditions.  Colin  places  the  average  daily  secretion  of  saliva 
in  the  horse  at  eighty-four  pounds,  and  in  the  ox  at  one  hundred  and  two 
pounds  ;  while  in  the  dog  Jacubowitsch  obtained  in  a  hour  49.19  grammes 
of  parotid  saliva,  38.94  of  submaxillary  and  24.84  of  sublingual  saliva. 
We  will,  however,  again  return  to  the  volume  of  saliva  and  the  different 
conditions  modifying  the  rapidity  of  secretion  when  we  come  to  con- 
sider the  secretion  of  the  separate  glands. 

When-  examined  under  the  microscope  mixed  saliva  is  found  to  con- 
tain numerous  epithelial' cells  from  the  cavity  of  the  mouth,  often  debris 
of  food,  inorganic  particles  of  tartar  from  the  teeth,  various  forms  of 
minute  bacterial  organisms,  and  the  so-called  salivary  corpuscles.  The 
latter  closely  resemble  white  blood-cells  in  appearance,  but  are  somewhat 
larger,  and  are  nucleated  protoplasmic  cells  without  a  cell-membrane. 


DIGESTION  IN   THE  MOUTH.  271 

When  placed  on  the  warm  stage  of  the  microscope  they  may  often  be 
seen  to  be  the  seat  of  amoeboid  movement,  and  to  contain  numerous 
granules  which  exhibit  the  Brownian  movement. 

The  chemical  composition  of  the  mixed  saliva  varies  somewhat  in 
different  animals.  The  solids  are  epithelium  and  mucin,  ptyalin,  serum- 
albumen  and  globulin,  and  salts.  The  following  table  represents  some 
of  the  different  anatyses  which  have  been  made  of  this  secretion  in 
different  domestic  animals.  According  to  Lassaigne,  mixed  saliva  con- 
tains as  follows : — 

Horse. 

Water, 992.00 

Mucus  and  albumen,  .......          2.00 

Alkaline  carbonates,  .        .        .        .        .        .        .          1.08 

Alkaline  chlorides, 4.92 

Alkaline  phosphates  and  phpsphate  of  linie,    .        .      traces. 

1000.00 
Cow. 

Water, 990.74 

Mucus  and  albumen, 0.44 

Alkaline  carbonates, 338  00 

Alkaline  chlorides,      .......  2.85 

Alkaline  phosphates,  .......  2.49 

Phosphate  of  lime, 0.10 


1000.00 

Sheep.  .  . 

Water, 989.00 

Mucus  and  albumen,  .        .        .        .        .        .  1.00 

Alkaline  carbonates,   .......  3.00 

Alkaline  phosphates,  .         .         .         .         .         .        :.  1.00 

Alkaline  chlorides, 6.00 

Phosphate  of  lime, traces. 


10CO  00 
Man. 

Water, 995.16 

Solids, 4.84 

Mucus  and  epithelium 1.62 

Soluble  organic  matter,       .         .         .         .         .         .  1.34 

Sulpho-cyanide  of  potassium, 0.06 

Inorganic  salts, 1.82 

Dog. 

Water 989.6 

Solids, 10.3 

Soluble  organic  matter,      .        .        .        .        .        .  3.58 

Inorganic  salts, 6.79 

The  following  represents   the  quantitative  composition  of  the  ash 
of  the  saliva  of  man  and  the  dog  (Jacubowitsch)  : — 

Man.  Dog. 

Salts, 1.82  6.79 

Phosphoric  acid, 0.51  )  n  ft0 

Sodium,    .  0.43  S 


Lime 0.03 

Magnesium 0.01  $ 

Alkaline  chlorides,  .  ,     0.84  5.82 


272  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

The  salts  consist  mainly  of  phosphates  of  sodium,  potassium  and 
magnesium,  and  alkaline  chlorides.  One  of  the  most  remarkable  con- 
stituents of  the  saliva  is  the  sulphocyanide  of  potassium  which  is  found 
in  small  amounts  in  many  but  not  in  all  salivary  secretions.  Treviranus 
in  1814  first  made  the  observation  that  when  saliva  is  mixed  with  a  solu- 
tion of  oxide  or  chloride  of  iron  and  hydrochloric  acid  a  bright-red 
coloration  is  produced,  which  was  recognized  by  Gmelin  to  depend  upon 
the  presence  of  the  sulphocyanide  of  potassium.  It  is  said  by  Gmelin 
to  be  present  in  largest  amount  in  the  saliva  of  the  dog  ;  it  is  almost  con- 
stantly present  in  the  saliva  of  man  and  in  the  saliva  of  the  horse.  It 
probably,  however,  may  be  detected  in  the  saliva  of  all  animals  by  dis- 
tilling the  saliva  with  phosphoric  acid  and  catching  the  first  drops  that 
pass  over  on  filter-paper  treated  with  dilute  hydrochloric  acid  and  ferric 
chloride,  and  then  dried.  Its  presence  may  also  be  recognized  by  the 
fact  that  paper,  impregnated  with  tincture  of  guaiacum  and  then  dried, 
with  an  almost  colorless  solution  of  sulphate  of  copper,  is  colored  blue 
by  the  saliva.  The  reaction  by  which  potassium  sulphocyanide  is  recog- 
nized— that  is,  the  red  color  which  it  forms  with  an  iron  salt — is  possessed 
also  by  meconic  acid ;  the  two  substances  may  be  distinguished,  how- 
ever, in  a  very  simple  manner.  If  a  few  drops  of  a  solution  of  mercuric 
chloride,  or  if  a  few  mercuric  chloride  crystals,  are  added  to  saliva  which 
has  been  colored  red  by  the  perchloride  of  iron,  the  color  is  at  once  dis- 
charged. When,  however,  the  red  color  is  due  to  the  presence  of 
meconic  acid  and  an  iron  salt,  the  red  coloration  is  permanent,  even 
after  the  addition  of  corrosive  sublimate. 

The  origin  of  this  salt  is  not  known,  although  the  majority  of 
authorities  seem  to  attribute  its  presence  to  a  spontaneous  decompo- 
sition of  the  saliva,  since  saliva  which  has  been  standing  for  some  time 
will  give  the  reaction  in  a  more  marked  degree  than  when  entirely  fresh. 
This  view  is  still  further  strengthened  by  the  fact,  determined  by  Ellen- 
berger  and  Hofmeister,  that  extracts  of  the  salivary  glands  of  all  the 
domestic  animals,  whether  made  from  dried  or  fresh  glands,  with  water, 
carbolized  or  alkaline  water  or  gtycerin,  entirely  fail  to  show  this  re- 
action. Absolute  data  as  to  the  origin  of  this  salt  are  entirely  wanting. 
Its  use  in  the  economy  is  also  clouded  in  obscurity,  as  it  is  eliminated 
unchanged  through  the  kidneys  and  may  be  recognized  in  the  urine. 
The  chlorides  in  saliva  may  be  recognized  by  filtering  and  acidulating 
strongly  with  nitric  acid ;  the  addition  then  of  a  few  drops  of  a  solution 
of  nitrate  of  silver  to  the  saliva  will  cause  quite  a  decided  white  precipi- 
tate which  is  readily  soluble  in  ammonia. 

Of  organic  constituents,  saliva  contains  albuminous  bodies,  as  may 
be  recognized  by  the  xanthoproteic  and  Millon's  reaction  ;  it  contains 
mucin,  as  maybe  determined  by  precipitating  with  acetic  acid;  and  it 


DIGESTION   IN   THE   MOUTH.  273 

contains  a  substance  of  the  nature  of  a  ferment,  which  is  termed  animal 
diastase  or  pt3*alin,  whose  presence  may  be  demonstrated  by  the  power 
possessed  by  the  saliva  of  converting  starch  mucilage  into  sugar.  Of 
the  albuminoid  bodies,  serum-albumen  and  a  globulin-like  bod}'  which 
may  be  precipitated  by  carbonic  acid  are  the  representatives. 

The  most  important  constituent  of  the  saliva  is  the  ptyalin.  This 
substance  belongs  to  the  group  of  soluble  ferments,  and  is  a  product  of  the 
cells  of  the  salivary  glands.  It  may  be  obtained,  according  to  the  method 
of  Colmheim,  by  adding  a  little  phosphoric  acid  to  mixed  saliva  and  then 
stirring  with  milk  of  lime  until  the  alkaline  reaction  is  restored  ;  the 
white  precipitate  is  then  filtered  off,  and  the  filtrate  shows  scarcely  any 
albuminoid  reaction,  while  it  still  possesses  in  an  almost  undiminished 
degree  its  diastatic  power.  A  considerable  quantity  of  the  ptyalin  still 
remains  clinging  to  the  albuminoid  matters  deposited  in  the  precipitate, 
and  if  this  is  washed  with  water  the  ptyalin  is  extracted,  while  it  leaves 
the  albuminous  matters  still  on  the  filter.  If  alcohol  is  added  to  the 
watery  extract  of  this  precipitate,  a  flocculent,  whitish  precipitate  is 
formed,  which  may  be  collected  by  decantation  and  dried  over  sulphuric 
acid.  A  grayish-white  powder  is  thus  obtained,  which  consists  of  pt}-alin 
mixed  with  phosphates ;  the  latter  may  be  removed  by  dissolving  in 
water,  precipitating  again  by  absolute  alcohol,  washing  the  precipitate 
with  dilute  alcohol  and  then  with  a  small  quantity  of  water,  and  drying 
at  a  low  temperature.  Ptyalin  so  obtained  is  a  nitrogenous  substance, 
but  not  an  albuminoid.  It  is  readily  soluble  in  water  and  glycerin  and 
possesses  the  power  of  converting  starch  and  gtycogen  into  maltose, 
and  this  property  is  exerted  whether  in  a  neutral  or  very  faintty  acid  or 
alkaline  medium.  An  excess  of  alkali  or  of  acid,  as  will  be  again  referred 
to,  prevents  its  activity.  The  ferment  may  also  be  extracted  from 
the  salivary  glands  by  mincing  fresh  glands  and  covering  them  with 
gtycerin.  As  the  ferment  is  soluble  in  glycerin,  it  is  extracted  from  the 
gland-tissue,  and  may  be  precipitated  again  from  the  glycerin  extract  by 
alcohol. 

The  saliva  contains  appreciable  volumes  of  different  gases  in 
solution,  as  determined  by  Pfliiger  in  the  case  of  the  submaxillary  gland 
of  the  dog.  He  estimates  the  different  amounts  of  gases  contained  in 
the  saliva  as  follows  : — 

Oxygen,    .        .  .        .      0.4  to    0  6  volume  per  cent. 

Nitrpsen.          .         .        .        .      0.7  to    0.8 
Carlion  dioxide,       .        .        .     49.2  to  64.7 

It  is  thus  seen  that  saliva  is  the  richest  in  CO,  of  any  fluid  in  the 
animal  body.  Only  a  small  proportion  of  the  above  amount,  however, 
can  be  extracted  with  the  gas-pump,  showing  that  the  remainder  is  held 
in  chemical  combination.  The  amount  capable  of  being  pumped  out 

18 


274 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


varies  from  19.3  to  22.5  c.c.,  while  from  22.9  to  42.5   c.c.  of  C02  are 

liberated  on  the  addition  of  phosphoric  acid. 

The  secretions  of  the  different  glands  of  the  salivary  system  present 

several  distinguishing  points  which  will  be  alluded  to  in  turn. 

1.  The  Parotid  Secretion. — 
In  order  to  study  the  pure  secre- 
tion of  the  parotid  gland,  the 
saliva  must  be  collected  before 
it  reaches  the  mouth  to  be  mixed 
with  fluid  from  the  other  glands. 
This  may  be  accomplished,  in 
man  or  in  the  dog,  by  catheter- 
izing  the  parotid  duct,  an  oper- 
ation which  is  readily  performed. 
It  is  only  necessary  to  open  the 
mouth  and  evert  the  cheek,  when 
the  papilla  of  entrance  m&y  be 
recognized  on  the  inner  surface 
of  the  cheek,  on  a  level  with  the 
second  molar  tooth  of  the  upper 
jaw.  A  slender  glass  tube  or 

silver  cannula  may  be  readily  inserted  within  the  orifice  of  the  duct  and 

the  fluid  collected  as  it  flows  through  the  tube.     Where  studies  as  to  the 


FIG.  111.— PAROTID  AND  SUBMAXILLARY  GLANDS 
OF  THE  DOG,  WITH  THEIR  EXCRETORY 
DUCTS.  (Btelard.) 

p,  parotid  gland:  m,  submaxillary  gland;  *,  duct  of  Steno; 
r,  duct  of  Wharton ;  v,  masseter  muscle ;  /,  temporal  muscle. 


FIG.   112.— RELATIONS    OF    THE    PAROTID  DUCT  OF  THE  DOG   WITH  THE 
FACIAL  VESSELS  AND  NERVE,  AFTER  BERNARD. 

The  dotted  line  indicates  the  line  of  incision  for  finding  the  duct  at  the  apex  of  the  angle  formed  by 
the  vessels  and  nerve.  V.  vasculo-nervous  fasciculus  forming  the  inferior  side  of  the  ang'e  :  N,  fasciculus 
forming  the  upper  side ;  D,  point  of  junction  of  these  two  fasciculi ;  C,  duct  of  Steno  bisecting  this  angle. 

mechanism  of  secretion  have  to  be  made,  or  where  a  considerable  quan- 
tity is  to  be  collected,  a  more  convenient  method  is  to  make  a  fistulous 


DIGESTION  IN  THE  MOUTH. 


275 
This  may  be 


opening  into  the  parotid  duct  before  it  reaches  the  mouth, 
readily  performed  in  the  horse  or  dog  (Fig.  111). 

To  make  a  parotid  fistula  in  the  clog,  the  animal  usually  employed  in  these 
experiments,  the  hair  is  first  shaved  from  the  cheek,  between  the  eye  and  the  angle 
of  the  mouth.  On  running  the  finger  along  the  lower  border  of  the  zygomatic 
arch,  just  before  it  is  inserted  into  the  superior  maxilla,  a  slight  notch  is  felt.  It 
is  just  at  this  point  that  the  duct  passes  into  the  mouth.  After  chloroforming  the 
animal,  an  incision  is  made  through  the  skin  from  this  point,  cutting  obliquely  in 
a  direction  from  the  inner  canthus  of  the  eye  to  the  angle  of  the  mouth,  passing 
through  the  subcutaneous  cellular  tissue,  when  the  facial  artery  and  vein,  branches 
of  the  facial  nerve,  and  parotid  duct  are  found  together,  the  duct  pearly  white  in 
hue,  passing  horizontally  across  the  fibres  of  the  masseter  muscle  parallel  to  the 
nerve,  usually  about  a  quarter  of  an  inch  below  it,  while  the  artery  and  vein  run 
from  above  downward  (Fig.  112).  The  vessels  and  nerves  must  be  carefully 
removed  from  before  the  duct,  which  is  to  be  isolated  and  closed  as  near  the 
mouth  as  possible  with  a  clip.  A  cannula  may  then  be  inserted  into  the  duct.  If 
it  is  decided  to  retain  the  fistula  permanently,  the  duct  must  be  freed  from  the 
connective  tissue  for  as  long  a  distance  as  possible,  divided,  and  then  brought  out 
at  the  angle  of  the  wound,  which  is  to  be  closed  with  sutures,  one  passing  through 
the  duct  to  retain  it  in  position.  After  a  few  days,  when  the  wound  is  healing, 
the  duct  will  mortify  and  drop  out,  leaving  a  fistulous  track  to  the  gland,  which 
must  be  kept  open  by  the  daily  passage  of  a  fine  probe,  as  it  has  a  decided  ten- 
dency to  close.  A  similar  operation  is  readily  performed  upon  the  horse  or  ox, 
where  the  large  size  of  the  duct  renders  it  easily  recognizable.  After  a  cannula 
has  been  inserted  into  the  duct  of  the  animal,  its  free  extremity  may  be  connected 
by  a  piece  of  rubber  tubing  with  a  rubber  bulb  or  glass  bottle,  in  which  the  saliya 
may  be  collected  (Figs.  113  and  114). 


FIG.  113.— PAROTID  DUCT  IN  THE  HORSE.    (Bernard.) 

The  dotted  line  indicates  the  contour  of  the  gland  and  the  course  of  the  duct  of  Steno. 

The  parotid  gland  of  the  horse  is  only  in  activity  when  the  animal 
is  masticating  food,  while  the  parotid  glands  of  the  ruminants  are  con- 
tinually secreting.  The  parotid  glands  constitute  almost  entirely  the 
posterior  or  serous  system  of  the  salivary  glands,  and  furnish  by  far  the 
largest  amount  of  the  fluid  which  impregnates  the  food.  The  parotid 


276 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


glands  secrete  alternately  during  mastication,  both  in  the  horse  and 

ruminant  animals,  and,  in  all  probability,  also  in  the  omnivora,  the 

secretion  occurring  on  the  side 
on  which  mastication  is  taking 
place.  Thus,  when  mastication 
is  takin»  Place  Between  the  right 
molar  teeth,  then  it  is  the  right 
parotid  alone,  in  the  horse,  which 
secretes,  and  it  is  the  right 
parotid  in  the  ruminant  which 
has  the  highest  activity.  Ex- 
IN  THE  HORSE,  periments  conducted  by  Colin, 
by  making  a  fistula  of  the  parotid 
ducts  in  the  horse  and  the  ass, 

have  demonstrated  the  truth  of  these  statements.     The  following  tables 

represent  some  of  his  results  : — 


2, 


FIG.  114.— PAROTID  FISTULA 
(Bernard.) 

a,  duct  of  Steno,  with  cannula  inserted,  and  rubber  bag  for 
collecting  the  saliva. 


Experiment. 

Time  in  Minutes. 

Right  Parotid.          Left  Parotid. 

Side  of  Mastication. 

1.   Horse, 

.     15 

910  grammes.       200  grammes 

Right. 

f* 

.     15 

580 

320 

Right. 

*  * 

,(       .15 

250 

'               700 

Left. 

2.   Horse, 

15 

570 

<               620 

Left. 

" 

.     15 

510 

820 

Left. 

" 

.     15 

500 

*              800 

Left. 

« 

.     15 

480 

750 

Left. 

" 

.     15 

720 

420 

»    Right. 

tt 

.     15 

540 

800 

Left. 

" 

.     15 

600 

740 

Left, 

3.   Horse, 

.    15 

620 

260 

Right. 

" 

.     10 

320 

200 

Right. 

" 

.        .5 

200 

120 

Right. 

" 

V        .     15 

410    . 

230 

Right. 

" 

.         .     10 

60 

320 

Left. 

" 

.       5 

20 

150 

Left. 

" 

.     15 

130 

520 

Left. 

4.   Horse, 

5 

160 

85 

Right. 

•< 

.      6 

150 

235 

Left. 

" 

.      4 

160 

40 

Right. 

** 

.        .4 

115 

70 

Right. 

M 

.        .      4 

95 

165 

Left. 

" 

.        .       6 

80 

210 

Left. 

5.    Horse, 

3 

50 

110 

Left. 

*« 

.      6 

200 

50 

Right. 

" 

.      4 

30 

100 

Left. 

" 

.      5 

200 

30 

Right. 

6.   Ass, 

.     15 

120 

10 

Right. 

*« 

.     15 

110 

60 

Right. 

•« 

.     15 

80 

170 

Left. 

" 

.     15 

150 

15 

Riffht. 

" 

.     15 

30 

160 

Left 

" 

.     15 

55 

135 

Left. 

« 

.     15 

50          '               165 

Left. 

DIGESTION   IN  THE  MOUTH.  277 

These  results  must  not  be  regarded  as  absolutely  correct,  since,  even 
in  the  horse,  the  operation  of  making  a  fistula  interferes  with  the  normal 
sequence  of  mastication,  as  it  is  always  longest  on  the  side  which  is 
opposite  to  the  fistula. 

Ellenberger  and  Hofmeister  found  that  the  parotid  of  one  side  in  one 
horse  secreted  1000  grammes  in  half  an  hour,  the  same  amount  in  another 
horse  in  a  quarter  of  an  hour,  and  in  a  third  horse  4000  grammes  in  two 
hours — oats,  hay,  and  chopped  straw  being  given  as  food.  During  the 
pauses  between  the  acts  of  mastication,  the  parotids  of  the  horse,  con- 
trary to  what  is  the  case  in  the  ruminant,  are  quiescent. 

In  ruminant  animals  this  alteration  of  activity  of  the  parotid  glands, 
although  depending  upon  the  side  of  mastication,  is  less  readily  deter- 
mined than  in  the  horse ;  for  when  a  fistula  is  made  the  ruminant  animal 
will  continuously  masticate  on  the  opposite  side  to  that  in  which  the 
fistula  is  present,  and  the  maximum  activity  of  secretion  is  therefore 
taking  place  on  the  side  opposite  to  the  fistula.  On  the  other  hand,  if 
two  fistulae  are  made  the  animal  will  change  the  direction  of  mastication 
two  or  three  times  a  minute,  and  the  process  of  mastication  is  much  in- 
terfered with  and  the  character  of  secretion  altered.  The  inequality  of 
the  secretion  according  to  the  side  on  which  mastication  is  taking  place 
is  also  seen  in  the  ruminant  animal  during  the  second  period  of  mastica- 
tion in  rumination. 

These  experiments  seem  to  show  that  mastication  is  the  normal 
stimulant  of  the  parotid  glands,  though  they  also  secrete  during  the 
pauses  of  rumination.  Further,  these  glands  are  insensible  to  other 
stimulants,  such  as  salt,  acids,  etc.,  brought  into  contact  with  the  mucous 
membrane  of  the  mouth.  Such  stimuli  produce  no  sensible  secretion  in 
solipedes  and  no  increase  in  the  constant  secretion  of  ruminants.  So, 
also,  sight  and  odor  of  food  have  no  effect  on  the  secretion  of  the  parotid, 
even  if  the  animals  are  in  a  state  of  great  hunger. 

The  character  of  the  parotid  saliva  also  differs  from  that  of  mixed 
saliva  and  that  of  the  other  salivary  glands.  It  is  thin,  limpid,  contains, 
with  the  exception  of  a  few  epithelial  cells,  scarcely  any  formed  elements, 
and  is  invariably  alkaline,  except  after  prolonged  fasting,  when  the  first 
few  drops  may  have  a  slightly  acid  reaction  from  the  contained  carbon 
dioxide.  Great  variation  exists  in  the  estimates  of  its  specific  gravity, 
it  having  been  said  to  vary  from  1003  to  1012.  It  contains  scarcely  any 
mucin ;  when  heated  to  boiling  it  becomes  turbid,  as  also  occurs  after  the 
addition  of  alcohol  or  mineral  acids,  showing  the  presence  of  an  albumen- 
like  body.  It  becomes  clearer  when  CO,  is  passed  through  it.  It  con- 
tains ptyalin.  Sulphoc3'anide  of  potassium  has  been  said  to  be  absent 
from  the  parotid  saliva  of  the  horse.  The  parotid  saliva  of  the  dog  has 
a  specific  gravity  of  1004  to  1007,  and  when  heated  deposits  a  slight 


278  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

sediment  of  calcium  carbonate.  When  allowed  to  slowly  evaporate  on  a 
glass  plate,  crystals  of  sodium  chloride  and  calcium  carbonate  are  formed. 
It  is  said  to  contain  no  diastatic  ferment. 

The  parotid  saliva  of  the  horse  contains  large  quantities  of  lime,  and 
when  -allowed  to  stand  in  the  air  deposits  beautiful  crystals  of  the  car- 
bonate of  lime.  The  parotid  saliva  is  largest  in  amount;  the  two  glands 
of  the  ox  are  said  to  produce  in  an  hour  eight  hundred  to  twenty-four 
hundred  grammes  of  saliva.  As  already  stated,  this  secretion  is  inter- 
mittent in  the  horse  and  constant  in  ruminants,  where  it  is  closely  con- 
cerned in  the  phenomena  of  gastric  digestion. 

The  diastatic  action  of  the  parotid  saliva  is  very  active  in  rodents, 
but  little  active  in  ruminants  ;  absent  in  the  sheep,  though  in  the  latter 
animal,  as  in  the  case  of  the  horse  and  ass,  watery  infusions  of  the  parotid 
salivary  glands  will  convert  starch  into  sugar.  In  carnivora  the  parotid 
gland  is  relatively  smaller  in  amount  and  is  almost  inactive. 

The  following  analyses  have  been  made  of  parotid  saliva: — 

Man. 

Water,  . 993.16 

Solids,    .        ...        .      <  . ":••:.        .        .        .  6.84 

Organic  matter,     .        .        .        .        .        ...  3.44 

Chlorides  and  carbonate  of  lime,        »        ,        .        .  3.40 

Dog. 

Water,   .       V      .     . '.  "    >        .-'.-'»       '.        .     995.3 
Solids,    .        ....    '....,        .        .....  ....      ,  .        .        4.7 

Organic  matter, 1.4 

Potass,  sulphocyanide  and  alkaline  chlorides,    .      •• .  •  "•   2.1 
Calcium  carbonate,       .    -  •  ,      '.*.'*  v-    -  .  .     .»        1.2 

Horse. 

Water,  .        .        . 992.92 

Solids,    .        .        .         . 7.08 

Epithelium  and  calcium  carb.      .        .        .        .        .  1.24 

Soluble  matter,      .        .        .         .'       ..        .        .        .  5.84 

Alcoholic  extractives,  .        .  •••'.. '.  .•  .        .        .        .  0.98 

Soaps,    .    .    , ..'..-      .      .  ,        .        .        .        .        .  0.43 

Cow. 

Water, 990.7 

Mucin  and  soluble  organic  matter,      ....  0.44 

Alkaline  carbonates, 3.38 

Alkaline  chlorides,       .-:..' 2.85 

Alkaline  phosphates,     .......  2.49 

Calcium  phosphates,     .        .        .        .        .        .        .  0.10 

Ram. 

Water, 989.0 

Mucin  and  soluble  organic  matter,  1.0 


Alkaline  carbonates, 
Alkaline  chlorides, 
Alkaline  phosphates, 
Calcium  phosphates, 


3.0 

6.0 

1.0 

traces. 


DIGESTION   IN   THE   MOUTH. 


279 


The  parotid  saliva  of  the  dog  contains  1.818  and  1.701  pro.  mil. 
volumes  of  combined  CO,. 

Salivary  calculi  are  formed  most  usually  in  the  parotid  duct  from 
the  deposition  of  lime  salts,  and  contain  no  other  ingredient  of  the 
saliva. 

2.  TJie  Submaxillary  Secretion. — The  saliva  of  the  submaxillary 
gland  may  be  collected  in  man  by  inserting  a  small  cannula  in  the  opening 
of  the  duct  in  the  papilla  of  entrance  at  the  side  of  the  fraenum  of  the 
tongue,  or  by  aspirating  it  by  a  small  syringe  whose  nozzle  will  grasp 
the  papilla  air-tight.  In  animals  the  maxillary  saliva  may  be  collected 
by  means  of  a  permanent  or  temporary  fistula  of  the  duct  of  Wharton. 


FIG.  115.— OPERATION  OF  ISOLATING  THE   DUCT  OF  THE   SUBMAXILLARY 
GLAND  IN  THE  DOG.    (Bernard.) 

a,  digastric  muscle  drawn  to  one  side ;  b,  mylo-hyoid  muscle  divided  and  drawn  to  one  side  ;  c  e,  duct  of 
Wharton ;  d,  duct  of  the  sublingual  gland ;  1,  lingual  nerve. 

To  discover  the  submaxillary  duct  before  its  entrance  into  the  mouth,  after 
etherization,  the  hair  is  shaved  from  the  under  surface  of  the  lower  jaw,  an 
incision  made  along  the  inner  border  of  the  ramus  of  the  lower  jaw  from  the 
anterior  insertion  of  the  digastric  muscle  forward  for  about  two  inches,  dividing 
the  skin  and  platysma,  every  vein  that  comes  into  view  being  tied  with  two 
ligatures  and  divided  between  them.  The  mylo-hyoid  muscle  is  then  in  view,  and 
is  to  be  very  cautiously  divided  at  its  middle,  avoiding  the  mylo-hyoid  nerve, 
which  lies  upon  it.  If  the  portion  still  in  connection  with  the  ramus  of  the  jaw 
is  elevated,  the  submaxillary  and  sublingual  ducts  will  be  found  running  forward 


280 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


side  by  side,  near  to  the  ramus  of  the  jaw,  to  enter  the  mouth,  the  submaxillary 
duct  being  somewhat  the  larger  and  lying  nearer  the  jaw  ;  the  ducts  are  crossed 
by  the  lingual  nerve.  Either  duct  may  then  be  isolated  or  divided  and  treated  as 
in  making  a  permanent  parotid  fistula  (Figs.  115  and  116).  In  the  horse,  rumi- 
nants, and  rabbits  the  operative  procedure  is  about  the  same  as  in  the  dog 
(Fig.  117). 

The  submaxillarjr  saliva  obtained  by  catheterization  or  from  fistulye 

is  a  limpid,  viscid  fluid  of  alkaline 
reaction.  Its  density  is  said  to  be 
greater  than  that  of  the  parotid  or 
mixed  saliva,  and  may  rise  to  1025 
after  feeding.  According  to  Eck- 
hard,  the  submaxillary  saliva  be- 
comes more  consistent  when  exposed 
to  tbe  air,  and  will  precipitate  a 
flocculent  deposit.  Corrosive  sub- 
limate causes  it  to  become  almost 
gelatinous  without  becoming  turbid. 
It  contains  a  considerable  quantity 
of  mucin,  to  which  this  viscidity  is 
due.  Albumen  seems  to  be  almost 
absent  from  the  submaxillary  saliva, 
or  to  be  present  only  in  traces, 
although  the  xanthoproteic  reac- 
tion1 will  demonstrate  the  presence 
of  proteids.  The  diastatic  power 
of  the  submaxillary  saliva  of  the 
dog  appears  to  be  but  slightly  de- 
veloped in  the  fresh  saliva,  although 
it  acquires  this  property  by  stand- 
ing one  or  two  days  in  the  atmos- 
phere. The  following  tables,  after 
Lassaigne  and  Herter,  represent  the  anatysis  of  this  secretion — 


IIG.  116.— ANATOMY  OF  THE  SUBMAXIL- 
J.AHY  AND  SUBLJNGITAL  GLANDULAR 
REGION  IN  THE  DOG.  (Bernard.) 

a  a,  digastric  muscle;  ft  b,  mylo-hyoid  muscle; 
c  e,  sublingual  gland ;  d.  sublingual  duct ;  e,  submax- 
illary duct : ./'  g,  submaxillary  gland ;  1,  lingual  nerve ; 
2,  chorda  tymp'ani. 


In  the  Horse. 


Water,      .        » 
Solids,      . 

Salts, 

Organic  matter, 


992.5 
7.5 


2.575 
4.925 


In  the  Cow. 

Water, 

Mucin  and  albuminous  matter, 
Alkaline  carbonates,       .         .         . 
Alkaline  chlorides, 
Alkaline  phosphates, 
Phosphate  of  lime, 


9U  14 
3.53 
0.10 
5.02 
0.15 
0.06 


DIGESTION   IN   THE   MOUTH.  281 

In  the  Dog. 

Water, 994.4 

Solids, 5.6 

Organic  matter, 1.75 

Mucin 0.66 

Soluble  ash 3.59 

Insoluble  ash 0.26 

Carbonic  acid  in  combination, 0.44 

The  submaxiljary  saliva  of  other  animals  has  been  less  studied  than 
in  the  dog;  that  of  the  rabbit,  according  to  Heidenhain,  is  clear,  not 
viscid,  and  alkaline.  It  does  not  become  turbid  when  exposed  to  the 
atmosphere,  contains  albuminoids,  but  no  mucin  or  ptyalin.  It  contains 
1.23  per  cent,  of  solids.  The  submaxillary  saliva  of  the  sheep  is 
strongly  alkaline  and  slightly  viscid.  The  first  few  drops  are  turbid, 
but  it  then  becomes  limpid,  to  again  become  turbid  when  exposed  to  the 


FIG.  117.— PAROTID  AXD  SUBMAXII/LARY  FISTULA  IN  THE  HORSE,  AFTER 

COLIN.     (Thanhoffer  and  Tormay.) 
K  Kf,  rubber  bulbs  for  collecting  saliva;  PS,  cannula  in  the  parotid  duct. 

atmosphere;  it  contains  considerable  quantities  of  albuminoids  and  a 
variable  amount  of  mucin,  but  always  less  than  in  the  saliA~a  of  the  dog. 
The  submaxillary  saliva  of  the  pig  contains  no  ptj'alin.  The  saliva  of 
the  calf  and  other  herbivora,  with  the  exception  of  the  rabbit,  is  said 
to  be  rich  in  ptyalin.  In  the  submaxillary  saliva  are  found  the  so-called 
morphological  elements  or  salivary  corpuscles,  which  appear  to  be  identical 
with  the  white  blood-corpuscles  and  possess  amoeboid  movements. 


282 


PHYSIOLOGY   OF   THE  DOMESTIC  ANIMALS. 


The  secretion  of  the  submaxillary  glands  is  not  unilateral,  as  in 
the  case  of  the  parotid,  and  the  side  on  which  the  greatest  secretion  is 
taking  place  does  not  appear  to  be  modified  to  any  great  extent  by  the 
locality  of  mastication.  The  largest  amount  of  submaxillary  saliva  is 
secreted  at  the  commencement  of  a  meal  and  almost  ceases  during  ab- 
stinence,— a  point  of  contrast  with  the  parotid  saliva.  The  stimulation 
of  the  sense  of  taste  by  sapid  substances  is  of  the  greatest  influence  on 
the  amount  of  submaxillary  saliva.  The  following  table,  compiled  by 
Colin,  illustrates  these  facts  : — 


Right  Submaxillary  Fistula  in  the  Horse. 


Time  in 
Minutes. 

15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 


Amount  in 
Grammes. 

31 
26 
24 
22 
17 
23 
19 
22 
31 
50 
23 
20 
26 


Side  of 
Mastication. 

Left. 


R  glit. 
Left. 


Right. 
Left. 


Food. 
Hay. 


Oats. 


Right  Submaxillary  Fistula  in  the  Cow. 


Time  in  Minutes. 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 


Amount  in  Grammes. 
110 
85 
65 
70 
80 
85 
70 
90 
70 
20 
40 
80 


Food. 
Hay. 


Salt. 

Juniper-berries. 
Pepper. 


Right  Submaxillary  Fistula  in  tlie  Ram. 
Time  in -Minutes.  Amount  in  Grammes.  Food. 


15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 
15 


27 

20 

25 

15 

26 

27 

20 

24 

4 

2 

8 


Hay. 


Salt. 

Hay. 

Fasting. 

Pepper. 

Salt. 


DIGESTION   IN   THE  MOUTH.  283 

The  diastatic  power  of  the  submaxillary  saliva  varies  very  con- 
siderably in  different  animals.  It  is  active  in  all  the  herbivora,  with  the 
exception  of  the  rabbit  and  guinea-pig.  In  the  sheep  the  submaxillary 
saliva  is  more  active  than  that  of  the  parotid,  while  it  is  faintly  active  .in 
the  horse,  and  is  almost  inactive  in  the  dog  when  freshly  secreted.  The 
general  characteristics  of  the  submaxillary  saliva  vary  in  different 
animals  under  different  conditions,  and  are  therefore  subject  to  much  con- 
tradiction. The  secretion  reaches  its  excess  during  mastication  follow- 
ing prehension  of  food.  It  is  suspended  entirely  during  the  mastication 
of  rumination  (Colin,  Ellenberger,  and  Hofmeister), — a  fact  which  is 
ver}T  remarkable  when  it  is  recollected  that  the  chemical  stimulation 
of  the  nerves  of  taste  must  be  then  much  more  marked  than  in  the 
hurried  first  mastication.  The  submaxillary  glands  are  also  nearly 
quiescent  in  the  intervals  of  rumination ;  its  secretion  is  called  forth  by 
pilocarpine  injections,  but  to  a  less  degree  than  in  the  case  of  the 
parotid. 

It  seems  almost  incomprehensible  that  the  submaxillary,  which 
during  rumination  remains  quiescent,  should  secrete  actively  during  the 


B 

FIG.  118.— SUBLINGUAL  GL.AND  OF  THE  Ox.    (Colin.) 

A,  submaxillary  duct ;  B,  inferior  duct  of  the  sublingual  gland ;  C  C,  superior  sublingual  ducta. 

mastication  of  a  tasteless  foreign  body,  such  as  a  piece  of  string  or  wood 
(Ellenberger).  This  fact  can  scarcely  be  explained  but  by  supposing 
that  the  products  of  fermentation  occurring  in  the  rumen  exert  an  in- 
hibitory influence  on  the  secretory  nerves  of  the  submaxillary  glands. 
Its  principal  function  seems  to  be  to  assist  in  the  appreciation  of  the 
sense  of  taste,  and  to  act  as  a  lubricant  to  aid  in  the  first  deglutition. 

3.  The  Sublingual  Secretion. — The  collection  of  pure  sublingual 
saliva  is  accomplished  in  the  same  way  as  the  submaxillary,  although  in 
general  it  is  more  difficult,  excepting  in  the  case  of  the  ox,  where  the  large 
size  of  the  duct  renders  the  operation  very  easy.  In  most  animals, 
however,  it  is  extremely  difficult  to  obtain  it  in  a  state  of  purity,  as  the 
gland,  especially  in  the  ox,  has  a  number  of  excretory  ducts  (Fig.  118). 
The  characters  of  sublingual  saliva  may  partially  be  determined  by 
preventing  the  parotid  and  submaxillary  secretions  from  entering  the 
mouth  by  li  gat  ing  their  ducts,  and  then  collecting  the  fluids  in  the  mouth 


284  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

by  an  opening  in  the  oesophagus.  Such  fluids,  of  course,  are  composed 
of  the  sublingual  saliva,  together  with  the  secretion  of  the  buccal  glands. 
The  sublingual  saliva,  obtained  in  man  by  the  introduction  of  a  fine 
cannula,  is  secreted  in  isolated,  clear,  very  viscid,  alkaline  drops;  hardly 
enough,  however,  has  been  collected  to  determine  its  properties.  In  ani- 
mals it  is  very  transparent,  thick,  and  so  viscid  as  scarcety  to  deserve  the 
name  of  a  liquid,  and  when  a  cannula  is  inserted  in  the  duct  it  flows  from 
the  orifice  in  a  continuous  thread.  It  contains  2.75  per  cent,  of  solids, 
according  to  Heidenhain,  while  according  to  Kiihne  the  proportion  may 
rise  to  9.98  per  cent.  Mucin  and  sulphocyanide  of  potassium  have  been 
detected  in  it.  It  apparently  contains  no  bicarbonate  of  sodium,  as  it 
does  not  effervesce  when  acids  are  added  to  it.  The  sublingual  secretion 
is  constant,  though  it  is  augmented  greatly  during  feeding,  and  the  prin- 
cipal stimuli  which  call  it  forth  are  those  which  pass  through  the  sense 
of  taste. 

In  addition  to  the  above  secretions,  fluid  is  also  poured  into  the 
mouth  by  the  various  buccal  glands.  Its  characters  can  only  be  studied 
by  ligating  all  the  salivar}*'  ducts.  When  this  is  accomplished  in  the  dog 
the  mucous  membrane  in  the  mouth  only  remains  moist  as  long  as  the 
mouth  is  closed.  Dry  food  is  then  only  with  the  greatest  difficulty  mas- 
ticated and  swallowed,  and  the  thirst  of  such  animals  is  consequently 
greatty  increased.  It  follows  from  this  that  the  secretion  of  the  mucous 
glands  of  the  mouth  must  be  very  slight,  and,  in  fact,  only  one  or;two 
grammes  may  be  collected  with  the  greatest  care  in  an  hour.  It  has  an 
alkaline  reaction,  and  has  been  determined  by  Bidder  and  Schmidt  to 
contain  9.98  per  cent,  of  solids.  Attempts  have  been  made  to  study  the 
properties  of  the  secretions  of  the  buccal  glands  by  making  aqueous 
infusions  of  these  glands  after  death.  The  superior  molar  glands,  which 
have  been  termed  the  accessory  parotids  in  the  ox,  give  a  viscid  extract 
with  water,  while  such  an  extract  of  the  inferior  molars  is  much  less 
viscid.  Yery  little  has  been  determined  as  to  the  properties  of  these 
secretions. 

4.  General  Characteristics  of  the  Salivary  Secretion. — Although  it 
has  been  seen  that  each  gland  differs  somewhat  in  its  manner  of  secreting 
nnd  in  the  results  of  that  process,  nevertheless,  the  general  salivary  sys- 
tem has  certain  distinguishing  characteristics,  which  have  been  carefully 
studied  by  Colin,  according  to  the  principal  conditions  in  which  ani- 
mals may  happen  to  be;  thus,  the  conditions  may  vary,  according  as 
the  animal  is  feeding,  ruminating,  fasting,  or  whether  stimulating  sub- 
Stances  are  in  contact  with  the  mucous  membrane  of  the  mouth.  Dur- 
ing feeding  two  of  the  glands  secrete  actively,  though  unequally ;  as 
has  been  seen,  the  parotid  on  the  side  of  mastication  gives  double  or 
•treble  as  much  saliva  as  the  opposite  gland.  The  amount  is  also  greater 


DIGESTION  IN   THE   MOUTH.  285 

when  mastication  is  rapid,  and  is  therefore  greatest  at  the  beginning  of 
a  meal,  unless  after  a  very  prolonged  fast,  when  a  certain  amount  of 
time  seems  to  be  required  b}^  the  glands  to  reach  their  maximum  activity. 
The  submaxillary  glands  secrete  together,  and  each  give  about  the  same 
quantity  of  saliva,  although  this  amount  is  not  one-third  of  that  secreted 
by  the  parotid,  even  in  animals  in  which  these  glands  appear  to  be  of 
about  the  same  size.  The  linguals  also  secrete  together,  and  the  same 
may  be  assumed  of  the  molars  and  other  glands.  These  characters  may 
be  determined  b}r  making  fistulse  of  the  different  excretory  ducts  of  the 
glands,  and  so  conveying  certain  portions  of  the  saliva  out  of  the  mouth 
and  then  weighing  the  increase  of  weight  in  the  food  in  its  passage 
through  the  mouth  to  a  fistulous  opening  in  the  oesophagus.  During 
rumination  the  parotids  have  been  found  by  this  method,  as  well  as  by 
the  production  of  parotid  fistulae,  to  pour  out  a  large  quantity  of  fluid, 
even  although  the  food  has  been  already  comminuted  and  thoroughly 
moistened  in  the  first  mastication  and  during  its  sojourn  in  the  rumen. 
The  quantity  of  saliva  is  very  little  less  than  that  poured  out  by  the  first 
mastication,  and  here  also  the  parotids  preserve  their  alternate,  intermit- 
tent action ;  but  the  food  does  not  pass  between  the  incisor  teeth  in  the 
second  mastication,  so  these  teeth  are  inactive,  and  the  anterior  salivary 
S3~stem  remains  almost  quiescent.  Though  they  continue  to  secrete,  they 
do  not  give  anjT  more  fluid  during  this  time  than  during  abstinence. 
This  is  a  peculiarity  of  the  salivary  secretion  during  rumination,  and 
shows  the  relative  independence  of  the  different  glands.  During  abstinence 
new  features  are  met  with,  which  vary  in  different  animals.  In  the  fast- 
ing horse  the  parotids  are  inactive,  and  the  submaxillaries  give  only  a 
few  drops  of  fluid,  but  the  mouth  is  always  moist,  and  the  horse  will 
often  be  seen  to  swallow  the  fluids  which  collect  in  the  mouth,  even  after 
fistulse  have  been  made  for  both  parotids  and  both  submaxillar}^  glands. 
Hence,  by  exclusion,  the  fluid  must  have  come  from  the  linguals,  tonsils, 
and  palatine  glands.  In  the  fasting  ruminants  the  parotids  are  not  in- 
active. They  pour  into  the  mouth  during  abstinence  about  one-eighth  or 
one  fourth  as  much  as  they  secrete  during  mastication.  Here,  also,  the 
submaxillaries  secrete  little  fluid,  but  the  sublinguals,  superior  molars, 
and  palatine  glands,  judging  by  the  viscidity  of  the  fluid,  must  be  more 
or  less  active.  This  continued  salivary  secretion  in  the  ruminant  we  will 
find  later  to  be  of  great  importance  in  aiding  the  function  of  rumination. 
Finally;. when  stimulated  by  sapid  substances  we  find  marked  differences 
in  the  response  of  different  glands  to  these  stimuli.  The  parotids  are 
not  sensibly  affected,  and  the  glands,  which  furnish  a  viscid  saliva,  are  all 
more  or  less  stimulated,  according  to  the  chemical  character  and  intensity 
of  the  excitation,  and  the  extent  of  surface  to  which  it  is  applied,  and 
its  duration. 


286  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

5.  The  Quantity  of  Saliva. — As  regards  the  total  quantity  of  saliva 
and  the  amounts  contributed  by  the  different  glands,  certain  data  may 
be  determined  in  all  domestic  animals  by  means  of  cesophageal  fistulae. 
To  accomplish  this,  the  food  is  first  weighed,  then  the  time  of  mastica- 
tion determined,  and  finally  the  food  is  weighed  again  as  it  escapes  from 
an  cesophageal  fistula.  By  subtracting  the  weight  of  the  food  when 
given  from  the  weight  as  it  is  collected  from  the  oesophagus,  the  amount 
of  fluid  added  may  be  determined.  In  this  way  Colin  found  that  a 
small  horse  secreted  five  thousand  grammes  of  saliva  in  an  hour,  a 
medium-sized  horse  five  thousand  two  hundred  grammes,  and  a  large 
horse  in  the  same  time  eight  thousand  eight  hundred  grammes ;  from 
which  it  may  be  concluded  that  a  horse  feeding  on  hay  secretes  from  five 
thousand  to  six  thousand  grammes  of  saliva  per  hour.  If  oats  are  given 
as  food,  the  amount  of  saliva  poured  out  is  one-third  less  than  the  above; 
only  one-half  as  much  is  secreted  when  green  fodder  constitutes  the  food, 
and  only  one-third  as  much  when  roots,  such  as  beets  or  turnips,  are 
given.  Further  experiments  have  shown  that  dried  fodder  absorbs  four 
times  its  weight  of  saliva,  oats  a  little  more  than  their  own  weight,  meal 
twice  its  own  weight,  and  green  fodders  half  their  own  weight.  Hence, 
the  amount  of  the  salivary  secretion  varies  with  the  amount  of  moisture 
contained  in  the  food.  It  is  believed  that  after  twenty-four  hours'  fasting 
the  salivation  is  more  active  at  the  commencement  of  the  meal  than  when 
hunger  commences  to  be  satisfied.  The  reverse,  however,  is  the  case  for 
the  parotids,  as  they  do  not  at  once  reach  their  maximum  activity  after 
a  long  fast.  The  above  statement,  however,  seems  to  hold  for  the  sub- 
maxillaries,  as  they  are  never  completely  inactive.  But  as  the  parotids 
secrete  the  greatest  volume  of  fluid,  the  food  first  swallowed  is  drier,  and 
therefore  swallowed  with  more  difficulty  than  later  when  the  parotids 
have  acquired  their  maximum  activity.  Then  the  quantity  of  secretion 
decreases  with  the  activity  of  mastication. 

The  quantity  of  saliva  poured  out  in  twentj-four  hours  may  be 
estimated  by  means  of  the  preceding  data.  For  if  hay  absorbs  more 
than  four  times  its  weight  of  saliva,  and  the  horse  swallows  one  hundred 
grammes  of  saliva  each  hour  during  fasting,  it  is  easy  to  estimate  the 
total  amount  secreted.  A  horse  which  consumes  five  thousand  grammes 
of  hay  and  five  thousand  grammes  of  dry  fodder  will  require  forty 
thousand  grammes  of  saliva  for  the  deglutition  of  its  food,  to  which 
must  be  added  about  two  thousand  grammes  for  the  eighteen  hours  of 
abstinence,  making  in  all  forty-two  thousand  grammes,  or  eighty-four 
pounds.  In  the  ruminant  the  total  amount  of  saliva  secreted  in  twenty- 
four  hours  is  much  larger.  If  we  assume  that  an  ox  takes  three  hours 
in  a  day  to  feed  and  five  hours  to  ruminate,  it  is  found  that  in  six  or 
eight  hours  forty  thousand  grammes  of  saliva  are  secreted,  and  during 


DIGESTION   IN   THE   MOUTH.  287 

the  sixteen  hours  of  abstinence  sixteen  thousand  grammes  are  secreted  ; 
in  all,  fifty-six  thousand  grammes,  or  one  hundred  and  twelve  pounds. 
This  is  certainly  an  inside  estimate.  In  these  animals,  also,  a  less  amount 
is  secreted  with  wet  and  green  food.  This  immense  amount  of  fluid  is 
again  absorbed,  and  is,  therefore,  not  lost  to  the  economy.  The  part 
which  each  gland  plays  in  the  secretion  of  this  volume  of  fluid  is  also 
determinable,  and  is  a  point  of  interest,  since  we  already  know  that  the 
chemical  composition  and  the  function  of  the  different  secretions  are  not 
uniform.  The  volume  of  saliva  poured  out  depends  on  the  dryness  of 
the  food,  and  not,  as  has  been  claimed,  upon  the  amount  of  starch  which 
it  contains,  indicating  that  the  mechanical  uses  of  the  saliva  are  of 
greater  importance  than  its  chemical  functions. 

The  volume  of  the  special  salivary  secretions  cannot  be  computed 
from  the  volume  of  the  glands.  Thus,  the  parotids  of  the  horse  are 
four  times  as  large  as  the  submaxillary  glands,  and  yet  they  secrete 
twentA-four  times  as  much  saliva.  The  parotid  of  the  ox  is  scarcely  as 
large  as  the  submaxillary,  and  yet  it  secretes  four  or  five  times  as  much 
saliva  as  the  latter.  In  the  horse  the  parotid  furnished  seven-tenths  of 
the  total  amount  of  fluids  poured  into  the  mouth,  a  fact  which  may  be 
readily  determined  by  means  of  cesophageal  fistulae,  conjoined  with 
closure  of  the  parotid  duct.  The  submaxillary  has  been  determined  by 
the  above  method  to  furnish  about  one-twentieth  of  the  total  salivary 
secretion.  These  figures  cannot,  of  course,  be  taken  as  being  rigorously 
correct,  since  the  necessary  operative  procedures  must  more  or  less 
modify  the  activity  of  the  glands.  In  the  non-herbivora  the  quantity 
of  saliva  is  much  less.  It  has  been  estimated  at  fifteen  hundred 
grammes  in  twenty-four  hours  for  a  man,  while  in  the  dog  the  parotid 
has  been  calculated  to  contribute  twenty-four  grammes,  the  submaxil- 
lary thirty-eight,  and  the  other  glands  twenty-four  grammes  in 
twent3-four  hours. 

6.  The  Physiological  Role  of  the  Saliva. — The  uses  of  saliva  are 
both  mechanical  and  chemical.  Mechanically,  it  assists  in  the  formation 
of  the  bolus  of  food,  after  having  previously  aided  its  mastication,  and 
acts  as  a  lubricant  in  its  passage  to  the  stomach.  It  aids  the  apprecia- 
tion of  taste,  and  by  lubricating  the  surfaces  of  the  mouth  and  teeth 
prevents  the  adhesion  of  viscid  substances,  and  in  man  permits  the 
movements  of  rapid  articulation.  In  the  ruminant  animals  the  en- 
trance of  saliva  into  the  paunch  is  essential  for  the  proper  maceration 
of  food,  so  as  to  enable  its  regurgitation  to  the  mouth  in  rumination. 

The  chemical  action  of  the  saliva  on  the  food  was  discovered  by 
Leuchs  in  1831,  who  found  that  the  saliva  was  capable  of  converting 
soluble  carbohy^ rates  into  dextrin  and  sugar.  The  cause  of  this  prop- 
erty of  saliva  lies  in  the  presence  of  ptyalin,  the  diastatic  ferment  of 


288  PHYSIOLOGY  OF  THE   DOMESTIC  ANIMALS. 

the  saliva,  which  we  have  already  found  to  exist  in  the  saliva  and  the 
aqueous  extract  of  the  salivary  glands  of  most  groups  of  animals. 

Experiments  as  to  the  cliastatic  action  of  the  saliva  may,  therefore,  be  made 
either  with  fresh,  filtered  saliva,  with  an  aqueous  or  glycerin  infusion  of  the  sali- 
vary glands,  or  with  an  aqueous  solution  of  pure  ptyalin.  A  mucilage  for  testing 
the  cliastatic  action  of  saliva  may  be  made  by  mixing  one  grain  of  powdered  starch 
into  a  thin  paste  with  a  few  drops  of  cold  water,  and  then  adding  the  paste  to  100 
cubic  centimeters  of  boiling  water  and  allowing  it  to  boil  for  ten  minutes.  Then, 
after  standing  until  the  sediment  has  settled,  the  clear  supernatant  fluid  is  filtered 
off  and  is  ready  for  use.  Equal  quantities  of  cold  starch-mucilage  are  poured 
into  three  test-tubes,  which  are  numbered  one,  two,  and  three  ;  tube  No.  1  con- 
tains starch-mucilage  alone  ;  to  tube  No.  2  a  few  drops  of  filtered  saliva  are  added; 
an  equal  quantity  of  saliva  is  boiled  thoroughly  for  a  few  minutes  and  added  to 
No.  3 ;  in  tube  No.  4  is  poured  a  small  quantity  of  saliva  alone.  The  four  test- 
tubes  are  placed  in  the  hot-water  bath  or  an  oven  at  a  temperature  of  about  38° 
or  39°  C.  After  a  few  moments  the  tubes  may  be  removed  for  testing.  If  to 
tube  No.  1,  which  contained  starch -mucilage  alone,  a  few  drops  of  dilute  iodine 
solution  are  added,  a  characteristic  blue  color  is  developed,  showing  the  presence 
of  starch,  while  Fehling's  solution  will  demonstrate  the  absence  of  sugar.  If  to 
tube  No.  2,  which  contains  starch -mucilage  and  saliva,  a  few  drops  of  the  same 
solution  of  iodine  are  added,  no  blue  color  will  be  developed,  showing  the  absence 
of  starch,  and  the  fluid  will  either  remain  colorless  or  may  take  on  a  more  or  less 
marked  reddish  tint  from  the  presence  of  dextrin,  showing  that  the  starch  has 
disappeared.  If  to  another  portion  of  the  same  fluid  contained  in  tube  No.  2  a 
few  drops  of  Fehling's  solution  are  added  and  the  fluid  boiled,  a  copious  yel- 
lowish-red precipitate,  due  to  the  reduction  of  cupric  to  cuprous  oxide,  will  be 
formed,  showing  the  presence  of  a  considerable  quantity  of  sugar.  Sugar  has, 
therefore,  in  this  test-tube  replaced  the  starch.  If  a  few  drops  of  iodine  are  added 
to  the  fluid  of  test-tube  No.  3,  which  contained  starch-solution  and  boiled  saliva, 
the  reaction  of  starch  will  still  be  developed,  and  Fehling's  fluid  will  show  the 
absence  of  sugar.  Boiling,  therefore,  has  prevented  the  conversion  of  the  starch 
by  the  saliva  into  sugar.  The  fluid  of  test-tube  No.  4,  which  consists  of  saliva 
alone,  will  give  no  reaction  with  iodine,  while  no  sugar  will  be  found  with 
Fehling's  test,  though  the  blue  color  may  be  turned  to  a  violet  from  the  presence 
of  proteids. 

Starch-mucilage,  when  subjected  to  the  action  of  saliva  at  a  temper- 
ature about  that  of  the  blood  for  a  few  moments,  is  converted  into  sugar. 
This  conversion  is  not  instantaneous,  although  it  was  taught  by  Bidder 
and  Schmidt  that  momentary  contact  with  saliva  and  starch  was  all  that 
was  necessary  to  turn  starch  into  sugar.  An  experiment  which  has  been 
long  used  to  substantiate  this  view,  and  which  appears  at  first  to  dem- 
onstrate its  truth,  is  really  by  no  means  conclusive.  The  experiment  is 
as  follows: — 

If  into  a  beaker  which  contains  a  little  saliva  warmed  up  to  40°  C. 
is  added,  drop  by  drop,  a  solution  of  starch  which  has  been  colored  blue 
by  iodine,  as  each  drop  falls  it  is  decolorized.  The  view,  however,  that 
the  loss  of  color  is  due  to  the  conversion  of  the  starch  into  sugar  is 
erroneous,  as  was  pointed  out  by  Schiff.  He  showed  that  the  decolori- 
zation  was  due  to  the  conversion  by  the  saliva  of  the  iodine  into 
hydriodic  acid,  and  that  many  other  organic  fluids  which  would  not  con- 
vert starch  into  sugar  would  decolorize  the  iodide  of  starch;  thus,  the 
addition  of  morphine  solution  or  of  dog's  urine  to  the  iodide  of  starch 


DIGESTION   IN   THE   MOUTH.  289 

discharges  the  blue  color  of  the  latter.  In  neither  of  these  substances  is 
there  the  property  of  converting  starch  into  sugar,  but  the  result  is  due 
to  oxidation  of  the  iodide.  There  are  two  practical  points  to  be  drawn 
from  this  demonstration :  first,  since  the  starch  is  not  instantaneously 
converted  into  sugar  upon  contact  with  the  saliva,  even  though  mas- 
tication be  prolonged,  by  no  means  all  of  the  starch  in  the  food  can  be 
converted  into  sugar  in  the  mouth;  and,  second,  starch  cannot  be 
considered  as  a  conclusive  test  for  iodine  in  the  various  secretions. 

It  is  often  desired  to  test  urine  for  iodine,  as  in  cases  of  iodism,  and  all  that 
is  deemed  necessary  is  to  add  a  solution  of  starch-mucilage  to  the  suspected  fluid, 
and  if  the  characteristic  blue  color  does  not  appear  it  is  concluded  that  no  iodine 
is  present.  This  procedure  is  doubly  fallacious,  not  only  because  these  fluids 
have  the  power  of  decolorizing  solutions  of  the  iodide  of  starch,  but  even  when 
iodine  is  present  it  is  not  in  the  form  of  free  iodine  but  of  hydriodic  acid,  the  very 
.agent  through  which  this  decolorization  is  effected.  If,  therefore,  iodine  is  present 
in  such  organic  fluids,  its  presence  can  only  be  detected  by  the  starch  test  by  first 
deoxidizing  the  hydriodic  acid.  This  may  be  accomplished  by  soaking  a  piece  of 
filter-paper  in  starch-mucilage,  drying,  moistening  with  the  suspected  fluid,  and 
then  allowing  a  drop  of  nitrous  acid  to  fall  upon  it.  If  iodine  is  present  in  the 
form  of  hydriodic  acid,  it  will  be  deoxidized  by  the  nitrous  acid,  and  the  free 
iodine  will  form  the  characteristic  blue  color  with  the  starch -paper. 

The  old  view  as  to  the  saccharification  of  starch  was  based  upon  the 
assumption  that  the  diastatic  ferment  first  converted  the  starch  into  dex- 
trin, and  that  then  dextrin  through  hy  drat  ion  was  converted  into  dex- 
trose. This  view  has  been  shown  to  be  erroneous  by  Musculus,  who 
found  that  the  subject  is  very  much  more  complex.  He  stated  that  in 
the  conversion  of  starch  into  sugar  all  the  starch  was  not  first  trans- 
formed into  dextrin  and  then  into  sugar,  but  that  these  two  bodies  were 
simultaneously  formed,  and  he  gives  the  following  formula  as  represent- 
ing this  conversion : — 

3C6H1005  +  2H20:=C6H1206-f2C6H1005 
Starch.  Dextrose.          Dextrin. 

Even  this  view  has,  however,  been  modified  b}r  subsequent  observa- 
tion. According  to  the  view  of  Musculus,  only  33  per  cent,  of  sugar 
could  originate  from  the  action  of  the  diastatic  ferments  on  starch , 
but  it  has  been  found  that  dextrin  also  is  converted  partially  into  sugar, 
and  from  20  to  30  per  cent,  of  sugar  may^  be  formed  in  this  way. 
Estimates  of  the  actual  amount  of  sugar  developed  through  the  action 
of  the  diastatic  ferment  on  starch  show  that,  instead  of  33  per  cent.,  over 
50  per  cent,  of  sugar  will  actually  form ;  so  that,  therefore,  while  the 
starch  may  first  be  split  up  into  dextrin  and  sugar,  this  dextrin  also 
undergoes  partial  conversion  into  a  fermentable  sugar.  Consequently, 
through  the  action  of  ptyalin,  starch  is  first  converted  into  dextrin  and 
sugar,  and  then  the  dextrin  itself,  through  the  action  of  the  ferments, 
undergoes  subsequently  a  progressive  hydration  and  results  in  the 

19 


290 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


formation  of  a  farther  quantity  of  sugar.  In  this  conversion  a  number 
of  by-products  are  formed,  which  behave  differently  to  iodine  and  to  the 
sugar  tests,  and  in  their  action  on  polarized  light.  The  following  table 
shows  these  changes  in  outline  : — 


Soluble  starch, 
Erythrodextrin, 


Rotation. 

2180 


3. 

4. 
5. 

Achroodextrin, 

Maltose, 
Grape-sugar, 

210 
190 
150 
150 

58 

12 
12 
28 
61 
100 

Behavior 
with  Iodine. 

Blue. 
Red. 


Colorless. 


Other  Tests. 

Precipitated  by  tan- 
nic  acid  and  alcohol. 

Not  precipitated  by 
tannic  acid  and  al- 
cohol. 


If  a  little  saliva  be  added  to  warm,  thick  starch-paste,  in  one  or  two 
minutes  the  thick  mucilage  will  be  converted  into  a  thin,  watery  fluid, 
which  will  not  yield  either  a  dextrin  or  sugar  reaction ;  it  will  still  give 
a  blue  with  iodine.  This  is,  therefore,  the  first  stage  in  the  diastatic 
action  of  saliva  on  starch — the  formation  of  soluble  starch.  If  a  longer 
time  is  allowed  to  elapse  before  the  testing  is  performed,  sugar  may  then 
be  found  in  the  fluid,  even  though  it  gives  a  distinct  blue  with  iodine. 
A  few  minutes  later,  testing  will  show  the  presence  of  a  larger  quantity 
of  sugar,  and  if  iodine  be  added  a  blue  color  will  be  produced ;  but  on 
diluting  this  and  adding  more  iodine  a  violet  color  will  appear,  showing 
the  presence  of  erythrodextrin,  together  with  soluble  starch  and  sugar. 
After  a  short  time  iodine  ceases  to  give  a  blue,  but  yields  a  deep-red 
color,  which  later  still  yields  to  a  yellowish-brown  color,  and  finally  no 
color  at  all  on  the  addition  of  iodine,  while  all  the  time  the  quantity  of 
sugar  goes  on  steadily  increasing.  These  reactions  show  that  the  soluble 
starch  gives  place  to  erythrodextrin,  giving  a  red  with  iodine,  and  finally 
to  achroodextrin,  which  has  no  color  reaction  with  iodine;  while,  from 
the  fact  that  the  sugar  continually  increases  as  these  substances  dis- 
appear, it  is  evident  that  the  sugar  results  from  the  progressive  conver- 
sion of  these  different  forms  of  erythro-  and  achroodextrin  into  dextrose, 
or  some  other  form  of  sugar.  Musculus  and  0 'Sullivan  have  proved 
that  the  sugar  which  results  from  the  action  of  diastatic  ferments  on 
starch  is  maltose,  which  is  a  fermentescible  sugar  belonging  to  the  group 
of  saccharoses,  having  a  formula  of  C^H^On.  This  substance  rotates 
the  plane  of  polarized  light  150°  to  the  right,  while  dextrose  has  only  a 
rotatory  power  of  -j-58°,  while  it  has  a  reducing  power  for  the  cupric 
oxide  sugar  test  of  61°,  as  compared  to  grape-sugar,  which  may  be  placed 
at  100°. 

In  order  to  explain  the  above  results  it  is  necessary  to  assume  that 
the  molecule  of  soluble  starch  is  a  composite  molecule,  composed  of 


DIGESTION    IN    THE   MOUTH. 


291 


several  members  of  the  starch  group  C13H20010,  and  the  assumption  that 
the  molecule  of  soluble  starch  has  the  formula  of  10(C12H20010)  greatly 
facilitates  the  comprehension  of  the  progressive  hydrolysis  of  starch  by 
diastase  (Brown  and  Heron). 

According-  to  this  view,  the  composite  molecule  of  soluble  starch  is 
resolved  through  the  action  of  diastase  into  two  molecules  of  achroo- 
dextrin  and  eight  molecules  of  maltose  by  the  following  succession  of 
steps : — 

One  molecule  of  soluble  starch --10(C12H20O10) -f  8(H2O)  = 


1.  Erythrodextrin, 

2. 

3.  Achroodextrin, 

4. 

5.- 

6. 

7. 

8. 


a  9(C12H20O10)  -f    (C12H22Oai)  maltose, 

ft  8(C12H20010)+2(C12H22011) 

a  7(C12H20010)+3(C12H220:1) 

n  a.f(*     w     o     \    i    ^/n     XT     (\     \ 


The  final  result  is  thus  represented  by  the  equation  :  — 


Soluble  Starch. 


Water. 


Maltose. 


Achroodextrin. 


Through  the  action  of  the  diastatic  ferment,  therefore,  the  large 
molecule  of  gelatinous  starch  is  first  separated  into  its  component  mole- 
cules of  soluble  starch,  and  if  we  assume  that  this  composite  molecule 
of  soluble  starch  is  composed  of  an  aggregation  of  ten  groups  of  the 
radical  C12H20O10,  then  progressively  each  one  of  these  radicals  assumes 
one  atom  of  water  and  becomes  a  molecule  of  maltose,  the  remainder  of 
the  starch  molecule,  at  the  withdrawal  of  each  radical,  constituting  one 
molecule  of  the  intermediary  dextrin  series.  The  dextrin  molecule  thus 
becomes  smaller  and  smaller,  that  is,  contains  fewer  and  fewer  component 
radicals,  the  higher  dextrins  giving  a  red  with  iodine,  while  the  lower 
dextrins  give  no  reaction  with  iodine  (Roberts). 

In  order  that  starch  should  be  converted  by  saliva  into  sugar,  it 
is  necessary  that  the  fluid  be  kept  at  the  temperature  of  about  39°  or 
40°  C.  A  temperature  elevated  above  this  will  prevent  conversion  by 
destroying  the  ferment,  while  a  lower  temperature  will  retard  it,  and  the 
temperature  of  freezing  will  prevent  it  completely,  although  the  power 
is  not  lost  and  may  be  regained  when  the  temperature  is  again  elevated. 
This  transformation  is  produced  in  a  neutral  or  feebly  alkaline  medium, 
and  also,  though  to  a  much  less  degree,  in  a  weak  acid  medium.  An 
excess  of  alkali,  or  even  a  slight  degree  of  acidity  (half  of  1  per  cent,  of 
hydrochloric  acid),  will  prevent  it  completely.  This  is  a  point  worthy 
of  note,  since  it  indicates  that  the  degree  of  acidity  present  in  the 
gastric  juice  during  active  digestion  is  sufficient  to  interrupt  the  action 


292  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

of  ptyalin  on  starch.  It  will  be  found,  however,  that  hydrochloric  acid 
does  not  appear  in  the  gastric  juice  of  the  horse  until  the  latter  stages 
of  gastric  digestion,  the  acidity  in  the  early  stages  being  due  to  the 
presence  of  lactic  acid.  It  has  further  been  proved  that  lactic  acid, 
even  when  present  in  2  or  3  per  cent.,  will  not  arrest  the  conversion  of 
starch  by  the  saliva.  Therefore  in  the  horse  starch  may  still  be  con- 
verted in  the  stomach  into  sugar.  In  the  ruminant  animal  all  the  starch 
is  probably  converted  into  sugar  in  the  rumen,  where  the  reaction  is 
alkaline,  and  here  also,  therefore,  the  acidit}'  of  the  gastric  juice  does  not 
interfere  with  the  digestion  of  starch,  even  though  it  may  not  take  place 
in  the  stomach,  whatever  starch  escapes  the  saliva  being  acted  on  by 
the  pancreatic  juice.  In  carnivora,  where  the  gastric  juice  is  highly 
acid,  starchy  matters  seldom  enter  into  the  composition  of  their  food, 
while  in  the  omnivora,  man  especially,  the  saliva  possesses  a  higher 
diastatic  power  than  in  other  animals  ;  therefore  the  conversion  of  starch 
in  the  mouth  will  be  much  more  rapid,  and  even  though  suspended  in  the 
stomach,  is  again  resumed  in  the  small  intestine  under  the  action  of  the 
pancreatic  juice.  So,  also,  when  the  amount  of  sugar  formed  reaches 
from  1^  to  2J  per  cent.,  saccharin" cation  is  arrested,  but  will  be  renewed 
when  the  fluid  is  diluted.  The  transformation  of  boiled  starch  mucilage 
is  very  much  more  rapid  than  that  of  raw  starch.  This  is  due  to  the 
fact  that  it  is  only  the  gfanulose  of  the  starch  granules  which  is  con- 
verted into  sugar.  In  the  raw  starch  granules  the  granulose  is  contained 
in  an  unyielding  cellulose  envelope,  and  is  not  accessible  to  the  salivary 
ferment.  When  starch  is  boiled  the  cellulose  envelopes  are  ruptured; 
the  granulose  then  passes  partly  into  solution,  and  is  then  readity  acted 
on  by  the  saliva. 

The  diastatic  action  of  the  saliva  of  different  animals  varies  very  con- 
siderably. In  almost  all  it  is  less  active  than  in  man,  with  the  possible 
exception  of  the  saliva  of  the  herbivora.  The  latter  appears  to  be  more 
active  on  raw  starch  than  that  of  the  carnivorous  animals.  Thus,  it  has 
been  found  that  the  saliva  of  the  horse  will  convert  crushed  raw  starch  into 
sugar  in  one-quarter  of  an  hour,  and  it  has  been  proved  experimentally 
that  in  the  horse  the  conversion  of  raw  starch  into  sugar,  through  the 
action  of  the  saliva,  takes  place  in  the  stomach.  It  is  worthy  of  note 
that  the  individual  salivary  secretions  of  the  horse  appear  to  possess 
this  amylolytic  power  to  a  less  degree  than  the  mixed  saliva.  It  has 
been,  however,  found  that,  in  addition  to  acting  on  starch,  the  saliva  of 
the  horse  is  also  capable  of  converting  cane  sugar  into  grape  sugar. 
The  saliva  of  the  horse  is  further  inactive  on  the  cellulose  of  ha}r. 

Examination  of  the  substances  escaping  from  an  oasophageal  fistula 
in  the  horse  fed  on  starchy  food  shows  that  practically  no  conversion 
of  starch  into  sugar  occurs  in  the  mouth.  This,  indeed,  would  be  ex- 


"DIGESTION  IN  THE  MOUTH.  293 

pected  from  the  fact  that  raw  starch  requires  several  minutes'  contact 
with  the  saliva  of  the  horse  to  be  converted  into  sugar.  It  is  not  to  be 
therefore  concluded  that  the  amylolytic  power  of  the  saliva  is  of  no 
practical  value,  since  it  will  be  found  that  in  the  horse  the  chemical 
action  of  the  saliva  may  continue  in  the  stomach. 

In  the  ruminants  the  diastatic  action  of  the  saliva  is  probably  about 
the  same  as  that  of  the  horse,  but  the  conditions  for  the  conversion  of 
starch  into  sugar  are  more  favorable,  since  the  saliva  is  constantly  being 
secreted,  constantly  swallowed  and  carried  to  the  rumen,  where  it  meets 
with  the  most  favorable  conditions  for  acting  on  the  starch — in  other 
words,  an  alkaline  medium  considerably  diluted  and  an  elevated  tem- 
perature. 

Of  the  other  animals,  the  following  series  represents  the  diastatic 
action  of  the  saliva,  it  being  most  marked  in  the  first  animal  and  least  in 
the  last :  hog,  rat,  rabbit,  cat,  dog,  sheep,  and  goat.  In  all  the  domestic 
animals  the  parotid  saliva  possesses  the  highest  degree  of  amylolytic 
power.  The  orbital  gland  of  the  dog  appears  to  produce  no  amylolytic 
ferment.  All  the  so-called  antiseptics  and  stronger  chemical  agents  pre- 
vent the  action  of  the  salivary  ferment.  The  duration  of  the  action  of 
human  saliva  on  raw  starch  before  the  presence  of  sugar  can  be  detected 
is  as  follows  :  On  potato-starch,  after  two  to  four  days  ;  on  starch  from 
peas,  after  one  and  one-third  to  two  hours  ;  on  wheat-starch,  after  one-half 
to  one  hour ;  on  barley-starch,  after  ten  to  fifteen  minutes ;  on  oat-starch, 
after  five  to  seven  minutes  ;  on  rye-starch,  after  three  to  six  minutes ;  on 
corn-starch,  after  two  to  three  minutes. 

If  raw  starch  is  finely  comminuted,  as  by  grinding  with  powdered 
glass,  the  time  of  the  reduction  is.  considerably  reduced. 

Extracts,  or  the  secretion  of  the  different  salivary  glands  in  the 
domestic  animals,  are  entirely  inert  on  fats,  proteids,  and  cellulose. 

7.  The  Mechanism  of  the  Salivary  Secretion. — The  numerous  inves- 
tigations which  have  been  undertaken  to  explain  the  mechanism  of  salivary 
secretion  have  yielded  results  of  far  more  importance  than  that  which 
they  possess  as  bearing  upon  the  secretion  of  saliva  alone.  It  is  from  the 
results  of  these  experiments  that  has  been  deduced  all  our  knowledge  of 
glandular  secretion,  its  dependence  upon  the  nervous  system,  and  its  rela- 
tion to  the  circulation.  In  the  case  of  the  saliva  it  has  already  been  men- 
tioned that,  under  ordinary  circumstances,  in  all  animals  the  secretion  of 
the  saliva  is  either  remittent  or  intermittent.  In  other  words,  as  a  rule 
but  enough  saliva  is  poured  into  the  mouth  during  abstinence  to  keep  the 
surfaces  moist.  When,  however,  food  is  taken  into  the  mouth  and  the 
process  of  mastication  commenced,  or  in  the  ruminant  animal  during 
the  process  of  rumination,  the  secretion  of  the  salivary  glands  is  at  once 
greatly  increased  in  activity.  Further,  allusion  has  been  made  to  the  fact 


294 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


that  the  quantity  of  saliva  poured  out  varies  under  many  different  circum- 
stances, as  to  the  character  of  the  food,  and  the  side  on  which  masti- 
cation is  taking  place.  It  might  be  already  concluded  from  this,  that 
the  secretion,  of  saliva  is  a  reflex  action  and  is  under  the  control  of  the 
nervous  S3Tstem.  As  long  ago  as  1832  Mitscherlich,  from  studies  made 
on  a  patient  with  a  salivary  fistula,  first  suggested,  that  the  salivary 
secretion  was  under  the  influence  of  the  nervous  system,  and  in  support 
of  that  statement  alluded  to  the  fact  that  while  the  secretion  of  saliva 
was  independent  of  the  will,  it  might  be  called  forth  by  stimulation  of 
the  mucous  membrane  of  the  tongue  and  mouth,  either  chemically  or 


FIG.  119.— NERVES  OF  STTBMAXII/LARY  AND  STTBLINGUAL  GT.ANDS.    (Bernard.) 

a,  submaxillarv  gland ;  c  c,  duct  of  Wharton ;  i  7i  g,  arterial  branches  to  the  submaxillarv  gland ; 
b,  sublingual  gland:  d  ft,  sublingual  duct:  1  1,  lingual  nerve;  22,  chorda  tympani :  r,  carotid  a'rtery,  on 
which  ramify  fibres  coming  from  the  superior  cervical  ganglion;  /,  internal  maxillary  artery. 


mechanically,  stimulation  of  the  nerve  of  smell,  or  ^stimulation  of  the 
gastric  mucous  membrane  by  the  food.  It  thus  is  clear  that  the  secretion 
of  saliva  is  a  reflex  action,  for  which  there  must  be  an  afferent  fibre, 
an  independent  nerve  centre,  and  an  efferent  fibre.  From  the  fact  that 
the  submaxillary  gland  is  the  most  exposed,  and,  therefore,  the  most 
readily  operated  on,  the  influence  of  the  nerves  on  the  secretion  of 
saliva  has  been  most  studied  in  the  case  of  this  gland.  The  afferent 
nerve  fibres  of  this  reflex  circle,  in  the  case  of  the  submaxillary  gland, 
are  the  lingual  branch  of  the  fifth  pair  and  branches  of  the  glosso- 


DIGESTION   IN   THE   MOUTH.  295 

pharyngeal — the  nerves  of  taste.  The  centre  is  in  the  medulla  oblon- 
gata  and  the  efferent  fibre  is  the  chorda  tj'mpani,  a  branch  of  the  seventh 
— the  facial — nerve  (Fig.  119).  The  influence  of  these  nerves  on  the 
secretion  of  saliva  is  readily  proved  by  experiment. 

The  animal  on  which  this  experiment  is  usually  performed  is  the  dog.  The 
operation  is  performed  as  follows  : — A  large  dog  is  chloroformed  and  fastened  in 
Bernard's  dog-holder.  The  hair  is  shaved  from  the  lower  surface  of  the  jaws  and 
the  side  of  the  neck,  and  an  incision  made  along  the  lower  border  of  the  lower 
jaw,  commencing  about  its  anterior  third  and  extending  back  to  the  transverse 
process  of  the  atlas,  dividing  the  skin  and  platysma  muscle.  After  clearing 
away  the  connective  tissue  and  fat,  carefully  avoiding  the  veins,  the  submaxillary 
gland  comes  into  view  just  below  the  angle  of  the  jaw.  It  is  then  seen  that  the 
gland  lies  in  the  angle  formed  by  the  junction  of  the  two  veins  which  go  to  make 
up  the  external  jugular  vein  (Fig.  120),  one  branch  coming  from  above  downward 
directly  behind  the  gland,  and  usually  receiving  a  small  vein  from  the  gland 
itself,  while  the  lower  branch  runs  horizontally  below  the  gland,  and  is  formed 
by  the  junction  of  two  other  branches,  one  coming  from  above  and  the  other  from 
below.  The  horizontal  branch  also  very  constantly  receives  a  vein  from  the 


FIG.  120.— VEINS  OF  THE  SUBMAXILLARY  GLAND  OF  THE  DOG.    (Bernard.) 

g,  submaxillary  gland  ;  j,  external  jugular  vein  dividing  into  two  branches:  jl  andj",  veins  which  sur- 
round the  gland ;  d,  anterior  glandular  vein :  d>,  posterior  glandular  vein. 

gland.  Both  branches  which  go  to  form  the  horizontal  branch  are  tied,  the  one 
coming  from  above  receiving  a  double  ligature  where  it  comes  from  the  ramus 
of  the  jaw,  and  the  otherwhere  it  joins  its  fellow,  the  intermediate  portion  being 
removed.  After  having  carefully  removed  the  cellular  tissue  from  the  portion  of 
the  wound  in  front  of  the  gland,  the  thick  belly  of  the  digastric  muscle  comes 
into  view,  its  fibres  running  forward  from  its  origin  in  the  temporal  bone  to  be 
inserted  in  the  middle  third  of  the  ramus  of  the  lower  jaw  immediately  in  front 
of  the  insertion  of  the  masseter,  from  which  muscle  it  is  separated  by  a  slight 
groove.  In  front  of  the  digastric,  the  floor  of  the  wound  is  formed  by  the  trans- 
verse fibres  of  the  mylo-hyoid  muscle,  crossed  by  the  mylo-hyoid  nerve,  which 
comes  out  from  under  the  jaw  at  the  point  of  insertion  of  the  digastric  muscle. 
The  connective  tissue  is  then  gradually  to  be  cleared  away  with  a  blunt  hook 
from  the  surface  of  the  digastric  muscle  and  from  the  groove  between  it  and  the 
masseter  muscle,  taking  care  to  avoid,  as  the  deeper  portion  is  reached,  the  facial 
artery,  which  passes  over  the  jaw  to  run  between  these  muscles,  and  the  artery  of 
the  gland,  which  conies  from  the  facial  artery  and  goes  in  this  groove  back  to 
the  gland.  In  the  same  locality  lie  also  the  ducts  of  the  gland  and  the  chorda 
tympani  nerve.  The  digastric  muscle  is  now  to  be  separated  by  means  of  an 
aneurism  needle  from  the  facial  artery,  avoiding  all  the  adjacent  structures,  and 
its  muscular  arterial  branch  tied.  The  muscle  is  then  divided  at  its  anterior  third, 


296 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


or  where  it  is  inserted  into  the  jaw,  and  its  posterior  extremity  seized  with  a  pair 
of  artery  forceps  and  gradually  cleared  back  to  its  insertion  in  the  temporal  bone 
and  surrounded  by  a  ligature.  When  it  is  assured  there  is  nothing  but  muscular 
structure  in  the  grasp  of  the  ligature,  it  is  pushed  back  to  the  temporal  bone  and 
tied,  and  the  digastric  muscle  divided  in  front  of  the  ligature  and  removed.  On 
carefully  tearing  away  the  connective  tissue  at  the  base  of  the  wound  and  drawing 
back  the  submaxillary  gland,  there  is  exposed  a  triangular  cavity  (Fig.  121). 
This  space  is  limited  above  and  behind  by  the  under  surface  of  the  submaxil- 
lary gland,  into  the  hylum  of  which  enter  the  artery,  chorda  tympani  and  sym- 
pathetic nerve  fibres,  and  the  glandular  duct.  Its  lower  margin  is  formed  by 
the  genio-hyoid  muscle,  and  its  upper  border  by  the  ramus  of  the  jaw  and  the 
masseter  muscle.  The  anterior  portion  of  its  floor  is  formed  by  the  transverse 
fibres  of  the  mylo-hyoid  muscle,  on  which  ramify  the  branches  of  the  mylo-hyoid 
nerve.  At  the  posterior  portion  of  this  space  the  external  carotid  artery  enters 
and  runs  along  the  base  of  the  triangle,  giving  off  first  the  lingual  and  then  the 


FIG.  121.—  PARTS  EXPOSED  IN  OPERATIONS  ON  THE  SUBMAXLLLARY  GLAND 
OF  THE  DOG.     (Bernard. 

M,  anterior  portion  of  digastric  muscle  elevated  with  a  tenaculum  ;  M',  posterior  extremity  of  the 
digastric  raised  up  so  as  to  show  the  carotid  artery,  1  1,  and  the  sympathetic  filaments  ;  G,  sul.maxillary 
gland  elevated  to  show  its  posterior  surface:  H,  submaxillary  and  snblingual  ducts:  J.  external  jugular 


. 

vein;  J',  posterior  branch;  J",  anterior  branch:  D,  glandular  vein;  F,  origin  of  inferior  glandular 
artery;  P,  hypoglossal  nerve;  L,  lingual  nerve:  T,  chorda  tympani;  S  S',  divided  mylo-hyoid  muscle; 
U,  masseter  muscle  at  angle  of  lower  jaw  ;  Z,  origin  of  mylo-hyoid  nerve. 

facial  arteries,  from  off  the  latter  of  which  comes  the  artery  of  the  gland.  Almost 
immediately  after  entering  this  space  the  carotid  is  crossed  by  the  large  hypo- 
glossal  nerve,  running  forward  to  be  distributed  to  the  muscles  of  the  tongue.  If 
this  nerve  is  divided  at  the  point  where  it  crosses  the  carotid,  and  the  central  end 
removed,  the  pneumogastric  nerve  comes  into  view,  lying  behind  the  artery.  On 
pulling  to  one  side  the  vagus  trunk,  below  and  behind  it  can  be  seen  the  white 
trunk  of  the  sympathetic  nerve,  which  here  separates  itself  from  the  vagus  to 
form  the  superior  cervical  ganglion,  from  which  two  small  filaments  pass  out  to 
accompany  the  carotid  and  the  artery  of  the  gland  to  enter  the  hylum.  Some  of 
the  sympathetic  fibres  also  pass  into  the  gland  along  the  arterial  branch  which 
comes  from  the  temporal  branch,  and  enter  the  exterior  part  of  the  gland.  Then, 
to  expose  the  chorda  tympani  and  salivary  ducts,  the  fibres  of  the  mylo-hyoid 
muscle  are  to  be  divided  transversely  at  about  their  middle,  avoiding  every  nerve, 
but  tying  all  veins,  and  the  upper  half  of  the  muscle  reflected.  The  lingual  nerve 
then  comes  into  view,  passing  from  under  the  ramus  of  the  jaw  and  running 


DIGESTION   IN   THE   MOUTH. 


297 


FIG.  122.— NERVES  OF  THE  SUBM AXILLARY  GLAND  IN  THE  DOG.  (Bernard.) 

G,  submaxillary  gland  ;  K,  submaxillary  duct :  C.  primitive  carotid  ;  L,  lingual  artery  ;  O,  glandular  artery,  branch 
of  the  facial ;  H  H',  hypoglossal  nerve  divided  so  as  to  show  the  superior  cervical  ganglion;  V,  pneutnogastric  nerve;  P, 


sympathetic  fibres  ;  D,  fibre  from  the  first  pair  of  cervical  nerves ;  R  R,  glosso- 


l  ganglion; 
pharyngeal 


nerve  ;  I,  anterior  filaments 


of  the  superior  cervical  ganglion,  forming  the  carotid  plexus:  P,  fibre  going  to  the  submaxillary  gland;  Q,  sympathetic 
filaments ;  M,  mylo-hyoid  nerve  :  U,  lingual  nerve,  giving  off  the  chorda  tympani,  T,  which,  after  anastomosing  with  the 
sympathetic  filaments,  is  distributed  to  the  submaxillary  gland  ;  S,  external  branch  of  the  spinal  accessory  nerve. 


298  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

downward  and  forward,  about  parallel  in  direction  with  the  hypoglossal.  On 
drawing  the  parts  toward  the  middle  line,  the  two  salivary  ducts  are  seen  passing 
along  close  together,  immediately  below  the  ramus  of  the  jaw,  the  submaxillary 
duct  lying  nearer  the  bone  and  being  a  little  the  larger.  On  tracing  back  the 
lingual  nerve  to  where  it  passes  from  under  the  jaw,  it  will  be  seen  that  a  delicate 
nerve-filament  here  leaves  the  lingual  and  curves  backward  along  the  ducts  to 
enter  the  hylum  of  the  gland.  This  is  the  chorda  tympani.  Immediately  after 
the  chorda  leaves  the  lingual  there  is  sometimes  seen  a  small  ganglionic  enlarge- 
ment, known  as  the  submaxillary  ganglion,  and  as  the  chorda  tympani  enters  the 
hylum  it  forms  a  slight  ganglionic  plexus  with  the  sympathetic.  The  nerve-  and 
blood-supply  of  the  submaxillary  gland  of  the  dog  are  further  shown  in  Fig.  122. 
Each  of  these  nerves  which  it  is  desired  to  study  should  be  carefully  isolated  and 
surrounded  with  a  thread,  and  a  cannula  should  be  inserted  into  the  submaxillary 
duct.  To  facilitate  this,  the  duct  should  be  freed  slightly  from  the  connective 
tissue,  and  closed  with  a  clip  or  ligature  ;  as  the  gland  is  passive,  the  chorda  should 
be  stimulated  with  a  very  weak  electric  current  for  a  few  seconds,  so  as  to  distend 
the  duct  with  saliva,  and  a  small  slip  of  wood  passed  under  it  to  act  as  a  support. 
If  the  duct  is  then  seized  with  a  pair  of  fine  forceps  and  snipped  with  a  pair  of 
sharp-pointed  scissors,  a  cannula  may  be  readily  inserted. 

The  above  is  the  mode  of  operation  employed  by  Bernard,  and  permits  of 
the  performance  of  all  the  more  important  experiments  on  the  physiology  of  the 
secretion  of  the  submaxillary  gland.  Where  it  is  simply  desired  to  demonstrate 
the  secretory  action  of  the  chorda  tympani  nerve,  the  operation  may  be  greatly 
simplified  by  simply  cutting  directly  down  on  to  the  mylo-hyoid  muscle,  dividing 
its  fibres  transversely,  and  exposing  the  ducts  and  chorda  tympani  nerve  by 
turning  the  parts  back  toward  the  ramus  of  the  jaw  In  the  sheep,  the  operation 
may  be  performed  in  the  same  manner,  the  duct  originating  in  the  union  of  a 
number  of  roots.  In  the  rabbit  the  operation  is  much  more  difficult,  from  the 
extreme  fineness  of  the  duct  and  the  fact  that  it  is  surrounded  by  the  tissue  of  the 
sublingual  gland. 

After  having  performed  the  operation  as  detailed  above,  the  first 
point  which  should  be  demonstrated  is  the  fact  that  the  secretion  of 
saliva  is  a  reflex  action,  and  that  the  reflex  circle  is  as  stated  above.  If 
a  few  drops  of  vinegar  are  placed  upon  the  tongue  of  a  dog  provided 
with  a  submaxillary  fistula,  almost  immediately  a  profuse  secretion  of 
saliva  will  set  in,  and  the  fluid  will  run  from  the  mouth  of  the  tube.  If 
the  trunk  of  the  lingual  nerve  is  divided  near  its  entrance  to  the  mouth, 
and  then  vinegar  or  acetic  acid  placed  on  the  animal's  tongue,  no 
secretion  will  result,  unless  the  stimulating  fluid  reaches  the  back  of 
the  mouth,  where  it  may  come  into  contact  with  the  terminal  fibres  of 
the  glosso-pkaryngeal  nerve.  If  the  central  end  of  the  divided  lingual 
nerve  is  stimulated  with  a  weak  electrical  current,  a  profuse  secretion 
of  saliva  will  be  set  up.  Therefore  the  lingual  nerve,  and,  to  a  certain 
extent,  the  glosso-pharyngeal,  constitute  the  afferent  path  by  which  the 
sensory  impressions  necessary  for  the  reflex  action  of  saliva  reach 
the  brain.  The  nerves  of  taste  are,  therefore,  the  afferent  nerves  for 
the  secretion  of  saliva.  The  nerve  centre  lies  in  the  medulla  oblongata, 
and  there  probably  exclusively,  although  Bernard  thought  that  he  had 
shown  that,  under  certain  circumstances,  the  submaxillary  ganglion 
might  act  as  a  reflex  centre  for  this  process.  The  efferent  nerve  is  the 
chorda  tympani.  This  nerve  is  a  delicate  filament  which  leaves  the  trunk 
of  the  facial  nerve  in  the  Fallopian  canal  about  four  or  five  millimeters 


DIGESTION   IN   THE   MOUTH.  299 

before  it  passes  out  of  the  st}Tlo-mastoid  foramen,  and  then,  arching 
upward  and  forward,  enters  the  middle  ear,  which  it  traverses  from 
behind  forward,  lying  within  the  thickness  of  the  membrana  tympani. 
Here  for  a  space  of  six  or  eight  millimeters  the  nerve  is  comparatively 
isolated,  lying  between  the  handle  of  the  malleus  and  the  vertical  process 
of  the  incus.  It  then  passes  toward  the  Glaserian  fissure,  and  leaves 
the  skull  in  the  neighborhood  of  the  spine  of  the  sphenoid  bone  to  join 
the  lingual  nejve.  It  has  already  been  stated  that  stimulation  of  the 
central  end  of  the  lingual  nerve  calls  forth  a  secretion  of  submaxillary 
saliva.  If,  however,  the  chorda  tympani  nerve  be  previously  divided, 
stimulation  of  the  lingual  is  without  effect. 

The  simplest  method  of  dividing  the  chorda  tympani  nerve  is  to  cut  it  where  it 
crosses  the  tympanum.  This  may  be  accomplished  by  introducing  a  small  sickle- 
shaped  knife  into  the  external  auditory  canal,  the  animal  being  profoundly  chloro- 
formed, keeping  the  cutting  edge  upward,  and  passing  the  back  of  the  blade 
downward  and  forward  along  the  inferior  wall  of  the  meatus  until  the  tympanum 
is  reached.  Pushing  the  blade  through  the  tympanum,  the  knife  is  inserted  in 
the  middle  ear,  and  on  depressing  the  handle  of  the  knife  in  this  position  the  nerve 
is  divided. 

The  fact  that  the  chorda  tympani  constitutes  the  efferent  nerve  in 
this  reflex  circle  is  not  only  proved  by  the  experiment  just  alluded  to, 
where  its  division  prevents  the  flow  of  saliva  after  stimulation  of  the 
lingual,  but  ma}T  be  positively  demonstrated  by  its  stimulation.  If  the 
chorda  tympani  nerve  is  directly  stimulated  with  a  weak  induced  electrical 
current  just  after  it  leaves  the  lingual  trunk,  in  a  few  seconds  the  saliva 
begins  to  flow  from  the  cannula,  and  runs  in  quite  a  stream. 

It  has  thus  been  shown  that  the  secretion  of  submaxillary  saliva  is 
a  reflex  nerve  mechanism;  that  the  sense  of  taste  is  the  normal  stimulus, 
and  that  this  stimulus  reaches  the  brain  through  the  fibres  of  the  lingual 
and  glosso-pharyngeal  nerves,  and  is  transmitted  to  the  gland  from  the 
medulla  through  the  fibres  of  the  chorda  tympani  nerve.  We  have  now 
to  study  the  mechanism  by  which  saliva  is  separated  by  the  gland  from 
the  blood  and  the  influence  of  the  various  nerves  and  different  conditions 
of  the  circulation  on  this  process. 

If  the  submaxillary  gland  is  exposed  as  described  above,  and  the 
chorda  tympani  nerve  stimulated,  not  only  is  there  a  copious  secretion  of 
saliva,  but  the  appearance  of  the  gland  itself  undergoes  great  change. 
If  examined  before  the  nerve  is  stimulated,  the  gland  will  usually  appear 
pale.  A, few  arborescent  vessels  will  be  seen  upon  its  surface,  and  the 
blood  which  leaves  the  gland  is  dark,  and  the  vein  small.  When,  how- 
ever, active  secretion  is  produced  through  stimulation  of  the  chorda 
tympani  nerve  the  surface  of  the  gland  becomes  rosy  red.  Numerous 
branching  vessels  are  seen.  The  blood  that  flows  from  the  gland  is 
almost  arterial  in  hue,  is  much  larger  in  quantity,  and  the  veins  are  seen 


300  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

to  pulsate  synchronously  with  the  heart.  Evidently,  then,  stimulation 
of  the  chorda  tympani  nerve  increases  the  blood-supply  of  this  gland, 
either  through  an  active  dilatation  of  the  vessels,  or  more  probably 
through  an  inhibition  of  a  local  vaso-motor  centre.  An  analogous  result 
will  be  seen  in  the  case  of  the  depressor  nerve,  a  nerve  whose  stimulation 
produces  paralysis  of  the  vaso-motor  centre  and  consequent  dilation  of 
the  blood-vessels.  Two  results  then  follow  stimulation  of  the  chorda 
tympani, — an  abundant  secretion  of  saliva  and  a  marked  hyperaemia  of 
the  gland.  Before,  however,  the  relation  between  these  results  are  dis- 
cussed, the  influence  of  the  sympathetic  nerve  011  the  submaxillary  gland 
must  be  alluded  to. 

As  is  well  known,  a  constant  result  of  stimulation  of  a  fibre  of  the 
sympathetic  system  is  a  contraction  of  the  arterioles,  and  a  consequent 
diminution  of  the  supply  of  blood  in  the  parts  supplied  by  the  nerve.  If 
the  filament  which  leaves  the  superior  cervical  ganglion  and  passes  to 
the  submaxillary  gland  along  the  carotid  is  irritated  with  a  weak  induction 
current,  there  is  a  momentary  flow  of  saliva,  and  the  character  of  the 
secretion  so  produced  differs  from  that  which  follows  stimulation  of  the 
chorda.  Sympathetic  saliva  is  very  viscid,  and  can  be  drawn  out  in  a  long- 
thread  from  the  orifice  of  the  cannula.  It  is  of  higher  specific  gravity 
and  richer  in  organic  elements  than  that  which  follows  stimulation  of  the 
chorda.  In  other  words,  the  chorda  saliva  contains  a  maximum  quantity 
of  water  and  a  minimum  of  organic  elements,  while  in  sympathetic  saliva 
the  proportions  are  reversed.  So,  also,  the  effects  of  the  sympathetic 
stimulation  on  the  blood-supply  of  the  submaxillary  gland  differ  from 
those  of  the  chorda  tympani.  If  the  sympathetic  filament  is  irritated,  the 
arborescent  vessels,  especially  over  the  surface  of  the  gland,  disappear, 
and  the  tissue  of  the  gland  becomes  pale  and  the  vein  of  the  gland  con- 
tracted and  carrying  a  small  quantity  of  black  blood.  In  fact,  therefore, 
in  both  respects  the  function  of  the  sympathetic  and  chorda  tympani 
nerves  are  antagonistic ;  and  if  each  nerve  be  stimulated  alternatel}r  at 
short  intervals  with  the  current  which  applied  alone  to  either  nerve 
would  produce  its  characteristic  effect,  there  is  no  result.  Evidently, 
then,  there  is  a  complete  opposition  in  function  in  these  two  nerves. 
But  is  the  secretion  of  saliva  simply  dependent  upon  the  vascular  con- 
dition of  the  glands?  Does  the  gland  act  as  a  sponge,  filtering  out  the 
saliva  from  the  material  within  the  blood,  the  quantity  being  solely 
dependent  upon  the  quantity  of  blood  in  the  organ;  or  is  there  some 
special  function  possessed  by  the  cells  of  the  salivary  glands,  by  which 
the  saliva  is  separated  from  the  blood  without  being  dependent  solely 
upon  the  supply  of  blood  ?  In  other  words,  what  is  the  mechanism  by 
which  the  salivary  glands  separate  the  salivary  secretion  from  the  blood  ? 
We  know  that  as  the  blood  passes  through  the  capillaries  of  the  systemic 


DIGESTION   IX   THE   MOUTH.  301 

circulation  it  not  only  loses  in  oxygen  and  gains  in  carbon  dioxide,  but 
there  is  also  an  actual  reduction  in  the  amount  of  fluid,  due  to  the 
transudation  of  the  serum  of  the  blood  into  the  lymph-spaces.  Such 
transudation  is  due  solely  or  mainly  to  blood-pressure,  and  does  not 
constitute  a  permanent  loss  to  the  blood ;  for  the  fluids  so  poured  out 
into  the  lymph-spaces  serve  largely  to  nourish  the  tissues,  and  are  then 
pushed  on  into  the  lymphatic  vessels  by  fresh  quantities  coming  after 
them,  and  finally  again  reach  the  veins,  and  thus  re-enter  the  circula- 
tion. Such  transudations  pervade  all  tissues,  but  in  glandular  organs 
not  only  is  there  a  constant  loss  from  the  nourishment  of  the  tissues 
forming  the  glands,  but  the  secretions  are  produced  at  the  expense  of 
these  filtrates  from  the  blood-vessels  into  the  lymph-spaces  of  the  gland- 
ular tissue.  Secretion  is,  thus,  the  passage  of  the  substances  from  lymph- 
spaces  to  the  exterior  of  the  body,  for,  as  has  already  been  referred  to, 
the  alimentary  canal  may  be  regarded  as  such. 

Various  views  have  been  proposed  to  explain  the  passage  of  the 
constituents  of  the  lymph  so  transuded  from  the  blood-vessels  into  the 
excretory  ducts  of  the  glands.  The  blood-pressure  is  evidently  con- 
cerned in  forcing  the  serum  of  the  blood  through  the  walls  of  the 
capillaries  into  the  lymph-s paces,  but  here  the  blood-pressure  ceases  to  be 
of  influence.  For  if  a  manometer  is  inserted  into  the  submaxillary  duct 
of  a  dog  and  the  chorda  tympani  nerve  stimulated,  the  pressure  in  the 
salivaiy  duct  will  be  found  to  be  greater  by  far — one-third  greater,  at 
least — than  that  of  the  carotid  artery.  Where,  therefore,  the  pressure 
is  greater  on  the  side  of  the  excretory  duct,  blood-pressure  of  course 
can  be  of  no  avail  in  causing  the  passage  of  the  fluids  through  the 
glandular  tissue  into  that  duct.  Osmosis  may  to  a  certain  extent  be 
concerned  in  producing  the  passage  of  the  fluid  through  the  gland- 
membrane,  though  there  are  scarcely  any  data  in  favor  of  this  view  other 
than  that  which  is  conceded  in  the  fact  that  the  stimulation  of  the  chorda 
tympani  nerve  may  result  elect rolytically  in  the  production  of  certain 
decomposition  products  which,  having  a  strong  affinity  for  water,  might 
extract  water  from  the  lymph-spaces  into  the  gland-cells.  The  produc- 
tion of  heat  in  secretion  to  a  certain  extent  favors  this  view,  since  it 
has  been  found  that  the  temperature  of  the  saliva  in  the  salivary  duct 
may  be  one  degree  or  more  higher  than  that  of  the  blood.  Secretion  of 
saliva  can,  thus,  not  be  a  process  of  mere  mechanical  filtration;  for  not 
only  do  we  find,  as  alread}'  mentioned,  the  greater  pressure  on  the  side 
of  the  salivary  duct,  and  an  actual  formation  of  heat  in  the  secretion, 
but  the  secretion  may  even  take  place  in  the  absence  of  the  circulation. 
Thus,  if  the  chorda  tympani  is  isolated  in  the  rabbit,  and  the  animal 
then  rapidly  decapitated,  the  flow  of  saliva  may  still  take  place  on 
stimulation  of  the  chorda,  and  it  ma}T  produce  in  a  few  moments  double 


302  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

the  weight  of  the  gland  in  saliva,  even  although,  of  course,  the  circulation 
has  been  arrested.  Then,  again,  the  action  of  various  drugs  on  the 
salivary  gland  show  the  independence,  to  a  certain  degree,  of  the  vaso- 
inotor  and  secretory  effects  of  the  stimulation  of  the  chorda  tympani. 
If  fifteen  milligrammes  of  atropine  in  solution  are  injected  into  the 
jugular  vein  of  a  dog  and  the  chorda  tympani  nerve  then  stimulated, 
there  is  no  flow  of  saliva,  but,  on  examining  the  gland,  the  vaso-motor 
phenomena  which  were  present  under  the  same  circumstances  before  the 
atropine  was  injected  may  be  seen.  In  other  words,  vascular  dilatation 
follows  stimulation  of  the  chorda  tympani  nerve  after  the  administration 
of  atropine,  while  the  secretion  of  saliva  is  prevented.  Then,  again,  by 
means  of  pilocarpine  the  paralyzing  effect  of  the  atropine  may  be  antag. 
onized  and  the  gland  may  be  made  to  secrete.  The  dose  of  pilocarpine 
which,  when  introduced  into  the  general  circulation,  would  be  able  to 
remove  the  effects  of  atropine  would  probably  be  fatal  to  the  animal.  If, 
however,  the  drug  is  allowed  to  enter  the  circulation  of  the  gland,  a 
much  smaller  quantity  will  be  efficient  without  danger  to  the  animal. 
Thus,  if  seventeen  milligrammes  of  pilocarpine  are  injected  into  the  sub- 
maxillary  duct  after  atropine  poisoning  and  the  chorda  tympani  then 
irritated,  a  slight  secretion  will  be  produced,  passing  off  again  as  the 
stronger  effect  of  the  atropine  makes  itself  felt.  Then,  again,  the  activity 
of  the  secreting  cells  may  be  paralyzed,  and  the  circulatory  changes 
produced  by  certain  drugs,  such  as  sodium  carbonate  in  5  per  cent, 
solution  or  hydrochloric  acid  in  y1^  per  cent.,  injected  into*  the  duct;  but 
as  the  increased  pressure  leads  to  trans udat ion,  and  as  the  cells  cannot 
secrete,  oedema  of  the  gland  is  rapidly  produced  when  the  chorda  is 
stimulated.  Further,  quinine  injected  into  the  duct  influences  vaso- 
motor  changes,  although  no  secretion  is  produced  even  though  the 
secretory  fibres  of  the  chorda  are  not  paralyzed.  Evidently,  then,  the 
chorda  tympani  nerve  must  contain  two  sets  of  fibres, — the  one  vaso- 
dilator, not  paralyzed  by  atropine,  and  the  other  the  secretory  fibres, 
paralyzed  by  that  poison.  It  is  only  by  the  existence  of  a  class  of  nerves 
which  act  through  calling  into  activit^y  the  protoplasmic  energy  of  the 
secreting  epithelial  cells  that  these  effects  can  be  explained.  When  the 
chorda  is  irritated  two  sets  of  impulses  travel  along  the  nerve,  one 
impulse  acting  on  the  blood-supply  of  the  glands,  while  the  other  acts 
on  the  secretory  elements  of  the  epithelial  cells  in  a  manner  analogous 
to  that  which  occurs  when  a  motor  nerve  going  to  a  muscle  is  irritated — 
the  muscle  contracts  through  the  stimulation  of  the  contractile  elements 
of  the  muscle-cells,  and  the  blood-vessels  dilate  through  vaso-motor  influ- 
ence. The  result  in  both  cases  is  probably  of  an  electrolytic  nature, 
with  the  production  of  acid  or  alkaline  decomposition  products,  and 
these  may  serve  as  stimuli  to  the  cells  themselves,  in  the  same  way 


DIGESTION   IN   THE   MOUTH. 


303 


Vlf. 


DUCT. 


as  when  the  same  products  (compounds  of  lactic  or  phosphoric  acid 
with  lime)  are  directly  brought  into  contact  with  the  muscles.  Indeed, 
we  may  carry  the  parallelism  still  further,  for  we  know  that  curare, 
b}^  destroying  the  irritability  of  the  motor  nerves,  will  prevent  contrac- 
tion of  all  the  muscles  when  their  nerves  are  stimulated,  in  the  same 
manner  that  atropine  will  prevent  the  secretion  of  the  gland  when  its 
secretory  nerve  is  stimulated.  In  both  instances  the  vaso-motor  phe- 
nomena remain. 

In  the  case  of  the  parotid  gland  the  circulation  during  secretion 
undergoes  the  same  changes  as  in  the  case  of  the  submaxillary.  Here, 
also,  secretory  and  circulatory 
nerves  have  been  determined.  Vaso- 
constrictor fibres  have  been  found  in 
the  sympathetic  branches  distrib- 
uted to  the  parotid  gland,  while 
the  glosso-pharyngeal,  according  to 
Heidenhain,  contains  fibres  whose 
stimulation  leads  to  a  dilatation  of 
the  parotid  blood-vessels.  Both  the 
facial  and  the  glosso-phaiyngeal 
nerves  contain  fibres  whose  stimu- 
lation leads  to  parotid  secretion, 
and  if  the  auriculo-temporal  nerve 
is  stimulated  the  secretion  at  once 
commences  ;  if  divided  the  secretion 
stops.  It  has  been  found,  however^ 
that  the  trigeminal  nerve  is  not  the 
source  of  these  secretory  fibres,  for 
when  the  trigeminal  is  stimulated 
within  the  cranium  no  parotid  secre- 
tion results.  They  are  consequently 
derived  from  the  facial  nerve,  and 
when  this  latter  nerve  is  stimulated 
within  the  cranium  parotid  secretion 
results  (Fig.  124).  The  passage  of  these  glandular  fibres  from  the  facial 
into  the  auriculo-temporal  nerve  has  been  explained  in  the  following 
manner  by  Bernard  :  If  the  facial  nerve  is  divided  at  its  exit  from  the 
stylo-mastoid  foramen,  and  the  central  end  divided,  parotid  secretion  is 
produced,  while  stimulation  of  its  peripheral  extremity  is  without  effect. 
The  secretory  fibres  do  not  pass  through  the  chorda  tympani,  as  was 
formerly  believed,  for  section  of  the  chorda  in  the  tympanum  does  not, 
as  in  the  case  of  submaxillary  secretion,  arrest  the  flow  of  parotid 
saliva.  Nor  do  they  pass  through  the  greater  superficial  petrosal  nerve, 


FIG.  123.— DIAGRAM  OF  NERVES  SUPPLY- 
ING THE  PAROTID  GLAND.    (Yeo.) 

The  dark  lines  indicate  the  course  of  the  nerves  of 
the  gland.  V,  inferior  division  of  fifth  cranial  nerve  and 
its  (AT)  auriculo-temporal  branch;  VII,  portio  dura; 
SCG,  superior  cervical  ganglion  sending  a  branch  to  the 
carotid  plexus  around  the  artery. 


304  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

for  extirpation  of  the  ganglion  of  Meckel  is  without  effect  on  the  parotid 
secretion.  As  a  consequence,  it  must  be  concluded  that  these  fibres 
pass  to  the  lesser  superficial  petrosal  nerve,  which  anastomoses  with 
the  otic  ganglion.  For  it  has  been  found  that  extirpation  of  the  otic 
ganglion,  or  section  of  the  lesser  superficial  petrosal  nerves,  arrests  sali- 
vation. According  to  Heidenhain,  the  glosso-pharyngeal  nerve  also  fur- 
nishes secretory  fibres  to  the  parotid,  the  fibres  passing  from  this  nerve 
to  the  nerve  of  Jacobsohn,  and  thence  into  the  lesser  superficial  petrosal. 
Relations  between  the  parotid  secretion  and  the  excitation  of  the  cere- 
bral glandular  nerves  seem  to  be  about  the  same  as  for  the  submaxillary 
gland.  The  proportion  of  solids  and  salts  augments  with  the  intensity 
of  the  stimulation,  while  the  proportion  of  organic  matter  increases  as 
long  as  the  glands  are  fresh,  but  diminishes  if  they  become  exhausted. 

The  secretory  influence  of  the  sympathetic  on  the  parotid  has  been 
the  subject  of  considerable  controversy ;  the  general  opinion  being  that 
the  sympathetic  influences  the  parotid  secretion  only  by  diminishing 
the  calibre  of  the  capillaries.  Certain  authors  have,  however,  held  that 
in  certain  species  excitation  of  the  sympathetic  produces  a  temporary 
increase  in  the  parotid  secretion.  According  to  Eckhard,  the  parotid 
of  the  sheep  continues  to  secrete  even  after  section  of  all  its  nerves, 
being  thus  analogous  to  the  secretion  poured  out  by  the  salivary  gland 
after  section  of  the  chorda  tympani. 

From  the  above  facts  it  appears  that  the  secretion  of  saliva  is  com- 
posed of  two  phases, — the  first,  a  preparatory  stage ;  the  second,  the 
essential  stage. 

The  preliminary  stage  of  salivary  secretion  is  that  of  filtration  of 
serum  of  the  blood  into  the  lymph-spaces  around  the  acini  of  the  salivar}^ 
gland.  This  act  is  entirely  under  the  control  of  the  vascular  nerves, 
which,  by  changing  the  calibre  of  the  blood-vessels,  and  by  thus 
increasing  or  decreasing  the  pressure  within  them,  facilitate  or  hinder 
the  transudation  of  serum.  The  influence  of  the  circulation  on  secretion 
is,  therefore,  indirect.  When  the  small  arteries  of  the  glands  dilate 
more  blood  passes  through  them,  a  larger  amount  of  nutritive  material 
filters  through  into  the  lymph-spaces,  and  is  appropriated  by  the  gland- 
cells,  whose  vital  processes  must  be  thus  quickened. 

The  second  stage  is  that  of  true  secretion  through  the  action  of  the 
gland-cells,  and,  as  has  been  already  shown,  is  independent  of  the 
circulation  and  is  under  the  control  of  the  secretory  nerves.  The  nature 
of  these  changes  occurring  in  the  act  of  secretion  within  the  gland-cells 
is  to  a  certain  extent  rendered  explainable  from  the  study  of  the  histo- 
logical  changes  which  occur  within  the  gland-cells.  As  has  been  already 
stated,  the  salivary  glands  ma3r  be  divided  into  two  types, — the  serous 
and  the  mucous  t}rpes.  This  distinction,  which  has  only  as  yet  been 


DIGESTION   IN   THE   MOUTH.  305 

based  upon  the  character  of  the  secretion,  is  farther  supported  by  actual 
morphological  differences  in  the  character  of  the  gland-cells.  In  the 
serous  glands,  which  are  exemplified  by  the  parotid  of  man  and  other 
mammals,  the  acini  are  lined  by  a  layer  of  granular  cells,  which,  in  the 
quiescent  condition,  completely  fill  the  acinus  (Figs.  124  and  125).  The 
nucleus  under  such  conditions  is  barely  distinguishable,  its  presence 
being  obscured  by  the  large  number  of  granules  present.  As  secretion 
takes  place,  these  granules  disappear,  seemingly  being  broken  up  and 
used  to  form  the  secretion.  During  activity,  therefore,  the  outer  portion 
of  each  cell  of  a  serous  gland  becomes  clear  and  transparent,  and  this 
condition  gradually  spreads  toward  the  centre  of  the  cell.  These 
changes  have  been  most  studied  in  the  parotid  of  the  rabbit.  When  at 
rest  the  nucleus  is  small,  irregular,  and  devoid  of  nucleoli.  When  caused 
to  secrete  by  stimulation  of  the  sympathetic  nerve  the  cells  become 


FIG.  125.— PAROTID  OF  RABBIT  AFTER  IRRI- 

FIG.   124.— PAROTID    OF    RABBIT    IN    THE  TATION  OF  THE  SYMPATHETIC  NERVE. 

RESTING  CONDITION.    (Heidenhain.)  (Heidenhain.) 

smaller,  the  nuclei  become  large  and  round,  while  the  nucleoli  may  even 
be  detected,  and  the  whole  cell  stains  more  deeply  with  carmine.  It  thus 
appears  that  -during  rest  granules  are  manufactured,  which  disappear 
during  the  activity  of  the  cell. 

In  the  mucous  glands,  of  which  the  submaxillary  or  orbital  glands  of 
the  dog  may  be  taken  as  a  type,  the  appearances  are  more  complex.  When 
a  microscopic  preparation  is  prepared  of  the  resting  salivary  gland,  the 
cells  only  stain  with  difficulty  with  carmine,  this  apparently  being  due  to 
the  presence  of  a  large  amount  of  mucin-like  substance  which  occupies 
the  entire  cell  with  the  exception  of  a  small  amount  of  unchanged  proto- 
plasm, readily  staining  with  carmine,  which  remains  around  the  nucleus. 
In  such  a  section,  prepared  of  the  resting  gland,  in  each  acinus  will  usually 
be  found  one  or  more  half-moon  shaped  cells  lying  outside  the  muciparous 
cells,  which  readily  stain  with  carmine,  which  possess  two  or  more  nuclei, 

20 


306 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


and  seem  to  be  cells  in  a  state  of  active  growth  and  multiplication. 
When  a  similar  section  is  prepared  from  a  salivary  gland  which  has  been 
exhausted  by  prolonged  stimulation  of  the  chorda  tympani  nerve,  the 
muciparous  cells  will,  as  a  rule,  have  largely  disappeared.  All  the  cells 
are  now  small  in  size  and  all  stain  deeply  (Figs.  126,  127,  and  128).  It 
would  appear  from  this  that  in  such  a  gland  stimulation  of  the  chorda 
nerve  leads  to  a  discharge  of  mucin,  or  to  a  total  breaking  down  of  the 


FIG.  126.— ORBITAL  GLAND  OF  THE  DOG  IN  THE  RESTING  CONDITION.    (Heidenhain.) 


FIG.  127.— ORBITAL  GLAND  OF  DOG— COMMENCE- 
MENT OF  CHANGES  DURING  ACTIVITY,  AFTEK 
LADVOVSKY.  (Heidenhain.) 


FIG.  128.— ORBITAL  GLAND  OF  DOG- 
HIGHEST  DEGREE  OF  CHANGE  IN 
ACTIVITY,  AFTER  LADVOVSKY. 
(Heidenhain. ) 


entire  cell,  whose  place  is  then  taken  by  the  new,  rapidly  growing,  half- 
moon  cells.     Both  statements  are  probably  correct. 

It  is  thus  seen  that  the  secretion  is  the  result  of  the  activity  of  the 
protoplasm  of  the  secreting  cell.  During  rest  the  mucous  gland  manu- 
factures mucin  at  the  expense  of  its  protoplasm.  When  such  a  gland 
secretes,  the  mucin  is  discharged  and  new  protoplasmic  cells  are  rapidly 


DEGLUTITION.  307 

developed.  In  the  case  of  tine  serous  cells  the  changes  are  not  so 
readily  recognizable,  since  the  microscopic  changes  are  less  marked,  but 
the  probability  is  that  the  same  sort  of  processes  occur.  In  the  actual 
formation  of  the  secretion  we  have  thus  two  processes  concerned.  We 
have  the  development  of  mucin  in  the  muciparous  cells,  and  of  ptyalin. 
During  activity,  from  dilatation  of  the  capillaries,  the  blood-serum,  more 
or  less  modified  in  composition,  reaches  the  acini,  and  from  there  passes 
into  the  glandular  cells,  while  at  the  same  time  the  fluid  filters  from  these 
cells  into  the  duct,  and  so  constitutes  secretion.  The  inorganic  con- 
stituents of  secretion  are,  therefore,  removed  from  the  blood  by  a  simple 
process  of  osmosis,  or  filtration,  while  the  organic  constituents  are  the 
results  of  active  manufacturing  processes  occurring  within  the  proto- 
plasmic cell-contents. 

V.   DEGLUTITION. 

By  the  term  deglutition  is  meant  the  various  co-ordinated  muscular 
movements  which  result  in  the  passage  of  the  food  from  the  mouth  to 
the  stomach. 

The  act  of  deglutition  m&y  be  divided  into  three  different  stages. 
In  the  first  stage,  which  occurs  in  the  mouth,  the  bolus  of  food  passes 
to  the  isthmus  of  the  fauces,  in  the  second  stage  it  passes  through  the 
pharynx,  and  in  the  third  stage  it  traverses  the»O3sophagus. 

When  the  food  has  been  sufficient!}'  masticated  it  is  gathered  into  a 
bolus  by  the  contraction  of  the  muscles  of  the  tongue,  the  tip  of  the 
tongue  being  raised  b}>-  the  intrinsic  muscles  of  the  tongue,  aided  by  the 
stylo-glossus,and  the  bolus  passes  back  between  the  tongue  and  the  hard 
palate  to  the  anterior  portions  of  the  fauces  (Fig.  129).  This  transferring 
of  food  from  the  mouth  to  the  pharynx  occurs  when  the  teeth  are  in 
contact,  since  the  jaws  must  be  closed  to  afford  support  to  the  hyoid 
muscles,  which  we  will  find  to  be  concerned  in  the  later  steps  of  the 
process,  and  in  the  herbivorous  animals  is  accomplished  so  rapidly  that 
110  more  marked  duration  of  closure  of  the  jaws  can  be  detected  than  at 
any  other  time.  When  the  bolus  is  very  large  mastication  ceases  at  the 
moment  of  deglutition,  as  in  carnivora  and  other  animals  that  swallow 
the  entire  contents  of  the  mouth  at  one  movement.  This  first  stage  of 
deglutition  is  entirely  within  the  control  of  the  will,  and  may  be  pro- 
longed or  accelerated,  and  the  movements  of  the  bolus  are  perceptible 
to  the  sensory  nerves  of  the  part.  When  the  bolus  has  once  been  placed 
upon  the  dorsum  of  the  tongue,  the  tip,  middle,  and  root  of  the  tongue 
are  successively  pressed  against  the  hard  palate,  and  the  contents  of  the 
mouth  are  thus  propelled  toward  the  pharynx ;  an  active  contraction  of 
the  mylo-hyoid  muscles  then  takes  place,  as  may  be  recognized  by  the 
finger  placed  below  the  lower  jaw,  the  dorsum  of  the  tongue  is  raised  up, 


308 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


and  the  bolus  of  food  forced  from  the  mouth  into  the  pharynx.  Almost 
at  the  same  time  the  hyo-glossal  muscles  also  begin  contracting  and, 
especially  those  portions  which  are  attached  to  the  cornua  of  the  hyoid, 
cause  the  free  surface  of  the  tongue,  which  at  rest  looks  upward  and 
backward,  to  move  backward  and  downward  upon  the  epiglottis  and 
mechanically  close  the  glottis.  The  rapid  narrowing  of  the  space  between 
the  mylo-hyoids  and  the  palate  which  is  thus  brought  about  also  rapidly 
raises  the  pressure  there.  This  effect  is  increased  by  the  pull  of  the 
hyo-glossal  muscles,  which  gives  the  tongue  a  backward  and  downward 


FIG.  129.— MEDIAN  SECTION  OF  THE  HUMAN  HEAD,  AFTER  HENLE.    (Mayer.) 

Vp,  the  position  of  the  soft  palate  during  rest ;  1,  orifice  of  Eustachian  tube ;  Vcl  and  Vc2,  first  and 
second  cervical  vertebras;  E,  epiglottis;  G,  glo 


cartilage ;  2,  hyoid  bone. 


3ttis ;  4,  arytenoid  cartilage  ;  5,  cricoid  cartilage ;  3,  thyroid 


movement.  Thus,  liquids  and  soft  foods  are  squirted  down  the  entire 
pathway  to  the  stomach  before  contractions  of  the  pharyngeal  or 
oesophageal  muscles  can  manifest  themselves  (Meltzer).  Fragments 
which  happen  to  remain  in  the  pha^nx  are  sent  down  later  by  the  suc- 
ceeding contraction  of  the  constrictors  and  with  a  slowness  peculiar  to 
these  muscles  (Fig.  130).  When  the  bolus  has  passed  the  anterior  pala- 
tine arches  its  return  to  the  mouth  is  prevented  by  contraction  of  the 
palato-glossi  muscles  which  lie  in  the  anterior  pillar  of  the  fauces,  and, 


DEGLUTITION. 


309 


coming  together,  lie  together  like  side-screens  or  curtains  (Landois), 
meet  the  raised  dorsum  of  the  tongue,  and  so  form  a  partition  between 
the  mouth  and  pharynx ;  the  occlusion  is  still  further  assisted  by  the 
contraction  of  the  stylo-glossi  muscles,  which  elevate  the  tongue  and 
press  it  against  the  palate. 

The  second  stage  of  deglutition  then  commences,  and  the  bolus  of 
food  is  now  entirely  beyond  the  control  of  the  will,  and  must  pass  down 
the  pharynx  into  the  oesophagus,  its  ejection  into  the  mouth  again  only 


FIG.  130.— POSITION  OF  THE  SOFT  PALATE  DUKING  THE  SECOND  STAGE  OF 
THE  ACT  OF  DEGLUTITION,  AFTER  FIAUX.    (Mayer.) 

A,  soft  palate ;  C,  bolus :  E,  orifice  of  Eustachian  tube :  B,  tongue ;  G,  pharynx ;  H,  epiglottis ;   I,  oesophagus. 

being  rendered  possible  by  an  active  coughing  or  gagging  movement. 
Its  downward  movement  during  this  stage,  which  lasts  while  the  food  is 
passing  from  the  anterior  pillars  of  the  fauces  to  the  entrance  of  the 
03sophagus,  is  still  attended  by  sensation. 

The  muscular  movements  of  the  second  stage  of  deglutition  are  much 
more  complex  than  in  the  first.  The  phar}aix  communicates  with  three 
cavities, — the  posterior  nasal  chamber,  the  O3sophagus,  and  the  larynx. 
Special  mechanisms  exist  which  direct  the  food  downward  toward 


310 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


the  opening  of  the  oesophagus  and  hinder  its  passage  into  the  nasal 
chambers  and  windpipe.  As  soon  as  the  bolus  of  food  reaches  the 
anterior  palatine  arches  the  soft  palate  is  raised  by  the  contraction  of 
the  levator-palati  muscles,  and  rendered  tense  and  directed  backward 
toward  the  posterior  walls  of  the  pharynx,  with  which,  in  many  animals, 
as  in  the  horse,  it  comes  in  actual  contact  (Fig.  131),  and  at  the  same 
time  the  palato-pharyngeal  muscles,  which  lie  in  the  posterior  arches  of 
the  fauces,  contract.  These  muscles  have  a  bony  insertion  in  the  posterior 
wall  of  the  pharynx,  and  then  are  inserted  into  the  soft  palate.  The 
action  of  the  levator-palati  muscles  has  the  effect  of  giving  these  muscles 
fixed  points  of  support.  In  their  condition  of  rest  they  form  a  curved 
line  on  each  side  from  the  centre  to  the  back  of  the  pharynx.  When 


FJG.  131.—  ANTERO-POSTERIOB  SECTION  OF  THE  HEAD  OF  THE  HORSE,  SHOW- 
ING THE  ENTIRE  MOUTH,  PHARYNX,  AND  NASAI,  CAVITIES.    (Gamgee.) 

1,  genio-hyoglossus;  2,  genio-hyoideus  ;  3,  section  of  the  soft  palate;  4,  pharynx  ;  5,  oesophagus  ;  6, 
guttural  pouch  ;  7,  pharyngeal  opening  of  the  Eustachian  tube  ;  8,  cavity  of  the  larynx  ;  9,  ventricle  of 
the  larynx;  10,  trachea;  11,  superior  turbinated  bone:  12,  inferior  turbinated  bone;  13,  ethmoid  cells; 
14,  portion  of  the  cranial  cavity  which  lodges  the  brain  proper;  15,  portion  of  the  same  which  lodges  the 
cerebellum  ;  16,  falx  cerebri  ;  17,  tentorium  ;  18,  upper  lip  ;  19,  lower  lip. 


these  muscles  contract,  downward  motion  of  the  soft  palate  having  been 
prevented  by  the  action  of  the  levator-palati  muscles  and  approxima- 
tion of  their  origin  and  insertion  being  thus  prevented,  the  effect  will 
be  to  form  a  straight  line  between  these  two  points.  Merkel  states  that 
the  inferior  portions  of  the  phaiyngo-palatine  muscles  cross  in  the 
middle  line  of  the  posterior  wall  of  the  pharynx,  and  thus  act  as  a 
sphincter  in  shutting  off  the  nasal  portion  of  the  pharynx,  the  two 
muscles  forming  a  circular  muscle,  like  the  orbicularis  oris.  The  dis- 
tribution of  these  fibres  is  shown  in  Fig.  132.  As  a  consequence,  the 
posterior  pillars  of  the  fauces  will  come  together  in  the  same  way  as 
the  anterior  pillars  to  form  a  screen  or  curtain,  which  will  shut  off  the 


DEGLUTITION.  311 

pharynx  from  the  posterior  nasal  fossa,  the  uvula  serving  still  further 
to  close  the  chink  between  their  two  free  borders.  An  inclined  plane 
is  thus  formed,  down  which  the  bolus  is  pressed  by  the  backward  move- 
ment of  the  tongue.  At  this  stage  the  elevation  of  the  soft  palate 
may  readily  be  demonstrated  by  placing  a  light  straw  along  the  floor 
of  the  nose,  so  that  its  posterior  end  rests  on  the  soft  palate  (Landois). 
If  now  a  motion  of  swallowing  is  made,  the  end  which  projects  from  the 
nose  will  descend,  showing  an  elevation  of  the  end  which  rests  on  the 
soft  palate.  At  the  same  time  there  is  a  distinct  rise  of  pressure  within 
the  nasal  chambers.  This  may  be  shown  by  introducing  a  water  ma- 
nometer into  one  nostril  and  closing  the  other  just  before  swallowing. 
As  the  food  passes  behind  the  anterior  palatine  arch  it  is  subjected 
to  the  action  of  the  pharyngeal  constrictor  muscles,  which  propel  it 
downward.  The  longitudinal  fibres  of  the  pharyngeal  constrictors  con- 
tract and  cause  an  elevation  (or  more  strictly  shortening)  of  the  walls 


FIG.  132.— DISTRIBUTION  OF  FIBRES  OF  THE  PALATO-PHARYNGEAT,  MUSCLES.   (Luschka.) 

A  anterior,  B  posterior  view. 

of  the  pharynx,  together  with  the  elevation  of  the  larynx,  this  elevation 
being  produced  by  a  contraction  of  the  stylo-pharyngeal  and  palato- 
pharj-ngeal  muscles,  the  lower  jaw  coming  in  contact  with  the  upper 
jaw  through  the  action  of  the  muscles  of  mastication.  The  food  then 
passes  within  the  grasp  of  the  upper  constrictor  of  the  pharynx,  which, 
contracting,  serves  to  squeeze  the  bolus  of  food  downward,  passage 
into  the  nasal  chamber  being  prevented  by  the  mechanism  above  alluded 
to,  and  the  bolus  being  propelled  downward  by  successive  contraction 
of  the  upper,  lower,  and  middle  constrictors  of  the  pharynx  until  it 
passes  into  the  oesophagus.  The  elevation  of  the  larynx  occurs  when 
the  bolus  enters  the  pharynx,  and  is  due  to  the  action  of  the  genio-hyoid 
and  mylo-hyoid  muscles.  It  is  very  perceptible  in  man,  less  so  in  animals 
in  which  the  larynx  is  very  near  or  very  far  from  the  base  of  the  skull, 


312  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

as  the  deer,  is  very  slight  in  the  horse  and  most  ruminants,  and  has  more 
of  a  forward  motion,  serving  simply  to  bring  the  larynx  beneath  the 
base  of  the  tongue.  The  elevation  of  the  larynx  serves  partly  to  prevent 
the  passage  of  food  into  the  larynx.  As  the  larynx  is  elevated  the 
arytenoid  cartilages  and  both  true  and  false  vocal  cords  are  approximated, 
and  as  the  thyroid  cartilage  ascends  by  the  action  of  the  laryngeal 
muscles  the  epiglottis  is  depressed  to  cover  the  glottis.  In  this  latter 
operation  the  depression  of  the  epiglottis  is  a  passive  and  not  an  active 
movement,  the  depression  being  due  not  to  an  action  of  any  intrinsic 
muscles,  but  to  the  ascent  of  the  larynx  beneath  the  epiglottis,  and  the 
mechanical  pressing  downward  of  the  epiglottis  by  the  weight  of  the 
bolus  of  food  and  the  descent  of  the  root  of  the  tongue.  The  epiglottis 
is  not,  however,  essential  to  the  prevention  of  the  entrance  of  food 
into  the  air-passages,  since  excision  of  the  epiglottis  in  the  dog,  or  its 
removal  by  disease  in  man,  does  not  interfere  with  normal  movements 
of  deglutition.  Colin  has  found,  by  inserting  a  finger  into  the  larynx 
through  an  opening  in  the  trachea  of  a  horse  which  was  swallowing,  that 
the  larynx  at  the  moment  of  swallowing  was  suddenly  elevated  and 
moved  anteriorly  toward  the  base  ef  the  tongue,  the  vocal  cords  closed, 
and  the  arytenoid  cartilages  came  in  contact  with  each  other.  Ity  these 
means  food  is  prevented  entering  the  larynx.  He  also  found,  by  making 
a  fistula  in  the  upper  part  of  the  oesophagus  of  an  ox  and  inserting  a 
finger,  that  at  each  movement  of  swallowing  the  epiglottis  was  depressed, 
and  the  entrance  to  the  oesophagus  elevated  and  thus  approximated  to 
the  isthmus  of  the  fauces.  In  the  horse  the  isthmus  of  the  fauces  is 
very  narrow,  and  the  bolus  passes  with  difficult}7,  even  if  not  very  large, 
and  is  often  arrested  behind  the  larynx,  and  yet  does  not  cause  coughing. 
This  is  often  seen  after  giving  a  bolus  to  a  horse,  particularly  in  cases  of 
angina.  In  ruminants  the  isthmus  of  the  fauces  is  large  and  the  phaiynx 
is  ample,  and  when  the  food  sticks  in  the  throat  in  these  animals  it  is 
usually  in  the  cervical  or  thoracic  portions  of  the  gullet,  which  is  also 
the  locality  where  the  food  is  apt  to  be  arrested  in  the  pig. 

In  those  animals  which  habitually  swallow  their  food  while  the  head 
is  bent  forward,  the  digastric,  in  addition  to  its  functions  in  depressing 
the  lower  jaw,  is  also  an  aid  to  deglutition.  Where,  as  in  reptiles,  birds, 
and  most  mammals,  the.  position  of  the  mouth  with  respect  to  the 
oesophagus  during  the  act  of  swallowing  the  food  is  almost  in  the  same 
right  line,  deglutition  is  easily  effected  by  the  mylo-  and  genio-hyoid 
muscles  drawing  the  hyoid  bone  and  larynx  forward  and  upward  so  as 
to  allow  the  masticated  mass  to  get  behind  them,  and  so  bring  it  within 
the  grasp  of  the  pharyngeal  muscles ;  but  in  those  animals  which  feed 
while  in  the  erect  or  semi-erect  position,  and  the  head  bent  forward  so 
that  the  cavity  of  the  mouth  is  at  right  angles  with  the  oesophagus,  it  is 


DEGLUTITION.  313 

evident  that  deglutition  must  be  a  much  more  complex  action.  In  that 
position  the  mylo-  and  genio-hyoid  muscles  are  relaxed,  and  cannot  act 
efficiently  in  drawing  the  hyoid  bone  upward  and  forward  so  as  to 
allow  the  masticated  mass  to  pass  into  the  oesophagus,  into  which  it  has 
to  pass,  in  fact,  around  an  angle.  The  difficulty  is  removed  by  the  con- 
nection of  the  digastric  muscle  with  the  hyoid  bone.  This  muscle, 
during  the  act  of  deglutition,  causes  the  hyoid  bone,  larynx,  and  base  of 
the  tongue  to  move  through  a  segment  of  a  circle,  the  anterior  part  of 
the  muscle  drawing  these  parts  forward ;  they  are  then  elevated  by  the 
joint  action  of  the  anterior  and  posterior  bellies,  and  finally  drawn  back- 
ward l>y  the  posterior  bellies,  so  as  to  force  the  masticated  mass  into 
the  oesophagus. 

The  second  stage  of  deglutition  is  facilitated  by  the  mucous  secre- 
tions of  the  parts  concerned.  This  secretion  ma}7  become  enormous,  as 
in  the  dromedary,  where  the  appendix  to  the  soft  palate  and  the  pharyn- 
geal  pouch  are  very  glandular.  In  all  animals  the  secretion  of  the 
mucous  membrane  of  the  mouth  and  pharynx,  aided  by  the  salivary 
secretion,  is  amply  sufficient  to  lubricate  the  food,  so  as  to  render  deglu- 
tition possible.  It  was  already  noted  in  the  chapter  on  the  salivary 
secretion  that  the  quantity  of  saliva  poured  out  was  largely  dependent 
upon  the  character  of  the  food ;  or,  in  other  words,  the  drier  the  food 
the  greater  the  amount  of  lubricant  needed,  and,  therefore,  the  greater 
was  the  salivary  secretion. 

The  second  stage  of  deglutition  is  involuntary,  and  when  the  bolus 
of  food  has  passed  beyond  the  anterior  pillars  of  the  fauces  it  is  no 
longer  within  the  control  of  the  will,  and  can  only  be  returned  to  the 
mouth  b}7  vomiting  or  violent  coughing.  Therefore,  in  giving  pills  or 
balls  to  animals  the}7  have  to  be  carried  mechanically  by  the  hand  behind 
the  pillars  of  the  fauces;  they  are  then  carried  down  to  the  stomach  by 
the  involuntary  contraction  of  the  pharynx  and  oesophagus. 

The  third  stage  of  deglutition  occurs  after  the  food  has  passed 
through  the  pharynx  and  has  entered  into  the  oesophagus.  This  stage 
of  deglutition  is  much  more  prolonged  than  the  two  preceding  stages, 
and  in  the  larger  domestic  animals  the  passage  of  the  food  by  the 
oesophagus  may  be  followed  by  the  eye  and  touch.  Where  the  secretion 
of  saliva  is  scanty  the  duration  of  this  stage  becomes  prolonged,  and 
sometimes,  as  in  the  horse,  the  food  ma}7  become  arrested  in  the  lower 
cervical  portion  of  the  oesophagus  until  pushed  on  by  the  next  succeed- 
ing bolus. 

The  rapidity  of  motion  in  the  oesophagus  varies.  Liquids  and  very 
soft  foods  are  very  rapidly  swallowed,  being  actually  squirted  through 
the  oesophagus  ;  dry  forage  is  swallowed  very  slowly.  In  the  horse  the 
boluses  have  to  be  very  small,  from  the  narrow  character  of  the  gullet 


314  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

in  these  animals.  Hence,  if  the  bolus  of  food  is  larger  than  three  or  four 
centimeters  in  diameter  it  is  apt  to  be  arrested.  In  the  ox  boluses  double 
the  size  pass  without  difficulty. 

When  once  the  alimentary  bolus  is  within  the  grasp  of  the  muscles 
of  the  oesophagus  it  moves  onward  with  considerable  force.  Mosso, 
in  his  experiments  made  on  the  dog,  found  that  even  when  the  bolus 
of  food  was  held  back  by  a  weight  of  four  hundred  and  fifty  grammes 
deglutition  was  not  interfered  with."  When  once  the  bolus  of  food 
reaches  the  upper  part  of  the  oesophagus  the  pharynx  falls,  and  the  bolus 
traverses  the  length  of  the  oesophagus  under  the  influence  of  the  succes- 
sive contractions  of  the  circular  and  longitudinal  muscular  fibres.  The 
longitudinal  fibres  contract  first,  and  draw  up  the  oesophagus  to  meet  the 
advancing  bolus,  which  is  pushed  down  by  the  contractions  of  the  annular 
fibres  behind  it.  Gravity  is  entirety  without  influence  on  the  motions  of 
deglutition,  as  swallowing  occurs  equally  well  even  when  the  head  is  on 
a  lower  plane  than  the  entrance  of  the  oesophagus  into  the  stomach. 

The  third  stage  of  deglutition  is  involuntary  and  is  unattended  by 
sensation,  though  pain  may  be  intense  when  too  large  a-  bolus  or  a  hard, 
irregular  mass  is  swallowed  ;  so,  also,  very  hot  or  very  cold  substances 
may  be  recognized  in  their  passage  through  the  oesophagus  by  the  sensa- 
tions which  they  occasion.  As  a  rule,  however,  the  passage  of  food 
through  the  oesophagus  is  entirely  unattended  by  any  feeling.  Even 
acids  cause  but  little  sensation: 

That  deglutition  may  be  accomplished,  it  is  essential  that  there 
must  be  something  to  be  swallowed.  When  the  mouth  contains  saliva 
alone  the  motions  of  deglutition  may  be  made,  but  as  the  quantity  of 
fluid  in  the  mouth  decreases  deglutition  becomes  more  and  more  difficult, 
until  finally  it  is  impossible.  This  fact  indicates  the  reflex  nature  of 
the  motion  of  deglutition.  As  before  pointed  out,  a  reflex  action  re- 
quires the  presence  of  a  stimulus,  its  conduction  to  a  nerve-centre,  and 
the  transmission  of  motor  impulse  through  efferent  nerves  to  a  muscular 
fibre.  The  stimulus  for  deglutition  is  found  in  the  contact  of  food  with 
the  mucous  membrane  of  the  mouth,  pharynx,  and  oesophagus.  The 
sensory  nerves  come  from  the  trigeminal,  the  glosso-pharyngeal,  and  the 
superior  laryngeal  nerves.  Excitation  of  any  of  these  nerves  produces 
movements  of  deglutition. 

In  the  case  of  the  oesophagus  the  pneumogastric  is  the  sensor}^ 
nerve.  The  centre  of  the  movements  of  deglutition  is  found  in  the 
medulla  oblongata.  The  motor  nerves  are  the  glosso-pharyngeal,  sup- 
plying the  muscles  of  the  pharynx;  the  hypo-glossal,  supplying  the 
muscles  of  the  tongue ;  the  trigeminal  and  facial,  supplying  the  muscles 
of  mastication,  and  the  pneumogastric,  supplying  the  muscles  of  the 
and  oesophagus. 


DEGLUTITION.  315 

In  the  horse,  ass,  dog,  sheep,  and  ox  the  lower  parts  of  the  oesoph- 
agus are  supplied,  as  in  man  and  the  rabbit,  by  the  recurrent  fibres  of 
the  vagi ;  the  upper  portions  are,  however,  supplied  by  a  long  branch 
of  the  pharyngeal.  nerve  which  descends  in  the  walls  of  the  oesophagus 
as  far  as  the  thorax.  In  birds  a  similar  state  of  affairs  also  holds. 

Deglutition  may  be  excited  by  mechanical  contact  with  the  fauces 
in  an  animal  in  which  the  cerebrum  has  been  removed;  it  is  only 
necessary  that  the -medulla  remain  intact. 

Deglutition  of  liquids  is  performed  by  a  mechanism  which  is  almost 
similar  to  that  concerned  in  the  deglutition  of  solids.  The  palate  is  raised 
and  made  tense,  the  palato-pharyngeal  muscles  contract,  the  glottis  rises, 
the  epiglottis  descends,  the  pharynx  ascends,  and  the  gullet  contracts  as 
in  the  case  of  deglutition  of  solids,  the  difference  mainly  consisting  in 
the  rapidity  with  which  liquids  are  forced  through  the  oesophagus. 

The  motions  of  deglutition  of  liquids  may  be  very  rapid.  Thus,  in 
the  horse  sixty-five  to  ninet}r  motions  may  be  made  in  each  minute, 
each  swallow  carrying  one  hundred  and  fifty  to  two  hundred  and  fifty 
grammes  of  liquid. 

The  rapidity  of  deglutition  varies  according  to  the  animal  and  the 
nature  of  the-  food.  The  horse  eating  hay  swallows  thirty-five  boluses 
in  fifteen  minutes  after  having  fasted  for  some  time,  and  only  ten  or 
twelve  boluses  in  the  same  time  as  hunger  commences  to  be  appeased, 
the  weight  of  each  bolus  varying  from  fifty  to  one  hundred  grammes. 
In  swallowing  liquids  the  horse  moves  the  ears,  advancing  them  at  each 
act  of  deglutition,  at  the  same  time  closing  the  jaws.  The  masseters 
may,  therefore,  be  seen  to  move  under  the  skin,  and  even  the  eyes  to 
move  in  their  orbits.  In  ruminants  during  deglutition  the  ears  either 
remain  motionless  or  move  unequally.  Rhythmical  motion  of  these 
organs  as  seen  in  the  horse  is  absent  in  ruminants. 

The  act  of  deglutition  is  performed  as  described  above  in  all  air- 
breathing  animals.  In  all,  from  the  mammalia  down  to  the  amphibia, 
the  pharynx  communicates  with  the  nasal  chambers,  the  cavities  of  the 
ear  on  both  sides,  the  mouth,  larynx,  and  oesophagus. 

In  the  young  kangaroo,  while  still  retained  in  the  abdominal  pouch 
of  the  mother,  and  in  cetaceans,  the  upper  part  of  the  lar}Tnx  is  elongated 
and  projects  into  the  posterior  nares,  so  that  during  suckling  the  milk 
passes  down  each  side  without  any  risk  of  entering  the  air-passages  and 
without  interfering  with  respiration. 

In  fishes  which  respire  in  the  water  by  gills  the  pharynx  has  no 
communication  with  the  nasal  passage,  while  the  larynx  and  trachea  are, 
of  course,  absent.  Hence,  the  pharynx  is  here  a  mere  passage  leading 
from  the  mouth  to  the  oesophagus,  and  the  process  of  deglutition  is  con- 
sequently greatly  simplified. 


316  PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 


VI.  HUMINATION. 

In  most  animals  the  food  after  being  swallowed  enters  the  stomach 
sufficiently  comminuted  to  be  at  once  acted  on  by  the  gastric  juice.  In 
others,  though  imperfectly  triturated,  the  food  may  be  at  once  digested, 
while  in  a  third  case  the  food  is  returned  to  the  mouth  for  a  second 
mastication. 

The  first  of  these  cases  is  seen  in  carnivora  and  omnivora ;  the 
second  occurs  in  granivorous  birds  and  crustaceans,  where  mastication 
in  the  mouth  is  entirely  absent,  but  where,  as  will  be  seen  later,  the 
stomach  is  provided  with  an  accessory  organ,  the  gizzard,  which  is 
capable  of  crushing  and  grinding  the  food. 

The  third  case  is  seen  in  ruminants,  where  the  food  is  carried  to  the 
stomach  after  only  having  been  subjected  to  a  preliminary  and  partial 
mastication  in  the  mouth.  It  is  then  macerated  by  the  fluids  contained 
in  the  stomach,  and  is  again  regurgitated  to  the  mouth,  to  be  subjected 
to  the  final  and  complete  process  of  mastication.  . 

Rumination,  or  the  returning  of  food  from  the  stomach  to  the 
mouth  for  a  second  mastication,  is  peculiar  to  polygastric  herbivora.  It 
differs  from  vomiting  in  that  the  motion  is  perfectly  voluntary,  is  a  nor- 
mal physiological  process,  and  the  matters  regurgitated  are  again  swal- 
lowed without  leaving  the  mouth.  All  true  ruminants  have  a  multiple 
stomach,  although  all  animals  with  multiple  stomachs  are  not  ruminants. 
Thus,  in  the  bird  three  stomachs  may  be  described,  and  in  certain  ceta- 
ceans, as  well  as  in  certain  edents,  as  the  sloth,  the  stomach  may  be 
divided  into  a  number  of  different  compartments  and  yet  rumination  not 
take  place. 

The  habits  of  ruminant  animals  necessitate  some  process  by  which 
the  food  is  hastily  collected  in  a  capacious  paunch,  to  be  again  returned 
to  the  mouth  for  mastication.  Ruminant  animals  in  a  state  of  nature 
instinctively  rely  on  quickness  of  sight,  acuteness  of  hearing,  and  agility 
to  enable  them  to  elude  their  enemies.  With  a  powerful  prehensile 
tongue,  long  and  thick  tufts  of  grass  are  rapidly  carried  into  the  mouth 
and  as  rapidly  swallowed.  However  tough  the  herbage  may  be,  it  is 
slightly  broken  down  by  one  or  two  strokes  of  the  molar  teeth ;  it  then 
passes  through  the  gullet  into  the  capacious  compartments  which  receive 
the  name  of  stomachs,  but  which  are  in  reality  pouches  of  the  oesopha- 
gus, and  are  situated  between  the  latter  tube  and  the  true  stomach.  By 
this  arrangement  herbivorous  ruminants  are  therefore  enabled  to  rapidly 
stow  away  in  these  reservoirs  a  supply  of  food,  where,  on  the  approach 
of  danger,  it  maybe  retained  until  an  opportunity  offers  for  its  return 
to  the  mouth,  when  it  may  be  masticated  at  leisure.  The  stomach  of 


KUMINATION. 


317 


ruminant  animals  consists  of  the  following  parts:  the  oesophagus  opens 
into  the  rumen,  or  paunch,  which  communicates  \)y  an  opening  with  the 
reticulum,  or  water  bag,  this  again  with  the  third  stomach,  or  psalter, 
omasum,  or  many  plies,  which  finally,  by  a  small  opening,  communicates 
with  the  fourth,  or  true  stomach,  or  abomasum. 

The  histological  structure  of  these  compartments  varies  consider- 
ably. Only  the  fourth  stomach  can  be  compared  with  that  of  animals 
which  possess  but  a  simple,  single  stomach.  The  rumen  is  coated  with 
horny  epithelial  cells,  arranged  in  rows  in  a  manner  somewhat  similar  to 
the  epidermal  cells  of  the  skin  (Fig.  133).  The  similarity  is  further 


FIG.  133.— SECTION  OF  WALL,  OP  THE  RUMEN.    (EUenberger.) 

A,  horny  layer ;    B,  lower  epithelial  1  aver:  C.  papilla;:    D.  submucous  muscular  layer ;    E,  inner  muscular 
coat ;  F,  ganglia ;  G,  external  muscular  coat ;  H,  serous  coat. 

completed  in  that  the  submucous  connective  tissue  in  the  rumen  is  also 
elevated  into  papillae,  similar  to  those  found  in  the  thickness  of  the  skin. 
It  is  well  supplied  with  muscles,  and  the  muscular  fibres  in  the  sub- 
mucous  layer  are  tolerably  well  developed.  But  few  glands  are  to  be 
found  in  the  rumen,  and  these  are  simply  of  a  mucous  type,  while  acinous 
glands  pass  through  the  submucous  connective  tissue  down  to  the 
muscular  fibres  below.  The  cavity  of  the  paunch  or  rumen  is  by  far  the 
largest  of  the  four  stomachs,  and  constitutes  about  nine-tenths  of  the 
space  represented  by  the  ruminant  stomach. 


318  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

The  second  stomach  is  called  the  honey-comb  bag,  or  reticulum,  and 
in  its  histological  structure  differs  but  slightly  from  that  of  the  rumen. 
Its  interior  is  likewise  lined  with  horny,  epithelial  cells,  arranged  in 
layers,  and  the  inferior  layers  of  the  mucous  membrane  are  arranged  in 
similar  papillae.  The  reticulum  owes  its  name  to  the  peculiar  arrange- 
ment of  the  mucous  membrane  which  lines  it  in  small  cells  or  cavities 
not  communicating  with  each  other,  but  all  Opening  freely  into  the 
general  cavity. 

In  the  camel  and  llama  and  other  animals  of  the  desert  similar 
collections  of  cells  are  found  in  the  rumen  also.  In  these  animals  they 
consist  of  a  number  of  large  cells,  arranged  in  parallel  rows,  and  sepa- 
rated from  each  other  by  folds,  the  free  margins  of  which  are  thickened 


-B- 


FIG.  134.— STOMACH  OF  LL.AMA.    (Colin.) 

A,  inferior  extremity  of  the  oesophagus  ;  B,  single  pillar  of  the  oesophageal  canal ;  C,  superior  orifice 
of  the  manyplies;  D,  reticulum;  E.  right,  or  anterior  water-cells;  F,  inferior  water-cells;  G,  fleshy 
column  separating  the  two  groups  of  cells. 

by  muscular  fibres  or  sphincters,  capable  of  closing  the  opening  by 
which  each  cell  communicates  with  the  cavity  of  the  rumen.  There  are 
eight  hundred  of  these  cells  in  the  camel  and  dromedary,  and  they  all 
usually  contain  water,  for  which  purpose,  indeed,  they  are  believed  to  be 
constituted.  One  group  of  these  cells  is  situated  to  the  left  and  the 
other  to  the  right  (Fig.  134).  These  groups. of  cells  are  each  capable  of 
containing  in  the  camel  about  five  quarts  of  water. 

The  reticulum,  or  honey-comb  bag,  is  the  smallest  of  the  four  com- 
partments, in  the  ox  being  fixed  above  by  the  oesophagus  to  the 
diaphragm,  connected  with  the  narrow  part  of  the  rumen,  and  attached 
below  also  to  the  di-aphragm.  Its  cavity  communicates  freely  with  that 
of  the  rumen  by  a  large  opening. 


RUMINATION. 


319 


The  third  stomach,  or  psalter,  omasum,  or  many  plies,  is  situated  on 
the  right  side  of  the  rumen  and  reticulum,  descending  from  before  back- 
ward, and  is  lined  by  mucous  membrane,  disposed  in  broad  folds 
(Fig.  135).  These  folds  are  of  varying  breadth,  from  twelve  to  fifteen 
in  number,  and  form  almost  complete  partitions ;  between  them  are  others 
gradually  diminishing  in  size.  The  external  surface  of  the  mucous 
membrane  of  these  folds  is  coated  with  an  epithelial  layer,  which,  when 
the  rumen  is  not  entirely  fresh,  is  readily  stripped  off.  Below  this  layer, 


FIG.  135.—  OMASUM  AND  ABOMASTJM  OF  THE  Ox,  LAID  OPEN. 

A,  omasum,  or  manyplies.  showing  its  folds:  B,  the  opening  communicating  with  the  reticulum.  or  honey-comb  bag;  C, 
aboiuasuin,  the  true  digestive  stomach,  opened  to  show  the  plicae,  D,  of  its  mucous  membrane. 


which  is  called  the  horny  layer,  comes  the  mucous  membrane  proper.  It 
is  also  provided  with  papillae,  which  are  larger  and  thicker  than  those 
found  in  the  reticulum.  The  mucous  membrane  consists  of  connective 
and  elastic  tissue-fibres  and  blood-vessels.  In  the  mucous  membrane  are 
also  found  oblique  muscular  fibres  of  the  unstriped  variety.  Glands  are 
entirely  absent.  The  folds  of  the  mucous  membrane  are  papillated  on 
the  surface,  the  eminences  being  flattened  on  the  side  and  pointed  at  the 


320 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


edge  of  each  fold.  When  the  contents  of  this  stomach  are  examined  in 
animals  slaughtered  in  perfect  health  they  are  always  found  dry,  and 
there  is  a  disposition  for  the  epithelium  to  become  detached  in  shreds 
and  adhere  to  the  pulp%y  mass.  In  the  hornless  ruminants,  such  as 
sheep,  these  folds  are  more  or  less  rudimentary. 

The  cesophageal  canal  communicates  on  the  left  with  the  paunch 
and  reticulum,  and  on  the  right  with  the  manyplies.  Its  direction  is 
from  above  outward  and  backward,  the  anterior  pillar  entering  the 
honey-comb  bag  and  the  posterior  the  paunch  (Figs.  136  and  131).  The 
lower  angle  is  raised  above  the  level  of  the  third  stomach,  especially 
during  the  action  of  the  gullet,  so  that  it  is  only  when  the  pillars  of  the 


FIG.   136. —  CESOPHAGEAL    CANAL,,    OPEN.       FIG.  137.— CESOPHAGEAL    CANAL,    CLOSED 

(Colin.)  BY  SUTURE.     (Colin.) 

A,  inferior  extremity  of  the  oesophagus ;  B,  cardiac  orifice ;  C,  superior  orifice  of  the  manyplies. 

canal  are  at  rest,  and  liquids  or  soft  foods  are  descending,  or  when  the 
contents  of  the  first  and  second  stomachs  strike  against  the  canal,  that 
any  food  enters  into  the  omasum. 

The  fourth  stomach,  or  abomasum  or  rennet,  corresponds  in  its  his- 
tological  structure  with  the  stamach  of  other  mammals.  Its  mucous 
membrane  is  arranged  in  numerous  larger  or  smaller  folds,  on  the 
summits  of  which  open  the  ducts  of  the  gastric  glands.  It  also  is 
supplied  with  muscular  fibres,  and  with  nerves,  blood-vessels,  and  lym- 
phatics. Its  mucous  membrane  is  arranged  in  folds,  which  are  trans- 
verse at  the  upper  end,  longitudinal  in  the  middle,  and  gradually  effaced 
in  the  pylorus.  The  fourth  stomach  of  the  ruminant  differs  from  that 
of  other  mammals  only  in  size  and  shape,  and  agrees  in  histological 


RUMINATION. 


321 


structure.     In  the  horse  we  find  that  a  less  important  peculiarity  is  also 
to  be  noticed. 

After  having  undergone  the  first  and  incomplete  mastication,  the 
food  passes  into  the  first  and  second  stomachs,  while  fluid  and  finely 
comminuted  food  ma};  enter  all  four  compartments,  passing  directly 
into  the  first  two  stomachs,  and  then,  by  means  of  the  oesophageal 
gutter,  into  the  third  and  even  into  the  fourth  stomach.  It  was  be- 
lieved formerly  that  the  oesophageal  gutter  conducted  fluids  entirely  and 
directly  into  the  third  and  fourth  stomachs,  but  Flourens  proved,  by 
making  fistulous  openings  into  all  four  compartments,  that  immediately 


FIG.  138.— STOMACH  OF  FULL-GROWN  SHEEP,  INFLATED  AND  DRIED  ;  ONE- 
FIFTH  THE  NATURAL  SIZE.    (Thanhoffer.) 

B,  rumen :  R,  reticulum  ;  S.  omasum  :  O,  abomasum :  c,  cardia :  p.  pylorus :  br,  oesophagus ;  <*, 
cardial  valve :  bv,  oesophageal  canal ;  r,  pillars  of  the  rumen ;  rn,  opening  of  the  reticulum ;  on,  opening 
of  the  abomasum  ;  b,  valve  between  reticulum  and  omasum ;  e.  duodenum. 

on  drinking  fluids  entered  all  four  stomachs  almost  simultaneously. 
When  an  animal  drinks  the  water  enters  the  paunch  and  the  reticulum, 
since  the  oesophagus  enters  at  the  junction  of  these  two  reservoirs, 
while  a  small  quantity  of  liquid  enters  the  third  stomach  directl}',  and 
from  there  into  the  fourth.  Moreover,  the  reticulum  is  the  seat  of  en- 
ergetic contractions  which  force  a  part  of  its  contents  into  the  rumen 
and  into  the  third  stomach :  consequently  it  would  seem  clear  that  the 
largest  portion  of  fluid  enters  the  first  two  stomachs  and  then  passes 
through  to  the  others,  though  some  directly  enters  the  third  and  fourth, 

21 


322  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

being  conducted  by  means  of  the  cesophageal  gutter.  The  amount  so 
conducted  must,  in  the  most  favorable  cases,  be  but  insignificant,  since 
the  oesophageal  gutter  is  not  a  direct  continuation  of  the  gullet,  but 
joins  it  in  an  oblique  angle  directed  toward  the  right  side.  The 
explanation  of  the  origin  of  the  large  amount  of  fluid  invariably  found 
in  the  first  and  second  stomachs  would  otherwise  be  impossible,  for,  as 
already  pointed  out,  the  lining  membrane  of  these  two  compartments  is 
but  sparsely  supplied  with  glands,  and,  therefore,  they  are  incapable  of 
furnishing  a  secretion  of  their  own. 

The  opening  between  the  second  and  third  stomachs  is  extremely 
small.  Coarsely  comminuted  food  is  therefore  incapable  of  passing  into 
the  manyplies,  and  accumulates  in  the  first  two  reservoirs.  The  rumen 
and  honey-comb  bag  invariably  contain  food,  even  after  animals  have 


FIG.  139.— STOMACH  OF  THE  NEWBORN  LAMB,  DRIED  AND  INFLATED;  TWO- 
FIFTHS  THE  NATURAL,  SIZE.    (Tttanhoffer.) 

B,  rumen ;  R,  retieulum  :  S.  omasum  :  O.  abomasum  :  c,  card  i  a ;  p,  pylorus  ;  fc,  oesophagus ;  eft, 
cardial  valve ;  hv,  oesophageal  canal ;  r,  folds  in  rumen ;  rn,  opening  into  reticulum  ;  on,  opening  into 
abomasum ;  r,  blood-vessels ;  «,  duodenum. 

fasted  for  twenty-four  hours.  Thus,  Colin  found  that  in  an  ox  which 
had  fasted  twenty-four  hours  the  rumen  might  contain  one  hundred  and 
fifty  to  two  hundred  pounds  of  food,  three-fourths  of  which  was  water, 
but  little  solids  being  found  in  the  reticulum. 

The  coarsely  ground  food  which  first  enters  the  paunch  and  reticu- 
lum is  subjected  there  for  a  variable  time  to  the  liquids  contained  in 
those  organs, — saliva,  mucus,  and  water ;  in  proportion  to  the  different 
nature  of  vegetable  food  is  its  presence  in  the  rumen  prolonged.  Liquids, 
such  as  milk,  which  need  no  second  mastication,  pass  chiefly  into  the 
second  and  third  cavities.  The  functions  of  the  rumen  are  then  dis- 
pensed with,  and,  as  a  consequence,  we  find  the  rumen  quite  rudimentary 
in  suckling  herbivorous  animals  (Figs.  138  and  139).  The  reaction  of 


RUMINATION.  323 

the  first  two  stomachs  is  slightly  alkaline.  Tiedemann  and  Gmelin 
found  it  acid  in  calves,  and  Colin  says  it  is  also  acid  when  digestion  is 
disturbed,  from  fermentative  change  occurring  in  the  food.  The  food 
left  in  the  rumen  and  reticulum  is  subjected  to  a  slow  churning  process, 
and  not  to  the  active,  grinding  movements  which  were  once  thought  to 
aid  in  trituration  and  regurgitation  of  food,  substances  dropped  into 
the  posterior  pouches  of  the  paunch  gradually  being  forced  forward  into 
the  reticulum  and  back  again,  without  any  very  sensible  contractions  of 
the  muscular  walls  of  the  viscous  (Fig.  140).  By  exposing  the  interior 
of  the  paunch  in  a  young  bull,  Colin  noticed  the  welling  up  of  the  fluid 
and  the  production  of  distinct  waves,  indicating  the  commotion  set  up 


FIG.  140.— RUMEN  AND  RETICULUM  OF  THK  Ox,  LAID  OPEN  BY  REMOVING 
THE  LEFT  WALJ.  WHILE  IN  SITU. 

A,  gullet :  B,  reticulum  ;  C,  anterior  pouch  of  rumen  :  D.  middle  pouch  :  E,  posterior  superior  pouch  ;  F, 
posterior  inferior  pouch  ;    G  K,  pillars  of  the  oesophageal  canal ;    I,  entrance  to  the  omasum. 

in  every  portion  of  the  contents.  The  newly  swallowed  food  is  therefore 
speedily  mixed,  however  long  the  animal  may  have  fasted,  with  the  por- 
tions which  must  necessarily  lodge  in  the  lower  pouches  of  the  rumen, 
even  in  the  most  perfect  digestion  (Fig.  141).  It  is  evident  that  pro- 
longed maceration  in  the  paunch  will  reduce  food  to  a  pulpy  mass,  thus 
facilitating  the  regurgitation  of  the  food  for  a  second  mastication.  All 
soluble  materials  which  the  saliva  and  other  fluids  swallowed  may  dis- 
solve are  rendered  fit  for  passage  into  the  alimentary  canal,  and,  how- 
ever feeble  the  actions  of  secretion,  the  saliva  swallowed  is  here  in  its 
most  suitable  conditions  for  transforming  starch}7  food  into  sugar.  The 


324  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

changes  of  the  food  in  this  stomach  are  probably  of  a  fermentative 
nature,  as  indicated  by  the  nature  of  the  gases  which  are  constantly 
present.  Thus,  C02,  HaS,  acetic  acid,  butyric  acid,  carbonate  of  ammo- 
nium, chlorides,  carbonates,  phosphates  and  sulphates  of  sodium  and 
potassium,  and  carbonates  and  phosphates  of  lime,  are  almost  constantly 
found.  The  solids  will,  of  course,  vary  in  relative  abundance  according 
to  the  food  which  has  served  as  a  diet  for  the  animal.  In  the  reticulum, 
also,  the  food  undergoes  changes  similar  to  those  which  have  been  ob- 
served in  the  rumen  ;  in  fact,  the  reticulurn  ma}'  be  regarded  as  an  exten- 
sion of  the  paunch.  Its  special  function  appears  to  be  to  retain  fluids, 
as  its  contents  are  always  liquid.  Its  reaction  is  also  alkaline. 


FIG.  141. — VERTICAL  SECTION  OF  THE  RUMEX  AND  RKTICUIATM.     (Colin.) 

AB,  superior  region  ;  C  D,  median  region;  E  F.  inferior  region  ;  G  II,  the  small  arrows  show  the  course  followed  by  th« 
food  which  passes  from  the  posterior  portions  of  the  rumen  to  be  ruminated. 

As  regards  the  mechanism  of  the  rejection  of  food  for  the  second 
mastication,  considerable  diversity  of  opinion  prevails.  All  authors, 
however,  agree  in  dividing  the  organs  of  rumination  into  the  essential 
organ — the  stomach,  and  the  auxiliary  organs — the  diaphragm  and  ab- 
dominal muscles.  It  is  not  perfect!}-  clear  from  which  compartment  the 
food  enters  the  oesophagus  to  be  ruminated. 

Colin,  Chauveau,  and  others  believe  Hint  it  pnsses  directly  out  of  the 
rumen  into  the  oesophagus,  while  Haubner  thinks  that  the  assistance  of 
the  water-bag  is  essential,  and  this  seems  most  probable  on  anatomical 
grounds.  The  rumen  is  an  organ  of  immense  size,  and,  as  has  been  shown, 
may  contain  as  much  as  two  hundred  pounds  of  material,  and  its  muscular 


RUMINATION.  325 

walls  are  proportionately  weak.  On  the  other  hand,  the  reticulum  is  the 
smallest  of  the  four  gastric  compartments ;  its  muscles  are,  compara- 
tively speaking,  strong,  and  under  stimulation  of  the  pneumogastric 
nerve  it  has  been  found  to  decrease  one-third  in  volume.  Furthermore, 
the  oasophagus  communicates  more  directly  with  the  second  than  with 
the  first  stomach,  its  opening  into  the  reticulum  having  somewhat  the 
shape  of  a  funnel.  The  lips  of  the  oesophageal  gutter  are  not  essential 
to  the  formation  of  the  cud,  for  Colin  found  that  stitching  the  lips  of 
this  canal  together  with  wire  sutures  did  not  interfere  with  rumination  ; 
so,  also,  the  reticulum  has  been  found  not  to  be  solely  concerned  in  this 
operation,  for  Flourens  excised  a  portion  of  this  organ  and  sewed  the 
remainder  to  the  abdominal  walls  in  a  sheep,  and  yet  rumination  was 
possible.  Colin  has  shown  that  the  gradual  insertion  of  food  between 
the  pillars  of  the  gullet  is  sufficient  for  the  regurgitation  essential  to  the 
act  of  rumination.  Moreover,  that  the  oesophageal  pillars  are  not  essen- 
tial to  the  formation  of  the  cud  is  proved  by  comparative  anatomy, 
where  we  find  rumination  occurring  in  the  llama  and  dromedary,  where 
only  a  single  pillar  is  present.  The  contents  of  the  first  two  stomachs, 
as  already  mentioned,  are  subjected  to  a  gentle  churning  motion,  and  the 
tendency  of  the  food  is  to  strike  forward  against  the  pillars  of  the 
oesophagus.  As  it  presses  forward  by  its  own  weight,  and  the  slight  degree 
of  impulse  which  the  contractions  of  the  rumen  and  reticulum  give  to  it, 
there  is  a  contraction  of  the  diaphragm  and  abdominal  muscles,  and  this 
causes  a  portion  of  the  contents  of  these  two  compartments  to  engage  in 
the  infundibular  orifice  of  the  gullet,  whence  they  are  carried  upward  by 
reversed  peristalsis. 

The  action  of  the  abdominal  muscles  and  diaphragm  are  necessary 
to  permit  of  rumination,  for  when,  as  was  proved  b}^  Flourens,  the 
diaphragm  is  paralyzed  by  section  of  the  phrenic  nerves,  although 
rumination  may  take  place,  the  abdominal  muscles  will  be  called  upon  to 
make  an  extra  effort.  When  the  abdominal  muscles  are  paralyzed,  as  by 
section  of  the  spinal  cord,  rumination  is  then  impossible.  This  is  also 
the  case  when  both  pneumogastric  nerves  are  divided.  That  the 
diaphragm  and  abdominal  muscles  are  the  organs  whose  contraction 
determines  the  act  of  regurgitation  is  probable  on  other  grounds.  The 
muscular  fibres  of  the  rumen  and  reticulum  are  largely  of  the  pale, 
unstriped  variet}^,  and  their  contraction  is  slow  and  prolonged.  The 
rapidity  of  the  act  of  regurgitation  points  to  its  being  produced  by  red, 
striped,  voluntary  muscles.  When  the  cud  engages  in  the  oesophagus,  a 
constant  movement  may  be  seen  in  the  flank,  more  sensible  than  the 
other  respiratory  movements,  and  which  is  due  to  contraction  of  the 
abdominal  muscles,  an  inspiration  being  followed  by  a  rapid  expiration. 
This  movement  is  coincident  with  the  entrance  of  the  bolus  into  the 


326  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

infundibuluin  of  the  oesophagus,  and  while  it  is  due  to  the  contraction 
of  the  auxiliary  organs,  this  contraction  is  not,  under  ordinary  circum- 
stances, very  energetic,  but  becomes  so  when,  as  a  consequence  of 
various  diseases,  the  food  in  the  rumen  becomes  more  or  less  dry.  The 
ascent  of  the  cud  is  not  only  due  to  the  pressure  of  the  contracting 
abdominal  and  gastric  muscles,  but  aspiration  to  a  certain  extent  assists 
its  onward  progress.  At  the  moment  of  the  act  of  rumination  the  glottis 
is  closed,  and  as  the  diaphragm  contracts  the  thoracic  capacity  is 
augmented  and  the  bolus  is  drawn  toward  the  thorax.  When,  and  as 
soon  as  the  bolus  of  food  is  engaged  in  the  oesophagus,  it  is  carried  to 
the  mouth  with  great  rapidity  by  the  action  of  the  muscular  fibres  of 
the  oesophagus,  the  process  being  the  reverse  of  deglutition;  that  is,  the 
longitudinal  fibres  first  contract,  and  so  widen  the  oesophagus,  and  then 
the  circular  fibres  successively  contract  below  the  bolus,  and  so  force  it 
upward.  The  ascent  of  the  cud  is  visible  throughout  the  entire  length 
of  the  neck  in  most  ruminants,  particularly  in  those  which  are  thin,  or 
which,  like  the  camel,  have  a  long  neck.  Its  ascent  is  also  perceptible  to 
the  touch  and  to  the  sense  of  hearing.  When  the  ear  is  placed  over  the 
course  of  the  oesophagus  in  a  ruminant  animal,  various  sounds  may  be 
recognized  during  the  act  of  rumination.  In  this  position  bubbling  or 
moist  friction  sounds  can  be  heard  from  the  region  of  the  rumen,  even  in 
the  intervals  of  the  rumination,  due  to  the  disengagement  of  bubbles  of 
gases  in  the  process  of  fermentation  which  so  often  occurs  in  this  viscus. 
These  sounds  are  most  marked  in  animals  which  are  fed  on  green  fodder. 
A  sound  very  closely  analogous  to  the  pleural  friction  sound  is  also 
heard  in  the  same  locality  coincident  with  the  movements  of  respiration. 
It  is  due  to  the  friction  between  the  rumen  and  the  diaphragm.  The 
peculiar  bubbling  sounds  due  to  the  motion  of  foods  may  also  be  heard, 
and  are  dependent  upon  the  entrance  of  saliva  or  food  into  the  first  and 
second  stomach  and  the  passage  of  currents  from  the  first  and  second 
stomachs,  and  vice  versa.  In  addition  to  these,  rumbling  and  churning 
sounds, due  to  the  motion  of  the  material  in  the  rumen  and  produced  by 
contraction  of  the  pillars  of  the  rumen,  may  also  be  heard.  During 
active  rumination,  if  the  ear  is  placed  over  the  cervical  path  of  the 
oesophagus,  that  is,  over  the  left  jugular,  the  passage  of  the  bolus  may  be 
distinctly  heard.  The  ear  perceives  the  tactile  impression  of  a  body 
passing  rapidly  beneath  it,  and  a  sound  is  heard  which  by  its  peculiar 
characteristics  indicates  that  the  bolus  is  impregnated  with  or  accom- 
panied by  a  quantity  of  liquid. 

As  soon  as  the  bolus  enters  the  mouth,  a  second  sound  is  heard 
which  indicates  the  rapid  downward  passage  of  liquid.  This  may  be 
repeated  two  or  three  times  at  short  intervals,  and  shows  that  the  bolus 
is  accompanied  in  its  ascent  by  a  quantity  of  liquid,  which,  as  soon  as  its 


RUMINATION.  327 

lubricating  function  has  been  served,  is  again  swallowed.  This  fluid 
consists  partially  of  saliva  and  water,  or,  in  other  words,  the  contents  of 
the  rumen  and  reticulum,  and  as  the  bolus  of  food  enters  the  oesophagus 
this  fluid  is  mechanically  driven  in  with  it.  Its  presence  is  absolutely 
essential  to  the  act  of  rumination,  for  rumination  is  impossible  in  animals 
when  deprived  of  water,  or  in  whom  the  secretion  of  saliva  has  been 
interfered  with. 

As  soon  as  the  cud  reaches  the  pharynx  the  soft  palate  suddenly 
rises  and  the  food  is  carried  by  the  tongue  between  the  molar  teeth  and 
cheeks,  the  mechanism  by  which  the  food  is  prevented  from  entering  the 
nasal  chambers  and  laiynx  being  precisely  the  same  as  has  already  been 
described  as  taking  place  during  deglutition.  The  amount  of  food 
raised  in  each  bolus  varies  from  one  hundred  to  one  hundred  and  twenty 
grammes.  It  is  at  first  only  coarsely  ground,  and  not  very  soft  or  fluid, 
but  it  soon  becomes  fine  and  comminuted  and  thoroughly  macerated  in 
the  second  mastication,  and  is  collected  in  a  little  cake  on  the  back  of 
the  tongue  preparatory  to  swallowing  a  second  time.  Since  the  quantity 
composing  each  bolus  may  be  readily  determined  by  withdrawing  the 
cud  from  the  mouth  as  soon  as  it  is  rejected  from  the  stomach,  it  is 
possible  to  calculate  how  many  of  these  rejections  are  necessary  for  the 
mastication  of  the  twelve  to  fifteen  kilos  of  hay  which  constitute  the 
ordinary  daily  ration  of  an  ox.  Since  it  has  been  shown  that  dry  fodder 
absorbs  in  mastication  and  in  the  rumen  four  times  its  own  weight  of 
fluid,  twelve  thousand  five  hundred  grammes  of  hay  will  acquire  a 
weight  of  sixty-two  thousand  five  hundred  grammes.  It  is,  therefore, 
necessary  that  five  hundred  and  twenty  rejections,  each  of  one  hundred 
and  twenty  grammes,  take  place.  In  order  to  permit  all  of  this  food  to 
undergo  a  second  mastication,  and  as  each  bolus  requires  about  fifty 
seconds  for  its  second  mastication,  at  least  seven  hours  would  be 
required  for  the  process  of  rumination ;  even  if  we  admit  that  one- 
seventh  of  the  food  is  not  masticated  a  second  time,  one-fourth  the  day 
is  required  for  rumination.  The  ox,  therefore,  cannot,  like  the  horse, 
be  used  for  constant  effort,  as  he  requires  time  for  rumination,  and,  as 
will  be  shown  directly,  rumination  is  very  readily  interfered  with  by 
any  active  exertion. 

As  soon  as  the  bolus  enters  the  mouth  it  is  subjected  to  a  second 
mastication,  which  differs  from  the  first  only  in  being  more  regular  and 
more  complete.  The  number,  rapidity,  and  regularity  of  the  movements 
of  the  jaw  in  this  second  mastication  appear,  however,  to  be  subject  to 
numerous  variations.  As  already  stated,  the  movements  of  the  jaws  are 
unilateral;  this  also  applies  to  the  second  mastication,  although  perhaps 
less  regularly.  Unilateral  rumination  is  seen  in  the  ox,  sheep,  giraffe, 
antelope,  and  other  animals,  and  is  most  usual.  Its  duration  may  be  as 


328  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

long  as  a  quarter  of  an  hour,  and  then  the  direction  of  mastication  may 
be  reversed,  the  change  usually  occurring  as  a  new  bolus  enters  the 
mouth,  and  not  during  the  mastication  of  one  which  has  already  entered 
the  mouth.  In  certain  animals,  as  in  the  dromedary,  the  mastication  of 
rumination  is  alternate;  that  is,  the  lower  jaw  moves  first  to  the  right  and 
then  across  the  centre  line  to  the  left,  and  so  'on.  In  young  animals  the 
rhythm  of  mastication  is  always  more  irregular  than  in  adult  animals ; 
the  number  of  strokes  of  the  teeth  to  each  bolus  varies  according  to  the 
species  of  animals,  the  age,  the  character  of  the  food,  etc.  Thus,  dry 
food  requires  more  chewing  than  green  food,  perhaps  thus  explaining 
the  statement  that  animals  ruminate  more  in  winter  than  in  summer. 
Young  animals  have  a  smaller  number  of  teeth  than  older  animals,  and 
therefore  require  a  longer  time  for  mastication,  as  is  also  the  case  in  old 
animals,  where  the  teeth  have  become  imperfect.  The  rapidity  of  motion 
of  the  second  mastication  closely  corresponds  in  character  with  the  other 
motions  of  the  same  animal.  In  those  animals  which  are  habitually  slow 
and  sluggish  in  their  movements,  as  the  ox,  buffalo,  etc.,  the  movements 
of  mastication  will  be  slower  and  more  deliberate  than  in  animals,  such 
as  the  antelope  and  gazelle,  in  which  the  muscular  actions  are  rapidly 
performed.  Even  in  animals  of  the  same  species  it  will  generally  be 
noticed  that  the  movements  are  more  rapid  in  youth  than  in  old  age. 
Toward  the  end  of  the  period  of  mastication  of  the  cud,  the  movements 
of  the  jaws  become  considerably  accelerated.  If  rumination  is  interrupted 
from  any  disturbance,  the  bolus  is  held  in  the  mouth  for  a  time  and  mas- 
tication again  completed  before  it  is  swallowed.  Even  when  so  inter- 
rupted the  average  number  of  strokes  of  the  teeth  to  each  bolus  is  not 
interfered  with.  If  the  disturbance  is  sufficiently  severe  to  prevent  the 
resumption  of  rumination,  the  bolus  is  held  in  the  mouth  for  some  time 
and  then  swallowed  by  several  rapid  movements  of  deglutition.  During 
the  mastication  of  the  cud  the  bolus  does  not  pass  between  the  incisor 
teeth,  but  remains  between  the  molars.  As  has  been  stated,  the  move- 
ments of  mastication  constitute  the  principal  stimulus  to  the  secretion 
of  the  parotid  glands.  It  is  these  glands,  therefore,  which  secrete  most 
actively  during  rumination,  while  the  salivary  glands  of  the  anterior  sys- 
tem are  almost  inactive.  In  the  ruminant  animal  the  secretion  of  the 
parotid  is  never  entirely  suppressed,  for  the  fluid  which  it  pours  out  is 
essential  to  active  rumination.  Since,  if  a  fistula  be  made  of  the  parotid 
ducts,  and  the  parotid  saliva  conducted  outside  of  the  mouth,  even  al- 
though the  animal  be  supplied  with  water,  rumination  becomes  more  and 
more  difficult,  and  after  three  or  four  days  becomes  impossible.  The 
saliva  is  therefore  essential  to  active  rumination.  When  the  food  enters 
the  mouth  the  secretion  of  the  parotid  again  becomes  more  active,  and 
these  glands  have  been  estimated  to  pour  out  nine  hundred  grammes  of 


RUMINATION.  329 

saliva  each  in  one-quarter  of  an  hour.  Besides  keeping  the  food  in  the 
rumen  moist  and  lubricating  the  oesophagus,  the  saliva  secreted  during 
abstinence  and  the  second  mastication  does  not  all  pass  into  the  rumen, 
but  some  of  it  also  passes  into  the  many  plies,  and  so  serves  to  keep  the 
oesophageal  gutter  lubricated. 

As  soon  as  the  mastication  of  the  cud  is  complete,  and  the  food  thus 
sufficiently  comminuted  and  impregnated  with  a  large  amount  of  liquid, 
it  is  a  second  time  swallowed,  the  mechanism  again  being  the  same 
as  was  described  under  the  heading  of  deglutition.  Only  about  four 
seconds  elapse  from  the  time  of  deglutition  of  one  bolus  before  the  next 
is  formed  and  ascends  to  the  mouth.  Of  this  period,  probably  one  and  a 
half  seconds  each  is  occupied  by  the  descent  of  the  bolus,  the  formation  of 
a  new  bolus,  and  the  ascent  to  the  mouth.  When  the  cud  has  been  swal- 
lowed a  second  time  it  is  now  so  finely  divided  that  it  is  able  to  pass 
through  the  opening  between  the  second  and  third  stomachs.  It  there- 
fore largely  follows  the  course  of  the  oesophageal  canal,  and  passes 
rapidly  into  the  manyplies,  and  from  there  into  the  true  stomach,  to  be 
subjected  to  the  action  of  the  gastric  juices.  Part  of  it,  however,  pos- 
sibly falls  directly  into  the  rumen  and  reticulum,  to  be  mixed  with  the 
materials  contained  in  these  cavities. 

In  order  that  rumination  may  take  place  the  stomach  must  be  dis- 
tended with  food,  otherwise  the  walls  of  the  rumen  will  be  flaccid  and 
the  abdominal  muscles  will  be  ineffective  in  aiding  in  the  passage  of  the 
bolus  upward  through  the  oesophagus.  Since,  then,  no  digestion  or 
absorption  occurs  within  the  first  three  gastric  compartments,  an  animal 
under  such  a  condition  might  die  of  hunger  with  its  rumen  still  almost 
filled  with  food.  On  the  other  hand,  the  paunch  must  not  be  very  much 
distended,  or  its  walls  will  be  paralyzed  and  will  be  prevented  from  re- 
acting on  its  contents.  Ruminant  animals  must  always  be  well  supplied 
with  water,  and  their  secretion  of  saliva  must  be  active.  Rapidly  grown 
grasses  from  irrigated  meadows  distend  the  rumen  far  more  in  propor- 
tion to  their  solid  elements  than  other  forms  of  food.  The  distended 
paunch,  however,  soon  diminishes  in  size,  and  then  appears  very  empty, 
and  animals  cannot  ruminate  as  effectually  as  with  harder  and  drier  food, 
as  a  certain  bulk  is  required  to  permit  of  regurgitation.  Rumination 
does  not,  as  a  rule,  commence  until  after  the  animals  have  been  watered, 
unless  fed  on  green  fodder  or  succulent  roots,  and  even  then  they  some- 
times require  water. 

The  position  which  the  ruminant  animal  assumes  during  the  act  of 
rumination  is  common  to  all  ruminants,  and  is  very  characteristic.  The 
animal  reclines  slightly  on  one  side,  resting  more  or  as  much  on  the 
chest  as  on  the  belly,  the  anterior  limbs  flexed  under  the  chest,  and  the 
posterior  limbs  brought  forward  and  partly  under  the  abdomen. 


330  PHYSIOLOGY  OF   THE   DOMESTIC   ANIMALS. 

Ruminant  animals  are  very  timid  and  easily  frightened,  so  very 
slight  causes  will  arrest  rumination.  As  soon  as  the  attention  is 
attracted  the  animal  abruptly  ceases  to  ruminate,  and  if  lying  down 
rises  and  often  runs  away.  A  sudden  sound,  a  falling  object,  or  some 
strange  sight  may  be  sufficient  for  this,  although,  of  course,  animals  in 
domestication  become  less  impressionable.  Slight  maladies  prevent 
rumination,  as  do  excessive  food  and  gases  in  the  stomach,  venomous 
or  narcotic  plants,  forced  marches,  fatigue,  rut,  and  suffering  of  all 
kinds.  Even  the  separation  of  a  mother  from  her  young  has  been 
known  to  temporarily  arrest  rumination.  The  longer  rumination  is 
postponed,  the  more  difficult  is  its  recommencement,  since  food  becomes 
dry  and  compactly  packed  in  the  rumen  and  the  inam^plies,  and  their 
membranes  become  irritated. 

It  would  appear  at  first  sight  as  if  the  act  of  rumination  was  a 
purely  voluntaiy  process,  since  the  least  psychical  disturbance  inter- 
feres with  its  accomplishment.  Nevertheless,  like  other  complex  co- 
ordinated movements,  such  as  deglutition  and  defecation,  which  are  par- 
tially under  the  control  of  the  will,  rumination  is  essentially  reflex  in 
nature,  and  has  for  its  point  of  departure  the  irritation  of  the  terminal 
filaments  of  the  sensory  nerves  of  the  rumen.  The  centripetal  path 
of  this  nervous  impulse  lies  in  the  pneurnogastrics,  and  explains  the 
suspension  of  rumination  when  these  nerves  are  divided ;  the  automatic 
nervous  centre  is  located  in  the  medulla  oblongata,  its  precise  position 
being,  however,  unknown ;  the  efferent  nerves  are  the  motor  nerves  of 
the  stomach,  diaphragm,  and  abdominal  muscles,  together  with  the 
nerves  going  to  the  muscles  of  mastication  and  deglutition,  and  to  the 
parotid  glands. 

In  goats  narcotized  with  morphine  Luchsinger  was  able  to  produce 
all  the  movements  of  rumination  by  artificially  stimulating  the  sensory 
nerves  of  the  rumen,  either  by  pressure  with  the  hand  on  the  surface 
of  the  rumen,  electrical  stimulation,  or  distensions  by  injections  of  warm 
water.  He  also  found  that  not  only  might  the  regurgitation  and  ascent 
of  the  bolus  be  so  produced,  but  that  movements  of  mastication  and 
deglutition  and  salivation  were  produced  even  when  by  division  of  the 
oesophagus  the  ascending  bolus  was  prevented  from  reaching  the  mouth, 
thus  indicating  that  these  processes  also  are  gastric  reflexes. 

Rumination  may  thus  be  regarded  as  a  species  of  vomiting,  modified 
in  such  a  manner  that  there  is  no  escape  of  the  ejected  matters  from  the 
mouth,  and  that  no  more  is  regurgitated  from  the  stomach  at  any  one 
time  than  can  be  conveniently  masticated ;  for  as  soon  as  the  bolus 
engages  in  the  gullet  the  oesophageal  pillars  become  firmly  contracted 
and  the  gastric  orifice  of  the  oesophagus  remains  closed  until  the  cud, 
having  been  subjected  to  a  second  mastication,  again  enters  the  stomach. 


VOMITING. 


331 


VII.    VOMITING. 

By  vomiting  is  meant  the  convulsive  rejection  of  the  contents  of 
the  stomach  through  the  mouth.  It  differs  from  rumination  in  that  in 
most  cases  it  is  a  pathological  and  not  a  normal  process,  and  that  the 
ejected  matter  usually  escapes  from  the  mouth,  and  is  not  again  swal- 
lowed. In  certain  animals,  however,  as  in  carnivorous  birds  and  fishes, 
vomiting  constitutes  the  normal  method  by  which  indigestible  sub- 
stances are  removed  from  the  stomach ;  thus  birds  readily  reject  the 
contents  of  their  crop,  and  the  matter  so  rejected  is  often,  as  in  the  case 
of  pigeons,  used  for  nourishing  their  young. 

Fish,  amphibia,  and  reptiles 
readily  vomit  through  the  contrac- 
tions of  their  stomachs,  and  by 
this  means  indigestible  matters 
are  removed.  In  frogs  this 
process  occurs  frequentl}'  in  June 
and  July,  and  then  is  of  less  fre- 
quent occurrence  as  the  winter 
approaches,  and  when  they  pass 
into  their  state  of  hibernation  in 
January  and  February  is  entirely 
wanting.  Among  mammals  there 
exists  the  greatest  difference  in 
the  degree  of  readiness  with 
which  vomiting  occurs,  the  car- 
nivora  and  most  omnivora  vomit- 
ing with  the  greatest  readiness, 
although  the  pig  with  difficult}' 
empties  its  stomach  by  vomiting. 
The  monogastric  herbivora  vomit 
very  rarely,  and  then  only  with  the  greatest  difficulty.  This  differ- 
ence in  the  degree  of  facility  with  which  vomiting  takes  place  is  due 
to  the  formation  of  the  stomach  and  the  character  of  the  aliments 
which  it  contains.  In  mammals,  which  vomit  readily,  as  Colin  has 
pointed  out,  the  stomach  is  simple,  and  the  oesophagus  is  inserted 
toward  the  left  extremity  of  the  stomach  far  from  the  pylorus.  The 
03sophagus  has  thin,  extensible  walls,  with  an  infundibular  dilation  at 
its  insertion  in  the  stomach  (Fig.  142).  In  animals  which  do  not 
vomit  the  stomach  may  be  either  simple  or  have  several  compartments, 
the  cardiac  orifice,  in  the  former  case,  being  near  to  the  pylorus,  and  the 
oesophagus  having  thick  walls  with  a  narrow  orifice  of  entrance  into 
the  stomach,  which  is  constantly  occluded  b}*  the  contractions  of  the 


FIG.  142.— STOMACH  OF  THE  DOG.    (Colin.) 

A,  oesophagus ;  B,  pylorus. 


332 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


powerful  sphincteric  muscle  (Fig.  143).  In  animals,  such  as  the  car- 
nivora  and  omnivora,  which  readily  vomit,  the  stomach  contains  sub- 
stances which  are  generally  soft  and  moist  and  frequently  finely  divided, 
and  when  subjected  to  pressure  readily  escape  into  the  dilatable  cardiac 
orifice  of  the  gullet.  In  herbivora  which  do  not  vomit  the  stomach  is 
usually  filled  with  imperfectly  divided  forage,  imperfectly  impregnated 
with  water  as  compared  with  animal  tissues  and  closely  mixed  together. 
When  these  matters  are  subjected  to  pressure,  the  liquids  which  they 
contain  are  pressed  out  and  escape  into  the  intestines  through  the  large 


FIG.  143.— STOMACH  OF  THE  HORSE.    (Colin.) 

A,  cardiac  extremity  of  the  oesophagus ;  B,  pyloric  ring. 

and  generally  patent  pyloric  orifice.  Pressure,  therefore,  simply  serves 
to  reduce  the  volume  of  the  gastric  contents,  while  small  portions  only 
are  separated  from  the  mass  and  engage  in  the  oesophagus,  and  can  then 
only  move  upward  with  great  slowness. 

Vomiting  is  inaugurated  by  a  special  nervous  impression,  termed 
nausea,  which  effects  the  combined  action  of  the  stomach,  oesophagus,  dia- 
phragm, and  abdominal  muscles.  The  sensations  of  nausea  are  usually 
accompanied  by  a  copious  secretion  of  saliva  (by  a  reflex  stimulation  of 
afferent  fibres  in  the  gastric  branches  of  the  vagus,  the  efferent  nerve 


VOMITING.  333 

being  the  chorda  t3Tmpani),  which,  together  with  air  contained  in  the 
mouth,  is  swallowed  and  so  carried  to  the  stomach.  Vomiting  is  usually 
preceded  by  a  series  of  ineffectual  retching  movements,  which  are  due  to 
spasmodic  contractions  of  the  abdominal  muscles,  but  which  are  ineffective 
from  the  fact  that  the  sphincter ic  muscle  of  the  oesophagus  remains 
contracted.  In  ejecting  the  contents  of  the  stomach  into  the  gullet, 
when  vomiting  commences,  a  deep  inspiratory  movement  is  made,  and 
by  this  means  the  diaphragm  is  depressed  and  by  its  contraction  forces 
the  stomach  down  into  the  abdominal  cavity,  while  at  the  same  time  the 
oesophagus  becomes  partially  distended  with  air.  The  glottis  is  then 
closed  and  the  abdominal  muscles  again  spasmodically  contract,  while  at 
the  same  time  the  longitudinal  fibres  of  the  oesophagus  by  their  contrac- 
tion serve  to  open  the  orifice  of  the  oesophagus  into  the  stomach.  As 
long  as  the  diaphragm  remains  in  its  contracted  position  and  the  glottis 
is  closed,  the  entire  force  of  the  contraction  of  the  abdominal  muscles 
is  expended  on  the  abdominal  contents,  and  as  a  consequence  the  stomach 
is  firmly  compressed  between  the  abdominal  walls  and  the  diaphragm. 

The  longitudinal  muscular  fibres  of  the  oesophagus  radiate  from  the 
gullet  over  the  walls  of  the  stomach,  and  the  contractions  of  the  dia- 
phragm having  served  to  a  certain  extent  to  give  a  fixed  point  of 
support  to  the  oesophageal  ends  of  these  fibres,  their  contraction  under 
these  circumstances  will  serve  to  pull  open  the  orifice  of  the  insertion  of 
the  gullet  into  the  stomach,  thus  overcoming  the  contraction  of  the 
cardiac  sphincter.  The  pressure  to  which  the  stomach  is  then  subjected 
by  means  of  the  contraction  of  the  abdominal  muscles  forces  some  of 
the  contents  of  the  stomach  into  the  gullet,  the  mouth  is  widely  opened 
and  the  neck  stretched  to  afford  as  straight  a  path  as  possible,  and 
the  contents  of  the  stomach  are  forcibly  driven  through  the  oesoph- 
agus and  ejected  from  the  mouth.  The  entrance  of  the  food  into  the 
larynx  is  prevented  by  the  closure  of  the  glottis  at  the  commencement 
of  the  act,  and  toward  its  completion  by  a  forcible  expiration.  Ordi- 
narily the  posterior  pillars  of  the  fauces  are  sufficiently  closely  approx- 
imated to  prevent  the  entrance  of  the  ejected  matter  into  the  nasal 
chambers;  but  when  the  vomiting  is  very  violent  their  contraction  is 
overcome  and  the  matters  are  forced  into  the  nasal  chambers  and  escape 
by  the  nostrils  as  well  as  by  the  mouth. 

Vomiting  thus  consists  of  two  distinct  operations, — the  active  dila- 
tation of  the  cardiac  opening  by  the  contraction  of  the  longitudinal 
fibres  of  the  oesophagus,  and  the  pressure  of  the  contracting  abdominal 
muscles  on  the  contents  of  the  stomach.  As  long  as  the  oesophageal 
ring  is  tightly  closed,  violent  contractions  of  the  abdominal  muscles  are 
entirety  ineffective  in  expelling  the  contents  of  the  stomach.  Without 
the  contraction  of  the  abdominal  muscles,  even  though  the  cardiac 


334  PHYSIOLOGY   OF  THE   DOMESTIC  ANIMALS. 

sphincter  may  be  relaxed,  the  stomach  cannot  entirely  empty  itself. 
This  indicates  that  the  intrinsic  contractions  of  the  muscular  walls  of 
the  stomach  are  of  little  importance  in  ejecting  the  contents  of  the 
stomach.  This  was  demonstrated  by  Majendie,  who  showed  that  vom- 
iting might  take  place  in  an  animal  from  whom  the  stomach  had  been 
excised  and  a  bladder  substituted  for  it.  When  such  an  operation  was 
performed  on  a  dog,  and  the  bladder  connected  with  the  oesophagus  and 
small  intestine  inserted  in  the  abdominal  cavity  and  the  wound  in  the 
abdominal  walls  closed,  injections  of  tartar  emetic  were  perfectly  capable 
of  producing  vomiting,  thus  showing  that  the  contractions  of  the 
walls  of  the  stomach  are  by  no  means  essential  to  the  act  of  vomiting. 

Schiff,  however,  found  that  if  the  cardiac  sphincter  was  not  removed, 
or  if  the  longitudinal  fibres  of  the  lower  extremities  of  the  oesophagus 
were  damaged,  as  by  crushing,  this  experiment  of  Majendie  would  then 
be  ineffectual,  thus  showing  that,  while  the  contractions  of  the  muscular 
walls  of  the  stomach  are  of  no  importance  in  the  mechanism  of  vomiting, 
the  action  of  the  longitudinal  oasophageal  fibres  in  overcoming  the  contrac- 
tion of  the  cardiac  sphincter  is  essential.  This  contraction  of  the  longi- 
tudinal fibres  always  precedes  by  a  few  seconds  the  act  of  vomiting,  and 
may  be  recognized  by  the  insertion  of  a  finger  through  a  gastric  fistula. 
As  a  consequence  of  this  opening  of  the  sphincteric  muscle,  the  pressure 
within  the  stomach  falls,  as  may  be  recognized  by  the  connection  of  a 
manometer  with  the  interior  of  this  organ. 

In  the  normal  process  of  vomiting  the  contraction  of  these  fibres 
is  enabled  to  open  the  cesophageal  sphincter,  as  pointed  out  by  Foster, 
through  the  support  which  descent  of  the  diaphragm  has  given  to  the 
stomach :  consequently,  in  the  horse  the  impossibility  of  the  stomach 
being  so  supported  by  the  diaphragm  will  largely  explain  the  difficulty 
of  vomiting  in  these  animals ;  for  the  longer  the  portion  of  gullet  be- 
tween the  diaphragm  and  the  stomach,  the  greater  will  be  the  effect  of 
the  radiating  fibres  in  pulling  down  the  oesophagus  and  the  less  their 
capability  of  dilating  its  orifice. 

The  nervous  mechanism  which  governs  this  process  of  vomiting  i& 
complicated,  and,  as  is  well  knowrn,  it  is  a  reflex  action,  and  the  afferent 
impulses  which  excite  this  process  may  reach  the  vomiting  centre  in  the 
medulla  oblongata  through  the  most  diverse  paths.  The  vomiting  centre 
lies  in  the  medulla  close  to  the  respiratory  centre,  and  this  connection  is 
probabty  partly  functional  as  well  as  anatomical,  since,  as  is  well  known, 
nausea  may  to  a  certain  extent  be  overcome  by  rapid  and  deep  respira- 
tions. Mechanical  stimulation  of  the  fauces,  irritation  of  the  stomach, 
obstruction  of  the  alimentary  canal,  may  all  serve  as  stimuli  which  in- 
augurate the  action  of  vomiting. 

Again,  vomiting  may  take  place  by  direct  stimulation  of  the  reflex 


VOMITING.  335 

centre  in  the  medulla  oblongata.  In  this  way  certain  emetics,  such  as 
tartar  emetic,  probably  act,  for  they  may  produce  vomiting  even  when 
injected  into  the  blood,  and  without  reaching  the  stomach  at  all. 

Again,  vomiting  may  be  produced  by  sensations  coming  from  the 
central  nervous  system  higher  up  than  the  medulla ;  thus,  offensive  smells 
or  tastes  or  disturbed  cerebral  circulation,  as  in  sea-sickness,  may  pro- 
duce vomiting.  The  efferent  path  of  this  action  seems  to  lie  mainly  in 
the  pneumogastric  nerve,  for  when  this  nerve  is  divided  the  cardiac 
sphincter  remains  tightly  closed,  and  vomiting  is  then  impossible.  Sec- 
tion, therefore,  of  these  nerves  will,  as  a  rule,  prevent  vomiting.  The 
efferent  paths  of  the  nervous  impulses  passing  to  the  muscles  of  vomit- 
ing are,  of  course,  through  the  motor  nerves  supplying  the  gullet,  the 
larynx,  and  abdominal  muscles. 

In  the  horse,  as  is  well  known,  vomiting  occurs  only  under  very  ex- 
ceptional circumstances.  The  explanation  of  this  fact,  as  pointed  out  by 
Colin,  is  to  be  found  in  the  anatomical  relations  and  physical  conforma- 
tion of  the  stomach. 

In  the  first  place,  in  the  horse  the  stomach  is  never  in  contact  with 
the  abdominal  muscles ;  hence,  it  is  not  readily  subjected  to  pressure 
when  the  abdominal  muscles  contract.  Again,  as  already  mentioned,  the 
portion  of  the  oesophagus  between  the  diaphragm  and  the  stomach  is 
longer  than  in  carnivorous  animals,  and,  as  the  stomach  cannot  be  sup- 
ported by  close  contact  with  the  diaphragm,  the  longitudinal  fibres  are 
unable  to  overcome  the  permanent  contraction  of  the  cardiac  sphincter. 

In  carnivorous  animals  which  readily  vomit  the  cesophageal  orifice 
is  at  the  left  extremity,  far  from  the  pylorus.  An  antiperistaltic  action 
tends  to  force  food  into  the  opening  of  the  oesophagus.  The  gullet  has 
dilatable  walls  and  an  infundibular  insertion  into  the  stomach  and 
marked  radiating  fibres.  The  pylorus  is  narrow  and  nearly  always 
closed,  while  the  stomach  is  large  and  directly  in  contact  with  the 
diaphragm  and  abdominal  walls,  and  is  thus  in  the  best  possible  condition 
for  being  subjected  to  pressure  through  the  contraction  of  these  muscles, 
while  the  cesophageal  fibres  are  supported  through  the  contractions  of 
the  diaphragm. 

In  the  horse,  on  the  other  hand,  or  the  hare  or  rabbit,  the  oesophageal 
orifice  is  in  the  middle  of  the  lesser  curvature  of  the  stomach  and  near 
to  the  pylorus.  Its  orifice  is  always  closed  by  a  powerful  sphincter 
muscle.  It  passes  obliquely  through  the  walls  of  the  stomach,  and  is 
further  obstructed  by  folds  of  mucous  membrane,  and  the  pylorus  is 
large  and  nearly  always  patulous  (Fig.  144). 

Subjection  of  the  stomach  to  pressure  in  the  horse  will,  therefore, 
still  more  tightl}'  close  the  cesophageal  orifice,  and  will  force  the  contents 
of  the  stomach  into  the  small  intestine.  Occasionally,  however,  vomiting 


336  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

has  been  noticed  to  take  place  in  the  horse.  Under  such  circumstances 
it  is  a  symptom  of  the  greatest  gravity,  and  in  most  cases  it  will  be 
found  to  be  due  to  the  partial  rupture  of  the  walls  of  the  oesophagus. 

Ruminants,  also,  habitually  do  not  vomit,  but  do  so  occasionally. 
When  the  structure  of  the  stomach  of  the  ruminant  animal  is  examined, 
all  the  conditions  would  at  first  appear  to  favor  vomiting.  The  gullet  is 
large,  dilatable,  and  has  a  funnel-shaped  opening  into  the  stomach ;  the 
stomach  is  large,  is  in  direct  contact  with  the  abdominal  walls  and  the 
diaphragm,  and  the  pylorus  is  far  removed  from  the  cardiac  orifice. 
Nevertheless,  vomiting,  even  when  intense  nausea  is  produced  by  emetics, 


FIG.  144.— ANTERIOR  HALF  OF  THE  STOMACH  OF  THE  HORSE,   INFLATED, 
SEEN  FROM  BEHIND.    (MUller.) 

Sch,  oesophagus ;  G,  cardiac  cul-de-sac ;  kC,  lesser  curvature ;  gC,  greater  curvature ;  1  A,  mucous 
membrane  of  the  left  half,  and  rA,  mucous  membrane  of  the  right  half  of  the  stomach:  R,  dividing  line 
between  right  and  left  halves  of  the  stomach ;  F,  fold  projecting  into  stomach  from  the  lesser  curvature ; 
L,  peptic  region ;  Sch.1,  mucous  region ;  gMs,  muscular  pillars  surrounding  the  opening  of  the  oesophagus  ; 
d,  section  of  the  muscular  fold  ;  P,  pylorus ;  PH,  pyloric  cavity  :  E,  constriction  separating  pyloric  por- 
tion from  right  half  of  stomach ;  Z,  duodenum ;  Erw,  pear-shaped  dilatation  of  duodenum ;  M,  opening 
of  the  bile  and  pancreatic  ducts. 

will  but  rarely  take  place,  and  wrhen  vomiting  does  occur  in  these 
animals  it  is  the  contents  of  the  rumen  and  reticulum  alone  which  are 
expelled,  while  true  vomiting  should  require  the  escape  of  the  contents 
of  the  fourth  stomach.  To  enable  this  to  take  place,  the  material  from 
the  fourth  stomach  would  have  to  pass  through  the  narrow  openings  of 
all  the  three  preceding  stomachs.  When  matters  are  ejected  from  the 
stomach  through  the  action  of  emetics  in  a  ruminant  animal,  if  at  all, 
the  contents  of  the  rumen  alone  are  ejected,  and  these  ma}^  be  again 
swallowed,  as  in  rumination,  without  escaping  from  the  mouth. 


GASTRIC  DIGESTION.  337 


VIII.   GASTEIC   DIGESTION. 

Nearly  all  the  digestive  acts  so  far  considered  are  purely  mechanical 
and  solely  preparatory  to  digestion  in  the  sense  in  which  the  term  diges- 
tion implies  production  of  changes  essential  to  absorption.  The  food 
has  been  seized,  carried  to  the  mouth  and  appreciated  by  the  sense  of ' 
taste,  masticated  and  impregnated  by  saliva,  swallowed,  and  in  the  case 
of  ruminant  animals  again  returned  to  the  mouth  for  further  preparatory 
change.  When  once,  however,  it  enters  the  stomach — and  it  must  be 
remembered  that  in  the  strict  sense  of  the  word  this  term  only  applies  to 
the  fourth  stomach  of  ruminants — it  is  subjected  to  more  or  less  pro- 
found chemical  and  physical  changes,  which  are  described  as  resulting 
from  the  processes  of  gastric  digestion  or  clvymification.  As  has  been 
already  seen,  the  organ  in  which  these  digestive  changes  are  inaugurated 
is  not  distinctly  defined  in  all  species  of  animals,  its  first  appearance 
being  a  mere  swelling  of  the  alimentary  tube  without  any  distinct  line  of 
demarcation  at  either  extremity.  Such  a  rudimentary  stomach  is  found 
in  all  animals  below  the  subkingdom  of  the  articulates.  In  the  mollusks 
and  articulates  its  separation  from  the  intestinal  tube  and  oesophagus 
becomes  more  evident,  while  in  insects  the  stomach,  with  its  glandular 
appendages,  becomes  an  important  organ  of  digestion. 

In  the  fish  the  stomach  is  separated  from  the  intestine  by  a  narrow 
pyloric  orifice,  but  still  lies  in  the  direction  of  the  long  axis  of  the  body, 
as  is  also  the  case  in  many  reptiles,  though  in  the  higher  members  of 
this  family  and  in  the  bird  it  acquires  a  considerable  degree  of  com- 
plexity and  tends  now  to  occupy  a  position  at  right  angles  to  the  axis 
of  the  bodj-.  The  highest  degree  of  complexity  of  the  stomach  is 
found  in  the  ruminant  herbivora,  and  indicates  that  the  diversity  and 
complexity  of  organization  of  the  gastric  parts  is  governed  by  the 
peculiar  alimentary  habits  and  needs  of  the  different  species  of  animals. 

Certain  general  properties  and  characteristics  of  gastric  digestion 
are  common  to  all  the  higher  mammals,  while,  again,  certain  special  dis- 
tinctive points  are  found  in  the  nature  of  gastric  digestion  according  as 
the  animals  are  carnivora,  ruminant  or  non-ruminant  herbivora,  or 
omnivora.  These  general  characteristics  will  first  be  alluded  to,  and  the 
peculiarity  of  gastric  digestion  in  carnivora,  ruminants,  and  non-ruminant 
herbivora  will  subsequently  demand  attention. 

In  the  first  place,  we  must  consider  the  mode  of  accumulation  of 
food  in  the  stomach,  the  changes  in  shape,  and  the  motions  thereby 
inaugurated  in  that  organ.  Then  we  must  study  the  secretions  poured 
out  in  the  stomach  as  the  result  of  contact  of  food  with  its  walls,  their 
composition  and  properties,  and  mode  of  separation  from  the  blood  ; 
then  the  changes  which  the  food  undergoes  in  the  stomach  and  during  its 

22 


338  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

gradual  passage  into  the  small  intestine,  with  the  consideration  of  the 
influence  of  the  nervous  system.  These  steps  in  the  process  of  diges- 
tion often  become  characteristic  of  gastric  digestion  in  the  different 
domestic  animals. 

If  abstinence  has  continued  for  some  time,  the  stomach  will  have 
emptied  itself  of  its  contents  more  or  less  completely,  and  contracted  so 
as  to  obliterate  its  cavity  in  different  degrees  according  to  the  different 
species  of  the  animals.  In  the  dog  and  other  carnivora,  after  abstinence 
has  continued  for  twenty-four  or  forty -eight  hours,  the  stomach  will  be 
found  to  be  contracted  to  a  small  volume,  and  will  be  irregular  and  ovoid 
in  shape.  Its  mucous  membrane  will  be  thrown  up  into  folds  and  its 
cavity  almost  obliterated,  while  the  reaction  of  its  mucous  secretion  will 
be  neutral,  or  even  alkaline.  In  omnivorous  animals,  such  as  the  pig, 
the  stomach  does  not  contract  so  completely,  nor  does  it  ever  become 
entirely  emptied,  but  will,  even  after  prolonged  abstinence,  be  found  to 
contain  a  bilious  liquid  and  fetid  gases.  In  the  horse,  after  prolonged 
fasting,  the  distinction  between  the  right  and  left  half  of  the  stomach 
becomes  more  marked.  The  right  half  of  the  stomach  behaves  in  these 
respects  almost  like  the  stomach  of  the  carnivora  and  becomes  highly 
contracted,  with  its  cavity  almost  obliterated.  The  left  portion  of  the 
stomach,  on  the  other  hand,  remains  dilated  and  will  nearly  always  be 
found  to  contain  saliva  which  is  swallowed  during  abstinence.  When 
food  enters  the  stomach  after  prolonged  abstinence,  it  dilates  insensibly 
and  changes  its  positions  and  relations.  In  the  fasting  condition  the 
pylorus  sinks,  and  the  stomach  tends  to  assume,  in  this  state  of  func- 
tional inactivity,  a  position  in  the  direction  of  the  long  axis  of  the  body, 
corresponding  more  or  less  with  what  is  its  normal  state  in  lower  groups 
of  animals,  in  whom  the  stomach  is  of  minor  importance.  When  food 
accumulates  in  the  stomach  the  pylorus  rises,  and  the  organ  now  occu- 
pies a  position  at  right  angles  to  the  axis  of  the  body,  while  it  rotates  on 
its  own  axis  so  as  to  cause  the  greater  curvature  of  the  stomach,  which 
in  the  position  of  rest  is  directed  downward  and  to  the  left,  in  the  state 
of  repletion  of  the  organ  to  become  transverse  and  directed  anteriorly 
(or  downward  in  quadrupeds). 

The  mode  of  accumulation  of  food  in  the  stomach  varies  according 
to  the  character  of  the  material  swallowed.  Soft  and  diffluent  foods  and 
liquids  will  mix  at  once,  and  if  the  food  is  swallowed  in  voluminous 
masses,  as  in  the  carnivora,  or  dry  or  in  more  or  less  firm  boluses,  as 
in  the  herbivora  feeding  on  dry  fodder,  and  in  the  non-ruminants,  the 
first  portions  which  enter  the  emptj'  stomach  are  deposited  in  the  cardia. 
Those  which  go  afterward  push  these  toward  the  greater  curvature  and 
toward  the  pylorus,  while  liquids  and  softer  food  fill  up  the  interstices 
between  them. 


GASTKIC   DIGESTION.  339 

The  capacity  of  the  stomach  is,  of  course,  very  variable  in  different 
animals  in  proportion  to  their  size.  It  is  very  considerable  in  the  car- 
nivora;  thus  the  dog's  stomach  may  contain  from  two  to  ten  litres;  in 
the  hog  seven  to  eight  litres  will  represent  the  average  capacit}' ;  while 
in  the  horse,  in  proportion  to  its  size,  it  is  relatively  very  much  smaller, 
the  capacity  of  the  stomach  of  the  horse  varying  from  sixteen  to 
eighteen  litres,  or  only  one-tenth  or  one-twelfth  of  that  of  the  intestines. 

In  the  ruminant  the  mean  capacity  is  stated  by  Colin  to  be  two 
hundred  and  ninety  litres.  It  must  be  remembered,  however,  that  in  the 
latter  case  the  stomach  of  the  ruminant  is  never  empty,  no  matter  what 
may  be  the  duration  of  abstinence.  Thus,  Colin  found  sixty-five  kilos 
of  dry  food  in  the  first  three  compartments  of  the  stomach  of  a  cow 
which  had  fasted  for  a  very  long  time;  in  another,  after  four  days'" 
abstinence,  fortj-two  kilos  were  found,  while  in  a  third  sixtj'-six  kilos 
were  found  after  a  fast  of  two  days. 

In  the  horse,  as  the  stomach  fills  up  with  food,  the  constriction 
between  the  right  and  left  halves  of  this  organ  disappears,  and  the  stom- 
ach then  takes  the  shape  as  seen  when  distended  by  air  after  death.  In 
the  horse,  no  matter  how  much  distended,  the  stomach  is  never  in  contact 
with  the  inferior  abdominal  walls,  but  is  always  separated  from  them  by 
the  infra-sternal  curvature  of  the  colon  and  a  portion  of  the  gastro-dia- 
phragmatic  curvature.  In  carnivora  the  stomach  is  in  contact  with  the 
lumbar  region  above,  and  with  the  abdominal  walls  in  the  epigastrium 
and  hypochondrium.  As  the  stonlach  becomes  expanded  with  food,  the 
cardiac  and  the  pyloric  sphincters  become  contracted,  and  the  alimen- 
tary matters  by  contact  provoke  contraction  of  the  muscular  walls  of 
the  stomach,  and  so  serve  to  mix  up  the  food. 

When  the  food  first  enters  the  stomach  these  movements  are  slight, 
but  they  gradually  become  more  and  more  vigorous,  and  cause  a  sort  of 
churning  motion  in  the  stomach,  the  food  travelling  from  the  cardiac 
orifice  along  the  greater  curvature  to  the  pylorus  and  returning  by  the 
lesser  curvature.  At  the  pylorus  the  circular  muscular  fibres  are  the 
seat  of  slow,  rhythmical  contractions,  which  serve  to  assist  in  the  pas- 
sage of  the  contents  of  the  stomach  into  the  small  intestine.  While 
these  movements  seem  to  be  started  by  the  contact  of  the  food  with  the 
mucous  membrane  of  the  stomach,  it  is  evidently  not  a  mere  mechanical 
stimulation  which  produces  them,  since,  when  the  stomach  is  fullest,  and 
when,  therefore,  this  mechanical  stimulation  must  be  at  its  height,  the 
movements  are  the  slightest,  and  become  more  vigorous  as  the  stomach 
empties  itself.  Apparently  these  contractions  are  started  up  by  the 
commencing  acidity  of  the  gastric  contents,  which,  at  first  alkaline, 
become  gradually  more  and  more  acid  as  digestion  progresses,  coinciding 
with  the  increase  in  vigor  of  the  muscular  movements  of  the  walls  of 


340  PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 

the  stomach.  The  muscular  movements  of  the  stomach  are  not  so  regu- 
larly peristaltic  as  in  the  intestines,  on  account  of  the  want  of  symmetry 
of  the  direction  of  the  muscular  fibres. 

The  nervous  mechanism  of  the  gastric  movements  has  not  been 
thorough!}'  cleared  up.  Numerous  nervous  ganglia  have  been  found  in  the 
walls  of  the  stomach,  and  this  fact,  in  addition  to  the  observation  which 
has  often  been  made,  that  these  movements  may  occur  in  a  stomach  which 
has  been  separated  from  the  central  nervous  system,  would  indicate  that 
the  ganglia  start  up  these  movements  in  this  organ.  Nevertheless,  the 
movements  of  the  stomach  are  dependent  on  and  governed  by  the  central 
nerv.ous  symptom,  since  the  movements  of  the  stomach  may  be  induced 
by  stimulation  of  the  peripheral  ends  of  the  pneumogastric  nerves  when 
the  stomach  is  full.  That  the  movements  of  the  stomach  are  not,  how- 
ever, solely  dependent  on  impulses  coming  through  the  pneumogastrics  is 
proved  by  their  occurrence  after  these  nerves  have  been  divided.  Stimu- 
lation of  the  S3rmpathetic  and  coeliac  plexus  is  said  to  evoke  contractions 
of  the  gastric  walls,  probably  through  changes  in  the  blood  supply  of  the 
stomach.  The  vagus  nerve  is  without  doubt  the  principal  path  through 
which  the  movements  of  the  stomach  are  controlled  by  the  central 
nervous  system. 

The  contractions  of  the  muscular  walls  of  the  stomach  not  only 
serve  to  mix  the  food  contained  in  this  organ,  but  also  to  bring  all  the 
contents  of  the  stomach  in  contact  with  the  secreting  portion  of  its 
Avails.  This  is  especially  important  in  such  animals  as  the  horse,  where 
only  one-half  the  organ  is  thus  active. 

The  oesophageal  sphincter  is  always  tightly  closed,  especially,  in 
horses,  where  it  is  very  firmly  constricted,  and  so  prevents  the  return  of 
the  flood  to  the  mouth,  even  when  the  stomach  is  strongly  compressed. 
The  p}doric  sphincter  is  not  so  powerful  and  its  contractions  are  not  so 
prominent,  but  are,  nevertheless,  well  marked  in  the  carnivora,  the  pig, 
and  the  ruminant. 

In  solipedes  the  contraction  of  the  pylorus  is  only  faintly  marked, 
and,  as  a  consequence,  the  opening  of  the  stomach  into  the  intestines  in 
these  animals,  for  reasons  which  will  be  given  directly,  is  nearly  alwa3*s 
patulous.  Oser  has  found  that  stimulation  of  the  pneumogastric  nerves 
in  the  neck  leads  to  an  immediate  contraction  of  the  pylorus,  the  intensit}r 
and  duration  of  the  contraction  depending  on  the  degree  of  stimulation. 
Stimulation  of  the  thoracic  portion  of  the  sympathetic  nerve  arrests  the 
spontaneous  contractions  of  the  pylorus,  the  influence  of  this  stimulation 
being  progressive,  attaining  its  maximum  in  one  or  two  minutes  and 
then  slowly  declining.  After  the  conclusion  of  the  stimulation  the 
spontaneous  contractions,  which  exist  even  after  section  of  the  vagi  and 
.splanchnic  nerves,  at  first  are  feeble,  and  attain  their  normal  degree  in 


GASTRIC   DIGESTION.  341 

about  three  minutes.  The  inhibitory  action  of  the  splanchnics  in  the 
thorax  is  less  marked  than  the  motor  action  of  the  vagi;  the  inhibitory 
power  of  the  left  splanchnic  is  greater  than  that  of  the  right. 

It  thus  would  appear  that  the  circular  muscular  fibres  of  the  pyloric 
ring  are  innervated  by  two  antagonistic  sets  of  nerves,  the  vagus  being 
the  motor  nerve  and  the  splanchnic  the  inhibitory  nerve. 

When  the  food  is  received  in  the  stomach  it  is  gradually  dissolved, 
and  we  have,  therefore,  to  study  tho  several  processes  which  are  concerned 
in  this  action.  The  general  outline  of  the  characters  of  that  change  will 
first  be  given,  then  the  properties  of  the  secretion  to  whose  action  it  is 
due,  the  action  of  this  secretion  on  the  various  food-stuffs,  the  nature  of 
the  resulting  products,  the  conditions  essential  to  gastric  digestion,  and, 
finally,  the  mode  in  which  the  gastric  juice  is  secreted. 

The  study  of  gastric  digestion  is  especially  a  study  of  chemical 
changes  It  was  seen  that  in  the  mouth  the  food  was  not  only  subjected 
to  the  chemical  changes  produced  by  the  saliva,  but  that  through 
mechanical  changes  resulting  from  mastication  and  the  close  mixing  of 
the  food  with  the  saliva  the  materials  destined  to  nourish  the  body  were 
brought  into  the  most  favorable  conditions  for  subjection  to  the  various 
solvent  juices  of  the  economy.  The  first  and  the  most  important  of  these 
with  which  the  food  comes  in  contact  in  its  onward  passage  through  the 
alimentary  canal  is  the  gastric  juice.  In  the  experiments  made  on  the 
saliva  the  precedent  was  established  of  performing  acts  of  digestion,  or 
at  least  acts  introductory  to  digestion,  outside  the  body,  the  natural 
conditions  being  preserved  as  far  as  possible.  In  the  study  of  gastric 
digestion  it  will  be  found  that  this  step  is  not  unwarranted.  All  the 
phenomena  of  gastric  digestion  may  be  as  completely  and  conveniently 
studied  in  an  artificial  stomach  as  in  the  living  organ,  a  fact  demonstrative 
of  the  essentially  chemical  nature  of  the  process. 

Not  only  may  such  experiments  be  conducted  outside  of  the  body, 
but  they  may  even  be  performed  with  artificial  gastric  juice. 

Such  a  fluid,  or  artificial  gastric  juice,  of  considerable  purity  may  be  obtained 
by  mincing  the  mucous  membrane  of  the  stomach  of  almost  any  animal,  drying 
the  fragments  between  layers  of  filter-paper,  and  allowing  them  to  remain  for 
twenty-four  hours  under  absolute  alcohol.  They  are  then  removed  from  the 
alcohol  and  covered  with  strong  glycerin.  In  a  few  days  the  glycerin  will 
become  strongly  impregnated  with  pepsin,  the  ferment  of  the  gastric  juice,  and 
may  be  preserved  for  almost  any  length  of  time  The  addition  of  a  few  drops  of 
this  glycerin  extract  to  one  hundred  cubic  centimeters  of  hydrochloric  acid  of 
.02  per  cent:  will  produce  a  fluid  of  high  digestive  power,  and  one  which  is  quite 
permanent. 

An  artificial  gastric  juice  may  also  be  obtained  by  rubbing  up  the  minced 
mucous  membrane  of  the  stomach,  from  which  the  mucus  has  been  removed  by 
gentle  scraping,  in  a  mortar  with  clean  sand  or  powdered  glass  and  water.  It 
should  then  stand  for  some  hours,  being  occasionally  stirred,  and  finally  filtered. 
The  filtrate  will  contain  pepsin  and  a  small  amount  of  peptones.  Added  to  an 
equal  bulk  of  .02  per  cent,  of  hydrochloric  acid,  it  will  form  a  powerful  digestive 
fluid,  which  may  be  kept  for  a  long  time,  not  even  losing  its  powers  when  mouldy, 


342  PHYSIOLOGY  OF   THE  DOMESTIC   ANIMALS. 

1.  CHEMISTRY  OF  THE  GASTRIC  JUICE. — That  the  gastric  juice  m&y  be 
obtained  pure  for  analysis  a  fistulous  opening  has  to  be  made  into  the 
stomach,  since  the  various  other  methods  employed  by  Reaumur  and 
Spalanzani,  of  allowing  sinimals  to  swallow  sponges  and  then  withdrawing 
them  and  obtaining  the  fluid  by  pressure,  will  not  succeed  in  yielding 
a  pure  gastric  secretion,  as  it  will  evidently  be  contaminated  with  the 
fluids  of  .-the  mouth,  pharynx,  and  oesophagus. 

The  method  of  performance  of  gastric  fistula  originated  in  the 
account  of  the  celebrated  case,  reported  by  Dr.  Beaumont,  of  the  Cana- 
dian trapper,  Alexis  St.  Martin,  in  whom  an  accidental  gunshot  wound 
of  the  abdominal  walls  left  a  fistulous  tract  communicating  with  the 
cavity  of  the  stomach.  It  was  through  the  data  obtained  by  Beaumont 
from  a  study  of  this  case  that  the  first  facts  as  regards  the  chemistry  and 
physiology  of  gastric  digestion  were  obtained.  Led  by  an  account  of 
this  case,  the  production  of  a  similar  fistulous  opening  communicating 
with  the  gastric  cavity  on  animals  was  first  shown  to  be  practicable  by 
Blondlot,  and  after  him  by  Bernard.  Blondlot's  method  was  to  make  an 
incision  seven  or  eight  centimeters  long  in  the  linea  alba,  commencing  at 
the  xyphoid  cartilage.  The  walls  of  the  stomach  were  stitched  to  the 
wound,  and,  after  adhesion  had  taken  place  between  the  peritoneal  cover- 
ing of  the  stomach  and  the  abdominal  walls,  an  opening  was  made  into 
the  cavity  of  the  former,  in  which  a  tube  was  inserted. 

Bernard  has,  however,  shown  that  it  is  not  necessary  to  allow  the 
stomach  to  become  adherent  to  the  abdominal  walls  before  opening  it, 
and  the  method  which  he  recommended  is  one  which  is  now  generally 
adopted. 


In  making  a  gastric  fistula,  an  animal  must,  of  course,  be  selected  in  which  the 
stomach  is  large  and  lies  close  to  the  abdominal  walls.  The  horse  is,  therefore, 
inappropriate  for  such  experiments,  since  in  the  horse  the  stomach  is  small, 
deeply  seated,  and  not  in  contact  with  the  abdominal  parietes.  On  the  other 
hand,  rabbits  cannot  be  employed,  since  their  stomachs  are  never  empty;  and 
cats  are  very  liable  to  die  of  peritonitis,  to  say  nothing  of  the  difficulty  in  their 
subsequent  management.  In  some  birds  with  a  muscular  stomach,  as,  for  example, 
in  the  crow,  gastric  fistulae  may  be  very  satisfactorily  made.  The  animal,  how- 
ever, which  is,  on  all  accounts,  most  suitable  is  the  dog.  Dogs  are  easily  man- 
aged, secrete  pure  gastric  juice  in  abundant  quantity,  and  are  not  very  liable  to 
peritonitis. 

In  order  to  perform  the  operation  of  making  a  gastric  fistula  on  a  dog,  the 
animal  is  well  fed,  so  as  to  distend  the  stomach,  or,  after  fasting  twenty-fourhours, 
the  stomach  may  be  distended  by  an  injection  of  air  through  the  oesophagus,  and 
is  then  chloroformed  and  securely  fastened.  The  first  step  is  to  shave  the  hair 
from  the  abdominal  walls  in  the  epigastric  region,  and  to  remove  all  the  hairs 
carefully  with  a  sponge,  so  as  to  prevent  their  entering  the  abdominal  cavity.  An 
incision  is  then  made  through  the  skin,  commencing  at  the  lower  margin  of  the 
costal  cartilages  and  about  an  inch  and  a  half  to  the  left  of  the  linea  alba,  and 
extending  downward  parallel  to  this  line  for  a  distance  a  little  less  than  the 
diameter  of  the  flange  of  the  cannula  which  it  is  desired  to  use.  Each  muscular 
layer  is  then  to  be  divided  in  a  direction  parallel  to  its  fibres,  every  bleeding  point 
being  tied  before  the  peritoneum  is  opened,  so  as  to  prevent  the  entrance  of  blood 
into  this  cavity. 


GASTEIC   DIGESTION. 


343 


When  it  is  certain  that  all  the  bleeding  has  stopped,  the  peritoneum  is  to  be 
opened  upon  a  director.  On  stretching  open  the  wound  the  distended  stomach 
conies  into  view,  its  oblique  muscular  structure  being  plainly  visible  through  its 
serous  covering.  The  gastric  wall  should  then  be  seized  with  a  pair  of  artery 
forceps  at  a  point  where  there  are  not  many  vessels  and  drawn  forward.  Two 
strong  silk  threads  are  then  passed  into  the  walls  of  the  stomach  with  a  curved 
needle,  at  distances  from  each  other  about  equal  to  the  diameter  of  the  tube  of 
the  cannula,  and  brought  out  again  at  a  similar  distance  from  the  points  where 
they  were  introduced.  An  incision  is  then  made  into  the  gastric  walls,  between 
the  two  threads,  rather  shorter  than  the  diameter  of  the  tube  of  the  cannula.  Im- 
mediately some  bubbles  of  gas  escape  and  some  of  the  fluid  contents  of  the 
stomach,  which  must  be  sponged  off  The  opening  into  the  stomach  is  now  to 
be  stretched  with  a  pair  of  blunt  hooks  until  it  is  large  enough  to  pass  the  inner 
flange  of  the  cannula,  which  is  to  be  then  introduced 
and  pushed  into  the  stomach  up  to  its  outer  plate. 
The  form  of  the  cannula  usually  employed  is  repre- 
sented in  Fig.  145  ;  it  consists  of  two  tubes,  each  ter- 
minating at  one  end  in  a  circular  plate,  the  two  tubes 
being  cut  with  a  screw-thread,  on  the  outside  of  one 
and  the  interior  of  the  other,  so  that  the  distance  be- 
tween the  two  plates,  when  the  tubes  are  joined 
together,  may  be  altered  at  will.  After  the  insertion 
of  the  cannula  the  stomach  is  fastened  to  it  by  the 
threads  which  were  previously  inserted,  and  the  ends 
of  these  threads  passed  through  the  abdominal  walls 
in  such  a  way  as  to  fasten  the  stomach  to  them,  and 
at  the  same  time  when  tied  together  keep  the  edges 
of  the  wound  in  the  abdominal  walls  in  apposition. 
The  sutures  need  not  be  carried  through  the  perito- 
neum, and  no  additional  means  of  closing  the  wound 
is  necessary.  After  the  animal  has  recovered  from 
the  ansesthetic,  the  cannula  must  be  left  uncorked  for 
at  least  half  an  hour  after  the  operation,  for  the  dog  is 
almost  certain  to  vomit,  and  were  the  cannula  not  open 
the  contents  of  the  stomach  would  be  apt  to  be  forced 
past  the  side  of  the  cannula  into  the  abdominal  cavity, 
and  cause  the  death  of  the  animal. 

After  the  operation  the  animal  must  be  fed  on 
milk  for  two  or  three  days  and  kept  in  a  warm  place. 
When  recovering  from  the  anesthetic  the  animal  will 
be  very  likely  to  make  attempts  to  tear  out  the  cannula 
with  his  teeth,  a  result  which  would  be  apt  to  be  fatal 
to  the  dog.  The  only  way  this  accident  may  be 
guarded  against  is  by  careful  watching.  It  will  not 
do  to  muzzle  him  and  leave  him,  for  if  he  then  should 
vomit  he  would  choke  to  death.  After  the  first  day 
the  wound  becomes  so  tender  that  no  further  attempts 
at  tearing  out  the  cannula  are  usually  made.  On  the 
second  or  third  day  after  the  operation  the  margin  of 
the  wound  becomes  much  swollen,  and  it  is  then 

necessary  to  lengthen  the  tube  of  the  cannula  so  as  to  avoid  ulceration  of  the 
skin  from  pressure  of  the  external  flange.  By  this  time  adhesions  have  been 
established  between  the  edges  of  the  wound  in  the  stomach  and  the  abdominal 
walls,  and  the  wound  in  the  latter  having  healed,  with  the  exception  of  the  space 
occupied  by  the  tube  of  the  cannula,  the  cavity  of  the  stomach  communicates 
with  the  exterior  by  means  of  a  more  or  less  elongated  fistulous  tract  (Figs.  146 
and  147).  The  cannula  may  be  closed  by  a  cork  or  it  may  be  fastened  with  a 
valve. 

If  everything  goes  well,  the  dog  will  be  ready  for  experiments  in  about  a 
week. 

In  ruminant  animals  fistulous  openings  may  be  made  into  anyone  of  the  four 
stomachs  or  gastric  compartments,  although,  of  course,  an  opening  into  the  fourth 
stomach  is  the  only  one  through  which  gastric  juice  may  be  collected.  The 


FIG.  145.  —  CANNULA  FOB 
GASTRIC  FISTULJE. 
(Bernard.) 

A  B,  section  of  the  cannula;  e, 
flange  of  the  cannula ;  C,  projections 
on  the  interior  of  tube  which  fit  in 
key,  D,  so  as  to  lengthen  or  shorten 
tube ;  E,  opening  of  tube. 


344 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


method  of  operation  is  the  same  as  that  employed  in  the  dog.  In  recent  times 
special  gastric  fistulas  have  been  performed  by  Klemensiewicz,  who  excised  in  the 
living  dog  the  pyloric  portion  of  the  stomach,  and  afterward  stitched  together  the 
duodenum  and  the  remaining  part  of  the  stomach,  thus  establishing  the  continuity 
of  the  latter  organ.  The  excised  part,  with  its  vessels  intact,  was  stitched  to  the 


FIG.  146.— GASTRIC  FISTULA,  LAID  OPEN.    (Bernard.) 

section  of  the  abdominal  walls;  «,  section  of  the  walls  of  the  stomach;  c,  folds  of  the  mucons 
membrane,  E ;  O,  cicatricial  tissue  at  the  orifice  of  the  fistula. 

abdominal  wall  after  closing  its  lower  end  by  sutures.  Heidenhain,  by  employing 
the  antiseptic  method,  was  able  to  preserve  three  dogs  out  of  seven  thus  operated 
on.  He  also  succeeded  in  isolating  in  the  same  manner  the  cardiac  extremity  of 
the  stomach  by  means  of  this  operation  ;  therefore,  it  is  rendered  possible  to  obtain 
pure  gastric  secretion  from  either  the  pyloric  or  the  cardiac  extremity  of  this 

organ,  and  the  characters  of  the 
secretions  from  these  parts  are 
rendered  accessible  for  study. 

In  order  to  collect  gastric 
juice  for  analysis  the  dog  must 
be  allowed  to  fast  for  at  least 
twenty-four  hours,  so  as  to 
empty  the  stomach,  and  the 
secretion  of  gastric  juice  may 
be  stimulated  by  tickling  the 
inner  surface  of  the  stomach 
with  a  feather  tied  to  a  glass 
rod.  The  gastric  juice  will  then 
flow  along  the  glass  rod  out  of 
the  stomach,  and  may  be  col- 
lected in  a  glass  beaker. 

Bernard's  method  of  stim- 
ulating the  flow  of  gastric  juice 
was  to  give  a  dog  which  had 
been  fasting  for  some  time  a 
hearty  meal  of  thoroughly 
boiled  tripe,  which  furnished  a 
normal  stimulus  to  the  gastric 
glands,  and,  being  almost  indi- 
gestible, does  not  contaminate  the  gastric  juice  to  any  great  extent,  and  is  there- 
fore in  some  respects  preferable  to  mechanical  stimulation. 

That  the  gastric  iuice  may  be  obtained  perfectly  pure,  the  salivary  ducts 
should  be  tied,  otherwise  the  fluid  obtained  from  the  stomach  will  be  more  or  less 
mixed  with  the  saliva. 


FIG.  147.— GASTRIC  FISTULA.    (Bernard.) 

E,  stomach;  D,  duodennm  ;    M,  muscles  of  the  abdominal  walls;    O, 
external  orifice  of  the  fistula. 


GASTEIC   DIGESTION".  345 

Gastric  juice  may  also  be  obtained  from  man  either  by  withdrawing  the  con- 
tents of  the  stomach  by  means  of  the  stomach-pump,  or  it  may  be  obtained,  as 
it  has  been  done  in  several  instances,  through  a  fistulous  opening  made  into  the 
stomach,  either  accidentally,  as  in  the  case  of  St.  Martin,  or,  as  in  the  case  studied 
by  Kichet,  in  which  the  operation  of  gastrotomy  was  performed  by  Verneuil  for 
impermeable  stricture  of  the  oesophagus. 

Gastric  juice  collected  from  a  gastric  fistula  is  a  thin,  limpid,  almost 
colorless  liquid  of  strongly  acid  reaction  and  of  a  specific  gravit}T  of 
about  1010.  It  has  a  peculiar  odor  which  is  generally  characteristic  of 
the  animal  from  which  it  is  obtained.  The  filtered  gastric  juice  of  the 
dog  contains  from  1.05  to  1.48  per  cent,  solids;  of  the  horse,  1.72  per 
cent.,  and  of  man,  1.2 1  per  cent.  It  rotates  the  plane  of  polarized  light 
to  the  left,  and  it  is  not  rendered  turbid  by  boiling,  and  resists  putrefac- 
tion for  a  long  time.  The  quantity  of  gastric  juice  secreted  in  twenty- 
four  hours  is  only  with  difficulty  determined,  and  the  great  discrepancy 
which  exists  between  the  various  estimates  which  have  been  placed  on 
this  amount  shows  that  it  must  vary  very  widely  under  different  con- 
ditions. Thus,  Beaumont  estimated  that  one  hundred  and  eighty 
grammes  of  gastric  juice  were  secreted  daily;  Griinewald,  from  studies 
made  on  a  similar  case  of  gastric  fistula,  concluded  that- 26. 4  per  cent, 
of  the  bod}'  weight  represented  the  amount  of  gastric  juice  dail}T  poured 
out ;  while  Bidder  and  Schmidt,  from  operations  made  on  dogs,  esti- 
mated that  the  daily  secretion  of  gastric  juice  corresponded  to  about 
one-tenth  of  the  body  weight. 

The  gastric  juice  of  a  dog,  even  after  having  fasted  for  a  long  time, 
can  never  be  collected  perfectly  pure  from  a  gastric  fistula,  since  it 
always  is  contaminated  and  mixed  with  remnants  of  undigested  food, 
sand,  and  hairs  from  the  edges  of  the  wound,  etc.  In  the  sheep  it  is 
even  more  difficult  to  obtain  perfectly  pure  gastric  juice,  since  Bidder 
and  Schmidt  have  found  that  even  after  thirty-six  hours  particles  of  food 
were  still  contained  in  the  fourth  stomach.  When  filtered,  gastric  juice 
is  always  clear  and  limpid,  almost  colorless,  or  yellowish  in  the  dog, 
brownish  in  the  sheep.  Gastric  juice  resists  putrefactive  changes  to  a 
remarkable  degree,  and  may  be  kept  for  an  almost  indefinite  period 
without  undergoing  change. 

Acids  and  heating  produce  no  precipitation  in  gastric  juice,  as  is 
also  the  case  with  lime,  chloride  of  iron,  sulphate  of  copper,  and  ferro- 
cj'anide  of  potassium;  alkalies,  on  the  other  hand,  produce  precipitation, 
which  consists  of  calcium  phosphate  with  iron  and  magnesium  phosphate 
and  some  organic  matter.  Corrosive  sublimate  always  produces  a  pre- 
cipitate, which  consists  mainly  of  the  digestive  ferments.  Alcohol  and 
acetate  of  lead  give  an  abundant  precipitate,  which  consists  mainly  of 
the  ferment. 

The  gastric  juice  is  poor  in  solids,  containing  not  more  than  two  per 


346  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

cent.  The  usual  salts  found  in  animal  fluids  are  also  here  present — 
chlorides  of  sodium,  potassium,  calcium,  and  ammonium  being  in  excess. 
Phosphatic  earths  with  some  iron  occupy  the  next  place,  while  the 
sulphates  are  either  absent  or  present  only  in  minute  traces.  The  con- 
stituents, therefore,  of  the  gastric  juice  consist,  in  the  first  place,  of  two 
soluble  ferments,  pepsin  and  the  milk-curdling  ferment,  which  represent 
the  organic  constituents  of  the  gastric  secretion ;  second,  a  free  acid, 
which  is,  in  all  probability,  hydrochloric;  and, third, the  mineral  salts. 

(a)  Pepsin. — Pepsin  belongs  to  the  category  of  soluble  ferments. 
As  yet  it  has  been  impossible  to  obtain  it  in  a  state  of  absolute  purity. 

The  procedure  which  gives  the  best  results  is  that  of  Briicke.  The  mucous 
membrane  of  the  stomach  is  digested  at  40°  C.  with  dilute  hydrochloric  acid.  It 
is  then  neutralized  with  lime,  which  is  thus  precipitated,  and  carries  down 
mechanically  with  it  the  ferment,  pepsin.  This  precipitate  is  washed  and  dissolved 
in  dilute  hydrochloric  acid,  and  to  this  is  added  a  solution  of  cholesterin  in  four 
parts  of  alcohol  and  one  part  of  ether.  The  cholesterin  throws  the  pepsin  out  of 
solution.  It  is  then  washed  with  water  and  with  ether.  The  ethereal  layer  is 
poured  off,  and  pepsin  remains  in  watery  solution,  from  which  it  may  be 'obtained 
by  evaporation.  Von  Wittich  treats  the  mucous  membrane  with  glycerin,  after 
having  allowed  it  to  remain  for  twenty-four  hours  in  alcohol,  so  as  to  precipitate 
the  proteids  in  the  tissue  of  the  stomach,  and  at  the  end  of  a  week  or  two  the 
glycerin  is  filtered  off,  and  pepsin  may  be  obtained  by  precipitating  the  glycerin 
solution  of  pepsin  with  absolute  alcohol. 

Obtained  by  either  of  these  processes,  pepsin  is  a  yellowish  powder, 
which  is  soluble  in  water  and  glycerin  and  insoluble  in  alcohol.  When 
precipitated  by  alcohol  from  its  aqueous  or  glycerin  solutions  it  does 
not  lose  its  solubility  in  water,  thus  differing  from  the  proteids;  it  is 
not  diffusible.  When  dried  it  may  be  warmed  up  to  110°  C.  without 
losing  its  activity.  While  in  solution  it  may  be  transformed  into  a  sub- 
stance which  is  less  active,  and  which  has  been  termed  isopepsin  by 
Finckler.  At  80°  it  becomes  entirely  inactive.  Pepsin  is  also  soluble 
in  dilute  acids.  If  pure,  pepsin  should  not  give  proteid  reactions.  It 
should  37ield  no  precipitate  with  nitric  acid,  tannic  acid,  iodine,  or 
mercuric  chloride.  It  is  precipitated  from  its  solutions  by  acetate  of 
lead  and  platinum  chloride. 

The  proportion  of  pepsin  in  the  gastric  juice  varies  at  different 
periods  of  digestion.  At  the  commencement  of  digestion  it  is  present 
in  the  smallest  amount,  and  acquires  its  maximum  between  the  fourth 
and  fifth  hours  of  digestion.  In  man  it  is  said  to  be  present  in  amounts 
varying  from  0.41  to  1.17  per  cent. 

Without  the  addition  of  dilute  acid  pepsin  manifests  no  specific 
action,  and  the  characteristic  test  of  the  presence  of  this  ferment  is 
known  as  the  pepsin  test  with  fibrin.  If  a  little  fibrin,  obtained  by 
whipping  the  blood  as  it  flows  from  a  divided  vessel,  is  washed  until 
perfectly  white  and  placed  in  a  test-tube  with  a  little  gastric  juice,  and 
warmed  up  to  35°  C.,  the  fibrin  will  entirely  disappear.  There  will  be 


GASTKIC   DIGESTION.  347 

.no  precipitate  upon  boiling,  and  but  slight  precipitation  on  neutraliza- 
tion. Since  no  other  substance  will  produce  this  result  with  fibrin,  it  is 
.characteristic  of  the  presence  of  pepsin  with  a  dilute  acid. 

(b)  Milk-Curdling  Ferment. — As  is  well  known,  when  milk  is 
brought  into  contact  with  the  mucous  membrane  of  the  stomach,  or: 
when  an  infusion  of  the  mucous  membrane  of  the  stomach  is  added 
to  milk,  it  coagulates.  This  process  is  made  use  of  in  the  manufacture 
of  cheese,  and  was  forinerly  attributed  to  the  acid  of  the  gastric  juice 
or  to  the  production  of  acidity  in  the  milk  from  the  development  of 
lactic  acid  from  milk-sugar.  It  has,  however,  been  shown  that  milk, 
while  completely  neutral,  may  be  coagulated  by  an  infusion  of  gastric 
juice,  or  by  a  neutral  infusion  of  the  mucous  membrane;  and  since  this 
specific  action  of  the  gastric  juice  in  curdling  milk  is  destroyed  by 
boiling,  it  also  is  attributable  to  a  specific  ferment,  which  is  termed  the 
milk-curdling  ferment,  or  rennet. 

This  ferment  produces  coagulation  of  the  casein  of  milk  without 
calling  in  in  any  way  the  action  of  the  acid,  and  will  produce  its  char- 
acteristic results  in  solutions  of  casein  which  are  entirely  free  from  milk- 
sugar  and  which  are  perfectly  neutral. 

Solutions  of  the  milk-curdling  ferment  may  be  obtained  by  digesting 
the  mucous  membrane  of  the  stomach  with  glycerin.  A  few  drops  of 
this  glycerin  extract,  which  also,  of  course,  contains  pepsin,  will  cause 
a  hundred  cubic  centimeters  of  fresh  milk  to  coagulate  within  a  few 
moments  if  heated  up  to  40°  C. 

Severn!  other  methods  have  been  proposed  for  the  extraction  of 
milk-curdling  ferment,  but  in  all  pepsin  is  nearly  always  present. 

Hammarsten  has  found  that  by  precipitating  with  carbonate  of  magnesium  or 
acetate  of  lead  solution,  a  solution  of  milk-curdling  ferment  might  be  obtained 
which  is  perfectly  free  from  pepsin  ;  for  although  both  ferments  are  carried  down 
by  this  precipitate,  all  the  pepsin  remains  in  the  precipitate,  while  a  considerable 
amount  of  the  milk-curdling  ferment  passes  through  the  filter.  By  this  means 
Hammarsten  was  enabled  to  obtain  solutions  which  would  coagulate  fresh  milk  in 
'one  to  three  minutes  at  the  temperature  of  the  body,  even  in  neutral  fluids,  while 
when  acidulated  they  were  entirely  incapable  of  dissolving  the  smallest  particles 
of  fibrin. 

Little  is  known  as  regards  the  chemical  reactions  of  the  milk-curd- 
ling ferment.  It  does  not  coagulate,  when  in  wateiy  solutions,  by  boiling, 
nor  is  it  precipitated  by  alcohol,  nitric  acid,  iodine,  or  tannin.  It  is 
precipitated  by  the  basic  acetate  of  lead ;  it  does  not  give  a  yellow 
color  with  hot  nitric  acid ;  it  does  not  diffuse  through  parchment- 
paper,  and  only  with  difficulty  through  unglazed  earthenware.  Milk- 
curdling  ferment  is  a  less  stable  substance  than  pepsin  and  is  destro3red 
.at  a  lower  temperature  than  pepsin ;  thus,  if  a  solution  which  contains 
both  pepsin  and  milk-curdling  ferment  is  heated  about  forty-eight  hours 
to  37°  or  40°  C.  in  a  .02  per  cent.  HC1.  solution,  it  loses  all  power  of 


34-8  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

coagulating  milk,  while  the  pepsin  remains  unaffected.  In  neutral  solu- 
tions, on  the  other  hand,  the  milk-curdling  ferment  may  be  heated  up  to  70° 
C.,  or  even  may  be  boiled  for  a  moment  without  being  entirely  destroyed. 
Alcohol  only  slowly  interferes  with  the  milk-curdling  ferment ;  caustic 
alkalies  rapidly  destroy  it.  Even  .02  per  cent,  of  caustic  soda  is  suffi- 
cient to  cause  a  previously  active  ferment  solution  to  become  entirely 
inactive.  Salicylic  acid  does  not  interfere  with  its  action.  In  common 
with  the  other  ferments,  an  almost  infinitely  small  amount  of  this  ferment 
will  coagulate  an  immense  volume  of  milk.  Hammarsten  precipitated  a 
gtycerin  extract  of  milk-curdling  ferment  with  alcohol,  dissolved  the 
resulting  precipitate  in  water,  and,  since  the  percentage  of  solid  in  this 
solution  could  be  readily  determined,  was  able  to  estimate  that  one  part 
by  weight  of  milk-curdling  ferment  would  coagulate  at  least  from 
four  hundred  thousand  to  eight  hundred  thousand  parts  of  casein.  The 
milk-curdling  ferment  is  entirely  without  action  on  sugar  solutions  and 
is  without  influence  in  the  digestion  of  albumen.  It  has  been  found  that 
milk-curdling  ferment  is  principally  secreted  by  the  glands  of  the  fundus 
of  the  stomach,  while  the  pyloric  region  furnishes  but  a  small  amount  of 
this  ferment.  Milk-curdling  ferment  may  almost  invariably  be  found 
in  wateiy  extracts  of  the  stomach  of  the  calf  and  sheep,  while  in  other 
mammals  and  birds  it  is  usually  absent,  and  is  scarcely  ever  to  be  de- 
tected in  the  stomach  of  the  fish,  even  although  watery  extracts  of  the 
stomachs  of  these  animals  become  effective  after  being  first  acidulated 
and  then  after  twenty-four  hours  again  neutralized.  This  would  seem  to 
show  that  the  acid  serves  to  develop  milk-curdling  ferment  out  of  some 
previously  inactive  body.  The  coagulation  of  milk  by  the  milk-curdling 
ferment  is  more  analogous  to  the  process  of  coagulation  of  the  blood 
than  to  our  generally  accepted  ideas  as  to  the  processes  of  fermentation ; 
for  the  casein,  a  soluble  albuminoid  body,  through  the  action  of  rennet 
simply  becomes  insoluble  without  undergoing  any  other  change.  Its 
action  is,  therefore,  directly  opposed  to  that  of  pepsin,  which  converts 
an  insoluble  albuminoid  into  a  soluble  bodty. 

A  difference  also  exists  in  the  result  of  coagulation  of  milk,  accord- 
ing as  this  coagulum  has  been  produced  through  the  action  of  the 
ferment  or  by  the  development  of  acid.  In  the  latter  case  the  precipi- 
tate is  still  casein,  in  the  former  case  it  is  cheese.  In  the  former  instance 
the  casein  is  precipitated  in  fine,  tender  flocculi,  which  are  readily  soluble 
in  dilute  acid,  but  solutions  that  are  coagulated  by  rennet  are  very  much 
less  soluble. 

The  process  differs  still  further  in  that  the  casein  precipitated  by 
acids,  if  carefully  washed,  may  be  obtained  perfectly  free  from  ash. 
Casein  precipitated  by  a  milk-curdling  ferment,  on  the  other  hand,  always 
contains  phosphate  of  lime,  and  this  salt  seems  to  be  essential  to  the 


GASTKIC  DIGESTION.  349 

action  of  the  milk-curdling  ferment ;  for  rennet  is  entirely  ineffective 
when  the  earthy  phosphates  are  absent.  Thus,  if  casein  is  precipitated 
by  an  acid  and  dissolved  in  a  small  amount  of  alkali,  after  careful  wash- 
ing rennet  is  entirely  incapable  of  producing  a  coagulum ;  so  also  milk, 
when  subjected  to  dialysis,  by  which  means  the  salts  are  removed,  is 
incapable  of  coagulating  under  the  influence  of  rennet.  As  to  whether 
there  is  a  chemical  association  of  the  phosphates  in  the  production  of 
the  coagulum  by  the  action  of  rennet  or  not,  or  whether  it  acts  merely 
mechanically,  is  not  known. 

In  addition  to  the  milk-curdling  ferment,  which,  as  already  stated,  is 
said  to  be  entirely  ineffective  on  milk-sugar,  there  appears  to  be  still 
another  and  third  ferment  in  the  gastric  juice,  different  from  both  pepsin 
and  milk-curdling  ferment,  and  which  has  for  its  action  the  conversion 
of  milk-sugar  into  lactic  acid  ;  for  both  pepsin  and  rennet  may  be 
destroyed  by  the  action  of  a  dilute  caustic  soda  solution,  and  the  result- 
ing fluid  will  still  be  able  to  convert  milk-sugar  into  lactic  acid. 

(c)  The  Acid  of  Gastric  Juice. — The  greatest  controvers}^  has  for  a 
long  time  existed  as  to  the  nature  of  the  free  acid  of  gastric  juice.  The 
contradictions  on  this  subject  are  evidently  due  to  the  fact  that  in  the 
process  of  anatysis  the  hydrochloric  acid  usually  found  might  possibly 
originate  from  the  breaking  up  of  the  metallic  chlorides  which  are  con- 
stantly found  in  this  secretion. 

Prout  first  separated  hydrochloric  acid  from  gastric  juice  by  distil- 
lation, and  Lehmann  suggested  that  when  metallic  chlorides  are  distilled 
with  lactic  acid,  hydrochloric  acid  will  always  pass  into  the  distillate; 
and  on  account  of  this  objection  it  was  for  a  long  time  believed  that  the 
acidity  of  gastric  juice  was  normally  due  to  the  presence  of  free  lactic  acid. 

Schmidt's  a'natysis  of  gastric  juice,  however,  overcame  this  objection 
raised  by  Lehmann,  as  he  found  in  the  secretion  more  hydrochloric  acid 
than  could  saturate  all  the  bases  present.  Numerous  proofs  have  since  then 
been  brought  forward  which  all  tend  to  demonstrate  that  hydrochloric 
acid  in  a  free  state  is  the  cause  of  the  acid  reaction  of  this  secretion  ;  thus 
Richet  proved  by  the  degree  of  solubility  in  ether,  according  to  the 
method  pointed  out  by  Bertholet,  who  found  that  while  mineral  acids 
were  soluble  in  ether  organic  acids  were  insoluble,  that  the  acid  of  gastric 
juice  must  be  a  mineral  acid,  and  from  what  he  termed  the  coefficient  of 
partage  with  ether  that  acid  was  hydrochloric.  Still  another  proof  is 
found  in  the  fact  that  gastric  juice  behaves  like  mineral  acids  in  giving 
the  color  of  sulphocyanide  of  iron  when  added  to  a  solution  of  sulpho- 
C}ranide  of  potassium  and  citrate  of  iron  and  quinine  (Reoch) ;  while, 
still  further,  the  addition  of  gastric  juice  to  starch-mucilage  containing 
iodide  of  potassium  will  develop  the  blue  iodide  of  starch  by  liberating 
the  iodine  from  the  potassium. 


350  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

In  addition  to  these  tests,  a  number  of  reagents,  such  as  tropeolin,' 
methyl-violet,   Congo-paper,   etc.,   have    been   proposed   to   distinguish 
mineral  from  organic  acids.     The  best  of  the  more  recent  tests  is  phloro- 
glucin-vanillin,  described  by  Wiesner  and  Gunzburg.     Two  grammes  of 
phloroglucin  and  one  gramme  of  vanillin  form  a  reddish-yellow  solution 
with  thirty  grammes  of  absolute  alcohol.     A  drop  of  this  solution  in  the 
presence  of  a  trace  of  a  free  mineral  acid  forms  a  brilliant  red  color,  at 
the  same  time  depositing  bright-red  crystals.    On  the  other  hand ,  organic 
acids,  such  as  lactic  or  acetic  acids,  or  even  chlorides  mixed  with  these: 
acids,  produce  no  change  in  coloration. 

There  is  no  doubt  but  that  lactic,  butyric,  and  other  organic  acids 
may  be  present  in  gastric  juice,  but  their  origin  is  to  be  explained  by; 
their  respective  fermentations,  from  articles  of  food,  or  from  decompo- 
sition of  their  salts.  The  amount  of  free  acid  found  in  gastric  juice  ina> 
state  of  health  may  vary  from  0.02  per  cent.,  as  stated  by  Bidder  and 
Schmidt,  which  is  probably  a  low  estimate,  to  0.5  per  cent.,  as  estimated, 
by  Heidenhain,  in  the  gastric  juice  of  the  dog. 

The  degree  of  acidity  of  the  gastric  juice  differs  in  different  animals 
and  under  different  conditions.  In  the  dog,  Bidder  and  Schmidt  found' 
that  one  hundred  parts  of  filtered  gastric  juice  required  0.390  grammes 
potassium  hydrate  for  neutralization  ;  in  the  sheep,  one  hundred  parts  of 
gastric  juice  required  only  0.264  grammes  potassium  hydrate,  indicating 
in  a  general  way  that  the  degree  of  acidity  of  this  secretion  is  higher  in 
the  carnivora  than  in  the  herbivora. 

The  degree  of  acidity  varies  also  with  the  stage  of  gastric  digestion. 
Rothschild,  found,  after  the  administration  of  fifty  grammes  of  rare 
meat  and  three  hundred  and  twenty-eight  grammes  of  water  through  the. 
oesophageal  sound  in  healthy  individuals,  that  hydrochloric  acid  was  the 
only  acid  present.  The  degree  of  acidity  was  determined  by  removing 
the  contents  of  the  stomach  by  the  stomach-pump.  The  following  table 
shows  the  results  of  his  investigations : — 

After    ihour,  .        .  0.74  per  mille,  HC1. 

1  0.84 

H  hours, 0.99 

2  1.40 

2£       " 2.46 

3  " stomach  empty. 

There  seems  to  be  certain  reasons  for  supposing  that  hydrochloric' 
acid  is  not  entirely  free,  but  in  a  state  of  partial  combination  with  some 
substance  which  does  not  entirely  destroy  its  free  acidity.  Thus,  gastric 
juice  has  been  found  to  dialyse  differently  from  a  solution  of  hydrochloric ; 
acid  of  the  same  percentage. 

Numerous  theories  have  been  proposed  to  explain  the  formation  of 
the  free  acid  of  gastric  juice.     No  one  of  these  views  has  reached  the; 


GASTKIC  DIGESTION.  351 

dignity  of  a  demonstration.  It  is  known  that  the  acid  is  formed  only 
by  the  parietal  cells  of  the  gastric  tubules,  and  the  free  acid  is  found  on 
the  free  surface  of  the  gastric  mucous  membrane.  An  experiment 
devised  by  Bernard  serves  to  demonstrate  this.  For  the  production  of 
Prussian  blue  through  the  union  of  potassium  ferroc3'anide  and  a  salt 
of  iron,  an  acid  reaction  is  requisite.  Claude  Bernard  injected  potassium 
ferrocyanide,  and  afterward  a  solution  of  lactate  of  iron  into  the  veins 
of  a  dog.  When  examined  after  death,  the  blue  color  was  found  only  in 
the  upper  layers  of  the  gastric  mucous  membrane,  showing  thus  that 
this  locality  was  the  sole  seat  of  the  acid  reaction.  As  to  the  origin  of 
this  acidity,  it  appears  that  the  parietal  cells  of  the  gastric  glands  form 
hydrochloric  acid  from  the  chlorides  which  the  mucous  membrane  takes 
up  from  the  blood;  for,  if  sodium  chloride  be  withheld  from  the  food, 
the  formation  of  hydrochloric  acid  ceases.  The  active  agent  in  this 
splitting  up  of  the  chlorides  is  probably  lactic  acid,  which,  by  splitting 
up  sodium  chloride,  forms  free  hydrochloric  acid,  while  the  bases,  forming 
alkaline  salts,  are  excreted  by  the  urine.  The  renal  secretion  is,  there- 
fore, less  acid  during  digestion  than  in  the  intervals  of  digestion. 

The  following  tables  represent  the  quantitative  composition  of  gastric 
juice  in  different  animals  : — 

Water 

Organic  matter  (especially  ferments), 
Sodium  chloride,     .... 
Calcium  chloride,    . 
Hydrochloric  acid,          .        . 
Potassium  chloride,        .,       -.        .. 
Ammonium  chloride,      ..»,.. 
Calcium  phosphate,  ) 

Magnesium     "          > ,        0.125 

Ferric  "          ) 

2.  THE  ACTION  OF  GASTRIC  JUICE  ON  THE  FOOD. — The  general  solvent 
effects  of  the  gastric  juice  on  food-stuffs  may  be  roughty  illustrated  by 
means  of  an  experiment  devised  by  Schiff,  in  which  the  stomach,  removed 
from  the  body  and  placed  in  an  acid  medium,  is  capable  of  digesting 
itself.  If  the  stomach  is  removed  from  a  dog,  minced  into  small  pieces, 
and  infused  in  four  or  five  hundred  cubic  centimeters  of  HC1  of  0.02 
per  cent,  in  an  oven  at  40°  C.,  at  the  end  of  eight  to  ten  hours  the 
fragments  of  the  stomach  will  be  found  to  be  almost  entirely  liquefied. 
In  the  structures  of  the  stomach  are  found  the  principal  animal  sub- 
stances which  serve  as  nutriment.  Albumen  and  fibrin  of  the  blood  are 
present,  muscular  tissue,  and  connective  tissue.  These  substances  then 
being  dissolved,  as  may  be  demonstrated  by  the  fact  that  the  liquid, 
which  may  be  filtered  off  from  the  small,  pulpy  and  yellowish  residue,  is 
free  from  solid  material,  it  remains  only  to  determine  in  what  form  these 
albuminoid  constituents  of  the  tissues  are  present  in  the  solution. 


352  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

As  has  been  already  stated,  albumen  is  precipitated  from  its  solutions 
by  boiling  or  by  a  concentrated  mineral  acid.  If  the  filtrate  from  this 
autodigestion  of  the  stomach  is  boiled  no  coagulum  will  be  formed,  nor 
will  an  addition  of  nitric  acid  cause  any  precipitate.  .  If  albumen  is 
present  in  this  solution,  it  must,  therefore,  exist  in  a  modified  form. 

Millon's  test  and  the  xanthoproteic  reaction  will  indicate  in  this 
filtrate  the  presence  of  an  albuminoid  bod}7.  If  the  filtrate  be  neutralized 
by  the  careful  addition,  drop  by  drop,  of  a  little  liquor  potassse,  when  the 
fluid  is  perfectly  neutral  a  precipitate  will  be  formed.  These  tests  show 
that  while  albuminoid  bodies  do  exist  in  the  filtrate,  they  have  been  trans- 
formed by  the  gastric  secretions  into  other  members  of  the  proteid  group. 

Recollecting  the  statement  made  in  a  preceding  chapter  as  to  the 
effect  of  dilute  acid  on  albumen,  it  was  found  that  if  a  dilute  acid  was 
added  to  a  solution  of  albumen,  the  albumen  totally  lost  its  power  of 
coagulating  by  heat  and  was  rendered  insoluble  in  water.  It  was  there- 
fore thrown  out  of  solution  by  neutralization.  When  such  a  solution  of 
acid  albumen  was  exactly  neutralized,  the  filtrate  was  found  to  be  entirely 
free  from  proteid  in  solution.  If,  on  the  other  hand,  in  this  experiment 
of  autodigestion  by  the  stomach  the  precipitate  produced  by  neutraliza- 
tion is  filtered  off,  the  filtrate  will  still  show  the  presence  of  proteid  in 
large  amounts.  The  results  of  gastric  digestion  are  not,  therefore,  entirely 
identical  to  the  action  of  a  dilute  acid,  for  we  find  a  portion  of  proteid 
which  is  still  soluble  in  neutral  solutions  and  is  nevertheless  not  coagu- 
lated by  boiling ;  consequently,  the  modifications  of  albuminoids  produced 
by  the  action  of  the  gastric  juice  are  not  due  solely  to  the  acid  alone. 

This  fact  can  be  still  further  demonstrated  by  a  simple  experiment. 

In  four  test-tubes  may  he  placed  some  fragments  of  boiled  blood-fibrin.  In 
one  tube  are  placed  ten  cubic  centimeters  of  hydrochloric  acid  of  .02  per  cent.; 
in  No.  2  are  placed  ten  cubic  centimeters  of  artificial  gastric  juice  made  by 
adding  a  few  drops  of  glycerin-pepsin  extract  to  dilute  hydrochloric  acid,  as 
already  described  ;  in  No.  3  are  placed  ten  cubic  centimeters  of  the  same  arti- 
ficial gastric  juice  carefully  neutralized;  and  in  No.  4  ten  cubic  centimeters 
of  gastric  juice  thoroughly  boiled.  All  of  these  tubes  are  then  to  be  placed  in 
an  oven  heated  by  40  degrees  centigrade.  At  the  same  time,  duplicates  of  tube 
No.  2  are  to  be  prepared,  one  being  surrounded  with  ice  and  the  other  kept  at  the 
temperature  of  the  room.  On  examination  of  these  tubes  after  four  or  five  hours, 
it  will  be  found  that  in  tube  No.  1,  which  contained  acid  alone,  the  fibrin  is 
swollen  up  into  a  stiff  jelly,  but  has  not  been  dissolved.  In  No.  2,  which  con- 
tained artificial  gastric  juice,  the  fibrin  will  have  entirely  disappeared.  In  No.  3, 
which  contained  gastric  juice  neutralized,  or,  in  otherwords,  pepsin  in  solution,  the 
fibrin  will  be  unaltered,  while  in  No.  4,  which  contained  the  boiled  gastric  juice, 
the  appearances  will  be  identical  with  those  of  No.  1  It  may  be  learned  from 
this  that  fibrin  is  not  dissolved  by  acid  alone  nor  by  pepsin  alone,  but  that  their 
combination  is  necessary  for  its  solution,  while  it  is  also  seen  that  pepsin  is 
destroyed  by  heat.  By  referring  to  the  other  two  tubes,  it  will  be  seen  that  the 
fibrin  will  present  the  same  appearance  almost  as  seen  in  tube  No.  1,  showing, 
therefore,  that  cold  prevents  the  action  of  gastric  juice.  If,  however,  the  tube 
which  was  in  the  ice  is  placed  in  a  warm  oven,  the  fibrin  will  be  rapidly  digested, 
showing  that  its  solution  was  simply  suspended  by  cold.  The  solvent  action  of 
the  gastric  juice  is,  however,  totally  destroyed  by  boiling.  If  tube  No.  1  be  exactly 


GASTKIC   DIGESTION.  353 

neutralized,  the  fibrin  will  regain  its  original  appearance.  If  tube  No.  3,  which 
contained  the  neutralized  gastric  juice,  be  acidulated  to  proper  degree,  the  fibrin 
will  be  dissolved.  If  tube  No.  2  is  neutralized,  there  will  be  a  precipitate  varying 
in  amount  with  the  duration  of  the  digestion.  If  that  precipitate  be  filtered  off, 
the  filtrate  will  still  show  the  presence  of  a  proteid  body. 

The  results  of  gastric  digestions  are.  thus,  not  dependent  upon  the 
acidity  of  the  gastric  juice  alone,  for  we  find  that  when  the  neutraliza- 
tion product  is  filtered  off  there  still  remains  in  solution  in  the  filtrate 
a  large  quantity  of  proteid  matter.  This  substance  is  termed  peptone, 
and  has  the  same  elementaiy  composition  as  albumen  and  gives  most  of 
the  proteid  reactions,  it,  however,  differing  from  the  ordinanr  proteids 
in  several  respects.  In  the  first  place,  solutions  of  peptone  diffuse  readily 
and  are  readily  filtered.  Tlie}r  are  not  precipitated  by  boiling  and  nitric 
acid,  acetic  acid  and  potassium  ferrocyanide,  and  saturation  with  com- 
mon salt.  They  are  precipitated  from  neutral  or  faintly  acid  solutions 
by  mercuric  chloride,  tannic  acid,  bile  acids,  and  phosphowolframic  acid  ; 
they  will  yield  the  Millon's  and  xanthoproteic  tests,  and  with  caustic  soda 
or  potash  and  a  small  quantity  of  cupric  sulphate  they  give  a  beautiful 
purple-red  color  instead  of  the  violet  yielded  by  other  albuminous  bodies 
(Biuret  test).  They  rotate  the  plane  of  polarized  light  to  the  left.  When 
injected  into  the  blood  they  do  not  appear  in  the  urine,  as  is  the  case 
with  egg-albumen,  but  when  injected  in  large  amounts  produce  the  S3^mp- 
toms  of  a  narcotic  poison  and  prevent  coagulation  of  the  blood.  When 
dried,  peptones  are  amorphous,  transparent,  3^ello wish-white,  hygroscopic 
powders,  while  when  freshly  precipitated  they  closely  resemble  coagu- 
lated casein  in  appearance. 

When  proteids  are  subjected  to  the  action  of  gastric  juice,  the  acid 
first  transforms  the  albuminous  bodies  into  a  substance  analogous  to  acid 
albumen,  termed  parapeptone,  this  substance  thus  standing  midway 
between  the  albumen  and  peptone.  By  the  continued  effect  of  the  action 
of  the  gastric  juice,  principally  through  the  influence  of  the  pepsin,  the 
parapeptone  passes  into  a  true  soluble  peptone,  its  formation  being  due 
to  the  taking  up  of  a  molecule  of  water.  Under  the  influence  of  the 
hydrotytic  ferment  of  pepsin,  the  greater  the  amount  of  pepsin,  within 
certain  limits,  the  more  rapidly  the  solution  takes  place,  although  it 
seems  that  the  pepsin  is  not  used  up  in  the  process  of  gastric  digestion  ; 
and  if  the  degree  of  acidity  be  kept  uniform,  almost  unlimited  amounts 
of  albumen'  may  be  digested  by  a  small  amount  of  pepsin.  Large 
amounts  of  peptones  appear  to  interfere  with  the  digestion  of  albuminous 
bodies ;  but  if  the  peptones  are  removed  as  rapidly  as  formed,  digestion 
may  go  on  until  all  the  albumen  is  converted  into  peptones,  or  until  the 
acidity  has  disappeared. 

The  gastric  juice  only  digests  the  albuminous  constituents  of  food, 
vegetable  albuminoids  being  digested  in  the  same  manner  and  with  the 

23 


354  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

same  products  as  albuminoids  of  animal  origin.  On  carbohydrates  the 
ferment  of  gastric  juice  is  without  effect,  the  cases  reported  in  which 
starch  has  promptly  been  converted  into  sugar  in  the  stomach  being 
attributable  to  the  action  of  saliva  which  had  been  swallowed.  The  sali- 
vary ferment  is  not  destroyed  in  the  stomach,  since  saliva  may  be  kept 
for  days  together  in  contact  with  gastric  juice,  and  if  the  acid  be  then 
neutralized  the  diastatic  power  of  the  saliva  may  still  be  exerted.  The 
change  of  starch  into  sugar  in  the  stomach  will  vary  in  intensity 
according  as  the  animal  is  carnivorous  or  herbivorous.  In  the  former 
case  the  saliva  possesses  but  little  diastatic  power,  and  the  food  being 
swallowed  without  mastication  no  conversion  of  starch  into  sugar  may 
be  said  to  occur  in  the  mouth,  while  the  high  degree  of  acidity  of  the 
gastric  juice  will  almost  entirely  prevent  the  action  of  saliva  in  the 
stomach.  Carbohydrates,  therefore,  when  given  to  carnivora,  pass 
through  the  stomach  almost  unchanged,  and  are  only  converted  into 
sugar  when  brought  into  contact  with  the  pancreatic  and  intestinal  secre- 
tions. In  the  case  of  ruminant  herbivora  the  food  and  saliva  are  carried 
together  to  the  rumen,  where  the  high  temperature  and  alkaline  reaction 
favor  the  conversion  of  starch  into  sugar.  In  the  non-ruminant  her- 
bivora, as  in  the  horse  and  rabbit,  the  sojourn  of  the  food  in  the  mouth 
is  much  more  prolonged  than  in  other  animals,  and  time  is  given  for  the 
partial  conversion  of  starch  into  sugar  to  take  place.  When  the  uncon- 
verted starch  and  saliva  reach  the  stomach  the  process  ma}^  still  go  on, 
for,  in  the  first  place,  the  acidity  of  the  gastric  juice  is  much  less  in 
these  animals  than  in  carnivora,  and,  in  the  second  place,  as  will  be  shown 
directly,  the  acid  of  the  gastric  secretion  in  these  animals  in  the  first 
stage  of  digestion  is  lactic  and  not  hydrochloric  acid,  and  the  action  of 
ptyalin  may  still  take  place  in  a  fluid  containing  2  per  cent,  of  the  former 
acid,  while  it  ceases  in  0.5  per  cent,  of  the  latter.  By  the  time,  there- 
fore, that  hydrochloric  acid  has  been  substituted  for  lactic  acid,  it  may 
be  concluded  that  the  starch  has  been  mainly  converted  into  sugar. 

Again,  cane-sugar  is  slowly  converted  in  the  stomach  into  invert- 
sugar,  apparently  through  the  influence  of  hydrochloric  acid.  Fats  are 
but  slightly  digested  by  gastric  juice,  it  appearing  that  a  small  part  of 
the  fat  is  broken  up  into  glycerin  and  fatty  acids.  When  adipose  tissue 
is  subjected  to  the  action  of  gastric  juice,  the  albuminous  cell-envelopes 
are  dissolved  and  the  fat  liberated  in  the  form  of  free  oil-globules,  only 
a  small  portion  of  which  is  broken  up  into  fatty  acids  and  glycerin,  while 
the  remainder  escapes  into  the  small  intestines  to  be  acted  upon  by  the 
pancreatic  secretion.  When  milk  is  introduced  into  the  stomach,  the 
casein,  through  the  action  of  the  milk-curdling  ferment,  together  with 
the  acid  of  the  gastric  juice,  is  coagulated  and  forms  the  curd,  in  which 
the  oil-globules  are  held.  In  a  subsequent  stage  of  digestion,  the  casein 


GASTEIC   DIGESTION.  355 

is  dissolved  and  converted  into  peptone,  and  the  oil  is  again  liberated. 
When,  therefore,  artificial  gastric  juice  is  added  to  milk  warmed  to  the 
temperature  of  the  body,  the  casein  is  rapidly  coagulated  and  a  toler- 
ably firm,  white  curd  is  formed,  floating  in  the  clear  fluid,  the  whey,  which 
contains  the  salts,  milk-sugar,  water,  and  albumen  of  the  milk.  As 
digestion  progresses,  the  casein  being  turned  into  peptone,  the  oil  is  set 
free  and  the  whey  again  becomes  milky,  from  the  oil  again  passing  into 
the  state  of  partial  emulsion. 

Gelatin  and  connective  tissues  are  dissolved  and  peptonized  by  the 
gastric  juice.  When  gelatin  has  been  subjected  to  the  action  of  gastric 
secretion,  its  solutions  no  longer  solidify  when  cold,  but  a  gelatin-pep- 
tone is  formed  which  is  soluble  and  diffusible,  although  it  differs  from  a 
true  peptone.  When  muscular  tissue  is  subjected  to  the  action  of  gastric 
juice,  the  sarcolemma  becomes  dissolved,  the  muscle-fibre  breaks  up 
traiisversel}' into  disks,  which  become  dissolved  and  converted  ultimately 
into  a  true  peptone.  Horny  tissues  are  unchanged  by  gastric  juice,  as 
is  also  anryloid  substance.  Red  blood-corpuscles  are  dissolved  in  the 
stomach,  the  haemoglobin  being  decomposed  into  haematin,  and  the  glob- 
ulin is  ultimately  transformed  into  peptone,  while  the  hsematin  is  partly 
unchanged  and  partly  converted  into  bile-pigment. 

That  the  stomach  is  able  to  digest  albuminous  bodies  of  the  most 
varying  nature,  and  yet  escape  digestion  itself  by  its  own  secretion,  is  a 
fact  of  which  explanation  has  as  yet  never  been  clearty  determined.  It  has 
been  attributed  to  the  alkalinity  of  the  blood  in  the  tissues  neutralizing 
the  gastric  juice  and  so  protecting  the  tissues  of  the  stomach  ;  if  that 
were  so,  we  would  expect  that  the  pancreatic  secretion,  being  most  active 
in  an  alkaline  medium,  would  be  aided  by  the  alkalinit}r  of  the  blood  in 
digesting  the  walls  of  the  intestine.  The  protection  of  the  walls  of  the 
stomach  during  digestion  has  been  attributed  to  the  mucus  or  the 
epithelium  lining  the  stomach ;  both  may,  however,  be  mechanically 
removed  through  a  gastric  fistula — and  both  are,  undoubtedly,  at  least 
partially  removed  in  the  use  of  the  stomach-sound — and  yet  without  the 
walls  of  the  stomach  being  digested. 

The  obscurity  is  rendered  still  more  intense  by  the  fact  that  under 
certain  circumstances  the  stomach  does  digest  itself.  If  an  animal  be 
killed  during  active  digestion,  and  the  body  kept  at  an  elevated  temper- 
ature, the  walls  of  the  stomach  will  be  digested ;  or  if  the  stomach  be 
excised  from  an  animal  and  covered  with  dilute  hydrochloric  acid,  it  will 
be  almost  -completely  dissolved.  These  facts  have  been  attributed  to  the 
absence  of  vitality ;  but  if  the  leg  of  a  living  frog  be  inserted  through 
a  fistula  into  the  stomach  of  a  dog  it  will  be  completely  digested,  and 
in  the  maintenance  of  a  gastric  fistula  in  dogs  it  will  often  be  noticed 
that  the  edges  of  the  wound  become  corroded  from  the  escape  of  gastric 


356 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


juice  along  the  sides  of  the  cannula.  The  subject  must,  therefore,  be  left 
where  we  started :  the  stomach  during  life  does  not  digest  itself,  but  its 
immunity  cannot  be  satisfactorily  explained. 

3.  THE  SECRETION  OF  GASTRIC  JUICE. — The  walls  of  the  stomach  are 
constituted  by  four  coats,  composed  externally  of  the  peritoneum  or 
serous  layer ;  second,  the  muscular  layer,  composed  of  longitudinal,  cir- 
cular, and  oblique  unstriped  muscular  fibres  ;  third  ^Q  subrnucous  layer 
of  connective  tissue,  in  which  are  found  numerous  blood-vessels,  lymphat- 
ics, and  glands;  and,  fourth,  the  inter- 
nal mucous  coat,  in  which  are  found 
the  glands  of  the  stomach.  The  mu- 
cous membrane  is  covered  throughout 
its  entire  extent  by  a  single  layer  of 
narrow,  cylindrical,  epithelial  cells 
similar  to  the  ordinary  mucus-secreting 
goblet  cells.  The  tubular  glands  of 
the  stomach  are  of  two  distinct  kinds, 
traversing  the  mucous  membrane  ver- 
tically and  differing  greatly  as  they 
are  located  in  the  cardiac  or  pyloric 
portions  of  the  stomach.  The  glands 
found  in  the  cardiac  portion  of  the 
stomach  or  fundus  are  called  the  peptic 
glands,  and  consist  of  several  short 
tubules  opening  into  a  broad  duct 
which  is  lined  by  epithelial  cells  similar 
to  those  on  the  free  mucous  membrane 
of  the  stomach.  The  lower  portions  of 
the  tubes,  those  portions  which  alone 
form  the  gastric  secretion,  are  lined  by 
a  layer  of  small  granular,  columnar, 
nucleated  cells  (Fig.  148).  These 
cells  border  the  lumen  of  the  gland 
and  are  termed  the  chief  or  central 
cells.  At  various  places  between 

these  cells  and  the  membrana  propria  are  large,  oval  or  angular  granu- 
lated, nucleated  cells,  which  are  termed  parietal  cells.  These  cells  are 
most  numerous  in  the  necks  of  the  glands  and  less  so  in  the  lower  ends  of 
the  tubules  (Fig.  149).  They  are  stained  deeply  by  osmic  acid  and 
aniline  blue,  and  bulge  out  the  membrana  propria  opposite  to  where  they 
are  placed,  and  are  thus  readily  recognized. 

The  pyloric  glands  (Fig.  150)  are  generally  branched  at  their  lower 
ends,  several  tubes  opening  into  a  single  duct,  which  is  long  and  wide. 


FIG.  148.— GLANDS  OF  THE  FUNDUS  OF 
THE  STOMACH.  (Heidenhain.) 


GASTRIC   DIGESTION.  357 

The  duct  is  lined  by  epithelium  like  that  lining  the  stomach,  while  the 
deeper  part  is  lined  by  a  single  layer  of  short,  fine,  granular,  columnar 
cells. 

It  is  thus  seen  that  the  glands  of  the  fundus  and  pylorus  are  histo- 
logically  different,  and  it  has  been  found  by  the  method  of  partial  fistula, 
by  excising  certain  portions  of  the  stomach,  that  the  character  of  the 
secretions  formed  b}^  these  cells  is  also  different.  Here  also,  as  in  the 
salivary  glands,  changes  occur  in  the  interior  of  the  cells  according  as 
the  gland  is  active  or  has  been  exhausted.  During  fasting  the  chief 
cells  of  the  fundus  and  all  the  cells  of  the  pyloric  glands  are  clear  and 
of  moderate  size.  During  digestion  the  chief  cells  become  enlarged 
or  turbid  and  granular ;  the  parietal  cells  also  enlarge,  while  the  pyloric 
cells  remain  unchanged,  and  only  become  enlarged  toward  the  ter- 


FIG.  149.— CROSS-SECTION  OF  THE  GLANDS  OF  THE  FUNDUS  OF  THE  STOMACH. 

(Heidenhain.) 
A,  through  the  body  of  the  gland ;  B,  through  the  neck. 

mination  of  digestion.  Often  during  the  last  hours  of  digestion  the 
chief  cells  again  become  larger  and  clearer,  the  parietal  cells  diminish, 
and  the  p3Tloric  cells  decrease  in  size  and  become  turbid.  We  therefore 
see  that  there  are  three  different  forms  of  anatomical  elements  found 
in  the  stomach,  and  these  different  cells  furnish  different  forms  of  gastric 
secretion  (Figs.  151  and  152).  When  the  stomach  is  empty  its  reaction  is 
alkaline  and  its  mucous  surface  is  covered  with  a  layer  of  mucus  which 
is  formed  from  the  cylindrical  epithelial  cells,  which  line  the  free  surface  of 
the  mucous  membrane  and  dip  into  the  ducts  of  the  glands.  The  gastric 
juice  proper  comes  from  the  tubules  which  line  the  entire  stomach  with 
the  exception  of  the  cardiac  and  extreme  pyloric  ends.  Gastric  juice, 
as  has  been  seen,  contains  pepsin,  In^drochloric  acid,  and  the  milk-curd- 
ling ferment.  The  pepsin  is  formed  by  the  chief  cells  found  throughout 


358 


PHYSIOLOGY   OF   THE   DOMESTIC    ANIMALS. 


all  the  tubular  glands  of  the  stomach.  When  these  cells  are  clear  and 
large  the}^  then  contain  their  maximum  amount  of  pepsin.  After  the 
secretion  of  gastric  juice  has  lasted  for  some  time,  these  cells  become 
contracted  and  turbid  and  then  contain  but  a  small  amount  of  pepsin. 
According  to  certain  authorities,  pepsin  is  not  directly  formed  in  the  cells 
of  these  tubular  glands,  but  results  from  the  transformation,  by  means  of 
hydrochloric  acid  or  sodium  chloride,  of  a  mother-substance  or  zymogen 
which  has  been  termed  pepsinogen. 


FIG.  150.— PYLORIC  G.LANDS  OF  THK  STOMACH. 
( Hcidcnhain. ) 


FIG.  151.  —  PYL.ORIC  GLANDS  —  COM- 
MENCING CHANGES  DURING  DIGES- 
TION, AFTER  EBSTEIN.  (Heidenhain.) 


These  statements  as  to  the  formation  of  pepsin  are  based  upon  the 
fact  that  the  secretion  withdrawn  from  the  isolated  cardiac  or  pyloric 
extremity  of  the  stomach  contains  pepsin  in  abundance,  although  the 
quantity  is  more  marked  in  the  secretion  formed  by  the  glands  of  the 
fundus.  So,  also,  in  the  frog,  glands  similar  in  character  to  those  con- 
taining chief  cells  are  found  in  the  tubules  located  in  the  lower  portion 


GASTEIC   DIGESTION. 


359 


of  the  oesophagus.  Here,  also,  the  secretion  poured  out  })y  the  glands 
of  this  locality  is  alkaline,  and  yet  contains  pepsin,  while  a  watery 
infusion  of  this  part  of  the  frog's  stomach  is  also  highly  peptic.  On  the 
other  hand,  the  hydrochloric  acid  is  formed,  according  to  Heidenhain,by 
the  parietal  or  associate  cells,  which  are  found  onl}-  in  the  glands  of  the 
fundus.  This  statement,  also,  has  been  proved  by  the  determination 
that  the  secretion  alone  of  the  fundus  during  active  digestion  has  an 
acid  reaction,  while  that  of  the  pylorus  never  acquires  any  acidity.  So, 


FIG.  152.— GLANDS  OF  THE  FUNDUS  OF  THE  STOMACH.    (Hcidenhain.) 

A  and  At,  during  fasting ;  B,  first  stage  of  digestion :  enlargement  of  the  chief  cells  and  commencing  turbidity  ;  C  and 
D,  secqnd  stage  of  digestion :  the  chief  cells  become  smaller  in  size  and  more  and  more  turbid. 

again,  in  the  frog  these  associate  cells  are  found  in  the  stomach,  and  not 
in  the  tubular  glands  of  the  oesophagus,  and  it  is  known  that  in  the 
stomach  alone  free  acid  is  formed.  Again,  in  hibernating  animals  the 
chief  cells  disappear,  and  in  these  animals  the  secretion  of  gastric  juice 
never  acquires  an  acid  reaction.  The  milk-curdling  ferment  is,  probably, 
also  formed  by  the  central  cells,  especially  those  of  the  pyloric  extremity, 


360  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

since  it  has  been  found  that  it  is  this  locality  of  the  stomach  which 
yields  the  milk-curdling  ferment  in  largest  amounts. 

As  regards  the  action  of  the  nervous  system  on  the  secretion  of 
gastric  juice,  very  little  is  known.  It  seems  clear  that  this  secretion, 
like  that  of  the  saliva  and  of  other  glands,  is  a  reflex  process;  for  when 
the  stomach  is  empty  there  is  no  secretion  of  gastric  juice,  which  only 
takes  place  when  proper  stimuli  are  applied  to  the  mucous  membrane  of 
the  stomach.  Such  stimuli  may  be  either  mechanical  or  chemical,  and 
the  immediate  result  of  their  contact  is  to  cause  an  increase  in  the 
activity  of  the  circulation  through  the  walls  of  the  stomach,  with  a  con- 
sequent increase  in  temperature  which  ma}^  amount  to  as  much  as 
1°  C.  The  mechanism  of  secretion,  therefore,  is,  in  all  probability, 
identical  with  that  of  other  glands.  The  nerves  which  influence  the 
secretion  are  almost  totally  unknown,  since  no  nerve  has  been  found 
whose  stimulation  leads  to  the  secretion  of  gastric  juice  in  a  manner  at 
all  analogous  to  that  which  results  from  the  stimulation  of  the  chorda 
tympani  in  producing  the  secretion  of  saliva.  It  seems  probable  that  the 
centres  whose  reflex  stimulation  leads  to  the  flow  of  gastric  juice  are 
located  in  the  stomach,  for  both  the  pneumogastric  and  sympathetic 
nerves  may  be  divided,  and  local  stimulation  of  the  gastric  mucous 
membrane  will  still  lead  to  a  flow  of  gastric  juice.  The  pneumogastrics, 
nevertheless,  besides  being  the  sensory  nerves  of  the  stomach,  seem  to  be 
concerned  in  the  production  of  the  vascular  dilatation,  which  is  of  such 
importance  in  the  production  of  the  secretion ;  for,  if  both  pneumo- 
gastrics are  divided  during  digestion,  the  mucous  membrane  of  the 
stomach  becomes  pale.  The  secretion  of  gastric  juice  is  also  undoubt- 
edly in  some  way  connected  with  the  central  nervous  system,  for  Richet 
has  noted  the  fact  that  in  a  case  of  complete  cesophageal  stricture, 
observation  of  the  stomach  through  a  fistulous  opening  into  this  organ 
proved  that  the  secretion  of  gastric  juice  followed  the  introduction  of 
acids  or  sugar  into  the  mouth. 

4.  GASTRIC  DIGESTION  IN  CARNIVORA — The  importance  of  the  stom- 
ach in  the  operation  of  digestion  varies  greatly  in  different  animals. 
In  the  carnivora  the  action  of  the  stomach  is  less  constant  than  in  the 
herbivora,  but  is  of  greater  importance.  While  its  action  is  intermittent, 
the  intervals  between  its  periods  of  activity  and  the  duration  of  its 
activity  are  more  prolonged.  Carnivora  swallow  their  food  in  large  frag- 
ments, torn  only  small  enough  to  be  swallowed,  and  in  many  cases 
swallow  their  prey  entire.  Their  mastication  is  of  slight  importance,  for 
they  feed  on  substances  readily  soluble  in  gastric  juice,  the  only  function 
of  the  saliva  being  to  render  the  food  easy  of  deglutition,  it  having 
scarcely  any  digestive  function  to  fulfill.  In  carnivora,  as  already  stated, 
the  conformation  of  the  mouth,  pharynx,  and  gullet  enables  large  masses 


GASTKIC  DIGESTION.  361 

of  animal  matter  to  be  introduced  into  the  stomach.  The  gastric  mucous 
membrane  secretes  gastric  juice  throughout  its  entire  extent,  and  the 
digestion  in  the  stomach  in  carnivora  is  the  most  important  stage  in  the 
preparation  of  food  for  absorption.  The  secretion  is  rapidly  poured  out 
after  taking  a  meal,  the  activity  being  in  accordance  with  the  degree  of 
stimulation  which  the  aliments  exercise  on  this  viscus.  Thus,  there  is 
less  secretion  formed  when  gelatin,  gum,  starch,  and  other  indigestible 
substances  are  swallowed,  while  the  secretion  is  copious  when  meat,  bone, 
and  other  albuminous  bodies  are  introduced  into  the  stomach.  The  total 
amount  of  gastric  juice  secreted  by  carnivora  can  only  be  determined 
with  difficulty.  It  has  been  stated  as  one  hundred  grammes  for  each  kilo 
of  body  weight — an  amount  which  is  evidently  too  large  ;  probably  one- 
fourth  the  amount  would  be  nearer  the  truth.  As  the  gastric  juice  of 
the  carnivora  is  obtained  with  the  greatest  readiness,  it  is  the  secretion 
which  has  been  most  studied.  It  contains  a  larger  percentage  of  acid 
and  pepsin  than  that  of  omnivorous  and  herbivorous  animals,  and  in 
equal  time  will  digest  four  times  as  much  cooked  albumen  as  the  gastric 
juice  of  the  sheep.  It  has  been  stated  that  a  dog  is  able  to  digest  one-, 
fifth  of  his  own  weight  at  one  meal.  Nevertheless,  the  gastric  juice  does 
not  convert  all  the  food  taken  into  the  stomach  into  peptones  ;  a  large 
part  is  merely  disintegrated  and  passes  into  the  small  intestine  to  be 
acted  upon  by  the  pancreatic  juice.  When  excessive  amounts  of  meat 
are  taken,  as  is  occasionally  the  case  in  young  dogs,  it  will  escape  entirely 
unaltered  through  the  intestines.  Considerable  time  is  required  for 
gastric  digestion  in  carnivora.  Thus,  albumen  given  to  dogs  has  been 
found  still  coagulable  by  heat  after  a  sojourn  of  three  hours  in  the 
stomach,  indicating  that  in  a  certain  portion  digestion  had  not  com- 
menced. Again,  coagulated  albumen  has  been  found^  unaltered  after  a 
period  of  four  hours ;  fibrin  has  been  found  swollen  and  transparent, 
but  not  dissolved ;  while  gluten,  after  having  remained  four  hours  in  the 
stomach,  has  been  found  almost  unaltered. 

Spallanzani  states  that  masses  of  meat  inclosed  in  tubes  were  found 
partially  undigested  after  eleven  hours,  while  Colin  claims  that  at  least 
twelve  hours  are  required  for  a  carnivore  to  digest  the  amount  of  meat 
which  it  would  take  spontaneously  at  a  single  meal.  Thus,  Colin  gave 
to  a  cat  which  had  fasted  for  twent.y-four  hours  two  hundred  grammes  of 
horse-meat,  'and  found  that  five  hours  afterward  the  stomach  contained 
one  hundred  and  fifty  grammes  of  unaltered  meat;  but  fort}T-five  grammes, 
therefore,  or  only  about  one-fourth,  having  been  disintegrated.  To  another 
cat  two  hundred  grammes  of  horse-meat  were  given  after  fasting  twenty 
hours,  and  after  twelve  hours  sixty-four  grammes  could  still  be  recog- 
nized. Similar  data  were  also  obtained  in  the  case  of  the  dog.  It  is  not 
astonishing  that  the  food  remains  so  long  in  the  stomach.  Time  is  given 


362  PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 

for  the  digestion  of  ligaments,  tendons,  and  often  cartilages  and  bones, 
and  such  substances  will  often  remain  in  the  stomach  for  days  at  a  time. 
The  digestibility  of  certain  kinds  of  animal  food  appears  to  be  altered 
according  as  the  substances  are  cooked  or  raw ;  gelatinous  tissues,  such 
as  tendons,  are  more  readily  digested  when  cooked,  evidently  due  to  the 
conversion  of  the  collagenous  bodies  into  gelatin.  Albuminous  tissues, 
on  the  other  hand,  especially  the  glandular  structures,  such  as  liver, 
kidney,  etc.,  lose  in  digestibility  when  cooked,  unless  the  cooking  is  very 
prolonged,  when  a  stage  of  peptonization  may  be  inaugurated.  Muscular 
tissue  seems  to  be  equally  digestible  when  raw  as  when  cooked.  Feed- 
ing on  raw  meat  is  the  natural  normal  diet  of  the  pure  caririvora,  and 
even  carnivorous  animals  in  a  state  of  domestication  appear  to  digest 
raw  meat  more  regularly  and  with  less  diarrhoea  than  when  fed  on  cooked 
meat,  which  is  often  followed  by  a  fetid  diarrhoea;  thus,  a  little  raw  meat 
given  to  dogs  will  keep  their  skin  supple,  the  hair  soft,  and  their  general 
condition  will  be  improved. 

From  what  has  been  said,  it  is,  then,  clear  that  ordinary  house  refuse  is  all 
that  dogs  require  for  food.  When  a  number  of  dogs  are  kept,  this  will  not,  as  a 
rule,  be  sufficient ;  so,  then,  it  is  necessary  to  give  some  further  idea  as  to  the 
best  and  most  economical  plans  of  feeding  a  kennel  of  dogs.  For  ordinary  feed- 
ing in  town,  as  recommended  by  Dinks  and  Mayhew,  beef-heads,  sheep-heads,  feet, 
and  offal  should  be  cleaned,  chopped  up,  boiled  in  water,  filling  up  the  kettle  as 
the  water  boils  away,  until  all  the  meat  separates  in  shreds.  To  this  may  be 
added  a  little  salt  and  any  cheap  vegetable,  such  as  cabbage,  parsnips,  potatoes, 
or  turnips.  Put  this  soup  aside,  and  then  boil  old  Indian  meal  till  it  is  quite  stiff; 
let  it  also  get  cold.  When  required,  take  as  much  meal  as  may  be  required,  and 
enough  broth  to  liquefy  it. 

In  the  country,  during  the  summer,  skimmed  milk,  sour  milk,  buttermilk,  or 
whey  may  be  used  in  place  of  the  broth.  In  the  winter  the  soup  should  be  alter- 
nated with  meal — never  use  new  Indian  meal,  it  scours.  Although  Indian  meal 
has  not  as  much  sugar  or  albumen  as  oats,  it  does  tolerably  well ;  but  when  a  great 
amount  of  work  is  expected  of  the  dogs,  as  in  a  month's  shooting  excursion,  oat- 
meal should  always  be  used,  as  a  less  bulk  is  more  nourishing  than  Indian  meal, 
and  old  meal  cannot  always  be  obtained,  or  meat  to  make  soup.  Oatmeal-porridge 
and  milk  are  capital  under  such  circumstances. 

In  a  house  there  are  always  bones,  potato-peelings,  and  pot-liquor  :  by  clean- 
ing all  the  potatoes,  and  throwing  all  into  the  dog-pot,  the  dogs  are  greatly 
benefited.  Rutabagas  are  good  boiled  in  soup.  Boiled  meat  alone  seems  to 
destroy  the  scent  of  dogs ;  so,  also,  greasy  substances. 

Alimentary  substances  introduced  into  the  stomach  are  changed  in 
the  way  already  indicated.  All  albuminous  bodies  are  converted  into 
peptone.  Starch  may  be  slightly  converted  into  sugar  through  the  action 
of  the  salivary  ferment,  or,  after  passing  into  the  intestine,  through  the 
action  of  the  pancreatic  ferment.  Herbaceous  matters  are  not  digested 
by  dogs,  even  though  often  taken  in  great  quantities,  and  they  are  either 
again  vomited,  pass  in  the  faeces,  or  may  cause  intestinal  obstruction. 
When  raw  vegetable  substances  are  swallowed  by  carnivorous  animals  it 
is  only  the  salts  of  vegetable  acids  which  are  extracted,  while  the  skele- 
tons, containing  starch  and  albuminous  matters,  remain  behind.  It  is 


GASTKIC   DIGESTION.  363 

probably  the  need  of  the  extraction  of  these  vegetable  acids  which  leads 
dogs  so  often  in  the  spring  to  eat  grass. 

As  the  substances  contained  in  the  stomach  are  liquefied,  they  pass 
gradually  by  the  contraction  of  the  walls  of  the  stomach  and  relaxation 
of  the  pylorus  into  the  small  intestine.  Indigestible  substances  may 
remain  in  the  stomach,  either  to  be  vomited  or  finally  to  pass  into  the 
intestine. 

5.  GASTRIC  DIGESTION  IN  OMNIVORA. — In  the  omnivora  gastric 
digestion  offers  similar  characteristics  to  those  noted  in  the  case  of  the 
carnivora,  though  it  is  slower  and  less  complete.  Thus,  Colin  states  that 
after  giving  one  thousand  grammes  of  raw  meat  to  a  hog  six  hundred 
grammes  were  found  in  the  stomach  six  hours  after  feeding,  while 
undigested  pieces  were  found  in  the  small  intestine.  In  another  case  a 
hog  which  had  received  three  kilos  of  meat  with  one  litre  of  water  had 
only  digested  three  hundred  grammes  in  six  hours.  We  thus  see  that 
while  the  hog  is  an  omnivorous  animal,  it  is  not  less  capable  of  digesting 
animal  matters  than  are  the  pure  carnivorous  animals.  While  this  is, 
however,  the  case,  from  their  imperfect  mastication  they  are  less  consti- 
tuted for  the  extracting  of  nutritive  principle  from  the  vegetable  matter 
than  the  purely  herbivorous  animals. 

The  stomach  of  the  hog  is  generally  described  as  a  simple  stomach, 
but  it  really  represents  a  stage  of  transition  between  the  simple  stomach 
of  carnivora  and  the  complex  stomachs  of  ruminants.  Even  on  external 
examination,  by  the  presence  of  a  constriction  at  the  cardiac  and  pyloric 
extremity  the  presence  of  well-marked  diverticula  is  evident.  On 
inspecting  the  interior,  Ellenberger  and  Hofmeister,  who  have  been 
mainly  followed  in  this  description,  show  that  the  organ  may  be  divided 
into  five  distinct  regions :  1.  The  cesophageal  portion,  which  is  coated 
with  a  mucous  membrane,  cutaneous  in  character,  similar  to  that  lining 
the  O3sophagus,  and  which  is  separated  by  a  distinct  border  from  the 
secreting  membrane.  It  contains  no  glands,  but  is  papillated,  though  to 
a  less  degree  than  the  left  half  of  the  horse's  stomach.  2.  The  cardiac 
diverticuium,  lined  with  a  white,  thin  mucous  membrane,  which  is  sepa- 
rated by  a  fold  of  mucous  membrane  from  the  fundus  of  the  stomach. 
The  mucous  membrane  of  this  portion  of  the  hog's  stomach  is  coated 
with  cylindrical  epithelium  and  contains  tubular  glands,  which  are  shorter 
than  the  fundus  glands,  and  composed  of  small,  transparent,  granular 
cells,  different  from  those  found  in  any  other  region.  Lymph-follicles 
are  numerous,  and  in  some  places  so  close  together  as  to  resemble 
Pe3-er's  patches.  3.  The  left  zone,  or  fundus,  constituting  one-third  or 
one-half  the  stomach,  lined  with  a  glandular  membrane,  similar  to  that 
of  the  cardiac  diverticulum ;  it  contains,  however,  a  smaller  relative 
number  of  follicles.  4.  The  central  zone  includes  the  greater  curvature, 


364  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

and  extends  toward  the  pylorus  and  cesophageal  portion,  its  extremities 
being  triangular.  The  mucous  membrane  in  this  region  is  very  thick 
and  brownish-red  in  color,  and  contains  the  so-called  fundus  glands. 
These  are  tubular  in  structure,  longer,  but  subdivided  to  a  less  degree 
than  the  pyloric  glands.  The  ducts  of  these  tubules  are  lined  with  epi- 
thelium similar  to  that  lining  the  cavity  of  the  stomach,  while  the  fundus 
contains  chief  and  associate  cells  similar  to  those  found  in  the  stomachs 
of  carnivora,  with  the  exception  that  the  associate  cells  lie  in  groups 
external  to  the  cylindrical  cells.  5.  The  right  or  pyloric  zone  includes 
the  pylorus,  as  much  of  the  lesser  curvature  as  does  not  belong  to  the 
cesophageal  portion,  and  a  small  portion  of  the  greater  curvature.  Its 
mucous  membrane  is  white  in  color,  and  in  the  pylorus  very  thin, 
though  much  thicker  at  the  entrance  to  the  pylorus  ;  the  submucosa 
is  sparsely  developed.  After  death  the  pyloric  zone  is  generally  found 
coated  with  a  thick  layer  of  mucus,  stained  yellowish  from  the  bile.  The 
glands  of  this  portion  are  considerably  longer  than  those  found  elsewhere, 
are  subdivided  and  convoluted.  Associate  cells  are  entirely  wanting  in 
the  pyloric  zone,  the  cells  being  cylindrical  and  granular  or  hyaline. 

As  Ellenberger  and  Hofmeister  pointed  out,  the  stomachs  of  mam- 
mals may  be  divided  into  two  different  .groups,  in  one  of  which  cesoph- 
ageal diverticula,  and  in  the  other  diverticula  of  the  stomach  itself, 
represent  the  mode  of  deviation  from  the  simple  gastric  form.  When 
both  forms  of  diverticula  are  present,  the  true  compound  stomach  is 
represented.  The  gastric  formation,  with  a  divert iculum  formed  from 
the  glandular  stomach  itself,  is  met  with  in  many  herbivora  and  omniv- 
ora,  and  such  carnivora  as  live  on  highly  indigestible  animal  substances. 

In  its  simplest  form  the  part  near  the  pylorus  is  dilated  into  a 
pouch-like  expansion ;  such  a  form  is  met  with  in  the  hog,  but  is  still 
further  complicated  by  a  saccular  expansion  at  the  cardiac  extremity. 
Such  a  formation  evidently  lengthens  the  period  of  retention  of  the 
food  within  the  stomach,  and  by  an  increase  in  the  internal  surface  of 
the  stomach  permits  of  a  more  continuous  action  of  the  gastric  juice, 
since  it  corresponds  to  an  increase  in  the  secreting  surface. 

In  the  development  of  the  compound  stomach  through  the  forma- 
tion of  cesophageal  dilatations,  the  stomach  of  the  hog  represents  the 
first  stage. 

The  second  stage  is  found  in  the  stomach  of  the  horse,  where  the 
entire  left  half  of  the  stomach  may  be  regarded  as  an  oesophageal 
expansion  ;  and  while  the  stomach  of  the  horse  from  external  view 
resembles  a  simple  stomach,  internal  examination  shows  that  it  is 
practically  a  compound  stomach. 

The  highest  degree  of  development  of  the  cesophageal  pouches  is, 
of  course,  seen  in  the  stomachs  of  ruminants. 


GASTRIC  DIGESTION.  365 

The  gastric  juice  of  the  hog  contains  the  same  ferments  as  are  found 
in  the  secretion  of  other  mammals  ;  it  dissolves  albuminates  and  con- 
verts them  into  peptone,  parapeptone,  and  syntonin,  and  coagulates 
milk,  and,  to  a  slight  degree,  as  in  the  case  of  other  mammals,  splits  up 
fats  into  glycerin  and  fatty  acids. 

The  secretion  obtained  from  different  portions  of  the  stomach  differs  ; 
that  obtained  from  the  greater  curvature  contains  more  mucin,  more 
acid,  and  more  ferment  than  that  from  the  other  portions,  while  the 
secretion  from  the  cesophageal  portion  is  free  from  ferment. 

In  the  secretion  from  the  greater  curvature,  as  obtained  by  the 
making  of  extracts  with  common  salt,  the  degree  of  acidity  varies  from 
0.03  to  0.07  per  cent. 

The  portion  of  the  stomach  supplied  with  the  associate  cells  con- 
tains all  the  ferments  in  the  greatest  quantity.  Small  amounts  are  found 
in  the  pyloric  region,  and  a  still  smaller  amount  in  the  cardiac  diver- 
ticulum. 

These  ferments  in  the  hog  are  with  difficulty  extracted  with  glycerin, 
but  are  readily  removed  by  means  of  dilute  hydrochloric  acid  and  salt 
solutions. 

Ellenberger  and  Hofmeister  further  claim  that  there  is  a  diastatic 
ferment  in  the  mucous  membrane  of  the  hog's  stomach,  and  they  have 
proved  by  carefully  controlled  experiments  that  the  conversion  of  starch 
into  sugar  by  means  of  artificial  gastric  juice  from  the  hog  is  actually 
due  to  the  presence  of  the  ferment.  It  does  not,  however,  seem  clear 
as  to  whether  this  ferment  is  actually  produced  in  the  gastric  mucous 
membrane,  or  whether  it  enters  that  membrane  by  imbibition  from  saliva 
which  has  been  swallowed.  The  gastric  juice  of  the  fundus  of  the  stom- 
ach of  the  greater  curvature  produces  coagulation  of  milk,  both  in 
alkaline  and  in  neutral  conditions  ;  this  power  is  not  possessed  by  the 
mucous  membrane  of  the  cardiac  sac,  and  only  to  a  slight  degree  by  the 
pyloric  portion.  No  lactic  acid  ferment  exists  in  the  hog's  gastric  juice. 

The  progress  of  gastric  digestion  in  the  hog  has  been  carefully 
studied  by  Ellenberger  and  Hofmeister,  by  administering  definite  amounts 
of  specific  foods  to  hogs  in  whom  the  stomach  had  been  emptied  by 
fasting  and  cleansed  by  copious  administration  of  water.  The  animals 
were  then  killed,  at  specific  intervals  after  the  administration  of  the 
food,  and  the  gastric  and  intestinal  contents  subjected  to  a  chemical 
examination.  These  authors'  experiments  were  restricted  to  the  cereals. 
The  largest  number  of  experiments  were  made  with  oats,  given  dry,  so 
as  to  produce  the  greatest  quantity  of  saliva.  In  other  instances  the 
food  was  given  moist,  so  as  to  reduce  the  secretion  of  saliva  to  a  min- 
imum. To  those  who  received  the  dry  food  water  was  always  given  to 
drink.  The  animals  on  whom  these  experiments  were  made  were  for  a 


366  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

few  days  previous  to  the  experiment  fed  on  such  food  as  could  be  readily 
recognized  in  the  intestinal  tube.  For  thirty-six  hours  before  the  exper- 
iment no  food  whatever  was  given.  The  animals  were  then  killed,  after 
the  administration  of  a  weighed  quantity  of  food,  at  one,  two,  three, 
four,  six,  eight,  ten,  and  twelve  hours  after  the  termination  of  the  meal, 
an  attempt  being  made  to  isolate  the  portions  obtained  from  the  dif- 
ferent parts  of  the  stomach,  the  cardiac  and  pyloric  halves  being  kept 
separate.  The  result  of  these  experiments  directed  attention  especially 
to  the  progress  of  digestion,  to  the  location  of  the  gastric  contents,  the 
nature  of  the  acid  and  quantity  of  the  ferment  present,  the  duration 
of  gastric  digestion,  the  source  of  gastric  juice,  and  the  character  of  the 
gastric  movements.  Their  experiments  teach  that  the  gastric  digestion 
of  grains  in  the  hog  may  be  divided  into  two  periods.  During  the 
meal  and  for  one  or  two  hours  afterward,  digestion  of  starch  alone  takes 
place,  the  starch  being  converted  into  soluble  starch,  dextrin,  and  sugar. 
Simultaneously  with  the  digestion  of  the  starch,  lactic  acid  fermentation 
occurs,  a  considerable  quantity  of  the  sugar  being  in  this  way  converted 
into  lactic  acid.  It  does  not  appear  from  their  results  as  to  whether 
cellulose,  also,  at  the  same  time  undergoes  fermentation  or  not.  During 
this  period  the  food  becomes  softened  and  swollen  from  maceration  in 
the  fluids,  and  a  great  part  of  the  soluble  matters  of  the  food  pass  into 
solution,  the  digestibility  of  the  vegetable  albuminates  being  facilitated 
b}'  the  presence  of  lactic  acid. 

The  conversion  of  the  starch  into  sugar  occurring  in  this  period 
is  due  to  the  saliva,  which  the  authors  have  found  in  the  hog  to  pos- 
sess amylolytic  power  in  a  high  degree.  It  is  strongly  alkaline,  and 
therefore  neutralizes  whatever  acid  was  first  present  in  the  stomach. 
Later,  the  cardiac  contents  become  acid,  due  at  first  to  the  presence  of 
lactic  acid,  which,  as  is  well  known,  does  not  interfere  with  the  action  of 
the  amylolytic  ferment.  It  is  also  probable  that  a  certain  amount  of  this 
amylotytic  ferment  comes  from  the  cardiac  sac  of  the  .hog's  stomach, 
which,  as  already  mentioned,  contains  a  special  character  of  glands 
whose  extract  always  yields  diastatic  ferments. 

As  regards  the  degree  of  digestion  in  this  period,  the  following 
figures,  taken  from  one  of  Ellenberger's  and  Hofmeister's  experiments, 
serve  as  an  example  : — 

The  animal  had  received  860  grammes  of  oats,  representing  73 
grammes  of  cellulose,  557  grammes  of  carbohydrates,  and  93  grammes 
of  albuminoids.  As  a  consequence,  22.5  per  cent,  soluble  nutritive  sub- 
stances consisted  of  albumen.  On  analysis,  only  47  grammes  of  undis- 
solved  albumen  were  found ;  hence  34  per  cent,  of  the  insoluble  albuminous 
bodies  had  passed  into  solution. 

In  feeding  with  animal  matters,  naturally  this  first  stage,  which 


GASTRIC   DIGESTION.  367 

might  be  called  the  am}'lolytic  period  of  digestion,  is  absent.  This 
amylolytic  period  lasts  for  about  three  or  four  hours,  including,  of 
course,  the  half-hour  or  hour  occupied  by  the  meal.  The  duration  is, 
however,  longer  in  the  cardiac  sac  than  in  the  fundus  and  pyloric 
portions  of  the  stomach,  where  it  becomes  gradually  converted  into 
what  might  be  termed  the  proteolytic  period,  in  which  the  proteids 
become  converted  into  peptones. 

The  digestion  of  proteids  in  the  hog  is  first  rendered  possible 
through  the  presence  of  lactic  acid,  During  this  stage  of  proteolysis 
the  digestive  processes  differ  in  the  cardiac  and  pyloric  portions  of  the 
stomach,  indicating  that  for  several  hours  a  well-marked  difference 
exists  between  the  contents  of  these  different  regions  of  the  stomach,  in 
the  former  of  which  only  lactic  acid  and  in  the  latter  both  hydrochloric 
and  lactic  acids  are  present.  This  fact,  for  which  we  are  also  indebted 
to  Ellenberger  and  Hofmeister,  is  in  opposition  to  the  generally  accepted 
views  as  to  the  rapid  diffusion  and  mixing  of  the  gastric  contents. 

The  second  digestive  period,  in  which,  while  the  cardiac  extremity 
is  still  digesting  starch,  the  pyloric  half  is  digesting  albumen,  begins 
at  about  the  third  or  fourth  hour  of  digestion,  and  may  continue  from 
nine  to  twelve  hours. 

In  the  third  period  the  digestion  of  starch  ceases,  from  the  great 
development  of  hydrochloric  acid,  although  it  should  be  remembered 
that  up  to  the  fourth  hour  of  gastric  digestion  the  cardiac  fluid  is  still 
capable  of  converting  starch  into  sugar. 

It  thus  would  appear  that  digestion  in  the  stomach  of  the  hog  con- 
tinues from  one  meal  to  the  other,  although  in  a  moderate  meal  part  of 
the  gastric  contents  maj^  pass  into  the  intestine  three  or  four  hours  after 
eating;  but  part,  nevertheless,  remains  in  the  stomach,  and  may  be 
found  there  even  thirty-six  hours  afterward. 

These  results  further  show  that  the  degree  of  mixing  of  the  con- 
tents of  the  stomach  produced  by  the  gastric  movements  is  by  no  means 
complete,  the  first  quantities  being  gradually  pushed  on  toward  the 
P3*lorus  by  those  coming  afterward.  The  degree  of  acidity  of  the  gastric 
contents  gradually  increases.  While  at  first  alkaline,  it  gradually 
increases  in  acidity  so  that  three  hours  after  the  meal  0.07  per  cent,  acid 
may  be  recognized  in  the  left  half  of  the  stomach  and  0.2  per  cent,  in 
the  right  half.  The  acid  within  the  left  half  of  the  stomach  then  com- 
mences to  increase,  until  finally  it  may  amount  to  0.3  per  cent.  When 
the  meals  rapidly  follow  each  other  gastric  digestion  is  interrupted,  and 
the  undigested  portion  is  forced  into  the  intestine,  undergoing  digestion 
there  by  means  of  the  intestinal  digestive  fluids.  As  a  consequence, 
in  large  meals  the  amylolytic  period  is  increased  and  the  proteolytic 
period  decreased,  while  the  degree  of  acidity  more  slowly  approaches  a 


368  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

maximum.  The  degree  of  mastication  is  further  of  influence  on  the 
completeness  of  the  amylolytic  change.  When  dried  food  is  given 
mastication  is  more  prolonged,  and  the  conversion  into  starch  is  more 
complete  than  when  soft,  watery  foods  are  given. 

6.  GASTRIC  DIGESTION  IN  SOLIPEDES. — The  simplicity  and  smallness 
of  the  stomach  in  these  animals,  the  vast  size  and  valvular  character  of  the 
colon,  and  the  importance  and  high  degree  of  development  of  the  caecum 
are  the  peculiarities  which  characterize  digestion  in  this  group  of 
herbivorous  animals.  The  type  of  digestive  parts  seen  in  the  horse  and 
other  solipedes  are  represented  also  in  the  pachyderms  and  among 
rodents,  where  the  intestinal  tube  is  constructed  on  a  similar  plan.  They, 
therefore,  possess  many  points  in  common  in  the  mode  of  action  of  the 
digestive  parts.  As  indicated  by  Colin,  the  following  points  characterize 
digestion  in  solipedes.  First,  the  slowness  of  the  mechanical  prepara- 
toiy  stage  of  digestion ;  second,  the  rapidity  with  which  the  work  of  the 
stomach  is  effected;  third,  the  rapiditj-  of  the  passage  of  liquids  into 
the  intestines,  and  their  accumulation  in  the  caecum  ;  fourth,  the  hardness 
and  globular  form  which  the  residue  of  alimentary  matters  assume  in  the 
posterior  parts  of  the  large  intestine. 

Mastication,  which  was  found  in  the  carnivora  to  be  insignificant, 
.becomes  in  the  herbivora  an  act  of  the  greatest  importance,  for  grass, 
hay,  corn,  or  oats  can  only  be  digested  after  the  most  perfect  comminution 
and  trituration,  for  the  vegetable  nutritious  matters  are  inclosed  in 
cellulose  envelopes  which  are  impervious  to  gastric  juice.  In  the  soli- 
pedes rumination  does  not  take  place;  hence,  mastication  is  slow  and 
perfect  and  completed  once  for  all.  A  horse  cannot  ordinarily  eat  two 
thousand  five  hundred  grammes  of  hay  in  less  than  one  hour,  or  even 
two  if  .the  teeth  are  at  all  defective,  while  twenty  to  fort}r  minutes  are 
required  for  the  mastication  of  the  same  quantity  of  oats.  Preliminary 
chopping  of  food  does  not  help  digestion  in  sound  animals,  and  cannot 
replace  the  process  of  mastication  in  animals  in  which  the  teeth  are 
defective,  for  it  is  impossible  to  carry  the  process  far  enough  unless  the 
substances  are  actually  milled  or  ground  to  a  powder.  This,  of  course, 
will  liberate^the  nutritive  matters  from  their  indigestible  cells,  and  may 
assist  digestion  in  animals  in  which  mastication  is  imperfectly  performed. 
Chopped  food,  in  fact,  may  prove  harmful  by  reducing  the  duration  of 
mastication,  and  so  decreasing  the  amount  of  saliva  poured  out.  Masti- 
cation in  solipedes  is  slow  and  prolonged,  not  only  from  the  necessity 
for  comminuting  the  food,  but  also  from  the  fact  that  in  the  mouth  the 
principal  action  of  the  saliva  on  the  food  commences. 

As  the  foods  enter  the  stomach  they  push  to  the  right  the  mass 
already  present,  and  as  the  capacity  is  only  fifteen  to  eighteen  litres,  this 
organ  cannot  .contain. an  entire  .single  meal. .  .  Thus,  when  a  horse  eats 


GASTKIC  DIGESTION.  369 

five  kilos  of  hay,  representing  one-half  its  daily  ration,  requiring  two 
hours  for  its  consumption,  and  impregnates  it  with  twenty  litres  of  saliva, 
the  mass  would  occupy  a  space  of  twenty-eight  to  thirty  cubic  decimeters. 
As  the  stomach  is  functionally  most  active  when  only  two-thirds  distended, 
that  is,  while  containing  about  ten  litres,  the  stomach  must,  therefore, 
till  and  empty  itself  two  or  three  times  during  one  meal.  It  is,  therefore, 
seen  that  the  small  capacity  of  the  stomach  has  the  effect  of  reducing  the 
duration  of  gastric  digestion,  and  the  greater  the  volume  of  food  the 
less  will  be  the  time  that  food  will  remain  in  the  stomach.  Consequently, 
oats,  taking  up  only  one-fifth  the  volume  of  an  equal  weight  of  hay, 
would  remain  in  the  stomach  four  or  five  times  as  long.  This  difference 
in  time  during  which  different  foods  remain  in  the  stomach  is  necessi- 
tated, as  indicated  by  Colin,  by  the  different  compositions  of  the  food. 
Thus,  a  horse  fed  on  hay  receives  in  this  food  44  per  cent,  of  carbo- 
hydrates, which  have  been  already  partially  modified  by  the  saliva 
and  whose  further  transformation  is  completed  in  the  intestine.  Four 
per  cent,  of  fats  is  present,  which,  as  has  been  seen,  are  not  acted  on  by 
the  gastric  juice,  while  only  7  per  cent,  of  albuminous  matter  is 
present.  It  is  the  albuminous  matter  alone  which  is  digested  by  gastric 
juice,  and,  since  we  have  only  7  per  cent,  of  albuminous  matter  pres- 
ent in  hay,  it  is  evident  that  but  a  short  time,  comparatively  speaking, 
would  be  required  for  the  digestion  of  this  albuminous  matter,  which  is 
finely  divided  and  in  the  most  favorable  condition  for  being  subjected  to 
its  solvent  action.  So,  also,  the  horse  fed  on  green  forage  receives  in 
its  food  9  per  cent,  of  carbohydrates,  barely  1  per  cent,  of  fat,  and  only 
3  per  cent,  of  nitrogenous  matters  which  are  digestible  in  the  stomach. 
Therefore,  in  green  fodder  but  a  short  time  is  required  for  gastric  diges- 
tion. Ou  the  other  hand,  oats  contain  about  11  per  cent,  of  nitrogenous 
matter,  and,  consequently,  we  find  that  the  small  relative  volume  of  oats, 
as  contrasted  with  other  forms  of  vegetable  foods,  enables  them  to  remain 
longer  in  the  stomach. 

In  the  horse  the  performance  of  gastric  fistulae  is  impossible  on 
anatomical  grounds,  and  various  attempts  have  been  made  to  collect 
gastric  juice  by  performing  cesophagotomy, — passing  a  sponge  .through 
a  tube  into  the  stomach,  killing  the  animal  after  a  certain  time,  tying 
the  pylorus,  and  collecting  the  contents.  This  method,  however,  fails 
to  secure  a  gastric  secretion  which  is  free  from  bile  and  pancreatic 
juice.  So,  also,  the  use  of  the  stomach-pump  is  rendered  difficult  or 
impossible  on  account  of  the  long  and  pendulous  soft  palate  and  the 
discomforts  and  struggles  which  it  causes  in  animals  when  attempts  to 
employ  it  are  made. 

By  means  of  the  method  referred  to  above,  the  fluids  obtained  from 
the  stomach  will  always  contain  saliva  and  various  food-products,  as  well 

24 


370  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

as  the  true  gastric  secretion  ;  but,  since  these  substances  are  always  mixed 
in  actual  digestion,  they  will  answer  for  the  study  of  the  process  of  diges- 
tion, even  although  they  will  prevent  accurate  statements  as  to  the 
chemical  constitution  of  this  secretion.  The  gastric  juice  in  the  horse 
is  secreted  only  by  the  glands  of  the  fundus  from  a  surface  about  two 
hand-breadths  in  extent.  Extracts  from  this  portion  of  the  mucous  mem- 
brane contain  more  acid,  more  ferments,  and,  what  is  remarkable,  more 
mucin  than  extracts  made  from  the  pyloric  portion.  Ellenberger  and 
Hofmeister  found  that  the  degree  of  acidity  immediately  after  eating  was, 
in  the  horse,  only  0.084  per  cent.  After  an  hour  the  acidit}^  rose  to 
0.1  per  cent.,  and  still  later  to  0.2  per  cent.  Immediately  after  eating 
no  hydrochloric  acid  was  present,  but  only  appeared  four  or  five  hours 
after  the  commencement  of  the  meal.  Lactic  acid  was  always  present, 
apparently  even  in  excess  of  hydrochloric  acid.  .This  ma}r,  perhnps,  serve 
to  explain  the  fact  that  in  the  horse's  stomach  the  change  of  starch  into 
sugar  may  go  on  even  in  the  presence  of  0.2  per  cent,  of  acid,  as  organic 
acids  interfere  less  than  mineral  acids  with  this  process.  The  charac- 
teristics of  the  acid  of  the  gastric  juice  have  been  found  to  depend  upon 
the  food.  Thus,  these  authors  have  found  that  the  distribution  of  acids 
was  as  follows : — 

Hydrochloric  Acid.    Organic  Acids. 

1.  Oats  and  chopped  straw,    .         .     0.163  per  cent.     0.287  per  cent. 

2.  Oats, 0.490       "  0.610 

3.  Hay,     .        .       ".        .        .        .     0.022       "  1.798       " 

It  is  thus  seen  that  when  the  food  consists  of  oats  the  maximum 
percentage  of  hydrochloric  acid  is  found  in  the  gastric  juice,  while  when 
hay  is  given  the  mineral  acid  falls  to  a  minimum,  while  the  organic  acids 
are  in  excess.  The  importance  of  these  facts  is  evident  when  it  is  remem- 
bered that  oats  contain  12  per  cent,  of  albuminous  matter  and  65  per 
cent,  of  carbohydrates,  including  cellulose,  while  hay  contains  only  9  per 
cent,  of  proteids  and  70  per  cent,  of  carbohydrates.  Hence,  when  oats 
are  given,  the  excess  of  hydrochloric  acid  is  especially  favorable  for  the 
peptonization  of  the  proteid  constituents,  while  it  interferes  with  the 
digestion  of  the  carbohydrates.  On  the  other  hand,  when  hay  is  given, 
the  excess  of  organic  acids,  as  already  mentioned,  does  not  interfere  with 
the  action  of  pt3^alin  on  starch,  while  still  permitting  the  peptonization 
of  the  proteids. 

The  watery  extract  of  the  mucous  membrane  of  the  fundus  differs, 
as  already  mentioned,  from  that  of  the  pylorus.  It  contains  more  mucus, 
more  acid,  and  more  ferment.  The  fundus  extract  contains  a  ferment 
which  converts  casein,  fibrin,  albumen,  and  gelatin  into  peptone  in  media 
containing  0.15  to  0.5  per  cent,  of  hydrochloric  acid.  While  0.6  per 
cent,  of  hydrochloric  acid  arrests  digestion,  in  the  case  of  organic  acids 


GASTRIC  DIGESTION.  371 

it  was  found  that  the  percentage  might  be  considerably  increased  above 
this  point  and  yet  digestion  go  on.  Thus,  the  gastric  extract  appeared 
to  possess  about  the  same  degree  of  activity  when  lactic  acid  was  present 
in  2  per  cent,  as  with  hydrochloric  acid  present  in  0.2  per  cent.  The 
ferment  is  only  diffusible  with  great  difficulty,  and  resists,  to  a  high 
degree,  putrefactive  and  alcoholic  fermentations.  Lactic  acid  fermenta- 
tion does  not  interfere  with  its  activitj7. 

The  ferment  is  soluble  in  water,  glycerin,  dilute  acids,  alkaline  and 
saline  solutions,  and  loses  its  activity  at  60°  C.  Such  an  artificial  gastric 
juice  extracted  from  the  mucous  membrane  of  a  horse's  stomach  will 
digest  animal  tissues  in  the  same  way  as  extracts  prepared  from  the 
mucous  membrane  of  the  stomachs  of  carnivora.  Extracts  prepared 
from  inflamed  mucous  membrane  are  totally  inactive.  In  addition  to  the 
pepsin,  the  gastric  juice  of  the  horse  also  contains  the  milk-curdling  fer- 
ment and  salts,  lactic  acid  ferment,  and  traces  of  a  diastatic  ferment,  all 
of  which  may  be  precipitated  by  alcohol.  The  distribution  of  these 
ferments  and  of  the  acidity  of  the  gastric  juice  is  the  same  as  in  the  dog, 
with  the  exception  that  no  secretion  takes  place  in  the  membranous  car- 
diac portion  of  this  organ. 

Gastric  digestion  in  solipedes  is  more  important  than  one  might  be 
led  to  suppose,  and  continues,  to  a  certain  extent,  from  one  meal  to  the 
next,  as  the  residue  remains  in  the  stomach  until  the  next  one  is  taken, 
and  therefore  the  stomach  does  not  completely  empty  itself  after  twenty- 
four  hours.  The  characters  of  this  residue  will,  of  course,  vary  with  the 
nature  of  the  food.  Thus,  the  contents  of  the  stomach  after  feeding  with 
oats  is  a  dried,  crumbling  mass,  containing  60  to  70  per  cent,  of  water. 
After  feeding  with  hay  the  percentage  of  water  may  be  as  much  as  80 
per  cent.  The  reaction  is  always  acid. 

Gastric  juice  obtained  as  above,  by  the  method  of  Ellenberger  and 
Hofmeister,  rapidly  converts  starch  into  sugar,  although  the  ferment  is 
not  derived  from  the  stomach,  but  from  the  swallowed  saliva. 

The  change  of  starch  into  sugar  goes  on  in  the  stomach,  as  is  proved 
by  the  fact  that  gastric  juice  outside  of  the  body  will  turn  starch  into 
sugar,  and  by  the  fact  that  after  feeding  starch  large  quantities  of  sugar 
ma}-  be  found  in  the  contents  of  the  stomach.  The  digestion  of  starch 
is  most  -active  in  the  first  two  hours  of  digestion  and  stops  after  five  or 
six  hours,  when  the  percentage  of  hydrochloric  acid  is  most  marked. 

When  dry  food  has  been  given,  the  conversion  of  starch  into  sugar 
may  continue  much  longer,  from  the  large  quantity  of  alkaline  saliva 
swallowed,  and  may  go  on  in  the  left  half  of  the  stomach  even  while  the 
fundus  is  digesting  proteids,  the  acidity  being  due  to  lactic  acid.  After 
feeding  with  oats, as  much  as  thirty-five  grammes  of  sugar  have  been  found, 
while  five  to  eight  and  one-half  grammes  of  sugar  have  been  found  after 


372  PHYSIOLOGY  OF   THE  DOMESTIC   ANIMALS 

feeding  with  hay.  Of  course,  this  does  not  represent  the  total  amount 
formed,  as  a  great  deal  will  have  been  absorbed,  some  converted  into 
lactic  acid,  and  some  will  have  passed  into  the  small  intestine. 

Ellenberger,  Hofmeister,  and  Goldschmidt  found  that  the  naturally 
mixed  saliva  of  the  horse  possessed  a  stronger  amylolytic  action  than 
the  artificially  combined  separate  salivary  secretions ;  and  that  each 
separate  salivary  secretion,  though  highly  amylolytic,  was  less  so  than 
the  mixed  secretions;  and,  finally,  that  the  conversion  in  the  horse's 
stomach  of  starch  into  dextrin,  sugar,  and  lactic  acid  occurred  to  a 
greater  degree  than  could  be  attributable  to  the  fermentative  action  of 
the  saliva  alone.  The  conclusion  is,  therefore,  drawn  that  in  the  horse's 
stomach  amylolytic  digestion  is  aided  b}^  ferments  developed  in  the 
alimentary  canal  and  in  the  food  itself.  This  latter  statement  is  con- 
firmed by  the  fact,  already  mentioned,  that  Hofmeister  has  found  in  oats 
an  amylolytic  ferment,  which  is  destroj^ed  at  the  temperature  af  boiling 
water,  but  which  is  active  at  the  body  temperature,  thus  explaining  the 
fact  that  more  starch  is  converted  into  sugar  in  the  stomach  than  is 
attributable  to  the  action  of  the  salivary  ferment  alone.  Finally, 
Goldschmidt  has  found  that  the  digestion  of  starch  in  the  horse  is 
aided  by  amylolytic  ferments  derived  from  the  air,  which  are  mixed 
with  the  saliva  in  the  mouth,  and  which  rapidly  develop  in  the  oral 
mucus  ;  --.  j.  t  ....4,*,  .r.  rL-  .-,. 

In  the  horse's  stomach  vegetable  albumen  is  rapidly  digested  mid 
turned  into  peptone,  which  increases  in  amount  with  the  duration  of 
digestion.  After  a  large  meal  the  peptonization  is  at  first  slight,  since 
the  glands  cannot  form  acid  and  pepsin  fast  enough  to  digest  a  large 
meal  rapidly.  If,  then,  another  meal  is  taken  before  the  first  is  digested, 
the  former  food  is  forced  in  an  undigested  state  into  the  intestine. 
After  a  moderate  meal  the  digestion  reaches  its  maximum  in  three  to 
four  hours;  in  other  words,  digestion  is  then  complete.  The  larger 
quantity  of  peptone  is  found  in  the  stomach  after  oats  have  been  given 
than  after  feeding  with  hay.  Five  to  forty  grammes  of  peptones  have 
been  found  after  oats  have  been  given,  while  only  about  six  grammes 
were  found  six  hours  after  feeding  with  ha}'.  Of  course,  these  figures 
do  not  indicate  the  total  amount  of  peptones  formed,  since,  probably,  a 
large  portion  would  be  absorbed  almost  as  rnpidly  as  formed.  As  hay 
absorbs  four  times  its  weight  of  saliva,  it  is  readily  digested  at  first 
without  water,  but  the  digestion  then  becomes  slow.  Colin  administered 
twenty-five  hundred  grammes  of  hay  to  a  horse,  and  then  killed  him. 
Only  seven  thousand  grammes  of  material  were  found  in  the  stomach, 
representing,  therefore,  but  little  more  than  one-half  the  amount  given, 
since  the  two  thousand  five  hundred  grammes  of  hay  would  have  absorbed 
ten  kilos  of  saliva.  Of  this  residue  only  one  thousand  grammes  were  dry 


GASTRIC  DIGESTION.  373 

hay  ;  the  remainder  had  passed  into  the  intestine.  Other  animals  killed 
at  longer  periods  after  meals  showed  the  passage  of  the  food  from  the 
stomach  into  the  intestine  was  not  as  rapid  toward  the  end  of  the 
repast  as  at  the  commencement.  There  appears,  therefore,  to  be  two 
periods  in  the  digestion  of  hay  in  the  horse :  In  the  first,  the  materials, 
as  soon,  almost,  as  they  enter  the  stomach,  are  rapidly  pushed  into  the 
intestine  by  the  food  that  comes  later;  in  the  second  period,  toward 
the  end  of  the  meal,  the  sojourn  is  more  prolonged,  and  chymification 
is,  therefore,  more  perfect.  Tlie  gastric  digestion  of  hay  appears  to  be 
abbreviated  by  the  ingestion  of  water,  as  the  water  carries  into  the 
intestine  a  good  deal  of  food.  Digestion  of  hay  does  not  appear  to  be 
modified  by  previous  chopping. 

When  oats  are  given  as  food,  at  the  commencement  of  the  meal,  a 
part  always  passes  into  the  intestine,  but,  as  oats  only  absorb  a  little 
more  than  their  own  weight  of  saliva,  the  volume  never  becomes  as  high 
as  when  hay  is  eaten.  Colin  reports,  also,  the  following  experiments  : 
A  horse  which  had  received  two  thousand  five  hundred  grammes  of 
oats  was  killed  two  hours  after  the  commencement  of  the  meal.  The 
stomach,  which,  together  with  the  oats  and  saliva,  had  received  five 
thousand  grammes  of  material,  was  now  found  to  contain  six  thousand 
and  seventy  grammes,  the  addition  being  derived  from  the  gastric  juice 
and  the  saliva  which  had  been  swallowed  during  the  meal.  Here,  also, 
two  analogous  periods  may  be  made  out,  but  less  accented  than  when 
hay  is  the  food.  It,  therefore,  seems  evident  that  small  meals,  frequently 
repeated,  would  serve  to  render  the  gastric  digestion  in  solipedes  more 
perfect.  Thus,  in  Paris,  according  to  the  statement  of  Colin,  the  horses 
in  the  omnibus  service  make  six  meals  from  4  A.M.  to  9  P.M.,  and  each 
of  these  meals  has  three  hours  for  digestion,  with  the  exception  of  the 
last,  which  has  six.  Water  is  only  given  when  hay  is  included,  and  not 
at  other  times.  It  follows  that  gastric  digestion  is  not  of  equal  impor- 
tance for  all  kinds  of  food,  and  it  is,  therefore,  possible  so  to  distribute 
the  constituents  of  a  meal  as  to  allow  of  a  longer  gastric  digestion  of 
oats,  which  have  a  greater  percentage  of  albuminous  bodies  and  carbo- 
hydrates than  hay.  Therefore,  in  the  feeding  of  a  horse  especial  atten- 
tion should  be  given  to  the  sequence  or  to  the  order  in  which  the  different 
constituents  of  the  horse's  meal  follow  each  other, — a  fact  which  is  of 
greater  importance  for  the  horse  than  for  man,  the  carnivora,  and  the 
ruminants,  in  which  all  the  constituents  of  a  meal  may  be  kept  in  the 
stomach  until  the  digestion  is  completed.  Experience  has  shown  that 
if  oats  are  given  first,  subsequent  eating  of  hay  forces  the  oats  into  the 
intestines  before  the  digestion  of  the  latter  is  complete ;  consequently, 
if  given  after  hay,  the  sojourn  in  the  stomach  is  much  more  prolonged, 
while  the  hay,  containing  a  minimum  of  albuminous  matter,  may  be 


374  PHYSIOLOGY  OF   THE   DOMESTIC  ANIMALS. 

partially  digested  in  the  stomach,  and  its  subsequent  changes  completed 
in  the  intestines.  Consequently,  oats  should  always  succeed  the  admin- 
istration of  hay  in  the  feeding  of  horses.  So,  also,  water  should  not  be 
given  after  a  meal  of  oats  to  the  horse,  or  else  it  will  wash  the  oats  out  of 
the  stomach  before  digestion  is  completed.  Consequently,  the  water 
should  precede  hay,  and  both  liny  and  water  should  precede  the  admin- 
istration of  oats. 

The  short  time  that  food  remains  in  the  stomach  is  probably  the 
reason  that  the  horse  does  not  readily  digest  animal  food,  although  in 
the  Tartar  steppes  it  is  stated  that  horses  become  accustomed  to  a  meat 
diet. 

In  addition  to  true  digestion,  fermentative  processes  also  occur  in 
the  stomach,  especially  in  the  earlier  stages  of  gastric  digestion,  when 
the  hydrochloric  acid  is  absent  or  present  only  in  small  amounts.  It 
has  been  shown  that  hydrochloric  acid  is  always  in  small  amount  in 
the  oesophageal  sac,  and  in  this  locality  lactic  acid  fermentation,  as  well 
as  fermentation  of  cellulose,  undoubtedly  may  occur,  though  the  time 
which  the  food  remains  in  this  part  of  the  stomach  is  too  short  to  permit 
of  any  extensive  change  of  this  character.  It  will  be  subsequently  shown 
that  the  conditions  for  the  fermentation  of  cellulose  are  much  more  favor- 
able in  the  intestinal  canal  of  the  horse  than  in  the  stomach. 

7.  GASTRIC  DIGESTION  IN  RUMINANTS. — Gastric  digestion,  which  has 
been  found  to  be  much  the  same  in  carnivora  and  solipedes,  takes  on 
a  new  form  in  the  ruminant  animals,  and  although  the  general  result  of 
gastric  digestion  is  the  same  in  all,  special  means  are  concerned  in  the 
accomplishment  of  this  result  in  the  ruminant  that  are  not  seen  in  ani- 
mals with  a  simple  stomach.  This  complication  is  practically  due  to  the 
preliminary  and  accessory  changes  which  occur  in  the  food  before  it  is 
subjected  to  the  action  of  gastric  juice.  Hence,  the  changes  in  the  first 
three  compartments  of  the  stomach  are  without  an  analogue  in  the  gastric 
digestion  of  monogastric  animals,  while  the  fourth  stomach  reproduces 
exactly  the  process  that  takes  place  in  this  viscus  of  the  latter  class  of 
animals. 

Although  the  four  gastric  reservoirs  of  the  ruminant  are  anatomi- 
cally connected,  they  are,  to  a  certain  point,  functionally  isolated,  each 
one  of  them  having  tolerably  distinct  functions  to  fulfill.  The  first  three 
are  concerned  in  the  storing  of  foods  and  liquids  in  rumination,  while  in 
the  fourth  alone  true  digestion  takes  place.  This  may  occur  during 
rumination  or  Curing  inaction  of  the  first  three  stomachs. 

The  rumen  receives  almost  all  of  the  aliments  when  swallowed  for 
the  first  time,  the  greater  part  of  liquids  drunk,  and  a  considerable 
portion  of  the  results  of  the  second  mastication  (Fig.  153).  It  keeps 
them  stored  up  for  a  certain  time  in  its  interior,  where  they  become  thor- 


GASTRIC  DIGESTION. 


375 


ougbly  macerated  and  soaked  in  fluid,  and  from  which  they  are  forced 
into  the  resophagus  during  rumination  or  into  the  honey-comb  bag  dur- 
ing the  intervals  of  rumination.  It  is  evident,  therefore,  that  the  food 
contained  in  this  pouch  may  undergo  changes  due  to  the  movements  to 
which  it  is  subjected,  the  temperature,  and  the  action  of  saliva  and  other 
fluids.  The  changes  are,  therefore,  physical  and  chemical.  The  walls  of 
the  rumen,  by  their  contractions  and  resulting  movements,  may  exert  a 
considerable  amount  of  mechanical  force  on  the  aliments  contained  within 
it,  although  this  has  been  greatly  exaggerated.  Nothing  like  trituration 
takes  place,  but  simply  thorough  mixing  of  the  new  and  old  food  together 


FIG.  153.— STOMACH  OF  THE  Ox.    (Colin.) 

A,  rumen  (left  hemisphere) ;  B,  rumen  (right  hemisphere) ;  C,  insertion  of  the  oesophagus ;  D,  reticulum ; 
E,  omasum ;  F,  abomasum. 

and  with  fluid ;  consequently,  it  is  not  necessarily  the  portion  of  food 
which  first  enters  the  paunch  which  is  the  first  to  leave.  The  maceration 
which  the  food  undergoes  in  the  fluids  of  the  paunch  is  especially  marked 
in  the  case  of  grain  and  dry  fodder,  and  is  greatly  assisted  by  the  tem- 
perature of  the  organ. 

The  fluids  contained  in  the  rumen  consist,  in  a  great  part,  of  water 
which  has  been  drunk  and  a  large  quantity  of  saliva,  which  is  swallowed 
with  the  first  mastication  and  in  the  intervals  of  the  act  of  rumination. 
The  rumen  has,  however,  no  secretion  of  its  own,  since  no  secretory 
glands  are  found  in  its  walls.  Its  reaction,  as  already  stated,  is  generally 


376  PHYSIOLOGY  OF   THE  DOMESTIC  AXHIALS. 

alkaline,  and  is  derived  from  the  saliva.  Occasionally,  the  reaction  of 
the  rumen  may  be  found  to  be  acid.  This  may  be  due  to  fermentation 
occurring  in  the  contents  of  this  organ,  and  is  especially  seen  in  nursing 
calves,  in  animals  fed  on  roots,  and  in  cases  of  faulty  digestion.  It 
nearly  always  occurs  in  animals  fed  on  green  fodder,  where  the  conditions 
are  favorable  to  the  fermentation  of  sugar.  Occasionally,  also,  the  reac- 
tion of  the  rumen,  which  may  be  found  to  be  acid  after  death,  is  due  to 
the  regurgitation  of  the  contents  of  the  fourth  stomach  into  the  first 
three  compartments.  In  the  rumen  the  conditions  are  especially  favor- 
able for  the  digestion  of  carbohydrates,  for  the  conditions  are  favorable 
for  the  action  of  saliva,  which  is  thus  enabled  to  convert  starch  into 
sugar.  Cellulose,  also,  is  said  to  be  digested  in  the  rumen  through  fer- 
mentative processes  to  as  much  as  60  to  70  per  cent.  Salts,  sugar,  muci- 
lage, gum,  and  other  soluble  substances  may  be  dissolved  out  of  the  food 
while  in  the  rumen,  and  so  prepared  for  absorption.  No  peptonization, 
however,  occurs  ;  for  all  the  various  bases,  salts,  and  albuminoids  which 
may  be  detected  in  the  contents  of  this  organ  come  solely  from  the  food 
and  the  secretions  and  liquids  which  have  been  swallowed,  and  not  from 
any  secretion  poured  out  by  the  rumen  itself.  The  function  of  the  rumen 
is,  therefore,  simply  to  act  as  a  reservoir,  in  which  the  food,  after  being 
swallowed,  is  collected,  undergoes  maceration,  and  is  again,  from  time  to 
time,  returned  to  the  mouth  for  a  second  mastication.  In  this  organ  the 
food  becomes  softened,  as  the  result  of  impregnation  with  liquids  warmed 
to  the  temperature  of  the  body. 

The  functional  importance  of  the  rumen  is  not  equally  marked  at 
all  periods  of  life.  This  is  especially  seen  in  suckling  animals,  such  as 
calves,  in  whom  the  rumen  is  capable  of  containing  one  thousand  one 
hundred  and  seventy-fiv£  grammes,  the  reticulum  one  hundred,  the 
manyplies  one  hundred  and  sixty,  while  the  cubic  capacity  of  the 
abomasurn  may  amount  to  three  thousand  five  hundred  grammes  (Colin). 
Hence,  digestion  in  the  suckling  ruminant  is  accomplished  almost  solely 
by  the  fourth  stomach,  and  the  rumen  does  not  acquire  its  great  pro- 
portionate size  seen  in  the  adult  ruminant  until  the  animal  commences  to 
live  on  a  solid  vegetable  diet. 

Although  the  reticulum  may  be  regarded  as  an  appendage  to  the 
rumen,  with  which  it  communicates  by  a  large  opening,  it  also  has  a 
special  function  to  fulfill,  which  appears  to  be  uniform  in  all  ruminants. 
It  constantly  contains  fluid,  since  its  base  is  on  a  much  lower  level  than 
the  openings  into  the  first  and  third  stomachs.  Fluid  can,  therefore, 
only  leave  this  compartment  as  a  result  of  its  own  vigorous  contractions, 
such  as  precede  the  insertion  of  the  cud  into  the  oesophagus  for  rumi- 
nation. 

The  function  of  the  oesophageal  canal  is  to  assist  in  the  transfer  of 


GASTRIC  DIGESTION.  377 

the  contents  of  the  reticulum  into  tlie  manyplies.  The  entrance  of  the 
contents  of  the  ruinen  through  the  contraction  of  its  walls  into  the 
reticulum  leads  to  a  contraction  of  the  muscular  walls  of  this  compart- 
ment, and  the  materials  contained  in  it  are  thrown  up  against  the  edges 
of  the  oesophageal  gutter.  Through  this  contact  the  cesophageal  pillars 
shorten  so  as  to  draw  up  the  opening  into  the  manyplies  nearer  to  the 
reticulum,  at  the  same  time  turning  spirally  on  their  own  axes,  the  left- 
hand  pillar  being  extended  downward  and  to  the  right.  The  contents 
of  the  reticulum  thus  find  a  means  of  ready  entrance  into  the  manyplies, 
large  particles  being  strained  off  by  the  papillae  at  the  orifice  of  the 
manyplies,  and  falling  back  into  the  reticulum. 

Although  the  reticulum  receives  all  the  matter  swallowed,  its  small 
size  prevents  it  from  retaining  more  than  a  small  portion,  the  remainder 
being  forced  into  the  rumen  and  manyplies,  the  fluid  and  finely  divided 
solids  alone  entering  into  the  latter  on  account  of  the  small  size  of  the 
communicating  orifice.  Its  function,  therefore,  is  to  assist  in  rumination, 
particularly  by  supplying  the  fluids  which  ascend  the  oesophagus,  and  by 
its  contraction  aiding  in  the  ascent  of  the  cud  and  in  keeping  up  the 
circulation  between  the  contents  of  the  first  and  second  stomachs.  It 
also  has  no  secretion  proper,  and  the  fluids  found  in  it  have  the  same 
source  and  same  functions  as  those  found  in  the  rumen. 

If  one  could  judge  of  the  importance  of  an  organ  b}^  its  complexity, 
the  functions  of  the  psalter  would  play  an  especially  important  role  in 
the  gastric  digestion  of  the  ruminant.  In  this  compartment  of  the 
stomach  the  openings  are  always  narrow,  are  always  close  together,  and 
are  both  on  the  uppermost  portion  of  this  organ,  while  the  free  borders 
of  its  folds  are  directed  downward  ;  consequently,  the  manyplies,  by 
means  of  its  folds  and  the  narrowness  of  its  openings,  the  one  into  the 
fourth  stomach  being  closed  by  a  powerful  muscle  and  numerous  large 
papillae,  like  a  sieve,  strains  off  solids  and  detays  the  passage  of  aliments 
into  the  true  stomach.  The  muscular  fibres  which  run  in  the  larger 
folds  are  inserted  into  the  borders  of  the  orifice  between  the  manyplies 
and  reticulum.  When,  therefore,  the  sphincter-muscle  of  this  opening 
contracts,  after  the  entrance  of  the  contents  of  the  reticulum,  the  folds 
are  simultaneously  drawn  up,  and  the  food  is  thus  forced  up  to  the  base 
of  these  partitions.  At  the  same  time,  through  the  contraction  of  its 
walls,  the  posterior  extremity  is  drawn  forward  so  that  the  prolongation 
of  the  cesophageal  canal  becomes  almost  perpendicular  to  the  opening  of 
the  third  into  the  fourth  stomach.  By  this  process  not  only  the  fluid  in 
the  cesophageal  canal,  but  a  portion  of  the  food  previously  in  the  many- 
plies  may  enter  the  rennet.  The  contraction  of  these  folds  does  not  take 
place  only  during  rumination,  but  also  during  its  intervals ;  the  water  in 
the  contents  of  this  compartment  is  then  pressed  out,  and  the  residue 


378  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

found  in  this  stomach  after  death  is  alwa}~s  dry.  The  mucous  membrane 
is,  however,  entirely  incapable  of  absorption,  and  the  dryness  of  its 
contents  cannot,  therefore,  be  explained  as  due  to  the  entrance  of  the 
fluid  from  its  contents  into  the  blood.  The  psalter  likewise  furnishes  no 
secretion  of  its  own,  and  the  changes  which  occur  in  its  contents  are  due 
simply  to  the  influence  of  the  saliva  and  the  fermentative  process  which 
occurs  in  the  two  preceding  stomachs.  Its  reaction  is,  however,  often 
acid,  evidently  due  to  the  regurgitation  of  the  fluids  from  the  fourth 
stomach.  It  is  worthy  of  note  that  in  the  llama,  the  camel,  and,  to  a 
less  extent,  in  the  sheep  the  folds  of  the  membrane  in  the  third  stomach 
are  but  slightly  developed,  and  there  is  no  constriction  between  the  third 
and  fourth  stomachs,  while  the  opening  into  the  reticulum  is  particularly 
narrow.  This  may  possibly  serve  to  prevent  too  great  dryness  of  the 
contents  of  this  compartment  in  these  animals,  which  are  so  frequently 
deprived  of  water.  Where  obstruction  of  the  stomach  occurs,  it  is 
nearly  always  to  be  found  in  this  compartment. 

The  action  of  the  first  three  stomachs  is  merely  preparatory  to 
digestion.  It  is  only  in  the  fourth  stomach  that  true  digestion  takes 
place.  Its  secreting  membrane  is  four  or  five  times  as  extensive  as  that 
of  the  right  half  of  the  stomach  of  the  horse,  and  is  relatively  less  in  the 
llama  and  dromedary  than  in  other  ruminants.  The  gastric  secreting 
membrane  is,  apparently,  in  all  respects  similar  to  what  has  already  been 
described  in  other  animals,  although  the  amount  of  pepsin  and  acid  in 
the  gastric  juice  of  ruminants  is  less  than  that  found  in  this  secretion  of 
carnivora.  Pauli  states  that  extracts  made  from  the  glandular  portion 
of  the  fuiidus  of  the  fourth  stomach  of  the  ox  possess  a  much  greater 
digestive  power  than  similar  extracts  made  from  the  pylori c  portion ; 
in  other  words,  the  amount  of  acid  added  being  the  same  in  both  cases, 
that  the  glands  of  the  pylorus  are  poor  in  pepsin,  the  glands  of  the  fund  us 
rich  in  pepsin ;  and  that  the  small  amount  of  pepsin  in  the  pyloric  por- 
tion is  almost  incapable  of  extraction  with  gtycerin,  but  is  removed  by 
hydrochloric,  acid  and  by  common  salt  solutions.  Pauli  would  infer 
from  these  statements  that,  the  histological  structure  of  the  ruminant's 
stomach  being  similar  to  that  of  other  mammals,  the  so-called  chief  cells 
are  not  the  peptic  cells,  but  perhaps  are  .concerned  in  the  elaboration  of 
other  ferments,  while  the  associate  cells  are  the  true  peptic  cells.  We 
have  alreacty  in  another  place  discussed  the  grounds  for  attributing  the 
acid  of  the  gastric  juice  to  the  action  of  the  associate  cells. 

Since  the  aliments  enter  the  stomach  but  slowly  and  graduall}r,  and 
some  already  in  a  fluid  state,  digestion  in  the  stomach  occurs  under  the 
most  favorable  circumstances,  and  is  rapidly  completed.  The  pylorus  is 
narrow  and  guarded  by  a  powerful  sphincter,  thus  resembling  that  of 
carnivora  in  contradistinction  of  what  has  been  noticed  in  the  horse,  and 


GASTKIC  DIGESTION.  379 

serves  to  keep  back  the  aliments  that  are  not  thoroughly  digested.  In 
other  respects,  gastric  digestion  in  ruminants  is  similar  to  that  seen  in 
other  animals.  In  other  words,  albuminoids  are  converted  into  peptones; 
gelatin  is  dissolved  and  converted  into  a  diffusible  gelatin  peptone,  and 
milk  is  coagulated  and  its  casein  is  converted  into  peptones.  Adipose 
tissue  is  dissolved  and  the  oil  liberated  and  partially  split  up  into  fatty 
acids  ;  cane-sugar  is  slightly  converted  into  inverted  sugar  through  the 
action  of  the  acid  ;  starch  which  has  escaped  being  converted  into  sugar 
through  the  action  of  saliva  in  the  rumen  passes  into  the  intestine  to 
be  acted  on  by  the  intestinal  secretions,  for  the  degree  of  acidity  of  the 
gastric  juice  is  sufficient  to  interfere  with  the  diastatic  action  of  ptyalin. 
Gastric  digestion  in  ruminants  is  much  more  complicated  than  in  other 
animals,  and  comprises  a  series  of  operations  which  are  carried  on  partly 
simultaneously  and  partty  alternately.  The  two  first  reservoirs  are 
concerned  in  rumination  and  in  the  maceration  of  food.  The  third 
stomach  has  nothing  to  do  with  rumination,  but  acts  as  a  strainer  and 
prevents  substances  passing  into  the  fourth  stomach  until  sufficiently 
comminuted  and  softened  to  be  subjected  to  the  action  of  gastric  juice, 
while,  finally,  the  fourth  stomach  is  the  true  digestive  organ,  in  which 
the  albuminous  contents  of  the  food  are  converted  into  peptone.  It  is 
thus  seen  that  gastric  digestion  in  the  ruminant  is  much  more  complete 
than  in  other  herbivora.  Therefore,  gastric  digestion  in  these  animals  is 
predominant,  while  intestinal  digestion  is  simplified. 

8.  GASTRIC  DIGESTION  IN  BIRDS. — Gastric  digestion  in  birds  differs 
very  essentially  from  that  of  mammals,  the  difference  being  dependent 
on  the  difference  of  plan  on  which  the  alimentary  tract  is  constructed. 
The  digestive  parts  are  simplest  in  birds  of  pre}7,  such  as  the  owl,  the 
buzzard,  and  hawk.  The  oesophagus  is  large  and  dilatable,  and  is,  as  a 
rule,  not  supplied  with  a  crop.  It  is  continuous,  without  any  marked 
line  of  demarcation,  with  the  small  longitudinal  stomach,  which  takes  on 
a  transverse  curve  where  it  ends  in  the  small  intestine.  Where  the 
oesophagus  terminates  it  has  a  calibre  almost  as  great  as  the  stomach, 
so  that  the  latter  seems  simply  to  be  a  prolongation  of  the  O3sophagus. 
The  superior  limit  of  the  stomach  is  marked  by  a  band  of  large  glands, 
which  may  often  be  seen  from  the  outside  of  this  organ,  and  which 
almost  seem  to  resemble  the  agminated  glands  of  the  small  intestine  of 
the  mammal.  Below  this  the  stomach  contracts,  and  again  dilates  to  a 
more  or  less  globular  pouch,  and  again  becomes  contracted  and  united 
writh  the  small  intestine.  The  pyloric  orifice  in  birds  of  prey  is  very 
narrow. 

In  gallinaceous  birds,  such  as  the  cock,  the  turkey,  and  the  pheasant, 
the  gullet  dilates  at  the  lower  portion  of  the  neck  (the  crop)  and  then 
contracts,  to  again  expand  .and  form  the  ventriculus,  which  has  thick, 


380 


PHYSIOLOGY   OF  THE   DOMESTIC  ANIMALS. 


glandular  walls;  then  comes  the  gizzard,  composed  of  two  thick,  red, 
striped  muscles,  covered  internally  witli  a  thick,  horny  epithelium. 
The  gastric  parts  of  this  class  of  birds  are  therefore  divided  into  three 
sections — first,  the  crop,  to  act  as  a  reservoir,  in  which  the  food  is  macer- 
ated ;  from  this  it  is  pushed  gradually  into  the  second,  the  stomach,  in 

which  it  undergoes  gastric 
digestion  simultaneously 
with  the  process  of  tritura- 
tion  which  occurs  in  the  giz- 
zard, or  the  third  digestive 
compartment  (Fig.  154). 
Grains,  etc.,  which  form  the 
food  of  gallinaceous  birds, 
first  go  into  the  crop,  which 
they  distend,  and  in  which 
they  accumulate  in  consid- 
erable quantity.  Here  the 
food  becomes  softened  and 
takes  on  an  acid  reaction. 
A  comparatively  profuse  se- 
cretion is  poured  out  in  this 
pouch,  whose  properties 
have  not  been  thoroughly 
investigated.  By  inserting 
substances  into  the  crop, 
Spallanzani  obtained  one 
ounce  of  fluid  in  twelve 
hours  from  the  crop  of  a 
pigeon,  and  seven  ounces  of 
the  fluid  from  a  guinea-hen  ; 
but  although  this  fluid  is 
thus  poured  out  in  consid- 
erable amount,  it  does  not 
appear  to  be  very  active  in 
softening  the  food.  It  is 
not  known  that  this  secre- 
tion has  any  digestive  prop- 
erties, although  it  seems 
probable  that  starch  would 
here  be  converted  into  sugar,  since  grain  remains  in  this  compartment  for 
twelve  or  thirteen  hours,  or  even  much  longer.  After  leaving  the  crop, 
the  food  then  passes  into  the  ventriculus  and  gizzard.  The  ventriculus  is 
supplied  with  a  large  number  of  tubular  glands,  which  secrete  an  acid  fluid. 


FIG.  154* — CROP  AND  STOMACH  OF  THE  PIGEON. 

( Bernard. ) 

M  M,  crop ;   I,  oesophagus  :    C,  proventriculus  :    S,  tubular  glands  of 
stomach ;  J,  gizzard  ;  D,  duodenum. 


GASTKIC  DIGESTION.  381 

When,  however,  the  food  comes  in  contact  with  this  secretion,  it  has  not 
yet  been  crushed  or  comminuted ;  consequently  it  is  incapable  of  being 
acted  on  by  the  gastric  juice,  which  is  powerless  to  digest  cellulose  mem- 
branes. The  contact  of  the  food  with  the  walls  of  the  ventriculus  leads 
to  the  pouring  out  of  a  profuse  acid  secretion.  Bathed  with  this  fluid, 
the  food  then  enters  the  gizzard,  where  it  is  reduced  by  crushing  to  a 
homogeneous  pulp.  The  gizzard  has  thick,  muscular  walls,  with  a  hard, 
hornj'  epithelium  lining  it,  and  is  capable  of  exerting  very  great  force. 
Thus,  it  has  been  stated  that  iron  tubes  capable  of  supporting  a  weight 
of  five  hundred  and  thirty -five  pounds  were  completely  flattened  out 
after  passing  through  the  gizzard  of  a  turkey.  This  crushing  is  indis- 
pensable for  the  digestion  of  grains,  and  is  aided  by  the  presence  of 
gravel,  etc.,  almost  always  to  be  found  in  this  organ. 

In  carnivorous  birds  gastric  digestion  is  simpler  than  in  the  her- 
bivora.  Such  birds  swallow  their  prey  entire,  if  small  enough  to  enter 
the  beak  and  O3sophagus  ;  if  not,  it  is  torn  with  the  beak  small  enough 
to  be  swallowed,  and  then  the  skin,  hair,  feathers,  and  all  are  carried  to 
the  stomach  with  the  flesh.  As  there  is  no  crop  in  such  birds,  and  the 
ventriculus  is  but  faintly  distinguished  from  the  gizzard,  which  is  com- 
paratively small,  and  whose  walls  have  become  thin  and  almost  mem- 
branous, we  have,  therefore,  a  simple  process  of  gastric  solution,  since 
the  gizzard  has  lost  its  crushing  power.  The  solvent  power  of  the  stom- 
ach of  carnivorous  birds  is  very  rapid  and  powerful,  muscles,  tendons, 
and  cartilages  being  rapidly  dissolved.  After  about  eighteen  or  twent}^- 
four  hours,  bones  and  matters  which  have  escaped  digestion,  or  which 
are  insufficiently  dissolved  to  pass  into  the  intestine,  are  regurgitated 
through  the  mouth,  since  the  very  narrow  pylorus  present  in  carnivorous 
birds,  as  in  carnivorous  mammals,  prevents  the  passage  of  everything 
except  fluids. 

There  exists,  again,  a  t}*pe  of  birds,  midway  between  the  purely 
omnivorous  and  the  granivorous,  where  the  gizzard  has  but  moderate 
thickness  and  power.  These  birds  also  vomit  indigestible  substances. 

Birds  have,  in  general,  a  very  active  digestion.  Some  may  make  as 
many  as  twelve  meals  a  day,  in  which  they  fill  not  only  the  stomach,  but 
also  the  gullet,  pharynx,  and  beak,  especially  when  feeding  on  soft  sub- 
stances like  larvae  or  worms.  Their  appetite  seems  to  return  as  soon  as 
there  is  the  least  place  which  can  hold  more  food.  The  diet  of  birds 
cannot  be  changed.  The  birds  of  prey,  without  gizzard  or  crop,  cannot 
feed  on  grains,  although  the  gallinaceous  birds  maybe  brought  to  accom- 
modate themselves  to  an  animal  diet. 

Colin  states  that  morsels  of  meat  fed  to  sparrows  appear  in  the  giz- 
zard in  less  than  an  hour,  and  reach  the  intestine  within  an  hour  and  a 
half;  while  debris  of  food  may  be  found  in  the  faeces  in  four  or  five  hours. 


382  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


IX.    DIGESTION  IN   THE   SMALL  INTESTINE. 

As  the  aliments  pass  into  the  duodenum,  after  being  subjected  to 
the  action  of  gastric  digestion,  they  immediately  mingle  with  the  three 
other  digestive  secretions, — the  bile,  the  pancreatic  juice,  and  the  intes- 
tinal secretion. 

I.  BILE. — The  bile  is  the  secretion  of  the  liver,  and,  strictly  speak- 
ing, occurs  only  in  vertebrates.  In  the  lowest  invertebrate  animals  a 
fluid  somewhat  analogous  to  the  bile  is  poured  directly  into  the  intes- 
tine, as  the  result  of  the  secretion  of  cells  attached  to  the  intestinal 
mucous  membrane.  In  others  it  is  formed  by  a  series  of  convoluted 
tubes  surrounding  the  intestine,  or,  it  may  be,  directly  surrounding  the 
stomach.  But  although  this  fluid  may  be  yellowish  or  brown,  it  is  not 
to  be  regarded  as  bile,  since  in  invertebrates  it  never  contains  the  specific 
bile  constituents,  bile  coloring-matters  and  acids,  and  the  glands  which 
form  it  differ  histologically  from  the  liver.  In  all  the  invertebrates  the 
so-called  bile  is  directly  poured  into  the  intestine  ;  in  many  vertebrates, 
however,  the  excretory  duct  is  in  communication  by  a  side  branch 
directed  obliquely  backward  from  the  course  of  the  duct  with  a  reser- 
voir for  the  bile,  termed  the  gall-bladder.  This  reservoir  is  present  in 
all  omnivora  and  carnivora,  and  in  most  herbivora,  birds,  and  reptiles. 
It  is  absent  in  certain  of  the  group  of  herbivora.  It  is  absent  in  the 
solipedeSjthe  horse,  mule,  and  ass,  and  among  the  ruminants  in  the  stag, 
camel,  and  dromedary ;  among  the  pachydermata,  in  the  elephant,  the 
rhinoceros,  and  tapir ;  in  the  wild  boar,  and  in  certain  cetaceans ;  while 
in  birds  it  is  absent  in  the  pigeon,  cuckoo,  paraquet,  and  ostrich.  It  is 
also  absent  in  the  mouse  and  marmot.  In  the  horse  and  elephant  the 
gall-duct  is  dilated  to  form  a  sort  of  pouch.  The  ultimate  gall-ducts 
all  unite  to  form  a  single  trunk,  or  ductus  communis  choledochus,  which 
in  many  animals,  such  as  sheep  and  goats,  communicates  with  the  excre- 
tory duct  of  the  pancreas  and  pierces  the  wall  of  the  duodenum  obliquely 
from  below  upward.  As  the  result  of  this,  an  increase  of  pressure  on 
the  intestinal  contents  simply  closes  the  orifice  of  the  duct,  and  regurgi- 
tation  of  intestinal  contents  into  the  duct  is  impossible. 

In  the  gall-bladder  the  bile  becomes  concentrated,  and  mucin  is 
added  to  it  as  a  result  of  the  action  of  the  secretion  of  the  mucous 
membrane  of  the  gall-bladder.  Little  or  no  mucin  is  found  in  bile  com- 
ing directly  from  the  hepatic  cells.  The  gall-bladder  is  necessary  in 
animals  whose  digestion,  as  in  the  carnivora,  is  intermittent.  It  is  less 
important  for  the  herbivora,  where  digestion  is  nearly  constant.  The 
liver  differs  from  all  other  organs  in  its  blood-supply.  In  proportion 
to  its  size,  it  receives  but  a  small  supply  of  arterial  blood,  and  although 
an  immense  amount  of  blood  passes  through  it,  the  greater  part  reaches 


DIGESTION  IN  THE   SMALL  INTESTINE.  383 

the  liver  through  the  portal  vein,  indicating  the   functional  relation  of 
the  liver  to  the  process  of  intestinal  digestion. 

1.  The  chemical  characteristics  of  the  bile  have  been  mostly  studied 
in  the  fluids  found  in  the  gall-bladder  of  the  ox  and  in  that  obtained 
from  fistulae  in  dogs.  In  the  fresh  state,  bile  is  a  clear,  thin,  or  more  or 
less  tenacious  liquid,  which,  with  the  exception  of  epithelial  cells  from 
the  gall-bladder,  contains  no  morphological  elements.  It  has.  a  neutral 
or  alkaline  reaction.  When  fresh,  in  man  and  carnivora,  it  is  of  a  golden 
3Tellow  or  greenish-brown  color  ;  it  is  green  in  herbivora  (brownish-green 
in  the  horse  and  ox,  greenish-yellow  in  the  hog,  and  dark  green  in 
sheep).  After  standing  exposed  to  the  air,  the  brownish-yellow  bile 
becomes  dark  brown,  and  the  greenish  bile  more  intensified  to  a  dark 
green.  Bile  has  a  peculiar  bitter  taste,  and  when  warmed  a  musk-like 
odor.  The  specific  gravity  varies  in  different  animals  from  1008  to  1030, 
the  highest  being  found  in  bile  taken  from  the  gall-bladder  of  man. 
Ox-bile  is  often  yellowish-brown,  though  usually  green  in  color,  and 
may  be  either  clear  or  turbid  ;  it  is  alkaline,  viscid,  and  contains  a 
large  amount  of  mucin ;  its  specific  gravity  varies  from  1022  to  1025. 
Sheep's  bile  is  usually  green,  is  odorless,  clear,  alkaline,  and,  although  it 
contains  mucin,  is  not  viscid;  specific  gravity,  1025  to  1031.  Calves' 
bile  is  green  or  yellowish-brown,  though  sometimes  golden  yellow  in  thin 
la}*ers ;  it  is  clear,  odorless,  viscid,  neutral  in  reaction,  and  contains  but 
little  mucin;  specific  gravitj7,  1020  to  1027.  Pig's  bile  is  clear  or  dark 
yellowish-brown  or  golden  yellow  (the  latter  when  diluted),  is  odorless, 
alkaline,  contains  large  amounts  of  mucin,  and  is  therefore  very  viscid  ; 
specific  gravity,  1020  to  1027.  Dog's  bile  is  usually  yellowish-brown, 
and  when  diluted  golden  yellow ;  it  may  be  either  neutral  or  alkaline, 
contains  mucin,  and  is  clear  and  odorless;  specific  gravity,  1025.  The 
bile  of  all  animals  may  be  kept  for  several  days,  even  at  a  high  tempera- 
ture, before  putrefaction  sets  in.  In  the  fresh  secretion  from  the  liver, 
the  solids  in  the  bile  of  the  cat,  dog,  and  sheep  amount  to  5  per  cent.,  in 
the  rabbit  2  per  cent.,  and  in  the  sheep  1-J-  per  cent.  In  the  gall-bladder 
in  cats,  dogs,  and  rabbits  the  solids  rise  from  2  to  20  per  cent.,  in  the 
sheep  to  8  per  cent.,  in  man  from  9  to  17  per  cent.,  and  in  the  ox  from 
7  to  11  per  cent.:  the  solids  in  the  bile  of  man,  the  pig,  and  the  ox  consist 
of  only  1.5  per  cent,  of  inorganic  matter,  and  in  the  dog  only  3.6  per  cent. 

Doer. 

In  100  parts  Bile.  Man.         Ox.  Pig.        , « , 

Fresh.  From  Bladder. 
Water,        .  86.3        90.4        88.8        95.3          85.2 


Solids, 

Bile  salts, 

Lecithin,  cholesterin 

Fats,  soaps, 

Mucin  and  coloring  matter, 

.Inorganic  salts, 


13.7  9.6  11.2  4.7  14.8 

7.4)  7.3  3.4  12.6 

>  8.0 

3.0)  2.2  0.5  1.3 

2.2  0.3  0.6  0.2  0.3 

1.1  1.3  1.1  0.6  0.6 


384  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

While  the  bile  is  entirely  free  from  proteicls,  it  contains  both  organic 
and  inorganic  constituents.  The  former  group  are  represented  by  mucin, 
a  compound  of  sodium  with  two  organic  acids  (glycocholic  and  tauro- 
cholic),  a  coloring  matter  which  undergoes  various  modifications  and 
whose  origin  is  a  source  of  considerable  interest,  lecithin,  small  quanti- 
ties of  fat  and  soap,  and  a  small  amount  of  diastatic  ferment.  These  will 
be  considered  in  turn. 

(a)  Mucin. — Mucin  gives  to  bile  its  viscidity,  and  is  the  product  of 
the  mucous  glands  of  the  larger  bile-ducts  and  gall-bladder.     The  longer 
the  bile  remains  in  the  gall-bladder,  the  larger  will  be  the  percentage  of 
mucin  found  in  it,  since  the  mucous  cells  in  the  walls  of  this  reservoir 
are  the  principal  sources  of  this  bod}7.     In  the  bile  of  animals  supplied 
with  a  gall-bladder,  mucin  will  be  found  in  larger  amounts  than  in  ani- 
mals in  whom  this  appendage  to  the  liver,  as  in  the  case  of  the  horse,  is 
absent.     The  smaller  bile-ducts  are  free  from  mucous  cells,  and,  as  a  con- 
sequence, bile  coming  directly  from  the  liver-cells  contains  no  mucin. 
The  longer  the  gall  remains  in  the  gall-bladder,  the  more  will  it  deviate 
from  its  general  character  when  freshly  secreted  by  the  liver-cells.     Yel- 
low bile  gradually  becomes  greenish,  and  its  consistence  will  become 
more  marked  from  the  addition  of  mucus.     The  general  characteristics 
of  mucin  found  in  the  bile  do  not  differ  from  those  of  mucin  found  else- 
where.    It  may  be  precipitated  by  acetic  acfd,  and  when  bile  containing 
mucus  is  precipitated  with  alcohol  it  loses  its  viscidity. 

(b)  The  Bile  Acids. — The  bile  acids  occur  in  the  bile  in  the  form  of 
compounds  with  sodium,  and  occasionally  with  minute  amounts  of  potas- 
sium, to  form  glycochplate  and  taurocholate  of  sodium, — two  salts  which 
are  highly  soluble  in  water.     The  relative  proportions  of  these  two  salts 
vary  considerably  in  the  ,bile  of  many  animals.     In  that  of  man,  as  well 
as  of  birds,  many  mammals    and    amphibia,  taurocholic   acid  is  most 
abundant.     In  other  mammals,  as  in  the  pig  and  ox,  sodium  gtycocko- 
late  is  in  largest  amount,  while  the  taurocholate  is  more  scanty.     In  the 
bile  of  the  dog,  cat,  bear,  and  other  carnivora,  taurocholate  is  almost  the 
sole  representative  of  these  salts,  while  the  glycocholate  is  almost  entirely 
absent.    In  the  bile  of  the  pig,  in  addition  to  these  two  salts,  the  hyocho- 
late  of  sodium  is  also  present. 

The  gall  of  the  hog  contains,  besides  hyoglycocholic  acid,  another  until 
lately  unknown  acid,  which  occurs  in  larger  quantity  than  the  first  known  acid 
(Jolin).  It  is,  for  the  present,  called  B-hyoglycocholic  acid.  It  is  with  difficulty 
obtained  pure,  as  neither  it  nor  its  salts  are  crystallizable.  It  is  distinguished 
from  the  A-acid  by  its  behavior  with  saturated  sodium  sulphate  solution,  which 
precipitates  the  sodium  salt  of  the  A-acid  almost  completely,  and  in  a  flocculent 
Ibrin,  whereas  the  sodium  salt  of  the  B-acid  is  only  partly  precipitated,  and  is 
at  first  colored,  and  easily  soluble  in  water.  The  purified  salt  is  separated 
from  the  alcoholic  solution  by  means  of  ether,  as  a  snowy-white,  cheesy  precipi- 
tate, which  soon  shrinks  to  a  yellowish  mass,  whereby  much  ether  is  pressed  out. 
This  mass  is  easily  soluble  in  water  and  alcohol,  and  the  solutions  allow  them- 


"  DIGESTION  IN   THE  SMALL  INTESTINE.  385 

selves  to  be  concentrated  to  a  syrupy  consistency.  The  aqueous  solution  gives 
a  precipitate  with  barium  chloride,  which  at  first  dissolves  again,  but  with  more 
barium  solution  a  lumpy  barium  salt  separates,  which  soon  changes  to  a  tough, 
shiny,  silky  mass.  The  salts  of  this  acid  have  a  very  bitter  taste,  which  is  not, 
however,  as  intense  as  that  of  the  A-acid  salts.  The  composition  of  the  acid  could 
not,  as  yet,  be  determined.  Analysis  proved  that  the  percentage  of  carbon  is 
much  less  in  the  B-acid  than  in  the  A-acid,  .whereas  the  percentage  of  nitrogen  is 
about  equal  in  both.  By  continued  treatment  with  alcohol,  the  B-acid  yields 
cholalic  acid.  In  how  far  this  acid  corresponds  to  the  one  obtained  in  a  similar 
manner  from  the  A-acid  has  not  yet  been  determined. 

Various  methods  have  been  proposed  for  the  separation  of  these  salts  from 
the  bile,  of  which  only  the  following  will  be  given.  The  bile  from  the  gall-blad- 
der of  an  ox  should  be  evaporated  to  one-fourth  its  volume  over  a  water  bath, 
rubbed  up  to  a  thick  paste  with  animal  charcoal,  and  completely  dried  at  100°  C. 
The  hot  mass  should  then  be  thrown  into  absolute  alcohol,  well  shaken  repeat- 
edly, allowed  to  stand  for  two  or  three  hours,  and  then  filtered.  A  part  of  the 
alcohol  may  be  removed  from  the  filtrate  by  distillation,  and  the  bile  salts  may 
then  be  precipitated,  in  the  form  of  a  resinous  syrup,  by  the  addition  of  a  large 
excess  of  ether.  After  standing  a  variable  time,  from  one  or  two  days  to  a  week 
or  more,  the  time  depending  upon  the  anhydrous  character  of  the  alcohol  and 
ether,  the  so-called  Platner's  crystallized  bile  separates  in  a  mass  of  glistening 
needles.  This  crystallized  bile  consists  of  a  mixture  of  taurocholate  and  glyco- 
cholate  of  sodium. 

These  salts  are  insoluble  in  ether  and  readily  soluble  in  alcohol  and 
water.  Their  aqueous  solutions  have  a  decided  alkaline  reaction,  and 
rotate  the  plane  of  polarized  light  to  the  right.  Both  these  salts  are 
highly  deliquescent,  and  when  exposed  to  the  atmosphere  the  crystals 
absorb  the  mixture  and  break  down  into  a  thick,  tenacious  S3*rup. 

To  separate  the  two  individual  bile  acids  from  each  other,  this  mixture  of 
crystallized  bile  may  be  dissolved  in  a  small  volume  of  water,  a  little  ether  added, 
and  then  dilute  sulphuric  acid.  After  stirring  well,  glycocholic  acid  crystallizes 
in  shining  needles,  the  taurocholic  acid  remaining  in  solution.  The  crj'stals  may 
be  collected  on  a  filter,  washed  with  water,  dissolved  in  dilute  spirits,  and  pre- 
cipitated with  excess  of  ether.  "Or  to  the  solution  of  Platner's  crystals  add 
neutral  and  then  a  little  basic  lead  acetate,  when  glycocholate  of  lead  will  be 
thrown  down.  Collect  on  a  filter,  wash,  and  dissolve  in  hot  alcohol,  and  remove 
the  lead  by  passing  a  current  of  sulphuretted  hydrogen  ;  filter,  and  by  the  careful 
addition  of  water  to  the  alcoholic  filtrate,  crystals  will  be  deposited.  To  the 
previous  filtrate  from  the  glycocholate  of  lead  add  acetate  of  lead  and  ammonia ; 
glycocholate  and  taurocholate  of  lead  will  be  precipitated,  and  may  be  washed 
and  decomposed,  as  with  the  glycocholate."  In  the  bile  of  oxen  from  certain 
districts,  glycocholic  acid  rapidly  crystallizes  on  the  addition  of  fivec.c.  of  hydro- 
chloric acid  and  thirty  c.c.  of  ether  to  each  five  hundred  c.c.  of  bile.  In  other 
.specimens  this  process  entirely  fails.  No  satisfactory  explanation  of  this  peculi- 
arity has  ever  been  given,  though  Hoppe-Seyler  suggests  that  the  acid  removes 
the  base  from  the  glycocholate,  and  the  liberated  glycocholate  acid,  being  insoluble 
in  water,  is  precipitated.  If  this  were  the  explanation,  the  process  should  invari- 
ably succeed  ;  such  is  not,  however,  the  fact. 

The  test  for  these  two  acids  is  known  as  Pettenkofer's  reaction  for  biliary 
acids.  If  a  little  cane-sugar  in  strong  solution  is  added  to  a  small  quantity  of  bile 
in  a  test-tube,  gently  warmed  to  about  60°  C  ,  and  then  an  equal  volume  of  strong 
sulphuric  acid  allowed  to  flow  down  the  side  of  the  tube,  a  bright-purple  color 
forms  above  the  level  of  the  acid.  This  test  may  be  even  better  shown  by  pre- 
paring the  bile  as  before  (solution  of  Platner  s  crystals),  warming  gently,  with  a 
cane-sugar  syrup,  then  shaking  well  until  a  layer  of  foam  forms  on  the  upper 
surface.  If  a  small  amount  of  sulphuric  acid  is  poured  down  the  inside  of  the 
tube,  the  froth  on  the  surface  of  the  bile  becomes  bright  purple  in  color ;  or  bile 
may  be  diluted  with  cane-sugar  solution,  and  a  piece  of  filter-paper  dipped  into  it 

25 


386  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

and  allowed  to  dry.  Dropping  a  little  sulphuric  acid  on  the  paper  thus  prepared 
will  in  a  few  seconds  produce  a  violet-red  color.  Proteids  will  also  behave  in  the 
same  way  as  Plainer' s  crystallized  bile,  but  the  reactions  may  be  distinguished  by 
the  fact  that,  when  examined  spectroscopically,  two  absorption  bands,  one  near  the 
line  E  and  the  other  opposite  F,  will  be  found  when  the  bile  is  examined,  and  will 
be  absent  from  the  color  produced  by  this  test  with  albuminoids.  Amylic  alcohol 
will  also  produce  a  similar  reaction,  and  here  again  the  spectroscope  will  serve  to 
distinguish  them.  This  test  depends  upon  the  fact  that  cholic  acid  is  first  pre- 
cipitated by  sulphuric  acid  in  a  whitish  form,  as  may  be  readily  seen  in  solutions 
of  crystallized  bile,  and  then  dissolved,  assuming  a  cherry-red  color,  which 
becomes  gradually  darker  in  hue.  The  pigments  and,  to  a  still  more  marked 
degree,  the  presence  of  nitrates  or  chlorates  will  interfere  with  this  reaction. 

The  source  of  the  biliary  acids  is  almost  unknown,  except  that  they 
probably  originate  from  the  breaking  down  of  albuminoids.  They  are 
not  found  in  the  blood,  but  are  formed  in  the  hepatic  cells,  the  nitrogen 
possibly  originating  from  the  albuminoid,  while  the  cholic  acid  radical 
may  be  derived  from  the  fats.  These  acids  are  compounds  of  taurin  and 
gtycochol  with  cholic  acid,  into  which  they  may  readily  be  split  up  by 
prolonged  boiling  with  alkalies  or  mineral  acids. 

Glycocholic  Acid  (C26H48N06). — Glycocholic  acid  occurs  in  large 
amounts  in  the  bile  of  herbivora,  while  it  is  only  found  in  small  quantities 
in  the  bile  of  carnivora  and  omnivora.  It  originates  from  the  union  of 
gtycochol  with  cholic  acid,  and,  like  taurocholic  acid,  is  closely  allied  to 
hippuric  acid.  When  boiled  with  hydrochloric  acid  it  is  decomposed 
into  glycochol  and  cholic  acid,  the  latter  being  a  non-nitrogenous  body. 
The  reaction  is  as  follows : — 

C26H43N06  +  H20:=C24H4005+C2H5N02. 
Glycocholic  Acid.    Water.    Cholic  Acid.        Glycochol. 

Glycocholic  acid  crystallizes  in  glistening,  white  needles,  which  are 
nlmost  insoluble  in  cold  water,  slightly  soluble  in  hot  water,  easily 
soluble  in  alcohol,  and  slightly  soluble  in  ether. 

Taurocholic  Acid  (C26H46"N '07S). — Taurocholic  acid  is  the  only  acid 
in  dog's  bile,  as  in  that  of  other  carnivora,  though  it  can  be  obtained  in 
small  amounts  from  ox-gall  after  the  removal  of  glycocholic  acid.  It 
contains  sulphur,  and  forms  white,  glistening  needles,  which  become 
fluid  when  in  contact  with  the  air.  Taurocholic  acid  is  soluble  in  water 
and  alcohol  and  insoluble  in  ether.  Of  these  acids  only  the  alkaline 
salts  are  soluble  in  alcohol  and  water.  Out  of  a  mixture  of  glycocholic 
and  taurocholic  acid  salts,  acetate  of  lead  will  precipitate  the  glycocholic 
acid  as  a  glycocholate  of  lead.  When  filtered  off,  the  addition  of  acetate 
of  lead  and  ammonia  will  precipitate  taurocholic  acid  as  a  taurocholate 
of  lead,  which  may  be  easily  dissolved  in  hot  alcohol,  and  the  lead 
removed  by  passing  a  current  of  sulphuretted  hydrogen  through  it. 

Taurocholic  acid  originates  in  the  breaking  down  of  albuminoids, 
from  which  the  sulphur  is  derived,  and  its  amount  in  the  bile  may  be 


DIGESTION  IN  THE   SMALL  INTESTINE.  387 

increased  by  an  increase  in  albuminoid  diet,  though  not  in  the  same 
degree  as  occurs  in  the  case  of  urea.  It  is  rapidly  decomposed  into 
taurin  and  cholic  acid ;  this  decomposition  also  occurring  in  the 
intestine. 

Glycochol  (C2H6y02),  or  glycin,  is  also  formed  by  boiling  gelatin  with 
dilute  sulphuric  acid.  It  is  a  crystallized  body,  slightly  soluble  in  water, 
insoluble  in  alcohol  and  ether.  Its  aqueous  solutions  have  a  faintly  acid 
reaction.  It  does  not  occur  as  such  in  the  animal  body,  but,  besides 
being  concerned  in  the  origin  of  the  bile  acid,  it  is  also  found  in  the 
urine,  especially  of  the  horse,  united  with  benzoic  acid  in  the  form  of 
hippuric  acid.  It  may  be  obtained  from  the  glycocholic  acid,  as  already 
indicated,  by  boiling  with  strong  hydrochloric  acid. 

Taurin  (C2H,NS03)  occurs  in  large,  glistening  columns  as  a  product 
of  splitting  of  the  bile  acids.  It  is  readily  soluble  in  water,  insoluble 
in  alcohol  and  ether.  It  is  also  found  in  the  intestinal  canal  and  in 
the  flesh  of  various  fish  and  of  the  horse,  and  in  the  kidneys,  spleen, 
and  lungs  of  various  other  animals.  It  is  also  found  in  putrid  bile, 
being  then  developed  at  the  expense  of  the  taurocholic  acid  in  the 
fermentation  of  the  bile.  It  combines  with  various  bases  to  form 
salts.  The  bile  acids  may  thus  be  regarded  as  compounds  of  glycochol 
and  taurin  with  cholic  acid,  whose  chemical  composition  and  general 
properties  are  not  certainty  known.  Cholic  acid  may  be  regarded,  there- 
fore, as  the  starting  point  of  the  biliary  acids. 

Cholic  Acid  (H^CwOs-f  HaO). — Cholic  acid  is  a  constant  product  of 
decomposition  of  biliary  acids,  nnd  is  therefore  found  in  the  intestinal 
contents,  occasionally  in  the  urine  of  jaundice,  but  not  in  fresh  bile  or 
elsewhere  in  the  organism.  Cholic  acid  occurs  in  an  amorphous  and  in 
a  crystallized  form;  it  is  insoluble  in  water,  soluble  with  difficulty  in 
ether,  and  moderately  soluble  in  alcohol. 

"It  may  be  prepared  by  boiling  bile  with  caustic  potash  for  twelve  to  twenty- 
four  hours,  then  precipitating  with  hydrochloric  acid,  and,  having  washed  the 
deposit  with  water,  dissolving  it  in  caustic  soda  containing  a  little  ether  ;  hydro- 
chloric acid  is  next  added,  and  after  some  time  crystals  form.  The  supernatant 
fluid  may  be  decanted,  and  the  residue  covered  with  ether  ;  drain  off  the  ether  in 
a  half-hour  or  so,  and  dissolve  the  deposit  in  boiling  alcohol ;  to  this  solution 
add  a  little  water  until  a  permanent  precipitate  appears,  and  tetrahedric  crystals 
soon  make  their  appearance." 

(c)  The  Coloring  Matters  of  the  Bile. — The  bile  under  different  con- 
ditions and  in  different  animals  contains  a  number  of  different  coloring 
matters,  to  which  its  different  shades  of  color  are  due.  The  essential 
coloring  matter  of  fresh  bile  is  bilirubin,  to  which  the  reddish-brown 
color  of  the  bile  of  man  and  the  carnivora  is  due,  and  which  appears 
to  be  the  starting  point  of  the  various  coloring  matters  which  are  found 
in  the  bile  of  different  animals ;  it  also  occasions  the  various  -changes 


388  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

in  tint  which  the  bile  undergoes  after  having  been  removed  from  the 
bod}r.  When  bile  remains  for  a  considerable  time  in  the  gall-bladder, 
and  when  bile  is  exposed  to  the  air,  provided  the  reaction  remains  alka- 
line, the  reddish-brown  coloring  matter,  bilirubin,  absorbs  oxygen  from 
the  atmosphere  and  acquires  a  greenish  color ;  it  is  then  termed 
biliverdin.  In  the  bile  of  herbivora  and  most  cold-blooded  animals 
this  pigment  exists  naturally,  and  is  present  even  before  it  passes  into 
the  small  intestine.  Both  these  substances,  bilirubin  and  biliverdin, 
are  insoluble  in  water,  and  their  state  of  solution  in  the  bile  is  to  be 
explained  on  the  basis  of  their  forming  soluble  combinations  with  alka- 
lies, and  partly  to  their  being  held  in  solution  by  the  bile  acids,  in  whose 
solutions  they  are  soluble.  They  are  slightly  soluble  in  ether  and 
alcohol,  and  readily  soluble  in  chloroform  and  in  alkalies.  The  test  for 
their  detection  is  known  as  Gmelin's  test,  which  is  claimed  to  be  suf- 
ficiently sensitive  to  detect  the  presence  of  one  part  of  bilirubin  in  eighty 
thousand  parts  of  solution. 

The  test  is  performed  by  adding  nitric  acid  which  contains  some  free  nitrous 
acid  to  bile.  This  causes  a  precipitate  which  disappears  on  the  addition  of  fresli 
acid,  and  results  in  the  formation  of  a  series  of  colors,  passing  through  green, 
blue,  violet,  red,  and  then  yellow,  and  is  due  to  the  different  degrees  of  oxidi- 
zation of  the  red  coloring  matter  of  the  bile.  Various  modifications  have  been 
proposed  for  this  test.  Briicke  recommends  the  addition  of  dilute  nitric  acid  to 
the  suspected  fluid,  and  then  pouring  a  quantity  of  concentrated  sulphuric  acid 
carefully  down  the  side  of  the  tube  ;  as  it  sinks  to  the  bottom  it  liberates  free 
nitric  acid,  which  produces' the  characteristic  play  of  colors  ;  or  a  concentric  solu- 
tion of  nitrate  of  sodium  may  be  added  and  then  sulphuric  acid.  When  only 
traces  of  bile  and  coloring  matters  are  present,  the  addition  of  the  tincture  of 
iodine  causes  the  appearance  of  a  green  color. 

Bilirubin  (C32H86N406). — Bilirubin,  which  is  also  called  hsematoidin, 
occurs  as  an  amorphous,  orange-yellow  powder,  which,  by  its  precipi- 
tation out  of  chloroform  (obtained  by  boiling  bile  with  chloroform), 
may  be  crystallized  in  red  prisms.  This  bile-pigment  is  more  frequently 
obtained  from  biliary  calculi,  especially  those  of  the  ox,  which  are  con- 
stituted almost  entirely  of  this  pigment  and  cholesterin. 

The  calculi  should  be  powdered,  exhausted  with  ether,  and  then  with  boil- 
ing water  containing  a  few  drops  of  hydrochloric  acid,  which  is  added  to  separate 
the  bilirubin  from  the  alkali  with  which  it  is  supposed  to  be  combined.  The 
residue  is  then  to  be  washed  in  pure  water,  then  dried,  and  then  boiled  with  chlo- 
roform and  finally  filtered.  From  the  filtrate  the  chloroform  may  be  distilled  off", 
the  residue  then  extracted  with  alcohol,  and  ether  and  pure  bilirubin  will  remain 
behind.  The  amorphous,  reddish  powder  which  remains  may  be  purified  and 
obtained  in  a  crystallized  form  by  re-solution  in  chloroform,  which  should  be 
allowed  to  evaporate  spontaneously.  In  the  preceding  process  the  ether  is  em- 
ployed to  remove  the  fat  and  cholesterin,  and  water  to  remove  the  other  soluble 
biliary  constituents. 


Bilirubin  is  only  slightly  soluble  in  water,  readily  soluble  in  chloro- 
form and  benzole,  and  sparingly  soluble  in  alcohol  and  ether.  It  seems 
to  play  the  part  of  an  acid,  and  unites  with  alkalies  to  form  combinations 


DIGESTION  IX   THE   SMALL  INTESTINE.  389 

which  are  insoluble  in  chloroform.  Bilirubin  is  the  most  important 
coloring  matter,  and  from  it  originate  the  others.  It  is  undoubtedly 
formed  in  the  liver-cells,  though  it  is  also  formed  in  other  localities. 
Pathologically,  it  occurs  in  old  blood-extravasations,  where  it  was  for- 
merly described  by  Yirchow  under  the  name  of  haematoidin  crystals ; 
physiologically,  it  is  found  in  the  corpora  lutea,  in  the  ovaries,  and  in 
the  borders  of  the  placenta  of  the  dog.  Bilirubin  evidently  originates 
in  the  haemoglobin  of  the  red  blood-corpuscles.  All  causes  which  pro- 
duce breaking  down  of  the  red  blood-cells  and  consequent  jaundice, 
such  as  poisoning  by  ether  and  chloroform,  lead  to  the  appearance  of 
bilirubin  in  the  urine.  This  decomposition  may  also  be  produced  by  the 
action  of  the  alkalies  of  the  bile  acids,  and  it  is  therefore  probable  that 
the  physiological  origin  of  the  bile  coloring-matter  is  due  to  the  action 
of  the  bile  acids  on  the  blood-corpuscles  in  the  liver.  When  oxidizing 
agents,  such  as  nitrous-nitric  acid,  are  added  to  a  solution  of  bilirubin  it 
displays  a  succession  of  colors  identical  with  that  seen  in  the  applica- 
tion of  Gmelin's  test.  Each  of  these  stages  represent  a  distinct  pig- 
mentary substance.  The  first  which  results,  or  the  greenish  color,  is  due 
to  the  appearance  of  biliverdin. 

Biliverdin  (C32H36\408)  occurs  through  the  action  of  oxygen  on 
bilirubin,  and  is  produced  even  when  the  solutions  of  the  latter  are 
allowed  to  stand  exposed  to  the  air.  This  body  is  found  in  abundance 
in  the  bile  of  cold-blooded  animals,  and  is  the  principal  pigment  of  the 
bile  of  herbivora.  Biliverdin  may  be  prepared  by  making  an  alkaline 
solution  of  bilirubin  and  exposing  it  to  the  air  in  a  shallow  vessel ;  after 
awhile  the  reddish  solution  becomes  intensely  green,  and  biliverdin  may 
be  deposited  as  a  green,  amorphous  powder  by  precipitation  with  hydro- 
chloric acid,  washing  with  water,  dissolving  in  alcohol,  and  finally  pre- 
cipitating with  water.  Biliverdin  then  forms  a  green,  amorphous  powder, 
which  is  insoluble  in  water,  ether,  and  chloroform  ;  is  soluble  in  alcohol, 
acetic  acid,  and  solutions  of  the  alkaline  carbonates.  When  subjected  to 
the  action  of  nitrous-nitric  acid  this  pigment  also  liberates  a  series  of 
different  colors,  which  pass  through  the  same  sequence  as  those  developed 
by  the  addition  of  this  acid  to  solutions  of  bilirubin,  the  only  difference 
consisting  in  the  absence  of  the  original  red  color.  The  first  change  is 
from  a  green  into  a  blue  or  violet  color,  and  is  due  to  the  formation  of 
choletlin,  which  finally  becomes  yello wish-brown.  Each  of  the  coloring 
matters  of  the  bile  has  a  distinctive  absorption  of  the  spectrum,  which 
is  yielded  when  the  solution  is  treated  with  nitric  acid.  The  bile  of 
carnivora  is  usually  free  from  absorption  bands,  unless  an  acid  be 
added,  in  which  case  the  absorption  bands  characteristic  of  bilirubin 
appear  in  the  spectrum. 

(d)   Cholesterin  (CjgH^O  (H2O))   is  also  an   important  constituent 


390  PHYSIOLOGY   OF  THE   DOMESTIC  ANIMALS. 

of  the  bile,  and  forms  the  bulk  of  the  so-called  white  gall-stones.  Choles- 
terin  rotates  the  plane  of  polarized  light  to  the  left,  and  forms  transparent, 
rhombic  plates,  which  usually  have  a  small,  oblong  piece  cut  out  of  one 
corner.  Cholesterin  is  insoluble  in  alkalies,  dilute  acids  and  alcohol, 
and  cold  water,  and  is  soluble  in  hot  alcohol,  ether,  glycerin,  chloroform, 
and  soap  solution  and  alcohol.  In  the  bile  it  is  kept  in  solution  through 
the  union  of  bile  salts.  Cholesterin  is  widely  distributed  through  the 
body,  occurring  usually  in  the  cerebro-spinal  axis  and  nerves,  and,  in 
fact,  seems  to  originate  from  the  breaking  down  of  nerve-tissues.  It  is 
likewise  found  in  the  yelk  of  eggs,  in  the  spleen,  and  in  various  patho- 
logical deposits  in  the  animal  body. 

It  may  be  prepared  by  powdering  white  gall-stones,  boiling  in  water  con- 
taining caustic  potash,  filtering  when  cold,  and  washing  the  resulting  mass  with 
boiling  alcohol,  and  filtering  while  still  hot.  Cholesterin  crystallizes  out  of  the 
alcohol  when  cold.  It  may  be  purified  by  redissolving  in  boiling  ether,  and 
adding  half  its  vglume  of  alcohol,  and  allowing  it  to  evaporate  spontaneously. 
Cholesterin  crystals  give  a  violet  color  with  80  per  cent,  sulphuric  acid  (Mole- 
schott). 

When  treated  with  nitric  acid,  dried,  and  touched  with  a  drop  of  ammonia, 
a  deep-red  color  is  produced,  which  is  not  altered  by  the  addition  of  caustic  soda. 
(Schiff). 

When  dissolved  in  chloroform  and  agitated  with  an  equal  volume  of  strong 
sulphuric  acid,  a  blood-red  solution  is  obtained,  which  becomes  gradually  violet, 
blue,  green,  and  then  yellow,  and  then  disappears  if  a  trace  of  water  is  present. 
The  layer  of  sulphuric  acid  in  this  test  shows  green  fluorescence.  If  crystals  of 
Cholesterin  are  heated  with  tolerably  strong  sulphuric  acid,  and  afterward  with 
a  little  iodine,  a  play  of  colors  is  produced,  passing  from  violet  through  blue, 
green,  red,  and  yellow  to  brown. 

Among  the  other  organic  constituents  of  the  bile,  lecithin,  which 
belongs  to  the  group  of  the  complex  nitrogenous  fats,  is  to  be  men- 
tioned. Its  formula  is  C^H^NPOg.  It  occurs  widely  distributed  through- 
out the  bod\',  occurring  especially  in  the  brain,  nerves,  yelk  of  eggs, 
semen,  and  pus.  When  pure,  it  is  a  colorless,  partially  crystalline  body, 
soluble  in  cold  and  hot  alcohol,  less  so  in  ether,  and  soluble  in  chloro- 
form, carbon  disulphide,  and  fats. 

It  is  not  yet  clearly  established  as  to  whether  the  lecithin  found  in 
the  bile  and  other  secretions  and  tissues  is  derived  from  the  breaking- 
down  of  food-stuffs  in  pancreatic  digestion,  or  whether  it  is  found  S3*n- 
theticalty.  The  reabsorption  of  lecithin,  however,  is  complete,  since  no 
trace  of  lecithin  or  glycerin-phosphoric  acid  is  to  be  found  in  the  faeces. 

(e)  The  Inorganic  Constituents  of  the  Bile. — Of  the  inorganic  con- 
stituents of  the  bile,  iron  is  of  special  importance,  as  indicating  the  red 
blood-corpuscles  as  the  source  of  bilirubin,  from  which-  process  of  decom- 
position the  iron  also  undoubtedly  originates.  No  close  relation,  how- 
ever, between  its  quantity  and  that  of  the  bile  coloring-matters  has  been 
ever  distinctty  made  out.  The  following  table,  after  Hoppe-Seyler,  indi- 
cates the  quantitative  composition  of  the  solids  found  in  bile  of  the  dog 


DIGESTION  IN  THE   SMALL  INTESTINE.  391 

drawn  from  the  bile-duct,  and  after  having  remained  some  time  in  the 
gall-bladder : — 


From 

Freshly 

Bladder. 

Secreted. 

Mucin,        .         .         .'.'"'•        •        . 

0.454 

0.053 

Taurocholic  alkali,    .      '  .        .        ... 

11.959 

3.460 

0449 

0.074 

Lecithin,   *. 

2.692 

0.118 

Fats,  .        .  .       .        .        .        . 

3.841 

0.335 

Soaps,         .•- 

3.155 

0.127 

Organic  bodies  insoluble  in  alcohol, 

0.973 

0.442 

Inorganic  bodies  insoluble  in  alcohol, 

0.199 

0.408 

K2S04,      

0.004 

0.022 

Na2SO4,     

0.050 

0.046 

NaCl,         

0.015 

0.185 

Na2Co3  

0.005 

0.056 

Cas2(P04),        
FeP04,      

0.080 
0.017 

0.039 
0.021 

CaCO,  

0019 

0.030 

MgO,           

0.009 

0.009 

2.  The  Secretion  of  the  Bile. — In  contradistinction  to  the  saliva  and 
gastric  juice,  the  secretion  of  bile  appears  to  be  continuous:  even  during 
prolonged  abstinence,  though  reduced  in  amount,  it  is  not  suppressed. 
Food  exercises  a  marked  influence  on  the  quantity  and  composition  of 
the  bile,  every  meal  producing  a  maximum  increase  in  the  amount  of 
secretion  which  is  reached  between  three  and  five  hours  after  the  com- 
pletion of  the  meal.  It  then  returns  gradually  to  its  original  quantity, 
to  be  again  subjected  to  a  second  increase,  which  occurs  between  thir- 
teen and  fifteen  hours  afterward.  This  increased  flow  of  bile,  it  will  be 
noticed,  co-exists  with  the  discharge  of  the  contents  of  the  stomach  into 
the  small  intestine,  and  it  would  appear,  as  has  been  determined  experi- 
mentally, that  the  application  of  the  acid  to  the  intestinal  surfaces  causes 
a  discharge  of  bile  by  causing  reflex  contraction  of  the  bile-ducts  and 
gall-bladder. 

Since  in  the  herbivora  eating  and  digestion  are  almost  continuous, 
the  amount  of  bile  secreted  is  much  larger  than  in  the  case  of  the 
omnivora  and  carnivora.  The  total  amount  has  been  estimated  to  be 
about  five  hundred  to  six  hundred  cubic  centimeters  in  twenty-four  hours, 
or  fifteen  grammes  of  bile  with  half  of  one  per  cent,  of  solids  per  kilo  of 
body  weight.  In  the  horse  the  amount  excreted  in  twenty -four  hours  is 
about  five  to  six  kilos.  In  dogs,  the  secretion  is  most  active  after  a  meal 
of  meat,  a  diet  of  fat,  however,  greatly  reducing  the  amount  of  this  secre- 
tion. According  to  Bidder  and  Schmidt,  for  every  kilo  of  body  weight 
each  hour  the 

Sheep  secretes  .  '   .  .  .  1.059  grammes  of  bile. 

The  dog      "  .  »  .  .  0.824 

The  cat       "  ."  .  .  .  0.608 

The  rabbit  "  .  .  5.702 


392  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

Colin  fixes  the  following  amounts  as  the  hourly  secretion  in  the 
domestic  animals  : — 

In  the  ox, 100  to  120  grammes. 

In  the  pig, 75  to  160 

In  the  sheep,    .    .    .    .    .    10  to  160 

In  the  clog,    .        .         .         .         .        .  8  to    15 

In  the  horse,        .        .        .        .        .  250  to  300 

It  would  seem,  therefore,  that  the  smaller  the  animal  the  greater  the 
relative  amount  of  bile  secreted  in  proportion  to  the  body  weight.  Thus, 
a  guinea-pig  weighing  one  kilo,  and  whose  liver  only  weighed  forty 
grammes,  secreted  in  twenty-four  hours  one  hundred  and  seventy-five 
grammes  of  bile,  or  more  than  four  times  the  weight  of  the  liver ;  and  as 
the  bile  of  the  guinea-pig  contains  1  per  cent,  of  solids,  one  kilo  of  liver- 
substance  would,  in  twenty-four  hours,  form  four  kilos  of  bile  with  fifty 
grammes  of  solids.  Since  the  liver  only  contains  25  per  cent,  of  solids, 
it  follows  that  in  twenty-four  hours  one-fifth  of  all  the  solids  in  the  liver 
must  be  eliminated  in  the  bile.  According  to  Colin,  the  liver  forms,  in 
twenty-four  hours,  in  the  horse  six  kilos,  in  the  ox  2.64  kilos,  and  in  the 
sheep  0.34  kilos. 

In  contradistinction  to  the  saliva,  the  bile  is  secreted  under  very 
low  pressure.  Ever}7  slight  obstruction  to  the  flow  through  the  duct 
leads  to  reabsorption  of  the  secretion  by  the  hepatic  lymphatic  ves- 
sels and  consequent  jaundice,  thus  showing  the  close  connection 
between  the  bile-ducts  and  lymphatics.  This  is  also  shown  by  the  fact 
that  microscopic  injections  of  the  bile-ducts  made  after  death,  under 
very  low  pressureT  often  pass  into  the  lymphatics  of  the  liver.  While 
the  pressure  under  which  the  bile  is  secreted  is  comparatively  low,  as 
compared  with  that  of  the  saliva  or  that  of  the  arterial  pressure,  it  has 
been  stated  by  Heidenhain  that  the  pressure  under  which  the  bile  is 
secreted  is  more  than  double  that  of  the  blood  in  the  portal  vein.  In 
the  liver,  therefore,  as  in  the  salivary  glands,  there  can  be  no  question  as 
to  the  formation  of  this  secretion  by  a  mere  process  of  filtration ;  it 
can  only  take  place  as  the  result  of  special  cell  activity,  the  specific  coiv 
stituents  of  the  bile,  the  bile  acids  and  the  coloring  matter,  being  found 
normally  neither  in  the  blood  nor  in  any  other  tissue  or  organ,  the  cases 
in  which  the}^  or  their  derivatives  are  found  elsewhere  than  in  the  bile 
being  capable  of  clear  proof  that  they  have  only  reached  those  localities 
through  the  bile.  Even  after  extirpation  of  the  liver,  no  accumula- 
tion of  bile  coloring-matter  can  be  detected  in  the  economy.  The  specific 
constituents  of  the  bile  must,  therefore,  be  formed  in  the  liver-cells,  and, 
as  already  indicated,  there  is  considerable  proof  that  the  coloring  matter 
originates  from  the  breaking  down  of  the  red  blood-cells,  the  process  of 
destruction  being  probably  due  to  the  action  of  the  bile  acids,  hsemo- 


DIGESTION   IN   THE   SMALL   INTESTINE.    ;  393 

globin  being  thus  liberated  and  then  decomposed  into  bilirubin,the  iron 
escaping  in  the  form  of  a  phosphate  in  the  bile.  As  regards  the  origin 
of  bile  acids  little  is  known,  though  they  are  probably  derived  from  the 
breaking  down  of  albuminoids. 

The  action  of  the  nervous  sj'stem  in  modifying  the  secretion  of  the 
bile  is  almost  entirely  unknown.  No  nerve  has  been  found  whose  stim- 
ulation leads  to  an  increased  flow  of  bile,  or  causes  its  arrest  when 
actively  flowing.  The  splanchnic  nerve  has  been  noticed,  when  stimu- 
lated, to  cause  an  increase  in  the  flow  of  bile  from  biliary  fistulas,  but  this 
action  is  evidently  due  to  the  production  of  contraction  of  the  biliary 
ducts. 

3.  The  Physiological  Action  of  the  Bile. — The  bile  enters  the  intes- 
tine, in  most  animals,  associated  with  the  pancreatic  juice,  as  seen  in  the 
horse,  goat,  and  dromedary,  while  in  the  ox  and  Babbit  the  bile-duct  is 
separated  fora  considerable  distance  from  the  opening  of  the  pancreatic 
duct.  The  fact  that  it  enters  the  intestine  simultaneously  writh  the  pan- 
creatic juice,  or  even  before  it,  shows  that  in  its  physiological  action  it 
must  be  associated  with  the  latter.  Its  action  on  the  food-stuffs  is  of 
but  slight  importance.  On  protejds  it  produces  no  distinct  action  what- 
ever, and,  in  fact,  would  seem  to  interfere  with  the  digestion  of  proteids 
as  commenced  in  the  stomach.  Thus,  when  bile,  or  a  solution  of  tauro^ 
cholic  acid,  is  added  to  the  products  of  gastric  digestion,  a  copious 
precipitate  takes  place,  which  consists  of  coagulable  albumen,  syntonin, 
and  pepsin, — the  latter  being  indicated  by  the  fact  that  when  this  precip- 
itate is  filtered  off  and  the  supernatant  liquid  acidified  it  has  no  peptic 
power.  This  precipitate  is,  however,  redissolved  in  an  excess  of  bile 
or  a  solution  of  bile  salts,  and  its  object  would  appear  to  be,  by  precipi- 
tating the  parapeptone  to  delay  its  passage  through  the  intestine  and  so 
give  the  pancreatic  juice  time  to  act,  while,  at  the  same  time,  by  precipi- 
tating the  pepsin  the  pancreatic  ferments  are  protected  from  the  solvent 
action  of  the  gastric  juice.  For  we  find  that  during  active  digestion, 
as  a  rule,  the  contents  of  the  small  intestine  are  strongly  acid  in  the 
greater  portion  of  its  upper  extremity,  and  were  the  pepsin  not  precipi- 
tated the  pancreatic  ferments  would  be  digested  and  therefore  destroj^ed 
through  the  action  of  the  gastric  juice.  The  re-solution  of  the  precipi- 
tate produced  by  bile  in  the  products  of  gastric  digestion  is  due  to  an, 
excess  of  taurocholic  acid.  In  most  animals  (ox,  sheep,  and  horse),  the 
bile  has  been  found  to  contain  a  ferment,  present  in  small  amount,  which 
is  capable  of  converting  starch  into  sugar.  A  similar  action  is  also  pro- 
duced on  glycogen.  This  action  is,  however,  secondary,  and  of  but  little 
importance  in  the  digestion  of  carbohydrates,  other  than  that  the  bile 
assists  the  amjdolytic  action  of  the  pancreas.  In  the  d'og's  and  pig's 
bile  no  diastatic  ferment  is  present. 


394  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

The  principal  function  of  the  bile  in  digestion  is  the  aid  which 
it  renders  to  the  digestion  and  absorption  of  fats.  Bile  has  a  solvent 
action  on  fats  in  small  quantities,  and  assists  in  the  eraulsification  of  fats. 
We  shall  iind  that  the  pancreatic  juice,  in  its  action  on  fats,  liberates 
fatty  acids.  A  similar  action  is  also  manifested,  although  to  a  very  much 
less  extent,  by  the  bile  of  the  horse,  ox,  and  sheep ;  it  is  absent  in  that 
of  the  hog  and  dog.  These  fatty  acids,  thus  liberated,  unite  with  the 
alkalies  of  the  bile  and  pancreatic  juice  and  form  soaps,  and  so  greatly 
assist  in  the  formation  of  a  permanent  emulsion.  By  means  of  the 
emulsion  thus  formed  the  absorption  of  fat  is  greatly  assisted;  while,  in 
addition,  it  has  been  found  that  when  membranes  are  moistened  with 
bile,  or  with  solutions  of  bile  salts,  the  passage  of  fats  through  such 
membranes  is  greatly  facilitated.  Thus,  if  two  filters  are  moistened,  the 
one  with  a  solution  of  bile  salts  and  the  other  with  water,  oil  will  pass 
with  comparative  readiness  through  the  former,  while  it  scarcely  suc- 
ceeds at  all  in  passing  through  the  filter  moistened  with  water.  Oil- 
drops  placed  on  the  surface  of  bile  spread  into  a  thin  layer,  like  solutions 
of  corrosive  sublimate  on  mercury,  and  in  tubes  moistened  with  bile 
the  oil  will  rise  above  its  level  outside  of  the  tube, — facts  which  point 
still  further  to  the  assistance  which  the  bile  renders  in  the  absorption 
of  fats.  The  bile  of  most  animals  contains  a  lactic  acid  ferment.  On 
other  food-stuffs  bile  is  quite  inert. 

It  is  evident  from  the  above  that  the  uses  of  bile  must  be  manifested 
in  some  other  direction  than  as  a  digestive  fluid ;  for  while  it  would  be 
presumed  from  the  fact  that  we  have  here  the  largest  gland  in  the  body, 
pouring  an  immense  volume  of  fluid  into  the  digestive  tract  at  a  point  at 
which  digestion  has  barely  commenced,  that  that  fluid  must  have  some 
important  role  to  fulfill  in  digestion,  the  facts  above  mentioned,  attained 
through  chemical  examination,  show  that  this  assumption  is  not  entirely 
warranted.  Still  another  method  of  examination,  that  of  the  production 
of  permanent  biliary  fistulae,  also  shows  that  the  functions  of  the  bile  are 
not  solely  manifested  in  assisting  in  digestion.  In  other  words,  the  bile 
is  not  only  a  digestive  secretion,  even  though  of  secondary  importance, 
but  is  also  an  excretion.  The  most  valuable  data  as  to  the  functions 
which  the  bile  fulfills  in  the  economy  are  obtained  from  the  maintenance 
of  biliary  fistulae. 

Biliary  fistulas  may  be  either  temporary  or  permanent.  The  former 
are  of  special  importance  for  the  study  of  the  secretion  of  bile  as  to  the 
influence  of  drugs  and  other  agents  on  the  amount  of  bile  poured  out. 
Dogs  are  most  suitable  for  such  an  operation,  which  may  be  performed 
upon  them  without  any  difficulty. 

The  dog  should  have  been  allowed  to  fast  for  several  hours  before  the 
operation,  as  then  the  gall-bladder  will  be  apt  to  be  filled  with  bile.  After 


DIGESTION  IN  THE  SMALL  INTESTINE.  395 

anaesthesia  has  been  produced,  an  incision  should  be  made  in  the  linea  alba  about 
an  inch  and  a  half  long  and  about  two  inches  below  the  xyphoid  cartilage,  tying 
each  bleeding-point  before  the  abdomen  is  opened.  On  pushing  aside  or  tearing 
through  the  omentum  with  the  forefinger  of  the  right  hand,  and  carrying  the 
finger  well  down  below  the  liver,  a  dense  band  may  be  felt  running  from  the 
liver  to  the  duodenum,  and  consisting  of  the  hepatic  vessels,  nerve,  and  common 
bile-duct.  Hooking  the  forefinger  under  this  band,  and  drawing  it  carefully  and 
slowly  forward,  a  blunt  hook  may  be  passed  under  it  with  the  free  hand,  and  the 
vessels  drawn  out  of  the  wound.  They  can  be  prevented  from  retracting  into  the 
abdominal  cavity  by  pushing  the  hook  through  so  that  the  vessels  lie  upon  its 
handle,  which  rests  transversely  over  the  wound.  The  duct  is  easily  isolated  and 
ligated  at  its  entrance  to  the  duodenum  to  secure  the  small  blood-vessels  on  its 
surface,  and  the  cannula  inserted  and  tied  in  the  duct.  On  removing  the  stilette 
from  the  cannula,  a  few  drops  of  bile  immediately  escape.  Probably,  however, 
a  similar  method,  and  one  less  likely  to  wound  the  hepatic  blood-vessels,  is  to 
open  the  abdomen  at  the  right  margin  of  the  right  rectus  muscle,  and  then  follow 
the  duodenum,  which  appears  in  the  wound,  and  may  be  recognized  by  its  large 
size  and  absence  of  mesentery,  up  toward  the  stomach,  where  the  duct  may  be 
readily  isolated  and  divided  at  its  insertion  into  the  duodenum. 

Permanent  biliary  fistulas  may  also  be  made  quite  readily  in  dogs,  and  have 
been  undertaken  to  decide  the  question  as  to  the  excrementitious  nature  of  the 
bile.  For  this  purpose  the  gall-bladder  is  selected  for  the  fistula  instead  of  the 
ductus  choledochus.  The  abdomen  is  opened  in  the  median  line,  or,  preferably, 
at  the  right  border  of  the  right  rectus  muscle,  care  being  taken  not  to  wound  the 
large  vessels  which  cross  the  wound  on  the  inner  surface  of  the  abdomen,  and 
the  common  bile-duct  isolated  as  before.  It  is  then  ligated  close  to  its  entrance 
into  the  intestine  and  at  its  junction  with  the  cystic  duct,  and  the  intermediate 
portion  excised. 

The  gall-bladder  is  then  drawn  down  and  fixed  to  the  edges  of  the  wound. 
The  operation  may  then  be  suspended  until  adhesion  has  occurred  between  the 
walls  of  the  bladder  and  the  edges  of  the  wound,  and  the  bladder  then  opened  ; 
or  it  may  be  treated  in  the  same  manner  as  when  making  gastric  fistulae,  and  a 
cannula  similar  to  the  one  employed  in  making  gastric  fistula?  inserted  at  once. 
In  this  mode  of  operation  the  object  has  been  to  exclude  the  bile  entirely  from 
the  intestine  ;  but  Schiff  has  shown  that  less  pressure  is  required  to  make  the 
bile  pass  from  the  hepatic  duct  into  the  gall-bladder  than  to  force  it  through  the 
common  duct  into  the  intestine.  This  excision,  then,  of  the  common  duct  is 
entirely  unnecessary,  apart  from  the  fact  that  it  sometimes  fails  in  its  object  by 
becoming  restored  ;  since  as  long  as  the  cystic  fistula  is  kept  open  the  bile  passes 
out  of  the  wound,  but  when  the  cannula  is  closed  it  passes  as  normally  into  the 
duodenum. 

When  the  operation  for  the  formation  of  a  permanent  biliary  fistula 
succeeds,  and  all  the  bile  is  conducted  outside  of  the  bod}',  animals 
rapidly  lose  weight  and  eventually  die,  under  ordinary  circumstances, 
under  the  phenomena  of  starvation.  Such  a  result  depends  upon  the  inter- 
ference with  the  digestion  of  fats  and  upon  the  direct  loss  of  bile  salts. 
Thus,  Yoit  has  found  that  a  dog  weighing  twenty  kilos,  which  in  its 
normal  condition  was  able  to  digest  from  one  hundred  and  fifty  to  two 
hundred  grammes  of  fat,  absorbing  99  per  cent,  of  this  amount,  was  only 
able,  after  a  permanent  biliary  fistula  was  established,  to  absorb  40  per 
cent,  of  the  fat  given.  The  loss  of  such  an  amount  of  fat  through  im- 
perfect absorption  naturally  produces  a  disturbance  of  nutritive  equi- 
librium. An  animal  which  before  the  operation  is  able  to  preserve  its 
nutritive  balance  with  a  certain  amount  of  meat  and  fat,  is  unable  to  do 
this  after  the  performance  of  a  biliary  fistula,  and  is  compelled  to  call  on 


396  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

the  reserve  store  of  tissue-albumen,  and  finally  dies  practically  of  starva- 
tion. If  the  animals  are  allowed  to  lick  the  wound,  and  so  cause  the  bile 
to  enter  their  alimentary  canal,  the  phenomena  of  impairment  of  nutri- 
tion are  very  much  less  marked.  So,  also,  if  they  are  fed  on  double 
the  amount  ordinarily  required  to  maintain  their  nutritive  equilibrium, 
the  carbohydrates  especially  being  in  excess,  the  phenomena  of  mal- 
nutrition may  be  largely  prevented.  In  animals  where  the  secretion  of 
bile  is  prevented  entirely  from  reaching  the  intestines,  we  find  that  obsti- 
nate constipation  is  usually  added  to  the  symptoms  of  disturbed  nutri- 
tion, and  that  the  faeces  which  are  occasional^  passed  are  clay-colored,' 
with  a  most  offensive  putrefactive  odor.  It  would,  therefore,  appear  that 
the  bile,  by  acting  as  a  stimulus  to  the  mucous  membrane  of  the  intestine, 
tends  to  maintain  the  normal  peristaltic  contractions  of  this  part  of  the 
alimentary  canal,  and  to  that  extent,  therefore,  acts  as  a  natural  purgative, 
while  at  the  same  time  it  largely  prevents  putrefaction  and  decompo- 
sition. The  bile  is,  however,  largely  an  excretion.  Many  of  its  con- 
stituents are  removed  unchanged,  while  some  of  them  are  reabsorbed  and 
again  enter  the  blood-current.  The  mucin  and  cholesterin  pass  through 
with  the  faeces  unchanged.  The  bile-pigments  undergo  decomposition  in 
the  intestinal  tube,  and  are  partly  excreted  with  the  faeces  under  the  form 
of  hydro-bilirubin,  a  characteristic  brown  coloring-matter  of  excrement, 
and  are  partly  eliminated  as  urobilin  by  the  urine.  The  bile  salts  are  for 
the  most  part  reabsorbed  by  the  walls  of  the  upper  portion  of  the  small 
intestine,  only  a  small  quantity  of  glycocholic  acid  being  found  in  the 
faeces.  The  taurocholic  acid  is  largely  absorbed,  it  being  previous^, 
perhaps,  decomposed  into  cholic  acid  and  taurin,  the  latter  being  con- 
stantly absorbed,  while  part  of  the  cholic  acid  may  perhaps  be  removed 
with  the  faeces. 

II.  THE  PANCREATIC  SECRETION. — The  pancreatic  fluid  is  poured 
into  the  small  intestine  immediately  after  the  entrance  of  the  bile, 
or  in  some  instances  simultaneously  with  it  and  the  secretion  of 
B runner's  glands.  While  the  pancreas  is  one  of  the  most  constant 
of  all  glands,  existing  in  all  mammals,  birds,  reptiles,  in  most  fish  and 
insects,  its  anatomical  form  is  subject  to  great  variation  in  different 
animals.  In  the  dog,  as  in  other  mammals,  most  birds,  and  reptiles, 
the  pancreas  is  situated  in  the  concaArity  of  the  duodenum.  Also  in 
the  dog,  and  in  other  mammals  in  wrlrich  the  duodenal  mesentery  is 
short  or  absent,  this  gland  is  thick,  elongated,  and  bilobed,  one  portion 
extending  horizontally  toward  the  spleen,  while  the  other  portion  de- 
scends at  a  right  angle,  parallel  to  the  duodenum  (Fig.  155).  At  the 
angle  the  pancreas  is  closely  adherent  to  the  duodenum,  and  often  over- 
laps it,  being  connected  by  a  multitude  of  small  blood-vessels,  while  the 
descending  portion  lies  free  in  the  abdominal  cavity.  There  are  in  the 


DIGESTION   IN   THE  SMALL   INTESTINE. 


397 


dog,  in  which  the  operation  for  making  pancreatic  fistulae  is  most  usual 
as  in  most  other  animals,  two  pancreatic  ducts — the  upper  and  smaller 
one  opening  into  the  duodenum  in  the  same  papilla  as  the  bile-duct, 
while  the  larger  and  lower  duct  opens  into  the  duodenum  about  two 
centimeters  lower  down.  These  ducts  communicate  by  frequent  anasto- 
moses, the  lower  being  always  selected  for  operation.  In  those  animals 
in  which  the  duodenum  has  a  wide  mesentery,  as  in  the  rodents,  the 
pancreas  forms  an  arborescent  mass  between  the  two  layers  of  the  mes- 
enter}r.  This  is  the  plan  of  arrangement  in  the  rabbit,  and  also  in  the 


FIG.  155.— PANCREAS  OF  THE  DOG.    (Bernard.) 

PP,  pancreas;  a,  pylorus;  ft,  glands  of  Brunner ;  c  c',  large  pancreatic  duct;  d,  eminence  formed 
by  the  duodenal  glands ;  e,  small  pancreatic  duct  at  its  opening  in  the  intestina  :  /,  a'nastomosis  between 
the  large  and  small  pancreatic  duct:  g,  orifice  of  the  biliary  duct;  h,  orifice  of  small,  and  t,  of  the  large 
pancreatic  duct;  k' ,  anastomosis  of  the  large  with  the  small  duct. 

cat.  In  the  rabbit  the  pancreas  has  two  ducts,  but  the  upper  one, 
which  enters  the  duodenum  with  the  bile-duct,  is  very  small,  while 
the  lower  one  is  very  long,  and  enters  the  intestine  about  thirty  to 
forty  centimeters  below  the  pylorus.  In  the  cat,  the  arrangement 
of  these  ducts  is  so  irregular  as  to  baffle  all  description.  In  most 
cases  there  are  several  of  them,  and  sometimes,  as  occurs  quite  con- 
stantly in  the  seal,  the  upper  duct  passes  into  a  sort  of  reservoir 


398 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


before  entering  the  intestine  (Fig.  156).     The  arrangement  of  the  pan- 
creatic ducts  in  the  bird  is  represented  in  Fig.  157. 

The  pancreatic  juice  is  a  colorless,  alkaline  fluid  secreted  by  the 
pancreas  or  the  so-called  abdominal  salivary  glands.  It  differs  from  the 
other  digestive  secretions  in  that  when  freshly  formed  by  a  normal  gland 
it  contains  a  large  amount  of  proteids.  Its  composition  varies  with  the 
rate  of  secretion,  and  when  studied  as  obtained  through  fistulae  differs 
accordingly  as  to  whether  a  temporary  or  permanent  fistula  has  been 
made. 


FIG.  156.— PANCREAS  AND  DUODENUM  OF  THE  CAT.    (Bernard.) 

a,  pylorus  ;  b,  section  of  duodenum  at  the  level  of  the  glands  of  Brnnner;  c  ct,  superior  pancreatic 
duct  opening  with  the  biliary  duct  into  the  intestine ;  a,  mucous  membniie  of  the  duodenum  ;  e,  inferior 
pancreatic  duct:  el,  point  of  its  anastomosis  with  the  descending  branch  of  the  pancreatic  duct ;  h,  com- 
mon opening  of  the  biliary  duct  and  superior  pancreatic  duct;  s,  pyloric  portion  of  stomach;  v,  biliary 
duct;  ppp',  pancreas. 

Temporary  fistulas  of  the  pancreas  are  best  made  on  the  clog,  since  in  this 
animal  there  is  the  greatest  probability  of  escaping  peritonitis, — a  complication 
which  if  present  is  disastrous  to  the  success  of  the  operation,  for  the  pancreas  is  ex- 
tremely susceptible  to  inflammation,  and  as  a  consequence  the  secretion  becomes 
perverted  and  its  properties  altered.  The  only  difficulty  in  the  operation  consists 
in  finding  the  duct  without  injuring  the  gland  or  its  numerous  blood-vessels.  To 
be  thoroughly  successful  the  operation  should  be  performed  as  rapidly  as  possible, 
so  as  to  avoid  exposing  the  parts  any  longer  than  is  necessary,  while  the  pancreas 
should  be  handled  with  the  greatest  gentleness.  The  operation  should  be  per- 
formed without  employing  an  anaesthetic,  to  avoid  subsequent  vomiting  and 
possible  vitiation  of  the  secretion.  The  dog  should  receive  a  hearty  meal  of  bread 
and  meat  two  hours  before  the  operation,  and  then  should  be  fastened  on  his 
left  side.  •  An  incision  should  be  made  in  the  right  hypochondrium,  descending 
downward  from  the  end  of  the  last  rib  about  five  centimeters  and  parallel  with 
the  linea  alba,  every  bleeding  point  being  tied  before  the  peritoneum  is  opened. 
Passing  the  index  and  middle  fingers  of  the  left  hand  into  the  wound,  the  duode- 
num is  easily  recognized.  The  fingers  are  then  carried  well  down  into  the  right 
hypochondrium,  and  then  backward  to  the  convex  surface  of  the  duodenum,  and 
keeping  their  palmar  surface  directed  upward,  the  fingers  are  carried  behind  the 
duodenum  and  pancreas,  which  are  then  to  be  drawn  together  out  of  the  wound. 
The  animal  being  in  full  digestion,  the  tissue  of  the  gland  is  of  a  rosy-pink  colora- 
tion. By  this  manipulation  the  parts  preserve  their  normal  relation,  and  the  an- 


DIGESTION   IN   THE   SMALL   INTESTINE. 


399 


terior  surface  of  the  pancreas  presents  in  the  wound.  The  next  step,  and  perhaps 
the  most  difficult,  is  the  finding  of  the  duct, — a  proceeding  rendered  difficult  not 
only  by  the  extreme  shortness  of  the  duct,  but  by  its  being  surrounded  by  nu- 
merous blood-vessels,  which  bleed  very  easily  and  which  bridge  over  the  duode- 
num and  the  overlapping  edge  of  the  pancreas.  By  keeping  the  anterior  surfaces 
directed  forward  this  difficulty  is  reduced  to  a  minimum,  since  here  the  duct  is 
nearer  the  surface  and  is  only  surrounded  by  a  few  small  blood-vessels,  while  on 
the  posterior  surface  the  vessels  are 
very  large,  and  it  is  just  back  of  a 
large  bundle  of  vessels  that  the 
duct  enters  the  intestine.  On 
carefully  pushing  aside  with  a 
blunt  hook  the  overlapping  edge 
of  the  pancreas  at  the  lower  border 
of  the  angle  formed  by  the  trans- 
verse and  vertical  portions  of  this 
gland,  and  about  two  centimeters 
below  the  ductus  choledochns,  the 
larger  pancreatic  duct  is  seen  and 
may  be  distinguished  from  the 
blood-vessel  by  its  larger  size  and 
white  color.  The  finding  of  the 
duct  may  be  facilitated  by  the  fol- 
lowing observations  :  Where  the 
vertical  segment  of  the  pancreas 
leaves  the  duodenum  there  is  al- 
ways to  be  found  a  thick  vein 
passing  from  the  intestine  to  the 
pancreas.  Above  this  the  pan- 
creas lies  directly  under  the  gut, 
joined  to  it  by  numerous  bundles 
of  veins.  The  opening  of  the  duct 
lies  usually  in  the  space  between 
the  first  two  of  these  or  between 
the  second  and  third.  After  the 
duct  has  been  isolated,  a  thread 
should  be  passed  around  it  and  it 
should  be  opened  with  a  pair  of 
fine  scissors;  a  small  silver  can- 
nula,  about  five  millimeters  in 
diameter  and  ten  centimeters  long, 
may  then  be  inserted  and  pushed 
up  to  the  first  division  of  the  duct, 
tying  it  securely  by  the  thread 
previously  passed  around  the  duct. 
To  make  the  cannula  still  more 
firm,  a  stitch  maybe  passed  through 
the  serous  coat  of  the  intestine  and 
then  the  cannula  fastened  there 
also.  The  duodenum  and  pan- 
creas are  then  returned  to  the  ab- 
dominal cavity,  retaining  the  ends 
of  the  thread  and  the  free  end  of 
the  cannula  in  the  wound,  which 
is  then  closed  by  sutures,  first 
sewing  together  the  muscles  and  then  the  skin.  Upon  withdrawing  the  stilette 
from  the  cannula  a  few  drops  of  colorless,  limpid  fluid  escape,  which  flow  more 
rapidly  when  the  animal  makes  any  movement  and  which  is  strongly  alkaline 
(Figs.  158  and  159).  The  secretion  may  be  collected  by  fastening  a  rubber  bulb 
furnished  with  a  stop-cock  to  the  cannula.  The  bulb  should  be  first  compressed 
so  as  to  be  emptied  of  air,  the  stop-cock  closed  and  connected  with  the  cannula. 
On  opening  the  stop-cock  the  tendency  of  the  bulb  to  expand  draws  the  fluid  out 
of  the  ducts.  Generally  the  fluid  is  secreted  quite  rapidly,  and  may  be  collected 


FIG.  157.— PANCREAS  OF  THE  PIGEON.  (Bernard.) 

P,  first  -pancreas  with  its  duct,  V  ;  P'  P",  second  pancreas 
with  two  ducts,  V  V"  ;  H,  biliary  duct  opening  into  the  duode- 
num, D,  below  the  gizzard,  G;  ch  and  h,  secondary  biliary  duct3 
opening  into  the  ascending  portion  of  the  duodenum ;  F,  liver ; 
S,  stomach;  P  P'  P",  pancreas;  a,  opening  in  duodenum  show- 
ing a  probe,  b,  inserted  into  secondary  biliary  duct. 


400 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


for  several  hours.  After  the  first  day,  however,  the  character  of  the  secretion 
alters  and  is  no  longer  normal  or  suitable  for  study.  If  it  does  not  flow  rapidly, 
it  may  be  stimulated  by  injecting  ether  through  a  tube  into  the  stomach.  Vom- 
iting stops  the  secretion.  Usually  after  the  second  day  the  tube  and  threads 
drop  out,  or  else  they  may  be  gently  removed,  and  the  wound  generally  heals 
readily  and  the  duct  becomes  restored.  The  same  animal  may  again  be  used  for 
the  same  purpose.  One  of  the  difficulties  that  will  be  met  with  in  this  operation 
is  that,  since  the  duct  is  so  short,  the  cannula  is.  very  apt  to  slip  out.  This  may 
be  partially  remedied  by  having  a  cannula  made  with  a  little  bulb  on  the  end  to 
be  inserted,  or  a  T-shaped  cannula  may  be  used,  the  duodenal  end  of  which  must 
be  closed.  If  such  a  cannula  is  used  it  is  better  to  have  one  made  in  two  sec- 
tions, one  being  first  inserted  in  the  duct  and  the  other,  which  is  to  come  out  of 
the  wound,  screwed  in  afterward. 

In  the  ruminant  animal  the  pancreas  lies  in  part  on  the  convolutions  of  the 
colon,  on  the  superior  right  portion  of  the  rumen,  extending  over  the  fissure  of  the 
liver  to  the  second  lumbar  vertebra.  Its  duct,  six,  eight,  or  nine  millimeters  in 
diameter,  opens  into  the  duodenum  in  the  ox  eighty  to  ninety-five  centimeters 


FIG.  1.58.— PANCREATIC  FISTULA  IN  THE  DOG.    (Bernard.) 

A,  principal  pancreatic  duct;  a,  entrance  of  the  duct  into  the  intestine;  a',  lesser  pancreatic  duct; 
a",  ligature  fastening  the  cannula  to  the  intestinal  wall ;  //,  ends  of  the  ligature ;  I,  duodenum ;  P  P', 
pancreas;  T,  cannula;  V,  rubber  bulb;  B,  stop-cock. 

below  the  pylorus,  and  in  the  sheep  and  goat  at  the  opening  of  the  bile-duct,  and 
is  often  free  from  gland-tissue  for  a  space  of  from  two  to  three  centimeters.  To 
make  a  pancreatic  fistula  in  the  ruminant,  an  incision  about  ten  to  twelve  centi- 
meters long  is  made  in  the  right  flank  parallel  to  the  last  rib  and  three  or  four 
fingers'  breadths  removed  from  it.  The  pancreas  then  comes  into  view  on  open- 
ing the  abdomen,  the  duct  may  be  readily  exposed,  and  the  cannula  inserted.  The 
operation  may  be  readily  performed  on  the  ox  without  uncovering  the  duodenum 
from  its  omentum,  and  without  dragging  on  the  pancreas  (Fig.  160). 

In  solipedes  it  is  difficult  to  study  the  pancreatic  secretion.  The  gland  is 
deeply  situated  against  the  vertebral  column,  its  duct  is  surrounded  by  gland- 
tissue  up  to  its  insertion  in  the  duodenum,  and  it  has  very  thin  walls.  To  make 
a  fistula  it  is  necessary  to  freely  open  the  abdominal  cavity  in  the  median  line 
from  the  sternum  almost  to  the  pubis,  to  withdraw  the  colon  from  the  abdomen, 
open  the  duodenum  and  insert  a  tube  through  the  opening  of  the  pancreatic  duct 
and  fasten  it  by  a  ligature,  which  must  also  include  part  of  the  gland.  The  colon 
and  duodenum  are  then  to  be  replaced  and  the  wound  sewed  up.  This  method 


DIGESTION   IN   THE   SMALL   INTESTINE. 


401 


was  first  employed  by  de  Graff  on  the  dog,  and  has  proved  successful  in  the  hands 
of  Leuret  and  Lassaigne  on  the  horse. 

As  before  stated,  the  operation  as  performed  as  above  described  does  not 
render  the  permanent  collection  of  this  secretion  possible.  It  has  been  found  that 
when  permanent  fistulas  are  established,  although  they  serve  a  useful  purpose  in 
permitting  the  study  of  various  conditions  which  may  modify  the  secretion  of 
pancreatic  juice,  yet  the  fluid  poured  out  by  the  glands  under  these  circumstances 
cannot  at  all  be  regarded  as  its  normal  secretion.  For  the  purpose  of  establishing 
a  permanent  pancreatic  fistula,  a  small  dog  may  be  selected,  since  in  small  animals 
the  pancreas  is  nearer  the  middle  line  than  in  large  dogs,  and  hence  the  parts  are 
not  as  much  disturbed  by  the  operation.  The  dog  having  been  kept  fasting  for 
twenty-four  hours,  so  that  the  pancreatic  vessels  should  contain  as  little  blood  as 
possible,  should  be  narcotized  by  a  subcutaneous  injection  of  morphine,  and  the  ab- 
domen opened  by  an  incision  about  two  centimeters  long  made  in  the  linea  alba  and 
about  midway  between  the  xy phoid  cartilage  and  umbilicus .  The  duodenum  and  the 


FIG.  159.— PANCREATIC  FISTULA  IN  THE  DOG.    (Bernard.) 

A,  cannula  on  which  is  fastened  the  rubber  bulb,  B  ;  C,  stop-cock. 


pancreas  are  then  to  be  drawn  out  of  the  wound  and  the  pancreatic  duct  isolated  and 
opened  by  a  little  cut  in  one  side;  instead  then  of  inserting  a  cannula,  two  pieces 
of  lead  wire  bent  at  an  angle  are  to  be  introduced,  one  wire  being  passed  toward 
the  gland -and  the  other  into  the  intestine  ;  the  remaining  halves  of  each  wire  are 
then  to  be  twisted  together  so  as  to  form  a  f  -shaped  piece,  the  middle  limb  of 
which  projects  through  the  wound.  Owing  to  the  shape,  the  wires  cannot  fall  out 
and  cannot  move  around  in  the  duct.  Fine  wire  should  be  selected  somewhat 
smaller  than  the  calibre  of  the  duct,  so  that  the  flow  of  the  secretion  will  not  be 
interfered  with.  The  duodenum  and  pancreas  are  then  returned  to  the  abdominal 
cavity,  care  being  taking  to  retain  the  wires  in  the  wound,  the  duodenum  is  to  be 
stitched  to  the  abdominal  peritoneum,  and  the  wound  then  closed.  Inflammatory 
adhesions  take  place  around  the  wound  and  the  wires  cause  the  formation  of  a 
fistulous  tract  which  communicates  with  the  ducts  and  through  which,  after  a  week 
or  so,  the  juice  may  be  collected. 

26 


402 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


Heiclenliain  has  employed  a  method  of  establishing  permanent  pancreatic 
fistulas  which  he  claims  to  have  yielded  in  his  hands  satisfactory  results.  He 
excises  that  portion  of  the  duodenum  which  contains  the  opening  of  the  pan- 
creatic duct,  restores  the  continuity  of  the  gut,  and  sews  the  excised  portion,  after 
division  lengthwise,  to  the  abdominal  wound,  so  that  the  orifice  of  the  duct  opens 
externally  upon  the  abdominal  surface. 

1.  The  Chemical  Composition  of  Pancreatic  Juice. — The  pancreatic 
secretion  differs  in  composition  and  physical  properties  according  as  it  is 
obtained  from  permanent  or  temporary  fistulas,  and  according  to  the  ani- 
mal from  which  it  is  obtained.  When  obtained  from  temporary  fistulas 
in  the  dog,  it  is  a  clear  fluid,  almost  of  the  consistency  of  syrup,  very 


FIG.  160.— PANCREATIC  FISTULA  IN  THE  Ox.    (Colin.) 

tenacious,  and  of  strongly  alkaline  reaction.  It  contains  few  or  no  struc- 
tural elements,  though  corpuscles  similar  to  those  found  in  saliva  have' 
been  claimed  by  Ku'hne  to  exist,  and  occasionally  free  particles  of  oil.  It 
has  a  decided  salty  taste,  and  under  the  action  of  heat  coagulates,  as  does 
the  white  of  egg,  to  a  firm  white  mass.  Alkalies  prevent  the  coagulation. 
When  alcohol  is  added  to  the  fresh  pancreatic  secretion  it  forms  a  copi- 
ous, white,  flocculent  precipitate,  which  is  subsequently  in  large  part, 
after  filtration,  soluble  in  water.  When  very  dilute  acids  are  added  to 
pancreatic  juice,  they  at  first  form  a  turbid  mass  which  subsequently 
dissolves  in  excess  of  acid.  This  action  is  to  be  explained  as  due  to  the 


DIGESTION   IN   THE   SMALL   INTESTINE.  403 

production  of  acid  albumen.  Dilute  acetic,  lactic,  and  phosphoric  acids 
are  without  apparent  action  on  pancreatic  juice,  but  it  is  precipitated  b}r 
metallic  salts,  tannic  acid,  iodine,  and  chlorine-  and  bromine-water.  The 
pancreatic  secretion  obtained  from  a  temporary  fistula  in  a  sheep  is  a 
clear,  tenacious  fluid,  which  may  be  drawn  out  in  threads  like  the  white 
of  an  egg.  The  first  portions  secreted  are  claimed  to  have  a  slightly 
acid  reaction,  which  soon  becomes  converted  into  an  alkaline  reaction. 
The  pancreatic  juices  of  the  horse,  the  rabbit,  the  chicken,  and  pigeon 
behave  in  a  similar  manner,  although  the  pancreatic  secretion  of  the 
rabbit  only  becomes  turbid  when  heated,  and  does  not  form  a  firm  eoagu- 
lum,  like  that  of  the  dog. 

The  pancreatic  secretion  differs  from  the  other  digestive  fluids  in 
the  large  amount  of  solids,  principally  proteid  in  nature,  which  it  con- 
tains. Its  specific  gravity'  as  obtained  from  temporary  fistulse'ma}-  be 
placed  at  1030  ;  obtained  from  permanent  fistulae  in  the  dog,  the  pancreatic 
secretion  is  a  thin,  watery  fluid,  with  a  specific  gravity  onl}T  of  about  1010 
or  1011;  the  lower  specific  gravity,  of  course,  being  due  to  the  smaller 
amount  of  solids.  In  the  fluid  from  permanent  fistuhe  the  solids  amount 
to  2  to  5  per  cent.,  while  in  that  obtained  from  temporary  fistulae  they 
may  rise  to  10  per  cent.  Otherwise  the  fluid  from  permanent  fistulse 
agrees  in  most  respects  with  that  from  temporary  fistulse,  it  is  clear  and 
colorless,  alkaline  in  reaction,  and  of  a  sickly,  saltish  taste.  When 
heated  it  becomes  turbid  and  may  even  coagulate,  while  it  may  also  be 
precipitated  by  alcohol,  the  precipitate  being  soluble  in  water.  When 
cooled  down  to  the  freezing  point,  it  is  said  to  deposit  transparent  mu- 
cus-like coaguli.  The  pancreatic  secretion,  in  contradistinction  to  that 
of  the  gastric  glands,  is  readily  decomposed ;  it  then  acquires  a  faecal 
odor  and  colors  chlorine-water  red.  After  standing  for  some  time,  it 
acquires  an  offensive,  putrefactive  odor  and  now  no  longer  gives  a  red 
with  chlorine,  but  with  nitric  acid  a  bright-red  color  is  produced.  This 
reaction  is  evidently  due  to  indol. 

The  pancreatic  secretion  contains  serum-albumen,  alkali  albuminate, 
fat,  soaps,  and  sodium  salts,  and  is  thus  very  closely  allied  to  blood-serum 
in  composition;  but  it  differs  from  it  in  containing  four  ferments, — 
an  amylolytic,  a  proteolytic,  one  which  splits  fats  into  glycerin  and  fatty 
acids,  and  the  milk-curdling  ferment.  The  first  three  of  these  ferments 
are  precipitated  by  alcohol  and  are  found  in  the  pancreatic  secretion  of 
both  carnivora  and  herbivora.  The  existence  of  the  milk-curdling  fer- 
ment is  not  entirely  beyond  question.  Pancreatic  juice  is  also  stated  to 
contain  peptones,  leucin,  and  tyrosin,  but  it  seems  probable  that  these 
elements  are  not  found  in  perfectly  fresh  juice,  with  the  exception,  may 
be,  of  a  trace  of  leucin,  but  are  formed  through  the  digestion  of  the 
albumen  in  the  pancreatic  juice  by  one  of  its  own  ferments. 


404  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

The  following  table  represents  the  composition  of  the  pancreatic 
juice  of  the  dog,  as  obtained  from  permanent  and  temporary  fistulas : — 

Temporary          Permanent 
Fistula.  Fistula. 

Water, 900.8  984.06 

Solids, .         .92.2  15.4 

Organic  matter, 90.4  9.2 

Ash,         .  8.8  6.1 

The  following  table  represents  the  analyses  of  the  ash  : — 

Temporary          Permanent 
Fistula.  Fistula. 

Sodium,  .        .        .        .        .        .      0.58  3.31 

Sodium  chloride,    .      '  .        .        .        .7.35  2.50 

Potassium  chloride,       ....       0.02  0.93 

Phosphatic  earths  with  traces  of  iron,  .       0.53  0.08 
Sodium  phosphates,       .         .         .         .... 

Lime  and  magnesium,  ....      0.32  0.01 

The  solids  in  pancreatic  juice  are,  however,  subject  to  great  vari- 
ation. Bernard  found  in  the  secretion  from  temporary  fistulae  in  the 
dog  8  to  10  per  cent,  of  solids,  Tiedemann  and  Gmelin  8.7  per  cent,  of 
solids,  of  which  7.89  per  cent,  were  organic  and  0.72  per  cent,  ash,  while 
in  the  secretion  of  the  sheep  3.6  to  5.2  per  cent,  of  solids  have  been 
found. 

According  to  Hoppe-Seyler,  in  1000  parts  of  pancreatic  secretion, 
obtained  from  a  diverticulurn  in  the  pancreatic  duct  of  the  horse,  982.5 
parts  were  water,  8.88  parts  organic  matter,  and  8.59  parts  ash. 

In  the  rabbit  the  solids  have  been  placed  at  1.76  per  cent.,  while  in 
the  ram  1.43  to  3.69  per  cent,  of  solids  have  been  determined  through 
various  analyses. 

The  Pancreatic  Ferments. — The  pancreatic  ferments  may  be  together 
extracted  from  the  fresh  gland  by  a  process  of  mincing  and  extracting 
with  glycerin ;  on  adding  alcohol  to  the  glycerin  extract,  the  proteo- 
lytic  and  amjdolytic  ferments  may  be  precipitated.  If,  however,  the 
gland  be  first  treated  with  alcohol  before  extraction  with  glycerin,  the 
proteolytic  ferment  will  not  be  found  in  the  solution,  while  the  diastatic 
ferment  will  be  present  in  large  amounts.  It  is  claimed,  however,  that 
if  the  pancreas  of  the  ox  be  allowed  to  remain  for  a  long  time  in 
alcohol,  and  then  extracted  with  glycerin,  a  preparation  will  be  obtained 
which  contains  all  three  of  these  ferments. 

Various  processes  have  beeji  proposed  for  the  isolation  of  these  three  fer- 
ments. Danilewsky  recommends  for  the  isolation  of  the  proteolytic  ferment 
that  the  pancreas  should  be  taken  from  an  animal  killed  six  hours  after  a  copious 
meal,  and,  after  washing,  should  be  ground  up  with  clean  sand  and  digested  for 
two  hours  with  water,  at  a  temperature  which  should  not  rise  above  30°  C.  The 
mixture  should  then  be  filtered,  and  the  filtrate,  which  contains  both  amylolytic 
and  proteolytic  ferments,  treated  with  an  excess  of  calcined  magnesia  to  remove 
fatty  acids,  filtered,  and  added  to  one-third  its  volume  of  thick  collodion,  which 
carries  down  the  fibrin-ferment  in  a  crumbly  mass.  The  ether  should  then  be 
evaporated,  and  the  resulting  mass  washed  with  alcohol  and  ether,  and  by  now 


DIGESTION   IN   THE   SMALL   INTESTINE.  405 

precipitating  with  alcohol  the  proteolytic  ferment  may  be  isolated  comparatively 
pure.  From  the  filtrate  of  the  precipitate  obtained  with  collodion  the  diastatic 
ferment  may  be  isolated  by  evaporating  under  an  air-pump,  filtering  off  the  pre- 
cipitate, again  precipitating  with  alcohol,  and  dissolving  the  precipitate  in  a 
mixture  of  two  parts  of  water  and  one  of  alcohol,  by  which  proteid  matter  is 
removed.  The  remaining  substance  will  convert  starch  rapidly  into  sugar,  but  is 
without  action  on  proteids. 

Kiihne's  method  is  to  form  an  aqueous  extract  of  a  pancreas  at  the  freezing 
point  and  to  precipitate  with  alcohol ;  the  precipitate  is  re-dissolved  in  water, 
again  precipitated  with  absolute  alcohol,  and  the  precipitate  a  second  time  re-dis- 
solved in  water  and  treated  with  acetic  acid  up  to  1  per  cent. 

The  same  treatment  is  repeated  a  second  time,  and  the  watery  solution,  after 
the  addition  of  acetic  acid,  is  warmed  to  40°  C.  and  then  filtered.  The  filtered 
liquid  is  made  alkaline  with  sodium  hydrate,  by  which  the  greater  part  of  the 
earthy  salts  and  tyrosin  are  precipitated,  the  trypsin  or  proteolytic  ferment  is  then 
freed  by  dialysis  from  tyrosin,  peptones  and  other  crystalline  substances,  and 
finally  precipitated  with  alcohol. 

Paschutin  recommends  a  process  for  the  isolation  of  these  ferments  which 
depends  upon  the  fact  that  solutions  of  different  salts  have  special  capabilities  of 
extracting  the  separate  ferments.  He  found  that  sodium  chloride,  calcium  chlo- 
rate, and  sodium  sulphate  were  able  to  dissolve  all  three  of  the  ferments,  while 
other  solutions  had  special  degrees  of  power  in  extracting  the  individual  ferments. 
Thus,  the  proteid  ferment  is  especially  dissolved  by  potassium  iodide,  potassium 
arseniate,  and  potassium  sulphate.  The  fatty  ferment  is  readily  extracted  by 
solutions  of  bicarbonate  of  sodium  containing  a  small  quantity  of  caustic  soda, 
while  the  diastatic  ferment  is  most  readily  extracted  by  a  solution  of  arseniate  of 
potassium  to  which  a  small  quantity  of  ammonia  has  been  added. 

2.  The  Action  of  the  Pancreatic  Juice  on  Food-Stuffs. — When  study- 
ing gastric  digestion,  it  was  seen  that  all  the  different  phenomena  could 
be  most  conveniently  studied  with  an  artificial  fluid  in  experiments  con- 
ducted outside  of  the  body.  The  same  conditions  prevail  in  the  study  of 
pancreatic  digestion.  An  artificial  pancreatic  juice  may  be  made  by 
three  different  processes : — 

First.  The  fresh  pancreas  of  a  dog  killed  some  hours  after  a  full  meal  is  cut  into 
pieces,  washed  to  remove  the  blood,  and  then  infused  for  two  hours  in  four 
times  its  weight  of  water,  warmed  to  25°  C.,  taking  care  to  keep  the  mixture  at 
that  temperature  during  the  whole  time  of  infusion.  It  is  then  to  be  filtered,  first 
through  muslin  and  then  through  paper.  Since  the  filtrate  will  be  usually  acid 
from  the  development  of  fatty  acids  through  the  action  of  ferments  on  fats  of  the 
pancreas,  it  must  be  neutralized  with  sodium  carbonate.  The  fluid  will  be  slightly 
opalescent  from  the  small  amount  of  fat  held  in  the  form  of  emulsion.  This 
preparation  has  all  the  properties  of  pancreatic  juice,  although  the  degree  of  its 
digestive  action  on  proteids  will  depend  upon  the  nutritive  state  of  the  pancreas 
from  which  it  was  made.  For,  if  the  pancreas  of  a  fasting  animal  was  employed, 
it  will  possess  scarcely  any  digestive  powers. 

Second.  An  artificial  pancreatic  juice  may  be  obtained  by  allowing  a  minced 
pancreas  to  remain  for  two  days  in  absolute  alcohol,  which  is  then  to  be  filtered 
off  and  the  residue  covered  with  glycerin  ;  this  glycerin  extract  will  contain  a 
considerable  quantity  of  the  ainylolytic  ferment,  while  the  quantity  of  proteolytic 
ferment,  as  in  the  first,  will  depend  upon  the  condition  of  the  gland. 

Third.  The  pancreas  may  be  taken  from  an  animal  in  full  digestion,  minced, 
and  rubbed  up  in  a  mortar  with  powdered  glass.  For  each  gramme  of  gland-sub- 
stance, one  cubic  centimeter  of  1  per  cent,  acetic  acid  shoulcl  be  added  and  mixed 
thoroughly  in  a  mortar  for  ten  minutes,  and  then  ten  times  its  volume  of  glycerin 
added,  and  the  whole  allowed  to  stand  for  three  days.  This  preparation  will  con- 
tain a  much  larger  proportion  of  proteolytic  ferment  than  was  obtained  by  either 
of  the  preceding  processes,  since  the  acetic  acid  seems  to  possess  the  power  of 
converting  into  ferment  the  zymogen,  or  the  substance  which  yields  the  proteo- 
lytic ferment. 


406  PHYSIOLOGY   OF    THE   DOMESTIC   ANIMALS. 

(a)  Action    on    Carbohydrates. — Valentin    pointed    out    that   the 
pancreatic  juice  was  capable  of  converting  starch  into  sugar,  and  nearly 
all  that  was  stated  with  regard  to  the  action  of  saliva  on  starch  might  be 
repeated  for  the  case  of  the  pancreatic  juice,  with  the  single  modification 
that  in  the  case  of  the  pancreas  the  amylolytic  power  possessed  by  its 
secretion  is  much  stronger  than   that  of  the  saliva.     The  secretion  and 
watery  extract  of  this  gland  in  both  herbivora  and  carnivora,  as  well  as 
the  secretion   obtained  from  this    gland    in   birds  (chicken   and  goose), 
rapidly  convert  starch  into  sugar.     All  the  conditions  which  were  found 
to  prevent  the  action  of  the  saliva  also  hold  here,  with  the  single  excep- 
tion that  a  slight  degree  of  acidity  seems  rather  to  favor  the  action.    The 
ferment  through  whose  action  the  pancreatic  juice  is  enabled  to  convert 
starch  into  sugar  is  apparently  formed  in  the  gland-tissue  by  the  trans- 
formation of  some  previously  existing  material;  since  it  has  been  found 
that  if  the  ferment  is  completely  extracted  from  a  fresh  gland  by  glyc- 
erin, and  the  inactive  residue  allowed  to  remain  on  the  filter  for  five  or 
six  hours  exposed  to  the  air,  a  further  production  of  ferment  occurs. 
This  new  formation  may  be  again  extracted  by  water  or  gtycerin.     That 
this  result  is  really  due  to  the  new  formation  of  ferment,  and  not  to  the 
occurrence  of  decomposition,  is  proved  by  the  fact  that  if  the  wateiy  ex- 
tract of  the  pancreas  is  once  deprived  of  its  action  on  starch  by  boiling, 
this  power  never  returns  in  any  stage  of  the  subsequent  decomposition. 
So,  also,  a  gland  which  has  been  exposed  for  twenty-four  hours  to  the 
air  is  more  active  than  a  fresh  gland.     The  amount  of  starch  which  by 
the  action  of  pancreatic  diastase  is  converted  into  sugar  is  almost  infinite. 
Roberts  has  calculated  that  pancreatic  diastase  is  able  to  transform  into 
sugar  and  dextrin  no  less  than  forty  thousand  times  its  own  weight  of 
starch.     The  rapidity  with  which  starch  is  converted  into  sugar  depends 
upon  the  proportion   of  ferment   brought  to  act  upon  it.     So  that  all 
grades  of  activity  may  exist  between  the  apparently  instantaneous  con- 
version of  a  small  amount  of  starch  with  a  large  amount  of  ferment,  and 
the  slow  and  gradual  action  of  a  small  amount  of  ferment   on  a  large 
quantity  of  starch.     The  products  which  result  from  the  action  of  pan- 
creatic ferment  on  starch  are  entirely  analogous  to  those  which  result 
from  the  action  of  ptyalin  or  malt-diastase  on  starch.     When  the  gland- 
tissue  is  itself  brought  into  contact   with  soluble  carbohydrates,  lactic 
acid  fermentation  ultimate! 3'  results.    Glycogen  is  also  rapidly  converted 
into  sugar  under  the  action  of  pancreatic  diastase.    Inulin  and  cane-sugar 
are  entirely  unaltered  by  it.      The  amylolytic  action  of  the  pancreatic 
juice  is  said  to  be  absent  in  newborn  children,  appearing  first  after  the 
termination  of  the  second  month. 

(b)  Action  on  Fats. — In  the  small  intestine  the  fats,  which  have  been 
seen  to  almost  entirely  escape  the  action  of  .the  gastric  juice,  are  broken 


DIGESTION   IX   THE   SMALL   INTESTINE.  407 

up  into  a  state  of  emulsion,  while  a  small  quantity  undergoes  chemical 
changes,  in  which  fatty  acids  are  liberated.  The  fatty  acids  thus  liber- 
ated combine  with  the  alkaline  bases  of  the  bile  and  pancreatic  juice  to 
form  soaps.  If  oil,  butter,  or  lard  is  stirred  with  pancreatic  juice  at  a 
temperature  of  35°  or  40°  C.,  almost  immediately  a  thick,  creamy  emul- 
sion is  formed  which  will  stand  for  a  long  time.  The  presence  of  gastric 
juice,  even  when  in  sufficient  amount  to  neutralize  the  alkalinity  of  the 
pancreatic  juice,  is  stated  by  Bernard  to  have  no  influence  on  the  emulsi- 
fying property  of  this  secretion  ;  but  to  produce  it  in  its  highest  degree 
the  secretion  must  be  normal,  and  that  obtained  from  permanent  fistula?  is 
much  less  efficacious  than  that  from  temporary  fistulas.  This  emulsifying 
power  possessed  by  the  pancreatic  juice  is  due  to  the  specific  action  of  a 
special  ferment,  termed  generally  the  emulsive  ferment,  which  is  claimed 
by  Bernard  to  first  emulsify  and  then  saponify  fats.  It  is  certain  that  in 
the  small  intestine  the  principal  change  is  merely  due  to  the  production 
of  an  emulsion,  and  nearly  all  the  fat  taken  up  by  the  absorbent  vessels  of 
the  small  intestine  is  in  the  form  of  an  emulsion  and  not  of  a  soluble  soap, 
although  both  changes  do  occur  in  the  small  intestine  ;  the  saponification 
is,  however,  most  marked  after  the  fats  have  been  absorbed.  The  emulsive 
ferments,  it  has  been  claimed  b}<  Paschutin,  may  be  readily  extracted  from 
the  pancreas  by  a  solution  of  bicarbonate  of  sodium,  and  this  solution 
will  readily  emulsify  fats.  It  is  doubtful  as  to  wrhat  importance  is  to  be 
attached  to  this  statement,  since  it  has  been  already  stated  that  a  solu- 
tion of  bicarbonate  of  sodium  constitutes  an  extremely  delicate  test 
for  the  presence  of  fatty  acids,  and  when  such  acids  are  present  the 
addition  of  the  bicarbonate  of  sodium  w^ill  almost  instantly  form  a  per- 
manent emulsion.  Since,  therefore,  it  is  almost  impossible  to  obtain  fats 
which  are  absolutely  free  from  the  presence  of  fatty  acids,  the  above 
statement  is  not  by  itself  sufficient  to  prove  that  the  emulsifjang  power 
of  pancreatic  juice  is  due  to  the  action  of  a  specific  ferment.  Other 
proof  is,  however,  found  in  the  fact  that  the  action  of  fresh  normal  pan- 
creatic juice  on  neutral  fats  does  result  in  the  development  of  free  fatty 
acids  and  glycerin.  This  result  may  even  take  place  when  the  pancreatic 
juice  has  been  diluted  with  twelve  times  its  volume  of  water ;  and  although 
gastric  juice  and  hydrochloric  acid  seem  to  interfere  with  this  action  of 
the  secretion,  the  bile  appears  to  facilitate  it.  Just  as  we  found  that  the 
solution  of  fibrin  with  acid  in  contact  with  peptic  glands  was  a  reliable 
test  for  the  presence  of  pepsin,  so  also  the  power  possessed  by  the  pan- 
creas of  decomposing  fats  and  forming  fatty  acids  and  glycerin  serves 
for  the  recognition  of  the  pancreas  in  lower  animals,  and,  as  emplo3Ted 
with  this  object  in  view,  has  been  highly  perfected  by  Bernard. 

The  emulsive  action  of  the  pancreatic  juice  is  destroyed  by  boiling, 
and   the  digestive  action  on  fats  through  the  influence  of  pancreatic 


408  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

juice  is,  therefore,  of  two  kinds.  Mechanically,  it  forms  an  emulsion 
with  the  oil,  while  chemically  it  liberates  the  fatty  acids  with  glycerin, 
the  formation  of  the  emulsion  being  largely  the  result  of  the  liberation 
of  fatty  acids. 

(c)  Action  on  Proteids. — The  action  of  pancreatic  juice  on  proteids 
coincides  with  that  of  gastric  juice  in  so  far  that  in  both  cases  the  con- 
version is  due  to  a  ferment  which  is  destroyed  by  heat,  and  that  both 
secretions  convert  proteids  into  peptones.  Many  points  of  contrast, 
however,  exist.  In  the  first  place,  it  was  seen  that  gastric  digestion 
required  the  presence  of  dilute  hydrochloric  acid.  In  the  case  of  pan- 
creatic digestion  it  will  be  found  that  a  half  of  1  per  cent,  solution  of 
sodium  carbonate  produces  the  most  active  results.  If  a  fragment  of 
.thoroughly  boiled  fibrin  is  placed  in  an  artificial  pancreatic  juice,  made 
by  adding  a  few  drops  of  the  glycerin-acetic  acid  extract  to  a  1  per  cent, 
solution  of  sodium  carbonate,  it  will  ultimately  dissolve,  but  the  process 
will  differ  from  that  occurring  in  gastric  digestion.  After  having 
remained  for  an  hour  or  two  in  contact  with  the  pancreatic  juice,  the 
fibrin  will  at  first  appear  to  be  unaltered,  but  if  it  is  stirred  with  a  glass 
rod,  many  small  fragments  dissolve,  and  on  removing  some  of  the  larger 
pieces  and  washing  them  with  water,  they  are  seen  to  be  corroded  and 
as  opaque  as  before,  but  not  swollen  and  transparent,  as  would  occur  in 
an  analogous  stage  of  gastric  juice.  Besides  these  superficial  changes, 
however,  the  properties  of  the  fibrin  have  been  considerably  modified. 
Undigested  boiled  fibrin  is  entirely  insoluble  in  dilute  acid,  and  if  this 
boiled  fibrin,  which  has  been  partially  digested  by  pancreatic  juice,  is 
placed  in  a  two-tenths  of  1  per  cent,  solution  of  hydrochloric  acid,  it 
will  be  rapidly  dissolved,  and  form  a  solution  of  syntonin,  which  may  be 
precipitated  by  neutralization.  Before  being  dissolved,  therefore,  boiled 
fibrin  is  rendered  by  pancreatic  juice  more  soluble  in  dilute  acid  than 
even  raw  fibrin,  which,  as  is  well  known,  will  not  dissolve  for  many 
hours. 

Again,  in  this  stage  of  pancreatic  digestion,  the  boiled  fibrin  becomes 
soluble  in  a  10  per  cent,  solution  of  sodium  chloride,  and  is  readily 
coagulated  by  nitric  acid  and  boiling;  it  thus  appears  that  the  first  step 
in  the  pancreatic  digestion  of  boiled  fibrin  is  to  change  it  to  a  soluble 
albuminoid,  somewhat  resembling  raw  fibrin. 

Again,  if  the  fibrin  be  allowed  to  remain  in  pancreatic  juice  until  it 
has  been  dissolved,  a  precipitate  may  be  formed  on  neutralization  which 
is  evidently  of  the  nature  of  an  alkali  albuminate  and  analogous  to  the 
parapeptone  formed  in  gastric  digestion ;  while  boiling  will  also  produce  a 
precipitate, — a  phenomenon  which  is  entirely  unrepresented  in  any  known 
stage  of  gastric  digestion.  Although,  as  already  mentioned,  an  alkaline 
reaction  appears  to  favor  pancreatic  digestion,  nevertheless,  it  appears 


DIGESTION   IN   THE   SMALL   INTESTINE.  409 

that  proteids  may  be  digested  in  pancreatic  infusions  with  a  neutral  or 
even  faintly  acid  reaction ;  it  even  appears  that  in  the  case  of  the  pig 
the  pancreatic  infusion  is  only  active  in  digesting  proteids  when  the 
intestinal  reaction  is  acid. 

As  already  mentioned,  the  pancreas  is  not  under  every  condition 
capable  of  forming  a  secretion  which  will  digest  proteids,  and  under 
many  circumstances  infusions  of  the  pancreas  will  be  entirely  inert  on 
proteids.  This  would  seem  to  indicate  that  while  trypsin,  or  the  proteo- 
iytic  ferment,  is  formed  in  the  cells  of  the  pancreas,  it  is  preceded  by 
another  substance  termed  zymogen,  which  is  gradually  in  the  normal 
conditions  of  the  gland  converted  into  trypsin.  In  support  of  this  state- 
ment it  may  be  mentioned  that  the  pancreas  obtained  from  the  slaughter- 
house or  from  fasting  dogs  is  often  inactive,  while  the  most  activitA'  is 
present  about  four  or  seven  hours  after  feeding.  It  is  supposed  that  the 
zymogen,  which  is  soluble  in  water  and  glycerin,  and  which  is  found  in 
the  inner  zone  of  the  secretoiy  cells,  is,  through  the  gradual  action  of 
oxygen,  converted  into  trypsin.  This  conversion  normally  occurs  in  the 
interior  of  the  gland  during  digestion,  but  even  inactive  glands  may  de- 
velop trypsin  through  exposure  to  the  air  after  death  or  by  the  action  of 
dilute  acetic  acid. 

Schiff  and  Herzen  claim  that  there  is  a  close  connection  between  the 
action  of  the  spleen  and  the  development  of  trypsin,  and  they  claim  to 
have  demonstrated  that  the  pancreas  of  an  animal  from  whom  the  spleen 
has  been  removed  is  incapable  of  digesting  proteids,  and  that  if  such  a 
pancreas  be  rubbed  up  with  a  portion  of  spleen  it  will  then  acquire  the 
power  of  digesting  proteids.  This  statement,  however,  needs  further 
confirmation. 

When  the  pancreatic  digestion  of  proteids  is  prolonged,  in  addition 
to  peptones,  various  other  bodies  make  their  appearance.  Leucin  and 
tyrosin  appear  in  large  amounts,  with  traces  of  asparaginic  acid,  xanthin, 
and  a  body  which  is  colored  red  with  chlorine-  or  bromine-water.  The 
longer  the  pancreatic  digestion  is  prolonged,  the  larger  will  be  the  amount 
of  leucin  and  tyrosin  present  and  the  smaller  the  amount  of  peptone ; 
from  which  it  would  appear  that  these  crystalline  substances  result  from 
the  gradual  breaking  down  of  the  peptone  itself. 

Kiihne  explains  this  result  by  supposing  that  the  albuminous  bodies 
under  the  action  of  trypsin  become  converted  into  two  forms  of  peptone, 
to  which  the  terms  respectively  antipeptone,  which  does  not  undergo 
further  change,  and  hemipeptone,  the  latter  in  normal  digestion  being 
converted  into  leucin,  tyrosin,  etc.,  and  readily  undergoing  putrefaction, 
resulting  in  the  formation  of  indol,  skatol,  and  phenol. 

If  a  pancreatic  digestive  mixture  be  neutralized  so  as  to  precipitate 
alkali  albumen,  and  then  treated  with  an  excess  of  alcohol,  the  greater 


410  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

part  of  the  peptone  will  be  precipitated.  If  the  alcoholic  fluid  be  then 
acidulated  with  acetic  acid,  boiled,  and  filtered,  leucin  and  tyrosin  will 
separate  when  the  nitrate  is  concentrated  by  evaporation.  By  heating 
this  deposit  with  water,  the  leucin,  which  is  readily  soluble  in  water,  may 
be  separated  from  the  tyrosin,  which  is  not  so  soluble. 

Leucin,  or  amido-caproic  acid  (C6H13NO2),  belongs  to  the  fatty  bodies,  and 
is  a  constant  decomposition  product  of  albumen  and  various  nitrogenous  sub- 
stances. Leucin  occurs  in  the  form  of  white,  shining  lamellae,  which  are  insoluble 
in  ether  and  chloroform,  readily  soluble  in  alkalies  and  acids,  especially  when 
hot.  It  readily  crystallizes  from  its  solutions  in  hot  water  in  spherical  masses, 
composed  of  groupings  of  thin,  white,  glistening  needles.  When  a  few  crystals 
of  leucin  are  placed  on  platinum-foil  and  evaporated  gently  with  a  drop  of  nitric 
acid,  if  a  few  drops  of  caustic  soda  are  added  to  the  colorless  residue  a  yellow  or 
brownish  mass  is  obtained,  which  forms  an  oily  drop.  (Scherer's  test.) 

If  a  dilute  solution  of  leucin  is  boiled  with  cupric  hydrate  in  excess,  bright 
violet  scales  are  deposited  on  cooling. 

Tyrosin  (CgH^NOg)  is  a  member  of  the  aromatic  group,  and  may  be 
obtained  from  almost  any  proteid  under  the  action  of  strong  oxidizing  agents.  It 
remains  in  the  deposit  of  pancreatic  digestion  of  albuminoids,  prepared  as  above, 
after  the  leucin  has  been  removed.  By  dissolving  this  residue  in  hot  water,  and 
rapidly  crystallizing  by  the  addition  of  ammonia,  tyrosin  may  be  obtained  in 
tolerable  purity.  It  then  occurs  in  the  form  of  fine,  white,  silky  needles,  gener- 
ally arranged  in  sheaf-like  bundles,  which  dissolve  in  hot  dilute  ammonia,  and  are 
deposited  on  cooling  the  solution  in  brilliant,  colorless,  radiating  stars.  It  is 
insoluble  in  absolute  alcohol  and  ether,  almost  insoluble  in  cold  water,  and 
slightly  soluble  in  hot  water,  but  readily  soluble  in  the  mineral  acids  and  in  warm 
dilute  ammonia. 

If  a  hot,  watery  solution  of  tyrosin  is  treated  with  a  few  drops  of  Millon's 
reagent  to  boiling,  a  dark-red  color  appears,  and  when  the  solution  is  concentrated 
deposits  a  dark-red  precipitate.  (Hoffman  s  test.) 

The  application  of  Scherer's  test,  as  in  the  case  of  leucin,  will  form  a  reddish- 
yellow  residue,  which  will  become  brown  on  the  addition  of  caustic  soda. 

In  the  small  intestine  the  pancreatic  juice  never  alone  comes  in 
contact  with  food-stuffs,  but  it  meets  with  undigested  matters  mixed 
with  the  results  of  gastric  digestion,  and  therefore  with  the  acid  gastric 
juice  and  bile. 

In  the  animal  economy,  therefore,  the  activity  of  the  pancreatic 
juice  must  be  different  from  that  which  has  been  stated  as  occurring 
outside  of  the  bod}r,  when  the  operation  of  the  pure  pancreatic  juice  is 
alone  considered. 

When  the  acid  chyme  from  the  stomach  reaches  the  small  intestine, 
the  alkalinity  of  the  bile,  pancreatic  and  intestinal  secretion,  to  a  certain 
extent,  partially  neutralizes  the  acid  of  the  gastric  juice. 

It  has  been  found  that  when  pancreatic  juice  is  mixed  with  gastric 
juice,  the  activity  of  the  resulting  medium  will  depend  greatly  upon  the 
relative  proportions  of  these  two  fluids.  As  a  rule,  gastric  juice,  by 
digesting  trypsin,  renders  the  pancreatic  secretion  entirely  inert.  The 
process  occurring  in  the  duodenum  is,  however,  somewhat  different : 
for  we  have  already  found  that  the  first  effect  of  the  bile  is  to  precipi- 
tate pepsin,  and  therefore  the  pancreatic  ferment  comes  into  contact  with 


DIGESTION   IN   THE   SMALL   INTESTINE.  411 

the  acid  constituents  alone  of  the  gastric  secretion,  which,  as  has  been 
already  mentioned,  has  but  slight  degree  of  acidity,  and  does  not  inter- 
fere with  pancreatic  digestion. 

The  bile,  on  the  other  hand,  while  disturbing  gastric  digestion,  con- 
siderably assists  the  action  of  the  pancreas,  not  only  in  facilitating  the 
emulsification  of  fats,  but  apparently  also  in  some  wa}'  aiding  the  solvent 
action  of  the  pancreas  on  proteids.  The  pancreas,  in  addition  to  the 
three  ferments  already  described,  is  also  said  to  contain  a  ferment  which 
coagulates  milk,  which  ma}'  be  extracted  from  the  gland  by  means  of  a 
concentrated  solution  of  common  salt,  the  ordinary  solvent  used  in 
making  rennet  from  the  calf's  stomach,  and  which  in  general  is  claimed 
to  behave  like  the  milk-curdling  ferment  of  the  gastric  juice. 

This  ferment  has  been  found  in  the  pancreas  of  the  pig,  the  sheep, 
the  calf,  the  ox,  and  the  fowl.  The  principal  difference  between  the 
action  of  the  milk-curdling  ferment  of  the  pancreas  and  that  of  the 
gastric  juice  lies  in  the  fact  that  even  1  per  cent,  of  sodium  bicarbonate 
does  not  prevent  coagulation  in  the  former  case,  while  one-fourth  of 
1  per  cent,  in  the  latter  case  does.  The  pancreatic  rennet  is  also  quite 
active  in  a  neutral  or  even  faintly  acid  medium.  Boiling,  as  with  other 
soluble  ferments,  destroys  its  power.  It  may  likewise  be  precipitated  by 
alcohol  and  again  dissolved  in  water  without  losing  its  activity. 

When  a  pancreatic  digestive  mixture  is  allowed  to  remain  in  contact 
with  food-stuffs,  it  rapidly  acquires  a  putrefactive  odor,  and  swarms  with 
microscopic  organisms.  Usually  in  eight  hours  a  high  degree  of  putre- 
faction has  taken  place.  It  is  to  be  supposed  that  a  similar  state  of 
affairs  occurs  in  the  small  intestine,  since  the  conditions  are  there  favor- 
able for  the  reproduction  of  bacteria  ;  for  it  is  scarcely  possible  to  assume 
that  the  acidity  of  the  gastric  juice  is  sufficient  to  destroy  the  germs 
which  we  must  suppose  are  constantly  taken  into  the  alimentaiy  tract. 
A  characteristic  result  of  the  putrefaction  and  decomposition  of  proteids 
is  indol,  to  which  the  ftecal  odor  of  putrefying  pancreatic  secretion  is  due. 
When  salicylic  acid  is  added  to  pancreatic  digestive  mixtures,  they  remain 
free  from  odor,  and  the  presence  of  indol  cannot  be  detected.  It  there- 
fore seems  clear  that  indol  is  a  result  of  putrefaction  of  the  results  of 
pancreatic  digestion,  and  is  not  normally  a  digestive  product.  Never- 
theless, the  constant  presence  of  indol  in  the  small  intestine  would  show 
that  in  this  portion  of  the  alimentary  canal  such  putrefactive  changes 
almost  invariably  result. 

In  addition  to  indol,  putrefying  pancreatic  solutions  will  develop 
ammonia,  carbonic  acid,  butyric  acid,  valerianic  acid,  acetic  acid,  phenol, 
sulphuretted  Irvdrogen,  carburetted  hydrogen,  and  hydrogen, — gases 
which  are  also  found  in  the  alimentary  canal. 

While  such  putrefactive  changes  undoubtedly  occur  in  the  alimentary 


412  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

canal,  the  extent  to  which  these  processes  take  place  can  be  scarcely 
estimated;  of  course,  the  more  proteid  which  is  so  broken  up,  the  greater 
will  be  the  nutritive  loss  to  the  economy,  since  such  putrefactive  products 
have  no  physiological  value.  It  may,  therefore,  be  assumed  that  it  is 
only  the  excess  of  proteids  which  is  so  broken  up,  for  under  normal 
conditions  it  may  be  assumed  that  peptone  is  absorbed  as  fast  as  it  is 
formed.  In  the  case  of  the  herbivora,  whose  long  intestinal  tract  is 
nearly  always  filled  with  residue  of  food,  this  decomposing  process  will 
probably  attain  a  higher  degree  than  in  the  case  of  the  carnivora.  That 
the  intestinal  contents  are  comparatively  free  from  putrefactive  odor  in 
these  animals  is  not  an  objection  to  this  statement,  since  it  is  always  so 
largely  composed  of  cellulose  and  other  non-putrefactive  substances. 

It  has  been  found  that  the  amount  of  indican  contained  in  the  urine 
is  a  measure  of  the  amount  of  putrefaction  occurring  in  the  intestine; 
and  since  indican  is  present  in  the  urine  of  herbivora  in  about  twenty- 
three  times  the  amount  found  in  the  urine  of  man,  it  is  evident  that  the 
putrefactive  process  in  the  intestinal  canal  of  the  herbivora  must  be 
also  largely  in  excess.  In  addition  to  the  fact  that  the  proteids  are 
rapidly  absorbed  as  soon  as  acted  on  by  the  digestive  secretions,  the 
influence  of  the  bile  is  also  to  be  alluded  to  as  a  preventive  of  putrefaction. 

3.  The  Secretion  of  Pancreatic  Juice. — In  the  pancreatic  secretion 
the  digestive  juices  reach  their  maximum  as  regards  intensity  of  action 
and  variety  of  food-stuffs  on  which  they  act.  Human  pancreatic  juice 
has  never  been  obtained  in  a  condition  of  purity,  and  were  it  not  for  the 
studies  made  on  animals  this  branch  of  our  subject  would  be  an  empty 
page.  The  volume  of  this  gland,  which  is  very  constantly  present  and 
subject  to  a  great  variety  of  changes,  is  much  larger  in  the  carnivora 
than  in  the  herbivora.  In  the  herbivora  the  secretion  is  constant,  in  the 
carnivora  it  is  intermittent,  while  in  the  ruminant  its  maximum  activity 
appears  to  coincide  with  the  end  of  rumination,  when  as  much  as  two 
hundred  to  two  hundred  and  seventy  grammes  may  be  secreted  per 
hour.  During  fasting  in  the  ruminant,  although  not  absolute^  sus- 
pended, its  secretion  is  greatly  reduced  in  amount.  In  the  horse,  from 
experiments  made  by  Leuret  and  Lassaigne,  Colin  was  able  to  determine 
that  the  maximum  hourly  secretion  was  two  hundred  and  sixty -five 
grammes,  or  about  the  same  as  that  of  the  ox,  though  part  was  probably 
lost  by  not  t}ang  the  supplementary  ducts.  As  in  the  carnivora,  so, 
also,  in  the  herbivora,  this  gland  is  extremely  liable  to  inflammation, 
which,  of  course,  will  affect  the  general  result. 

Another  method  by  which  the  amount  of  pancreatic  secretion 
poured  out  was  estimated  was  to  ligate  the  bile-duct  and  pylorus,  then 
empty  the  intestine  by  pressure,  and  then  to  tie  its  lower  extremity.  In 
this  way  six  hundred  to  one  thousand  grammes  of  clear,  limpid  fluid 


DIGESTION   IN   THE   SMALL   INTESTINE.  413 

were  collected  in  an  hour,  though,  of  course,  the  fluid  was  not  derived 
solely  from  the  pancreas,  but  contained  the  secretion  poured  out  by  the 
intestinal  glands. 

The  pancreatic  secretion  in  the  hog  has  certain  characteristics  which 
are  readily  determined.  The  fistula  is  made  in  the  same  manner  as  in 
the  dog,  and  it  is  then  seen  that  the  hourly  secretion  is  five  to  fifteen 
grammes,  and  that  the  activity  of  the  pancreatic  secretion  is  in  inverse 
ratio  to  that  of  the  bile. 

In  the  carnivora  the  study  of  this  secretion  is  most  readily  carried 
out.  In  the  sheep  it  is  open  to  difficulties,  and  has  not  been  as 
thorough  as  in  the  dog.  No  ratio  between  the  size  of  the  animal 
or  of  the  gland  and  the  quantity  of  pancreatic  juice  is  capable  of 
demonstration.  Thus,  the  pancreas  of  the  horse  and  ox  weigh 
each  three  hundred  grammes ;  both  animals  are  about  of  the  same 


FIG.  161.— SECTION  OF  THE  PANCREAS  OF  THE  DOG  IN  THE  FASTING  CONDITION, 
HARDENED  WITH  ALCOHOL  AND  STAINED  \VITH  CARMINE.    (Heidenhain.) 

size,  and  also  secrete  the  same  amount  of  pancreatic  juice.  In  the 
sheep  the  pancreas  weighs  from  fifty  to  sixty  grammes,  or  one-fifth  as 
much  as  in  the  large  ruminants,  and  yet  only  pours  out  seven  to  eight 
grammes  per  hour.  In  the  hog  the  pancreas  weighs  from  one  hundred 
and  forty  to  one  hundred  and  eighty  grammes,  and  only  secretes  ten  to 
fifteen  grammes  per  hour.  These  results,  of  course,  cannot  be  too  posi- 
tive^ accepted,  on  account  of  the  many  disturbing  causes. 

In  the  pancreas,  as  in  other  glands,  we  may  distinguish  a  period  of 
rest,  during  which  the  gland  is  pale  and  free  from  blood,  and  a  period  of 
activity,  during  which  it  is  swollen  and  its  vessels  gorged  with  arterial 
blood.  Changes  occur,  therefore,  in  the  pancreas  such  as  have  been  al- 
ready described  in  the  case  of  the  salivary  glands.  In  the  carnivorous 
animals  the  secretion  commences  when  the  food  is  introduced  into  the 


414  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

stomach  and  rapidly  reaches  its  maximum  two  or  three  hours  thereafter. 
Toward  the  fifth  or  seventh  hour  it  decreases  in  activity,  and  about 
twelve  hours  after  feeding  again  becomes  increased  in  amount,  the  second 
increase  being  apparently  coincident  with  the  escape  of  the  acid  chyme 
into  the  small  intestine.  The  cells  of  the  pancreas  also  undergo  marked 
histological  changes  during  the  period  of  active  secretion.  .In  the  pan- 
creas of  a  fasting  dog  two  zones  may  be  recognized,  the  inner  zone  highly 
granular  in  nature,  and  with  difficulty  stained  with  carmine,  and  a  smaller 
homogeneous  outer  zone  which  readily  stains  red.  The  nucleus,  which  is 
generally  irregular  in  shape,  lies  between  these  two  zones  (Fig.  161).  If, 
on  the  other  hand,  a  microscopic  inspection  be  made  of  an  animal  in  full 
digestion,  the  outer  homogeneous  zone  will  be  found  to  have  greatly  in- 


FIG.  162.— PANCREAS  OF  THE  DOG  IN  THE  FIRST  STAGE  OF  DIGESTION.    (Heidenhain.) 

creased  in  extent,  while  the  inner  granular  zone  will  be  almost  absent, 
the  whole  cell  being  smaller  and  readily  stained  with  carmine  (Fig.  162). 
After  digestion  has  been  completed,  the  appearance  described  in  the  fast- 
ing cell  will  be  again  regained  (Fig.  163).  It  would  appear  from  these 
facts  that  the  secretion  of  the  pancreatic  juice  is  formed  at  the  expense 
of  the  granular  material  found  in  the  inner  zone  of  the  secreting  cells, 
while  these  granules  result  from  the  amorphous  homogeneous  matter 
found  in  the  external  zone,  and  which  during  digestion  is  built  up  from 
the  matter  taken  from  the  blood.  We  have  already  alluded  to  the  fact 
that  to  obtain  an  active  pancreatic  extract  the  gland  must  be  taken  from 
an  animal  in  full  dig'estion,  and  that  if  the  gland  of  a  fasting  animal  be 
rubbed  up  with  glycerin  and  acetic  acid,  the  glycerin  extract  from  such 
a  gland  will  be  strongly  proteolytic.  These  results  are  to  be  explained, 


DIGESTION   IN   THE   SMALL   INTESTINE.  415 

as  alreadjr  mentioned,  by  the  fact  that  the  gland  itself  contains  but  little 
ready-formed  proteolytic  ferment,  but  a  substance  termed  zyrnogen, 
which,  from  exposure  to  the  atmosphere,  or  under  the  action  of  dilute 
acid,  is  readily  converted  into  ferment. 

Heidenhain  luis  determined  that  the  amount  of  zymogen  in  the  pan- 
creas coincides  in  amount  with  the  extent  of  the  granular  zone ;  there- 
fore, in  pancreatic  secretion,  as  in  the  case  of  saliva,  the  act  of  secretion 
possesses  two  phases :  the  first,  the  preliminary  stage  of  separation  from 
the  blood;  the  second,  the  stage  of  manufacturing  of  those  constituents 
into  the  specific  ferments  of  the  secretion. 

As  regards  the  action  of  the  nervous  S3*stem  on  the  secretion  of 


FIG.  163.— PANCREAS  OF  THE  DOG  IN  THE  SECOND  STAGE  OF  DIGESTION.    (Heidenhain.) 

pancreatic  juice  but  little  is  known.  Both  section  and  stimulation  of 
the  central  end  of  the  pneumogastrics  temporarily  arrest  the  flow  of 
pancreatic  juice ;  vomiting  also  has  the  same  effect,  the  result  being 
probably  due  to  the  stimulation  of  this  nerve.  Stimulation  of  the  gland 
itself  by, an  induction  current,  as  well  as  stimulation  of  the  medulla 
oblongata,  seems  to  produce  an  increase  in  the  secretion,  but  section  of 
the  spinal  cord  does  not  raise  it.  When  all  the  nerves  going  to  the 
pancreas  are  divided,  a  continuous  flow  of  pancreatic  juice  commences, 
and  under  these  circumstances  the  fluid  formed  has  but  slight  digestive 
power,  and  its  amount  is  not  influenced  by  the  taking  in  of  food.  Injec- 
tions of  ether  into  the  stomach  produce  an  increased  flow  of  pancreatic 
juice,  while  the  secretion  is  suppressed  in  the  dog,  though  not  in  the 


416  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

rabbit,  by  the  action  of  at  r  opine  and    by    stimulation  of  the    sensory 

nerves. 

The  pressure  under  which  the  pancreatic  juice  is  secreted  is  not 
much  higher  than  that  of  the  bile,  amounting  only  to  about  seventeen 
millimeters  of  mercury. 

III.  THE  INTESTINAL  JUICE. — In  addition  to  the  fluids  poured  out  by 
the  liver  and  the  pancreas,  the  walls  of  the  small  intestine  are  also 
abundantly  supplied  with  glands,  which  pour  out  a  secretion  which 
possesses  a  certain  digestive  value.  The  largest  amount  of  this  fluid  is 
poured  out  by  the  so-called  duodenal  follicles,  or  glands  of  Lieberkiihn, 
to  which  is  added  the  scanty  secretion  of  the  small,  convoluted,  tubular 
Br miner's  glands.  The  latter  are  morphologically  identical  with  the 
glands  of  the  pylorus  and  stomach,  and  their  cells  are  turbid  and  small 
during  hunger,  while  during  digestion  they  are  large  and  clear.  In  the 
sheep  the  Brnnner's  glands  form  a  continuous  laj^er  and  their  walls  pour 
out  a  fluid  containing  mucin  and  ferments  which  possess  the  power  of 
dissolving  proteids  and  of  converting  starch  into  sugar.  Any  data  as  to 
the  action  of  the  secretion  formed  by  these  glands  are,  however,  obtained 
with  the  greatest  difficulty  on  account  of  the  smallness  of  the  glands  and 
impossibility  of  isolating  their  secretion ;  consequently,  the  greatest 
uncertainty  surrounds  their  functions. 

The  glands  of  Lieberkiihn  are  small,  tubular  glands  set  vertically  in 
the  mucous  membrane  and  are  lined  by  c}dindrical  epithelial  cells,  among 
which  numerous  goblet,  mucous  cells  may  be  found.  These  cells,  appar- 
ently, are  the  main  source  of  intestinal  juice,  the  so-called  succus  entericus. 

Yarious  methods  have  been  proposed  for  obtaining  the  fluid  poured 
out  by  these  glands.  Thiry's  method  was  to  withdraw  a  loop  of  small 
intestine  from  the  abdomen,  and  excise  a  portion  several  inches  in 
length,  leaving  its  blood  supply  intact,  and  then  restoring  the  continuity 
of  the  intestine  by  stitching  together  the  ends  above  and  below  where 
the  excised  portion  had  been  removed.  One  end  of  the  excised  portion 
was  then  closed  by  stitches,  while  the  other  extremity  was  kept  open 
and  stitched  into  the  abdominal  wall.  By  this  means  a  small  portion  of 
the  small  intestine  was  isolated,  and  as  it  communicated  with  the  exterior 
the  secretion  which  it  formed  could  be  readily  collected.  Yella  improved 
the  method  employed  by  Thiry  by  leaving  both  ;ends  of  the  isolated 
portion  open,  after  restoring  the  continuity  of  the  bowel,  and  stitching 
them  to  the  abdominal  wound.  It  is  evident  that  after  this  operation 
the  small  intestine  cannot  be  regarded  as  being  in  its  normal  condition, 
for  it  is  entirely  removed  from  contact  with  the  secretions  and  chyme, 
and  undergoes  a  considerable  amount  of  atrophy ;  and  although  its 
secretion  is  not  contaminated  by  any  other  digestive  fluid,  it  cannot 
be  regarded  as  being  in  a  normal  condition. 


DIGESTION  IN  THE   SMALL  INTESTINE.  417 

Colin  collected  a  considerable  amount  of  fluid  by  placing  a  clamp  on 
the  small  intestine  of  the  horse  and  emptying  a  considerable  portion 
below  it  by  gentle  pressure,  and  then  clamping  it  several  feet  below  the 
upper  clamp.  In  this  Tvny  he  obtained  from  eighty  to  one  hundred  and 
twenty  grammes  of  fluid  in  half  an  hour  from  two  meters  of  the  small 
intestine  of  the  horse.  He  states,  however,  that  this  fluid  may  be  greatly 
increased  by  the  injection  into  the  loop  of  a  solution  of  aloes,  manna,  or 
soda;  and  since  its  composition  coincides  almost  exactly  with  that  of 
blood-serum,  it  is  probably  an  exudation.  No  reliable  experiments  seem 
to  have  been  made  as  to  the  digestive  properties  of  the  fluid  obtained  in 
this  wa}r. 

Moreau  has  also  succeeded  in  obtaining  a  large  quantity  of  liquid 
by  clasping  the  intestine,  as  in  Colin's  method,  and  then  dividing  the 
nerves  going  to  the  isolated  portion  of  the  intestine.  In  this  operation, 
also,  it  is  probable  that  the  fluid  is  an  exudation,  as  it  coincides  almost 
entirely  with  blood-serum  in  composition;  and  here  also  no  experiments 
as  to  its  digestive  powers  have  been  made. 

The  author  has  employed  a  method  for  collecting  the  secretion  of 
the  small  intestine  which  is  free  from  most  of  the  objections  which 
may  be  urged  against  the  methods  already  described.  A  fistula  is  made 
into  the  duodenum  in  the  same  way  as  in  making  a  gastric  fistula,  and  a 
small  tube  inserted.  The  operation  is  readily  performed,  but  in  a  large 
number  of  animals  so  treated  the  tube  will  tear  out  of  the  intestine,  and 
the  experiment  will  consequently  fail.  When  the  wound  lias  healed  the 
dog  should  be  allowed  to  fast  for  at  least  twenty-four  hours,  and  then 
the  intestine  washed  out  by  an  injection  of  lukewarm  water  through  the 
cannula.  A  rubber  bulb  is  then  to  be  inserted  through  the  tube  into 
the  small  intestine  and  pushed  back  toward  the  stomach,  taking  care, 
however,  that  it  lies  below  the  opening  of  the  pancreatic  and  bile  ducts ; 
it  then  may  be  distended  by  water  so  as  to  occlude  the  intestine,  and  a 
small  bulb  with  a  long  tube  is  then  pushed  down  the  intestine  and  dis- 
tended with  water  so  as  to  occlude  it  below. 

In  this  way  a  variable  portion  of  small  intestine  is  shut  off  from  the 
contents  of  the  alimentary  canal  above  and  below,  and  its  secretion  in  a 
state  of  comparative  purity,  and  in  considerable  amount,  may  be  then 
collected. 

Obtained  in  this  way,  the  intestinal  juice  has  an  alkaline  reaction  ; 
its  specific  gravity,  1010;  it  gives  no  coagulum  on  boiling,  and  yields 
Millon's  reaction,  and  deposits  a  heavy  precipitate  when  thrown  into 
absolute  alcohol.  Its  composition  in  one  hundred  parts  is  as  follows: 
Water,  98.86 ;  organic  matter,  0.54 ;  inorganic  matter,  0.59.  The  inor- 
ganic matter  is  represented  by  chlorides  and  sulphates  and  carbonates 
of  sodium  and  potassium.  With  chlorine-water  no  red  is  given,  and  in 

27 


418  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

certain  instances  it  lias  been  found  to  turn  acid  on  standing.  As  regards 
its  digestive  action,  it  contains  three  ferments,  which  may  be  precipitated 
by  alcohol  and  again  redissolved  in  water.  It  will  rapidly  convert 
starch  into  sugar  in  a  neutral  or  faintly  alkaline  medium,  while  2  per 
cent,  of  acid  and  5  per  cent,  of  liquor  potassa  will  prevent  it.  This  has 
also  been  established  by  Ellenberger  and  Hofmeister  to  apply  to  the 
intestinal  secretion  of  the  horse.  There  is  a  special  ferment  present 
which  will  convert  cane-sugar  into  invert-sugar,  or  a  mixture  of  laevulose 
and  dextrose.  This  is  the  only  secretion  in  the  body  which  possesses 
this  power.  The  transformation  of  cane-sugar  into  invert-sugar  is 
represented  in  the  following  formula  : — 

SC^H^O^  +2H20  =  C12H24012  +  C12H24O12. 
Saccharose.        Water.          Dextrose.  Lsevulose. 

The  inversive  ferment  has  been  found  by  Bernard  in  the  small  intes- 
tine of  dogs,  rabbits,  birds,  and  frogs.  Roberts  has  recognized  it  in  the 
small  intestine  of  the  pig,  the  fowl,  and  the  hare,  while  Balbiani  has 
found  it  in  the  intestine  of  the  silk-worm.  It  is  absent  from  the  large 
intestine.  When  a  watery  infusion  is  made  of  the  mucous  membrane  of 
the  small  intestine,  it  possesses  the  power  of  inverting  sugar,  but  loses  it 
when  the  infusion  is  filtered,  seeming  to  indicate  that  the  ferment  remains 
attached  in  such  infusions  to  some  of  the  formed  elements  contained  in 
the  intestine.  It  is,  however,  possible  to  precipitate  the  ferment  from 
intestinal  juice,  and  then  obtain  a  watery  solution  of  the  precipitate 
which  will  invert  sugar.  The  intestinal  juices  will  also  dissolve  proteids, 
albumen,  and  fibrin,  and  convert  them  into  peptone,  after  first  passing 
through  a  stage  similar  to  that  of  alkali  albumen.  The  action  of  the 
intestinal  juices  resembles  that  of  the  pancreatic  secretion  in  its  general 
characters  and  in  the  resolution  of  the  fibrin  peptone  into  leucin  and 
tyrosin  and  indol.  The  ferment  which  is  concerned  in  the  digestion  of  pro- 
teids is  apparently  either  not  carried  down  by  the  alcohol,  or  is  not  capable 
of  resolution  in  water,  for  all  the  author's  experiments  failed  in  obtaining 
an  active  solution  of  the  ferment  in  water,  acid,  or  alkali  after  precipi- 
tation with  alcohol.  When  fibrin  is  digested  by  the  intestinal  juices,  a 
peculiar  substance  is  formed,  which  gives  a  red  with  nitric  acid,  the  color 
disappearing  on  heating. 

IV.  FERMENTATION  PROCESSES  IN  THE  SMALL  INTESTINE. — In  the 
small  intestine  are  found  numerous  examples  of  the  lower  organisms 
which  enter  the  alimentary  canal  through  the  foods  and  liquids  which 
are  swallowed,  and  which  induce  various  fermentations  and  putre- 
factions in  the  contents  of  the  alimentary  canal,  resulting  in  the  evolu- 
tion of  various  gases.  These  gases  consist,  in  the  first  place,  of  air,  which 
is  swallowed  with  the  food,  of  which  a  large  portion  of  the  oxj^gen  is 


DIGESTION  IN   THE  SMALL  INTESTINE.  419 

absorbed,  while  the  nitrogen  remains  unaltered.  Therefore,  the  oxygen 
will  be  in  smaller  relative  proportion,  as  contrasted  with  the  nitrogen, 
than  is  found  in  the  atmosphere;  the  carbon  dioxide,  which  is  also 
present,  will,  on  the  other  hand,  be  in  relative  excess,  since  a  certain 
quantity  of  this  gas  diffuses  from  the  venous  blood  into  the  interior  of 
the  alimentary  canal.  Hydrogen,  ammonia,  and  carburetted  and  sulphu- 
retted hydrogen  are  also  found  as  the  results  of  various  decompositions. 

Y.  INTESTINAL  DIGESTION  IN  DIFFERENT  ANIMALS. — The  contents 
of  the  stomach  do  not  pass  suddenly,  but  gradually,  into  the  small 
intestine,  their  entrance  into  this  portion  of  the  alimentary  canal 
not  being  due  to  the  forcible  contraction  of  the  stomach,  but  to  a 
series  of  periodic  relaxations  of  the  pylorus,  as  a  result  of  special 
stimuli ;  during  the  intervals,  the  pylorus  is  tightly  closed.  Transition 
into  the  intestine  rarely  occurs  before  digestion  has.  made  considerable 
advances;  the  necessary  stimuli,  therefore,  cannot  be  of  a  purely 
mechanical  nature,  especially  as  it  has  been  found-  that  mechanical  stimuli 
lead  to  more  marked  contraction  of  the  p}'loric  ring  rather  than  to  its 
relaxation.  The  stimulus  which  leads  to  a  relaxation  of  the  pyloric 
sphincter  is  probabty  of  a  chemical  nature,  but  its  exact  mode  of  opera- 
tion is  entirely  unknown.  It  would  seem,  however,  that  fat  is  almost 
incapable  of  causing  an  opening  of  the  pylorus,  for,  no  matter  how  much 
fat  be  given  in  the  food,  nearly  the  same  amount  will  be  found  in  the 
intestine  after  four,  five,  or  twent3'-one  hours,  showing  that  the  pylorus 
allows  no  more  to  pass  than  may  be  taken  up  by  the  villi ;  therefore, 
there  is  never  an  accumulation  of  fat  in  the  intestine. 

If,  during  the  latter  stage  of  gastric  digestion,  a  transverse  section 
is  made  through  the  duodenum,  on  the  mucous  surface  will  be  found  a 
white,  pasty  emulsion  ;  then  comes  a  yellowish,  cheesy  precipitate,  pro- 
duced by  the  bile,  and  in  the  centre  will  be  found  a  thin,  j^ellowish-brown 
liquid,  containing  particles  of  undigested  food.  If  such  a  section  be 
made  still  lower  down  in  the  intestine,  further  from  the  stomach,  the 
fatty  layer  will  be  found  to  have  decreased  in  amount,  while  the  central 
fluid  will  be  relatively  more  abundant,  and  becomes  darker  and  darker 
in  color,  until  at  the  lower  portion  of  the  small  intestine  it  is  of  a  deep- 
green  color.  Some  of  the  fluid  constituents  contain  many  gas-bubbles. 
The  central  fluid  has  alwajrs  a  more  strongly  acid  or  less  alkaline  reac- 
tion than  the  portion  of  the  intestinal  contents  in  contact  with  the 
intestinal  walls. 

As  we  have  seen,  the  chyme,  as  it  issues  from  the  stomach,  is  sub- 
jected to  the  action  of  the  intestinal  secretions  before  being  ready  for 
absorption.  The  character  of  the  chyme,  as  indicating  the-character  of 
the  digestive  processes,  varies  in  different  animals,  and  has  been  closely 
studied  by  Colin,  whose  description  is  here  mainly  followed.  In 


420  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

carnivora  the  chyme  is  scanty,  gradually  giving  up  matters  ready  for 
absorption,  and  passes  slowly  through  the  intestine.  Thus,  seven  to 
eight  hours  after  a  meal  of  one  thousand  grammes  of  meat,  only  fifty  to 
one  hundred  grammes  represent  the  weight  of  intestinal  contents.  The 
small  intestine  in  carnivora  is  never  distended,  as  in  the  case  of  the 
omnivora,  and  especially  the  herbivora,  but  it  is  always  a  flattened 
cylinder.  The  stomach  appears  to  regulate  the  amount  which  passes 
into  the  small  intestine.  The  small  intestine  in  non-ruminant  herbivora, 
as  the  horse,  receives  large  volumes  of  chyme  from  the  stomach,  and 
rapidly  disperses  it  through  the  entire  small  intestine ;  but  although 
the  small  intestine  has  a  capacity  four  times  as  great  as  the  stomach, 
it  never  contains  as  much  as  may  be  contained  in  the  stomach  when 
distended,  for  after  a  meal  the  contents  of  the  stomach  are  rapidly 
distributed  between  the  small  intestine,  stomach,  and  caecum.  If  the 
contents  of  the  small  intestine  of  the  horse  be  examined  at  various 
intervals  after  feeding,  it  will  be  found  that  40  to  50  per  cent,  of  the 
carbohydrates  in  the  food  have  been  digested  in  the  stomach,  while 
30  to  50  per  cent,  of  the  albuminoids  and  40  to  60  per  cent,  of  the 
non-nitrogenous  constituents  may  still  be  recognized. 

In  the  horse,  the  fluid  found  in  the  duodenum  and  jejunum  is  usually 
acid  in  reaction,  yellowish  in  color,  turbid,  and  viscid.  It  is  capable  of 
digesting  proteids  and  starch,  and  its  ferments  may  be  precipitated  by 
alcohol  and  redissolved  in  water  without  losing  their  activit}^.  In  the 
ileum  the  contents  are  usually  alkaline  in  reaction,  brownish-yellow  in 
color  from  the  bile-pigments,  turbid,  but  contain  less  mucin  than  the 
duodenal  contents.  Intestinal  digestion  in  the  horse  is  of  considerable 
importance  ;  only  from  23  to  52  per  cent,  of  undigested  albumen  and 
from  38  to  59  per  cent,  of  undigested  carbohydrates  are  to  be  found  in 
the  duodenum,  although  there  can  be  no  doubt  but  that  large  amounts 
of  entirely  undigested  food  pass  from  the  stomach  into  the  small  intes- 
tine. When  the  food  has  a  prolonged  sojourn  in  the  stomach  but  2  to 
10  per  cent,  of  its  proteid  constituents  ma}^  be  left  untouched  for  diges- 
tion by  the  intestinal  secretions,  but  where  this  is  not  the  case  it  may  be 
safely  stated  that  at  least  60  per  cent,  of  the  proteids  have  to  be  digested 
in  the  small  intestine.  These  facts  would  -seem  to.  indicate  that  in  soli- 
pedes  digestion  is  almost  continuous.  In  ruminant  herbivora  the  state 
of  affairs  is  different ;  there,  the  contents  of  the  intestine  only  represent 
one-eighth  to  one-tenth  the  amount  contained  in  the  stomach,  and  when 
rumination  is  suspended  but  a  comparatively  small  part  of  the  food 
remains  unchanged  to  be  acted  on  by  the  intestinal  secretions.  In  car- 
nivora, still  another  state  of  affairs  occurs.  The  stomach  holds  almost 
all  the  alimentary  matter,  only  small  quantities  of  liquefied  chyme  pass- 
ing into  the  intestine,  and  as  the  gastric  digestion  in  these  animals  is 


DIGESTION  IN   THE   SMALL  INTESTINE.  421 

very  complete  the  contents  of  the  small  intestine  amount  to  only  one- 
tenth  or  one-twentieth  of  the  gastric  contents.  Aliments  more  or  less 
liquefied,  according  to  the  quantity  of  fluid  contained  in  the  alimentary 
tract,  present  a  different  character  iii  each  portion  of  the  intestinal  tube. 
In  solipedes,  for  example,  in  the  small  intestine  they  are  mixed  with  a 
thick,  yellowish,  viscid  fluid;  in  the  caecum  they  are  suspended  in  a  large 
amount  of  fluid  not  deprived  of  viscidity  ;  in  the  great  fixed  colon  they 
are  still  soft,  but  as  the  floating  colon  is  approached  they  acquire  pro- 
gressive dryness  and  are  moulded  into  balls,  which  stick  to  the  valvulae 
conniventes. 

The  bile  of  the  hog,  as  has  been  mentioned,  contains  no  amylolytic 
ferment,  but  is  capable  of  emulsifying  rancid  fats.  The  intestinal  juice, 
according  to  Ellenberger  and  Hofmeister,  contains  a  diastatic  but  no  other 
ferment,  a  statement  which,  in  view  of  the  general  presence  of  the  invert 
ferment  in  the  secretion,  needs  confirmation.  The  pancreatic  juice  con- 
tains three  ferments,  and  is,  therefore,  possessed  of  the  same  properties 
as  in  other  mammals.  Consequently,  in  the  intestinal  canal  of  the  hog, 
albuminoids  are  peptonized,  starch  converted  into  sugar,  and  fats 
digested  and  emulsified.  Absorption  in  these  animals  is  exceptionally 
rapid,  so  that  examination  of  the  intestinal  contents  will  reveal  but 
small  amounts  of  digestive  products.  Peptone,  espeeiall}-,  seems  to  be 
absorbed  as  rapidly  as  it  is  formed,  while  69  to  75  per  cent,  of  the 
albuminous  food-stuffs  and  65  to  72  per  cent,  of  the  carbohydrates  found 
in  the  small  intestine  has  been  digested. 

The  reaction  of  the  small  intestine  of  the  hog  is  usually  acid  through- 
out half  its  extent,  the  acidity  sometimes  extending  through  five-sixths 
its  length. 

After  feeding,  the  first  portions  of  the  meal  appear  in  the  small  intes- 
tine in  from  three  to  four  hours,  while  three  hours  later  a  portion  of  the 
intestinal  contents  has  already  reached  the  caecum.  Intestinal  diges- 
tion, therefore,  in  the  hog  is  of  but  short  duration. 

One  is  accustomed  to  speak  of  the  reaction  of  the  small  intestine  as 
self-evidently  alkaline,  and  it  is  almost  universally  taught  that  as  soon 
as  the  acid  chyme  enters  the  duodenum  its  acid  reaction,  through 
the  influence  of  the  bile  and  pancreatic  juice  and  intestinal  secretion, 
at  once  passes  into  an  alkaline  reaction.  This,  however,  is  an  error.  As 
a  rule,  an  alkaline  reaction  is  rarely  met  with  until  the  very  lowest  por- 
tion of  the  ileum  is  reached.  It  has  been  already  mentioned  that  the 
acid  chyme  produces  precipitation  in  the  bile,  the  glycocholate  of  sodium, 
glycocholic  acid,  and  mucin  being  carried  down,  while  the  acid  reaction 
is  still  maintained,  and  that  this  precipitate  carries  the  pepsin  mechan- 
ically down  with  it.  The  importance  of  this  is  seen  when  it  is  remem- 
bered that  in  acid  solutions  pepsin  will  destroy  the  pancreatic  ferments. 


422  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

The  pepsin  is  only  released  when  the  strongly  alkaline  reaction  of  the 
lower  portion  of  the  small  intestine  dissolves  the  bile  precipitate.  It 
can  then  do  no  harm,  as  pepsin  is  inactive  in  alkaline  solutions;  while,  on 
the  other  hand,  the  acid  does  not  interfere  with  the  pancreatic  digestion, 
since  the  pancreatic  ferments  are  still  capable  of  producing  their  charac- 
teristic effects,  even  in  a  faintly  acid  medium. 

The  acid  reaction  of  the  small  intestine  is  most  marked  in  carniv- 
orous animals,  and  in  them,  consequent^,  putrefactive  and  fermentative 
changes  occur  to  a  less  degree  than  in  omnivora  and  herbivora.  In  the 
fasting  horse  the  contents  of  the  small  intestine  are  invariably  alkaline, 
this  reaction  being  more  marked  the  greater  the  distance  from  the  stom- 
ach. In  digesting  animals,  the  acid  reaction  decreases  below  the  point 
of  entrance  of  the  bile  and  pancreatic  juice,  and  becomes  decidedly  alka- 
line at  the  lower  portion  of  the  small  intestine.  This  holds  in  the  horse, 
ox,  and  sheep,  whether  fed  on  dried  or  green  fodder,  on  oats,  grain,  or 
roots.  The  cause  of  the  alkalinity  of  the  reaction  of  the  intestinal  con- 
tents is  due  to  the  bile,  pancreatic  juice,  and  intestinal  secretions,  and  is 
more  marked  the  more  active  is  intestinal  digestion.  The  acidity  of  the 
intestinal  contents  when  present  is  due  not  only  to  the  acid  gastric 
juice,  but  also  to  the  liberation  of  fatty  and  lactic  acids  from  lactic  and 
butyric  acid  fermentations. 

It  is  seen  from  the  above  that  in  the  small  intestine  secretions  are 
met  with  which  are  capable  of  establishing  digestion  of  the  various  food- 
stuffs, so  as  to  render  them  capable  of  absorption.  Starch  becomes  con- 
verted into  sugar  through  the  action  of  the  pancreatic  and  intestinal 
secretions ;  cane-sugar  is  converted  into  invert-sugar  through  the  action 
of  the  special  ferment  of  the  intestinal  secretion;  fats  are  partially 
saponified  and  emulsified  through  the  influence  of  the  bile  and  pancreatic 
juice,  while  albuminoids,  through  the  influence  of  the  pancreatic  and 
intestinal  fluids,  are  turned  into  peptones. 

As  regards  the  changes  which  occur  in  albuminoids  in  the  small 
intestine,  it  is  worthy  of  note  that  in  all  probability  the  formation  of 
leucin  and  tyrosin  has  been  greatly  overestimated,  for  since  the  intestinal 
juices  are  almost  always  acid,  and  since  leucin  and  tyrosin  only  form 
in  alkaline  digestive  juices,  perhaps  these  bodies  never  form  normally  in 
the  intestine.  It  is,  at  any  rate,  certain  that  but  mere  traces  of  leucin 
and  tyrosin  are  to  be  found  in  the  intestinal  contents  during  digestion 
of  large  amounts  of  albumen.  It  is  also  worthy  of  note  that  the  acid 
reaction  of  the  intestine  does  not  interfere  with  the  digestion  of  fats,  for 
the  lacteals  will  be  found  filled  with  a  milky  emulsion  after  feeding,  even 
though  the  reaction  of  the  intestinal  contents  is  almost  as  acid  as  the 
gastric  juice. 

At  the  lower  end  of  the  small  intestine  the  reaction  of  the  intestinal 


DIGESTION   IN   THE   LARGE   INTESTINE.  423 

contents  is  usually  strongly  alkaline,  and  we  have  then  to  deal  with 
processes  which  are  evidently  putrefactive  in  nature.  But  a  small 
portion  of  the  nutritive  parts  of  food  will,  however,  be  subjected  to 
these  changes,  since  probably  digestion,  especialty  in  carnivora  and 
ruminants,  is  completed  before  this  portion  of  the  tract  is  reached. 
Indol  and  phenol  are  here  found,  and  result  from  the  putrefactive  changes 
in  albuminoids,  while  lactic  acid,  butyric  acid,  acetic  acid,  carbonic  acid, 
and  hydrogen  are  met  with  and  result  from  changes  in  carbohyd rates. 
The  different  gases  found  in  the  small  intestine  have  been  already  men- 
tioned ;  their  character  and  amounts  vary  according  to  the  nature  of  the 
diet. 

The  following  table  represents  their  relative  amount  from  different 
diets  in  dogs  : — 

CO2.  N.  H.  O. 

Meat  diet,          .        .        .    40.1  45.5  13.9  0.5 

Bread  diet,        .        ...     38.8  54.2  6.3  0.7 

Vegetable  diet,         .        .47.3  4.0  48.7 

X.  DIGESTION  IN  THE  LARGE  INTESTINE. 

The  absorption  of  all  the  alimentary  elements  which  are  essential  to 
nutrition  is  in  the  carnivora  achieved  in  the  small  intestine.  In  these 
animals  the  caecum  is  absent  or  rudimentary,  and  the  colon  is  short  and 
apparently  uncomplicated ;  but  in  the  immense  caecum  of  solipedes  and 
certain  other  herbivora  the  digestive  process  goes  on,  and  the  changes 
which  the  food  undergoes  in  this  part  of  the  alimentary  tract  now 
deserve  attention. 

1.  THE  FUNCTIONS  OF  THE  CAECUM. — The  caecum,  or  blind  gut,  is  that 
portion  of  the  large  intestine  which  usually  occurs  as  a  diverticulum  at 
the  point  of  junction  of  the  small  and  large  intestines,  and  in  which  the 
contents  of  the  former  empty.  In  man  and  carnivora  this  reservoir  is 
rudimentary,  and  receives  the  alimentary  mass  after  all  its  nutritive 
properties  have  been  extracted.  In  this  class  of  animals,  therefore, 
the  caecum  can  have  no  physiological  function  to  fulfill.  In  reptiles, 
batrachians,  and  the  fish  the  small  intestine  is  directly  continuous  with 
the  large  intestine,  scarcely  increasing  in  diameter,  and  no  caecal  append- 
age is  present,  the  reservoir  only  being  represented  by  a  long,  lateral 
dilatation.  It  is  only  in  mammals  and  in  birds  that  one  or  two  pouches 
are  found  at  the  point  of  union  of  the  small  and  large  intestines,  and 
which  furnish  a  new  reservoir  to  the  alimentary  matters  before  permitting 
them  to  enter  into  the  large  intestine  to  be  finally  expelled. 

In  birds,  the  caecum  varies  in  development  and  importance  according 
to  their  normal  diet.  In  the  flesh-eating  birds,  the  stomach  and  small 
intestine  are  amply  sufficient  to  produce  the  necessary  chemical  trans- 
formations in  the  food  to  render  it  capable  of  being  absorbed.  Their 


424  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

caeca  are  consequent^  rudimentary  or  absent.  In  vegetable-eating  birds, 
on  the  other  hand,  the  caecum  acquires  a  high  degree  of  importance. 
The  caecal  apparatus  in  these  animals  is  double,  and  consists  of  two  long 
tubes,  symmetrically  located  to  the  right  and  left,  and  connected  with 
the  alimentary  canal  at  the  point  of  junction  of  the  small  and  large 
intestines.  Their  mucous  membrane  is  arranged  in  folds,  so  as  to 
increase  their  internal  surfaces.  Their  internal  surface  is  supplied  with 
glands,  which  secrete  a  fluid,  and  with  villi,  which  facilitate  absorption. 
While  it  thus  would  appear  that  in  these  animals,  as  we  find  it  the  case 
in  mammals,  the  development  of  the  caecum  is  in  proportion  to  the  com- 
plexity of  the  food,  there  are,  nevertheless,  certain  exceptions  to  this 
rule.  In  the  nocturnal  birds  of  prey  the  caecum  is  highly  developed. 
This  is,  perhaps,  to  be  explained  from  the  fact  that  it  acts  as  a  compen- 
sation to  the  extreme  shortness  of  the  intestinal  canal  in  this  species. 
On  the  other  hand,  in  the  gallinaceous  birds  the  caecum  is  voluminous, 
and  yet  in  the  pigeon  it  is  entirely  absent.  This  latter  fact  is,  perhaps, 
to  be  explained  by  the  statement  that  in  the  pigeon  the  starchy  mat- 
ters are  completely  digested  before  the  caecum  is  reached,  while  such 
is  not  the  case  in  the  gallinaceae.  Moreover,  in  the  pigeon  the  crop  is 
double,  so,  perhaps,  acting  as  a  substitute  for  the  caecum.  In  mammals, 
also,  the  caecum  varies  in  importance  according  to  the  character  of  the 
substances  with  which  they  are  nourished.  In  carnivora,  such  as  the 
dog  and  cat,  whose  foods  are  readily  digestible  and  assimilable, 
the  caecum  is  absent  or  rudimentary.  Its  structure  is  analogous  to  the 
large  intestine ;  that  is  to  say,  this  organ  forms  part  of  the  excretory 
portion  of  the  alimentary  canal.  The  herbivora,  on  the  other  hand,  find 
their  food  in  substances  which  are  poor  in  nutritious  principles,  and  in 
which  the  nutritive  matters  are  inclosed  in  resisting  cellulose  envelopes. 
As  a  consequence,  we  find  the  digestive  apparatus  in  these  animals 
reaching  a  high  degree  of  perfection.  Their  apparatus  of  mastication  is 
complete;  their  salivary  secretion  abundant.  Their  intestine  is  extremely 
long  and  of  considerable  volume,  so  as  to  multiply  the  secretory  and 
absorbent  surfaces  and  prolong  the  action  of  the  digestive  juices. 

We  find  in  the  ruminants  a  complex  and  voluminous  stomach,  where 
the  food  is  delayed  for  a  considerable  time  before  being  subjected  to  the 
action  of  the  solvent  juices :  but  in  the  horse  and  rabbit  the  stomach  is 
simple  and  small,  and  we  find  in  the  highly  developed  ca?cum  a  sub- 
stitute for  the  voluminous  gastric  pouches  of  the  ruminant.  In  these 
animals  the  caecum  takes  on  the  form  of  an  immense  pocket,  whose 
length  may  exceed  that  of  the  body,  and  whose  capacity  may  be  two 
or  three  times  greater  than  that  of  the  stomach,  while  its  volume  is 
so  great  as  to  cause  it  to  occupy  the  greater  part  of  the  abdominal 
cavity.  In  structure,  also,  the  caecum  no  longer  resembles  that  of  the 


DIGESTION  IN  THE  LAEGE  INTESTINE.  425 

larger  intestine,  but  more  nearly  approaches  that  of  the  small  intestine. 
In  it  are  found  numerous  folds  of  mucous  membrane,  villi,  glands  and 
follicles,  and  large  lymphatics. 

Comparative  anatomy  thus  shows  that  in  all  animals  whose  diet  is 
composed  of  substances  difficult  to  digest  and  rich  in  cellulose,  the 
caecum  is  nighty  developed,  if  some  other  organ  is  not  specialized  for 
this  purpose,  as  in  ruminants.  While  its  volume  is  proportionate  to  the 
volume  of  food  which  these  animals  require  for  their  nourishment,  while 
it  is  absent  in  the  sable  and  those  of  the  bear  tribe  which  nourish  them- 
selves on  fruits  or  substances  easily  digested,  and  while  it  is  slightly 
developed  in  the  carnivora  and  herbivora  which  feed  on  tender  plants,  it 
is  highly  developed  and  acquires  a  value  closely  allied  to  that  of  the 
stomach  in  animals  whose  ordinary  food  is  composed  of  bulky  vegetable 
substances  difficult  to  digest.  Such  a  state  of  affairs  is  seen  in  most  of 
the  rodents.  It  reaches  its  maximum  development  in  the  solipedes,  the 
rhinoceros,  and  some  herbivorous  marsupials.  Its  development,  again,  is 
not  only  dependent  upon  the  degree  of  the  digestibility  of  the  food,  but 
it  is  inverse  with  the  size  of  the  stomach  (hence  its  great  size  in  soli- 
pedes) and  with  the  presence  of  special  organs  to  facilitate  gastric  diges- 
tion (hence  its  small  size  in  ruminants).  In  cases,  therefore,  where  we 
have  a  voluminous  stomach  provided  with  an  extensive  mucous  mem- 
brane and  followed  by  a  long  small  intestine,  we  may  be  sure  the  caecum 
will  be  poorly  developed.  These  facts  prove  that  the  caecum  is  a  com- 
pensatory organ  to  the  stomach,  and  that  the  development  of  the  two  is 
in  inverse  ratio. 

Apart  from  the  oesophageal  dilatations  of  the  ruminant,  we  have 
certain  other  animals  in  which  annexes  to  the  alimentary  tube  serve  to 
assist  in  the  digestion  of  almost  indigestible  food.  These  annexes  may 
replace  the  cesophageal  pouches  and  caecum.  Thus,  we  have  in  birds  the 
crop,  analogous  to  the  ruminant's  pouches,  highly  developed  in  pigeons, 
chickens,  and  geese,  with  the  addition  of  a  muscular,  crushing  stomach. 
In  these  birds,  with  the  exception  of  the  pigeon,  the  caecum  is  also 
present,  and  all  together  are  needed  for  the  digestion  of  foods.  Here 
the  apparatus  of  mastication  is  absent.  The  crop,  gizzard,  and  caeca  all 
fulfill  the  same  end.  In  the  solipedes,  again,  the  caecum  therefore  fulfills 
the  same,  general  functions  as  the  pouches  of  the  ruminant's  stomach, 
which  again  are  analogous  to  the  crop  of  the  gallinaceous  birds. 

Most  of  the  earlier  phj'siologists  regard  the  caecum  as  a  second 
stomach  from  some  obscure  analogy  of  form,  and  from  the  fact  that  its 
contents  were  said  to  be  almost  invariabty  acid.  This  theory  as  to  the 
analogy  of  the  functions  of  the  caecum  and  stomach  held  until  it  was 
discovered  that  the  glands  of  the  caecum,  instead  of  secreting  an  acid 
fluid,  poured  out  an  alkaline  secretion  like  that  coming  from  the  glands 


426  PHYSIOLOGY  OF  THE   DOMESTIC  ANIMALS. 

of  Lieberkiilm  ;  but  just  as  the  caecum  is  the  recipient  of  the  contents  of 
the  ileum,  and  this  often  has  an  acid  reaction,  so  may  the  contents  of  the 
caecum  be  acid,  especially  in  carnivorous  animals,  a  fact  which  may  serve 
to  illustrate  the  error  of  applying  results  found  in  carnivora  to  similar 
functions  in  herbivora,  where  the  processes  are  evidently  different. 

Colin  claims  that  the  reaction  of  the  contents  of  the  caecum  in  the 
horse  is  almost  invariably  alkaline,  and  that  to  a  greater  degree  than  in 
the  small  intestine,  whether  the  animal  be  digesting  or  fasting.  When 
an  acid  reaction  has  been  found  in  this  cavity  it  is  almost  invariably  to  be 
explained  as  due  to  acid  fermentations  occurring  in  the- food-constituents. 

Ellenberger  shows  that  the  caecum  has  a  special  value  in  the  horse. 
In  this  animal,  as  we  know,  the  small  intestine  is  comparatively  small, 
with  a  relatively  small  extent  of  digestive  mucous  membrane.  The 
stomach  is  so  small  that  it  cannot  contain  the  amount  taken  at  one 
meal,  so  the  stomach  forces  its  contents  into  the  intestine  even  while  the 
animal  is  eating ;  gastric  digestion  is,  therefore,  imperfect  in  these 
animals.  But,  as  the  horse  is  nourished  on  substances  which  are  diffi- 
cult of  digestion,  it  should  possess  a  special  digestive  organ,  which,  by 
its  activity,  should  compensate  for  the  loss  of  functional  activity  in  the 
stomach.  Nothing  can  be  more  natural  than  to  suppose  that  this  sup- 
plementary organ  is  found  in  the  vast  caecum  of  these  animals,  and  wre 
may  admit  that  this  is  to  a  certain  extent  true,  without  being  compelled 
to  acknowledge  that  this  organ  liberates  an  acid  digestive  secretion. 
The  caecum  is,  hence,  of  special  importance  in  the  monogastric  herbivora, 
where  the  small  size  of  the  stomach  prevents  accumulation  of  food  and 
drink.  It  is,  therefore,  a  reservoir  for  intestinal  digestion. 

Its  anatomical  arrangement  leads  to  the  retaining  of  its  contents. 
Its  bottom  corresponds  to  the  region  of  the  xyphoid  appendage,  while 
its  narrow  opening  into  the  colon  is  in  the  most  superior  part,  so  that 
everything  to  enter  the  colon  must  be  forced  up  against  gravity,  and 
should  desiccation  of  its  contents  occur  obstruction  is  sure  to  result, 
and  the  result  is  apt  to  be  fatal.  In  length  it  is  about  one  meter,  while 
its  capacity  is  from  thirty-two  to  thirty-eight  liters,  or  nearly  twice  as 
large  as  the  stomach.  It  has  an  extensive  mucous  membrane,  well  sup- 
plied with  glands,  like  the  duodenal  follicles  (Fig.  164). 

Ellenberger  reports  a  number  of  experiments  which  he  made  on  the 
horse  to  determine  the  length  of  time  the  food  remains  in  the  caecum 
and  the  alterations  to  which  it  is  subjected  there.  To  determine  this,  he 
fed  a  series  of  horses  during  a  certain  number  of  da}<s  with  a  certain 
amount  of  food  of  known  composition ;  the  animals  were  then  killed  at 
given  periods,  and  the  contents  of  the  intestine  examined. 

The  results  of  these  experiments  showed  that  they  might  be  divided 
into  four  groups,  according  to  the  nature  of  the  food  given. 


DIGESTION   IN   THE  LARGE  INTESTINE. 


427 


FIG.  164.— C-S:CUM  OF  THE  HORSE.    (Colin.) 
A,  caecum ;  B,  ileum ;  C,  colon. 


428  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

Thus,  when  dried  peas  are  given,  traces  of  them  are  to  be  found  in 
the  caecum  after  the  lapse  of  twelve  hours.  After  twenty -four  hours 
grain  and  dry  forage  are  still  to  be  found  in  the  caecum,  and  after  thirty 
hours  chopped  hay  still  remains  in  the  caecum.  After  seventy -two  hours 
the  greater  part  of  the  hay  had  alread}^  passed  into  the  colon.  Thus,  in 
resume,  twelve  hours  after  feeding,  forage  is  to  be  found  in  the  stomach, 
with  some  traces  in  the  jejunum  and  caecum;  after  twenty-four  hours, 
principally  in  the  caecum,  with  a  certain  amount  of  residue  in  the  jejunum  ; 
after  forty-eight  hours,  in  the  ventral  colon,  with  some  debris  in  the 
caecum;  after  seventy-two  hours,  in  the  dorsal  colon;  and  after  ninety 
hours,  in  part  in  the  dorsal  colon  and  rectum. 

As  regards  the  functions  of  the  caecum,  it  would  appear  that  after 
twelve  hours  already  traces  of  food  are  to  be  found  in  the  caecum,  and 
after  twenty -four  hours  nearly  all  the  alimentary  mass  has  arrived  at  the 
caecum,  in  which  some  is  still  to  be  found  after  forty -eight  hours.  Food, 
therefore,  usually  remains  twent3r-four  hours  in  the  caecum  of  the  horse. 
The  contents  are  always  alkaline,  highly  fluid,  and  of  a  special  odor. 
The  color  varies  with  the  nature  of  the  food. 

From  the  fact  that  a  larger  amount  of  undigested  food  is  found  in 
the  caecum  than  in  the  colon,  it  follows  that  digestion  must  take  place  in 
the  caecum,  its  extent  being  placed  by  Ellenberger  at  from  10  to  30  per 
cent,  of  the  food  ;  the  nature  of  this  action  is  determined  by  examination 
of  the  caecal  contents. 

The  acid  reaction  of  the  stomach  and  upper  portion  of  the  intestine 
gives  place  to  an  alkaline  reaction  in  the  lower  portion  of  the  ileum,  and 
that  of  the  caecum  is  invariably  alkaline.  In  the  colon,  again,  the  reac- 
tion may  become  acid  from  fermentative  changes  in  food. 

Digestive  changes  are,  therefore,  merely  the  continuation  of  the 
ordinary  intestinal  digestion. 

Bureau  has  succeeded  in  obtaining  a  secretion  from  the  caecum  of 
the  rabbit,  but  in  such  small  amount  as  contrasted  with  the  quantity  ob- 
tained from  the  small  intestine  by  the  same  method  (double  ligature)  that 
he  concludes  that  the  digestive  processes  occurring  in  the  caecum  are  due 
to  the  action  of  the  intestinal  fluids  which  come  down  from  above. 

In  the  duck,  however,  by  ligating  the  caecum,  after  introducing  small 
fragments  of  cooked  meat,  a  large  amount  of  clear  alkaline  fluid  may  be 
obtained,  although  the  morsel  of  meat  will  have  remained  unaltered. 
This  fluid  is  said  to  have  the  power  of  converting  starch  into  sugar,  but 
is  without  action  on  other  food-stuffs. 

By  making  caecal  fistulae  in  rabbits,  Bureau  found,  in  the  first  place, 
that  the  reaction  was  invariably  alkaline.  Raw  meat  appeared  to  be 
unchanged  in  the  caecum,  while  cooked  meat  becomes  somewhat  softened 
and  reduced  in  volume.  Boiled  starch  is  converted  into  sugar. 


DIGESTION   IN  THE  LAKGE  INTESTINE.  429 

Ligation  of  caeca  in  chickens  caused  diarrhoea,  loss  of  flesh,  and 
death  from  inanition. 

The  most  important  function  of  the  crecum  is,  in  all  probabilit}^,  to 
be  found  in  the  digestion  of  cellulose,  which  occurs  in  it.  It  is  well 
known  that  from  30  to  40  per  cent,  of  cellulose  disappears  in  passing 
through  the  intestinal  canal  of  the  horse,  and  the  poorer  the  food  is  in 
true  nutritive  substances  the  greater  will  be  the  amount  of  cellulose 
digested.  Experiment  has  proven  that  the  saliva,  gastric  juice,  and 
pancreatic  secretion  are  entirely  inactive  on  cellulose.  On  the  other 
hand,  the  fluids  collected  from  the  small  intestine  of  a  newly  killed 
horse  have  been  found  to  dissolve  from  40  to  78  per  cent,  of  cellulose 
(Hofmeister),  and  this  power  is  lost  when  these  fluids  are  previously 
boiled,  indicating  the  probable  dependence  of  this  digestive  process  on  a 
true  ferment.  Admitting  these  facts,  the  share  which  the  caecum  bears 
in  digesting  cellulose  is  evident;  it  acts  as  a  reservoir  for  fluids  and 
undigested  food-stuffs  coming  down  from  above,  and  by  its  reaction, 
temperature,  etc.,  favors  fermentative  changes. 

The  nature  of  the  substances  resulting  from  the  digestion  of  cellu- 
lose are  clouded  in  obscurity  :  the  most  natural  presumption  would  be 
that  it  was  converted  into  sugar,  but  no  experimental  proof  of  this  has 
ever  been  adduced,  though  it  is  generally  assumed  that  the  cellulose  in 
digestion  is  changed  into  some  nutritive  substance,  which  is  absorbed. 
According  to  this,  cellulose  should  be  classed  among  the  food-stuffs. 
Unfortunately,  this  also  does  not  admit  of  proof.  It  is  well  known  that 
in  fermenting  cellulose  may  be  converted  into  marsh-gas,  and  Hofmeis- 
ter's  experiments  seem  to  prove  that  the  substance  resulting  from  the 
digestion  of  cellulose  by  the  intestinal  fluids  of  the  horse  is  gaseous  in 
nature.  While  this  may  be  so,  and  there  is  no  denying  that  the  gas  may 
be  met  with  in  the  alimentary  canal,  it  does  not  follow  that  all  the 
digested  cellulose  is  converted  into  marsh-gas.  For,  as  Ellenberger  has 
pointed  out,  we  often  meet  with  a  lactic  acid  fermentation  of  sugar  in 
the  stomach  and  intestine,  but  do  not  infer  from  that  that  all  the  sugar 
which  disappears  from  the  alimentary  canal  has  been  converted  into 
lactic  acid.  The  case  may  be  similar  with  cellulose  ;  when  in  excess,  or 
not  needed,  it  may  and  probably  is  converted  into  marsh-gas;  when 
needed  by  the  economy,  it  is  absorbed  in  some  soluble  form,  probably  of 
the  nature  of  a  sugar.  This  view  is  supported  by  the  fact  already 
alluded  to,  that  the  poorer  the  food  the  greater  the  quantity  of  cellulose 
which  disappears. 

2.  THE  FUNCTIONS  OF  THE  COLON. — The  colon  in  the  carnivora  con- 
stitutes a  simple  reservoir  for  excrementitious  matters,  and  in  the  her- 
bivora  it  is  doubtful  if  it  has  a  more  important  role  to  perform  in  the 
digestive  elaboration  of  food.  In  the  walls  of  the  large  intestine  are 


430 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


found  follicular  glands,  apparently  similar  to  those  in  the  small  intestine, 
and  which  furnish  a  secretion  which  it  is  claimed  will  turn  starch  into 
sugar  and  albumen  into  peptone.  The  latter  statement,  which  is  made 
by  Thanhoffer,  seems  to  need  confirmation.  It  is,  at  any  rate,  clear  that 
the  degree  of  digestion  occurring  in  the  large  intestine  must  be  slight, 
since  the  greater  part  of  the  food-stuffs  which  reach  the  large  intestine 
have  already  undergone  complete  solution  in  the  upper  portion  of  the 
alimentary  canal.  In  the  large  intestine  in  carnivora  the  contents  of  the 


FIG.  165.— CAECUM  AND  GREAT  COLON  OF  THE  HORSE.    (Strangeways.) 

A,  caecum:  B  C,  its  muscular  bands;  D,  termination  of  ileum;  E,  first,  E',  second,  F,  third,  and 
F',  fourth  divisions  of  colon  :  G,  pelvic  flexure  ;  H,  origin  of  floating  colon.  The  arrows  indicate  the 
course  of  the  food  through  the  colon. 

alimentary  tube  undergo  no  further  digestive  changes,  but  become  more 
condensed  from  the  rapid  absorption  of  water  and  other  fluids  which 
takes  place  through  its  walls.  In  the  solipedes  the  large  intestine  is  par- 
ticularly active  as  an  absorbent,  removing  water  and  various  fluids 
secreted  by  the  upper  portions  of  the  alimentary  tube  and  the  alimentary 


DIGESTION   IN   THE  LARGE   INTESTINE. 


431 


principles  which  have  escaped  absorption  in  the  small  intestine.  Its 
enormous  capacity,  five  or  six  times  that  of  the  stomach,  enables  it  to 
retain  immense  quantities  of  materials  which  move  slowty,  and  which 


FIG.  166,— INTESTINAL  CANAI,  OF  THE  Ox.    (Mitller.) 

a,  duodenum  :    6  and  r,  jejunum  and  ilenm  :    d,  caecum  ;    e,  colon,  with  its  various  convolutions :  /,  rectum ; 
g,  commencement  of  colon  ;  TO,  mesentery  of  large  intestine;  m>,  mesentery  of  small  intestine. 

are  brought  in  contact  with  an  immense  extent  of  mucous  membrane. 
The  contents  enter  by  a  narrow  and  valvular  opening,  and  descend  first 


432  PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 

to  the  substernal  curvature,  then  they  mount  to  the  pelvic  curvature, 
which  is  always  higher  than  the  sternal  curvature,  and  then  up  the  dia- 
phragmatic curvature,  and  finally  descend  abruptly,  passing  by  the  left 
kidney  to  enter  the  convolutions  of  the  floating  colon,  where  they  make 
two  ascents  and  two  descents  (Fig.  165). 

The  large  intestine  of  the  ox  is  shown  in  Fig.  166. 

The  interior  arrangement  of  the  colon  consists  in  the  formation  of 
pockets,  in  which  portions  of  the  contents  remain  temporarily,  while  the 
centre  of  the  gut  is  free.  The  disposition  of  certain  parts  of  the  colon 
leads  to  a  difference  in  the  physical  characters  of  its  contents  at  different 
points.  The  diaphragmatic  curvature,  on  account  of  its  dependent  posi- 
tion, contains  large  volumes  of  liquid,  in  which  certain  salts  are  abundant, 
such  as  ammonio-phosphate  of  magnesium,  especially  after  oat  diet,  and 
in  this  localit}7  these  salts  are  often  deposited  as  intestinal  calculi. 

Digestion  in  the  large  intestine  caunot,  therefore,  be  said  to  take 
place,  although  absorption  is  highly  active,  and  numerous  cases  are  on 
record  in  which  life  has  been  preserved  through  the  absorption  by  the 
walls  of  the  large  intestine  alone  of  alimentary  substances  introduced 
into  the  rectum.  In  the  large  intestine  complex  fermentations  take 
place,  and  true  decomposition  frequently  occurs  in  the  contents  of  this 
portion  of  the  alimentary  tube,  especially  when  the  reaction  is  alkaline. 
Man}^  of  the  gases,  such  as  oxygen  and  nitrogen,  which  are  found  here 
have  probably  entered  with  the  food ;  others  are  derived  from  different 
fermentations ;  thus,  for  example,  hydrogen  is  liberated  in  the  butyric 
acid  fermentation,  sulphuretted  hydrogen  and  ammonia  from  the  putre- 
faction of  animal  substances. 

XI.   THE  COMPARATIVE  DIGESTIBILITY  OF  DIFFERENT  FOOD-STUFFS. 

The  quantity  and  chemical  composition  of  the  faeces  is  of  special 
interest  on  account  of  the  insight  which  it  permits  as  to  the  degree  of 
digestibility  and  convertibility  of  the  different  food-stuffs,  for  it  is  evi- 
dent that  if  we  know  the  amount  and  composition  of  any  food  given  to 
an  animal  for  a  series  of  days,  the  loss  of  these  materials,  determined  by 
an  analysis  of  the  faeces,  will  indicate  within  certain  limits  the  amount 
which  has  been  digested  and  absorbed  in  its  passage  through  the  bod}-. 
In  making  these  calculations,  however,  it  must  be  remembered  that  a 
large  amount  of  fluid  is  added  to  the  food  in  the  form  of  the  digestive 
juices,  which,  to  be  sure,  is  again  largely  absorbed ;  but  we  have  further 
seen  that  certain  excretory  ingredients  have  been  added  to  the  faeces, 
and,  further,  that  the  different  food-stuffs  may  undergo  decompositions 
other  than  digestive  in  the  alimentary  tract.  The  digestive  processes, 
as  we  have  seen,  are  of  the  same  nature  in  all  our  domestic  animals, 
simply  varying  in  degree.  This  difference  we  have  also  seen  to  be  due  to 


COMPARATIVE  DIGESTIBILITY  OF  FOOD-STUFFS.  433 

the  different  degrees  of  perfection  with  which  mastication  is  accom- 
plished, to  differences  of  construction  in  the  alimentary  canal,  different 
constitutions,  and  the  different  degrees  of  concentration  of  the  digestive 
juices.  Thus,  the  herbivora,  through  the  high  development  of  their 
molar  teeth,  the  roomy  and  long  digestive  eanal,  and  large  amounts  of 
amylolytic  ferments  in  their  digestive  secretions,  are  especially  suited  for 
digesting  carbol^drates.  Their  gastric  juice  is  comparatively  poor  in 
acid,  and,  as  a  consequence,  prevents  their  living  on  a  highly  albuminous 
diet ;  while  the  highly  alkaline  nature  of  their  intestinal  contents  facili- 
tates putrefactive  changes  in  albuminoids,  the  characteristic  results  of 
such  fermentations  being  met  with  in  large  amounts  in  their  urine.  In 
the  carnivora,  on  the  other  hand,  we  find  a  short  and  less  capacious 
intestinal  canal,  with  a  relatively  voluminous  stomach  and  an  active  acid 
gastric  secretion,  thus  fitting  them  for  the  digestion  of  albumen,  while 
the  conditions  for  the  digestion  of  carboh}rdrates  are  less  favorable. 

Omnivora  naturally  occupy  a  mean  between  these  two  classes.  It 
is  to  be  remembered,  however,  that  as  long  as  animals  are  fed  on  their 
mothers'  milk  there  is  no  difference  in  the  digestive  act  in  the  carnivora 
or  in  the  herbivora. 

Not  all  the  nutritive  substances  which  are  contained  in  the  food  are 
actually  digested,  but  a  considerable  proportion,  under  the  most  favorable 
circumstances,  is  apt  to  remain  undigested  and  pass  unchanged  into  the 
faeces.  The  cause  of  this  is  frequently  to  be  found  in  the  fact  that  the 
food  is  taken  in  such  quantities  that  the  amount  of  digestive  secretion 
poured  out  by  the  alimentary  tract  is  insufficient  to  act  upon  it.  There 
appears  to  be,  again,  a  limit  of  absorbability  even  of  the  amount  of  food 
digested.  This  limit,  of  course,  varies  in  each  group  of, animals,  and  the 
residue  of  food,  even  though  it  may  be  digested,  remains  unabsorbed  in 
the  alimentary  canal  to  undergo  breaking  down  into  various  decompo- 
sition products,  such  as  leucin,  tyrosin,  etc.  Again,  another  cause  for 
indigestibilit}'  of  food  is  to  be  found  in  the  fact  that  in  many  cases, 
especially  in  the  food  of  the  herbivora,  the  nutritive  principles  are  con- 
tained in  resisting  envelopes  which  are  impermeable  to  the  digestive 
secretions,  and  which  require  mechanical  comminution  in  mastication 
before  being  accessible  to  the  act  of  digestion.  Imperfect  mastication, 
therefore,  from  whatever  cause,  will  reduce  the  digestibility  of  food.  By 
this  term,  digestibility  of  food,  is  meant  the  amount  of  any  food-stuff 
which  through  digestion  is  rendered  capable  of  absorption  and  does 
actually  enter  the  blood,  in  proportion  to  the  amount  which  remains 
undigested  or  which  is  not  so  absorbed.  This  quantity,  which  may  be 
termed  the  co-efficient  of  digestion,  varies  according  to  the  composition 
of  food  and  to  the  mode  of  digestion  of  different  classes  of  animals.  We 
will,  therefore,  allude  to  these  sources  of  variation  in  turn  : — 


434  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

First.  Vegetable  fibre  is  capable  of  being  digested  to  a  more  or 
less  degree  by  all  herbivora  and  even  to  a  certain  extent  by  the  hog,  the 
co-efficient  of  digestion  lying,  in  green  and  dry  fodders,  between  45  and  75 
per  cent.  In  vegetable  foods,  such  as  grains,  roots,  and  bulbs,  and  the 
artificial  nutritive  substances  made  from  such  materials,  all  of  which  are 
rich  in  cellulose,  the  digestibility  becomes  greatly  reduced,  and,  in  fact, 
many  such  products  may  be  said  to  be  entirely  undigestible.  It  is  prob- 
able, again,  as  already  mentioned,  that  a  certain  amount  of  cellulose 
which  disappears  in  its  passage  through  the  intestinal  canal  may  be  ex- 
plained as  due  to  the  development  of  carburetted  hydrogen  and  carbon 
dioxide  and  other  fermentations. 

Second.  The  non-nitrogenous  extractive  matters,  as  found  in  beets 
and  potatoes  and  seeds,  are  almost  completely  digested,  only  about 
2  per  cent,  escaping  the  action  of  the  digestive  fluids,  though  in  green 
fodders  the  digestive  co-efficient  of  these  materials  may  sink  from  84  to 
48  per  cent.  In  this  connection  the  remarkable  fact  appears  that  the 
amount  of  soluble  non-nitrogenous  food-constituents  which  undergoes 
digestion,  together  with  the  amount  of  cellulose  which  is  digested,  almost 
exactly  equal  the  total  sum  of  non-nitrogenous  extractive  matters  found 
in  the  food,  and  in  this  we  have,  therefore,  a  means  of  estimating  the 
quantity  of  non-nitrogenous  extractive  matters  actually  digested  and 
absorbed.  The  digestible  portion  of  the  non-nitrogenous  extractive 
matters  in  any  food  may  be  estimated  in  nutritive  value  as  pure  carbo- 
hydrate, and  therefore  compared  with  starch. 

Third.  As  regards  fat,  it  may  be  stated  that,  when  perfectly  pure, 
fat  is  entirely  digested,  but  since  fat  in  the  ordinary  foods  is  not  pure 
and  contains  other  indigestible  constituents,  it  is  evident  that  the  digest- 
ive co-efficient  of  fat  will  be  subject  to  great  variation.  In  clover  and 
various  oil-cakes  this  co-efficient  varies  between  80  and  90  per  cent.;  in 
seeds,  between  60  and  90  per  cent.  In  beets  and  potatoes  fat  may  be 
regarded  as  entirely  digested,  while,  on  the  other  hand,  the  fat  in  green 
foods,  although  present  in  smaller  amount,  still  varies  in  digestibility 
through  very  wide  limits.  Thus,  80  per  cent,  may  be  absorbed,  or  only 
20  per  cent.  In  general,  in  this  connection,  clover  is  more  readily 
digested  than  grasses,  while  straw  of  the  hulled  fruits  is  more  digestible 
than  the  straw  of  the  hulled  cereals. 

Fourth.  The  nitrogenous  constituents  of  the  food  are  generally 
regarded  as  albumen,  although,  of  course,  other  nitrogenous  materials 
are  often  constituents  of  foods.  In  beets  and  potatoes  albuminous 
matters  are,  as  a  rule,  entirely  digested,  in  seeds  a  certain  amount 
escapes,  the  co-efficient  of  digestion  varying  from  60  to  90  per  cent.  In 
green  and  dried  fodder  great  variation  is  met  with,  the  co-efficient  of 
absorption  varying  between  17  to  75  per  cent.,  as  a  rule,  the  digestibility 


COMPAKATIYE  DIGESTIBILITY  OF   FOOD-STUFFS.  435 

of  albuminous  matters  being  greater  in  the  green  than  in  the  dry  fodder, 
even  though  of  the  same  material ;  while  still  further  the  statement 
may  be  made  that  the  larger  the  relative  proportion  of  albuminous  matter 
and  the  smaller  the  amount  of  the  cellulose,  the  greater  will  be  the  amount 
of  albuminous  matter  digested. 

Fifth.  The  digestive  co-efficient  of  the  different  food-stuffs  may  be 
altered  through  the  addition  to  the  food  of  different  nutritive  substances. 
Thus,  it  has  been  shown  that  the  administration  of  a  readily  digestible 
albuminous  diet  is  without  influence  on  the  co-efficient  of  digestion  of 
the  other  foods;  but,  on  the  other  hand,  the  addition  of  starch  or  sugar 
will  reduce  the  digestive  co-efficient  of  the  albuminous  bodies  when  the 
amount  of  carbohydrates  given  exceeds  by  15  per  cent,  the  solids  of  the 
other  food-stuffs.  This  depression  of  digestibility  is  especially  marked 
in  the  dry  foods.  A  similar  result  is  also  manifested  when  beets  and  pota- 
toes are  added.  The  addition  of  oil  is  without  influence  on  the  digestive 
co-efficient  so  long  as  it  is  not  given  in  great  amounts.  When  the  amount 
given  exceeds  the  proportion  of  one-tenth  gramme  to  one  kilogramme  of 
body  weight,  slight  disturbances  of  digestibility  are  readily  produced. 
When  the  food  is  composed  of  several  nutritive  substances  combined, 
the  proportion  of  the  nitrogenous  and  the  non-nitrogenous  constituents 
of  the  total  amount  is  of  great  influence  on  the  digestibilit}^  This 
nutritive  relationship  of  the  non-nitrogenous  substances  is  found  by 
adding  the  amount  of  fat  to  the  sum  of  the  non-nitrogenous  extractive 
matters,  the  amount  of  cellulose  being  excluded.  Ordinarily  the  amount 
of  fat  is  multiplied  by  two  and  four-tenths  or  two  and  five-tenths,  and 
this  product  then  added  to  the  amount  of  extractive  matters, — a  pro- 
cedure which  is,  however,  apt  to  give  an  erroneous  idea  as  to  the  nutri- 
tive value  of  the  fat. 

The  general  result  may  be  stated  that  a  food  is  readily  digestible 
when  the  proportion  between  nitrogenous  and  non-nitrogenous  con- 
stituents varies  from  1  : 5  to  1 :  7.  An  increase  of  this  proportion  causes 
a  certain  amount  of  the  non-nitrogenous  constituents  to  remain  undi- 
gested while  an  increase  of  the  nitrogenous  substances  causes  a  waste. 
It  is  evident  that  the  above  statement  as  to  the  digestibility  of  food  may 
be  only  regarded  as  in  general  true.  Each  group  of  animals  will  possess 
special  facilities  for  digesting  special  foods ;  these  will  deserve  considera- 
tion in  turn. 

As  might  be  expected,  the  time  required  for  undigested  food  to 
appear  as  faeces  after  feeding  very  closely  corresponds  in  different 
animals  with  the  comparative  length  of  the  intestinal  canal.  Thus,  it 
has  been  found  that  in  oxen  fed  with  oat-straw  the  first  traces  appear  in 
the  fneces  about  thirty-six  hours  after  feeding,  and  disappear  after  seventy- 
two  to  ninety-six  hours,  while  in  the  goat  seven  days  were  required  after 


436  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

giving  certain  food  for  its  traces  to  disappear  from  the  faeces.  In  the  calf 
three  days  were  required  for  the  removal  of  traces  of  a  previous  meal  of 
barley,  while  four  days  'were  required  for  an  ox  under  the  same  condi- 
tions. In  the  sheep  fed  with  hay,  it  has  been  determined  that  the  food 
remains  20  hours  in  the  first  three  stomachs,  and  in  the  fourth  stomach 
1.2  hours;  in  small  intestine,  2.3  hours;  in  caecum,  7  hours;  and  in  colon, 
5.5  hours;  or,  in  all,  36  hours  before  appearing  as  faeces. 

Carnivora  fed  on  pure  flesh  diet  produced  but  little  faeces.  A  dog 
weighing  thirty-five  kilos,  and  fed  with  a  half  to  two  and  a  half  kilos  of 
meat,  produces  from  twenty-seven  to  forty  grammes  of  faeces,  in  which 
there  will  be  only  nine  to  twenty-one  grammes  of  solids ;  therefore  it 
may  be  said  that  with  a  flesh  diet  only  1  per  cent,  of  the  amount  of  solids 
taken  with  the  food  escapes  from  the  body  in  the  form  of  faeces. 

Omnivora  form  considerably  larger  amounts  of  faeces.  Animals 
living  on  a  mixed  animal  and  vegetable  diet,  like  man,  will  pass  daily 
about  one  hundred  and  thirty  grammes  of  faeces,  containing  thirty-four 
grammes  of  solids,  which  will  represent  about  5  per  cent,  of  the  solids 
taken  as  food.  When  the  vegetable  diet  is  in  excess,  this  may  rise  to 
13  per  cent.,  so  that  only  seven-eighths  of  the  solids  are  finally  absorbed. 
Hogs  pass  in  their  faeces  only  about  20  per  cent,  of  mixed  matter  taken 
in  food.  However,  when  fed  on  sour  milk,  with  beans  and  peas,  only 
about  1  per  cent,  escapes  absorption.  So,  also,  according  to  Wolff,  pigs 
digest  almost  completely  the  residue  remaining  after  making  meat  ex- 
tracts. The  hog  is  able  to  digest  both  vegetable  and  animal  matter, 
and  is  claimed  to  be  capable  of  digesting  fully  50  per  cent,  of  cellulose. 

The  following  table  gives  the  percentage  of  constituents  absorbed  in 
hogs  fed  with  sour  milk : — 

Albumen, 96.06  percent. 

Non-nitrogenous  substances,          .        .        .98.90      " 
Inorganic  matter, 64.46      " 

So,  also,  of  the  following  vegetable  foods,  the  figures  indicate  the 
amount  digested  and  absorbed  : — 


Horse-beans, 
Peas, . 
Oats,  . 
Barley, 
Rye,  . 


99.8  per  cent. 
99.7      " 
98.7      " 
92.7       " 
90.7      " 


The  largest  amount  of  faeces  is  formed  by  the  herbivorous  animals. 
In  the  horse  and  ox,  of  one  hundred  parts  of  food  about  40  per  cent.,  as 
a  rule,  escapes  unchanged  in  the  faeces,  so  that  only  three-fifths  of  the 
food  swallowed  serves  any  nutritive  purpose.  This  follows  from  the 
fact  that  a  large  part  of  vegetable  food  is  absolutely  indigestible,  and  all 
is  very  difficult  of  digestion.  The  horse,  as  a  rule,  digests  a  smaller  pro- 
portion of  dry  fodder  than  does  the  ox. 


COMPAKATIVE  DIGESTIBILITY  OF  FOOD-STUFFS.  437 

•    As  a  rule,  it  may  be  stated  that  the  ox  is  capable  of  digesting  the 
following  amounts:  — 


Albuminoids.  Cellulose. 

Oats,         .  49  per  cent.  55  per  cent.  44  per  cent. 

Wheat-straw,  26  52  39 

Bean-straw,  51        "  36      •"  62 

Clover-straw,  51       «'  39       ««  67 

Barley-hay,  60       "  60       '*  67       " 

Henneberg  has  found  that  the  digestibility  of  a  fodder  is  altered 
when  a  second  nutritive  substance  is  added  to  it.  Thus,  the  digestibility 
of  any  fodder  is  reduced  by  the  addition  of  starch,  while,  on  the  other 
hand,  the  addition  of  fat  facilitates  the  digestion  of  albuminoids  and 
cellulose.  In  general,  it  may  be  stated  that  the  digestibility  of  any  dry 
fodder  is  decreased  by  the  addition  of  any  readily  digestible  substance, 
such  as  albumen,  starch,  sugar,  and  in  ordinary  fattening  diet  a  loss  of 
at  least  20  per  cent,  of  nutritive  substances  may  be  calculated.  This 
author's  experiments  have  further  shown  that  at  least  five  days  are 
required  after  the  change  of  diet  before  the  traces  of  indigestible  food 
are  removed  from  the  faeces,  and  that  the  removal  of  the  residue  of 
prairie  haj^  occurred  about  thirty  hours  before  that  of  wheat-straw.  In 
the  calf,  experiments  have  been  made  to  determine  the  digestibility  of 
cereals  and  grains  taken  whole,  with  the  following  results:  — 

Oats.         Flaxseed.       Barley.         Wheat. 

Digested,         .        .'      .     91.4  58.2  94.6  36.3 

.        .        .     91.5  57.4  94.9  36.7 

In  the  sheep  the  same  results  have  been  obtained  as  in  the  ox.  An 
addition  of  starch  or  sugar  to  the  food  diminishes  considerably  the 
digestibility  of  the  albumen  and,  when  in  small  amount,  of  the  cellulose 
also.  Pure  albumen  has  slight  influence  on  the  digestibility  of  the  food. 
Substances  containing  sugar,  with  the  exception  of  beets,  are  almost 
entirely  digested,  while  in  potato-starch  80  per  cent,  is  digestible,  and  fat, 
when  added  to  fodder,  is  usually  absorbed,  though  its  administration 
when  given  in  large  amounts  interferes  with  the  digestion  of  cellulose. 

According  to  Wildt,  lambs  which  were  fed  with  barley-straw,  and 
then  the  residue  from  meat  extracts,  absorbed  95  per  cent,  of  the  latter. 
Experiments  on  the  horse  have  also  proved  that  this  animal  is  capable  of 
digesting  cellulose  to  about  50  per  cent.  In  comparison  with  the 
ruminants,  the  horse  is  less  capable  of  digesting  all  the  constituents  of 
hay.  The  loss  in  the  horse,  as  in  other  herbivora,  is  much  greater  than 
in  the  carnivora.  The  carnivora  may  be  said,  as  a  rule,  to  absorb  about 
98  per  cent,  of  albuminous  matter  given  in  the  food.  In  a  man  fed  on 
milk  and  meat  diet  only  2J  to  10  per  cent,  escapes  in  the  faeces  ;  with 
vegetable  diet,  rice,  bread,  and  potatoes,  the  loss  may  amount  to  30  per 


438  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

cent.,  though  the  carbohydrates  are  almost  completely  absorbed,  only 
1  per  cent,  being  lost,  and  only  5  per  cent,  of  fats  escapes  absorption.  In 
the  herbivora  the  loss  is,  however,  much  greater.  Thus,  a  horse  fed  with 
six  kilos  of  oats  and  fifteen  liters  of  water  will  pass  about  twelve  kilos 
of  faeces,  composed  of  three  kilos  of  solids,  containing  5  per  cent,  of 
albuminous  matter,  20  per  cent,  of  fat,  20  per  cent,  of  starch,  and  60  per 
cent,  of  cellulose.  If  the  horse  is  fed  with  a  mixed  diet,  composed,  for 
example,  of  three  and  a  half  kilos  of  oats,  five  and  a  half  kilos  of  hay, 
and  one  and  three-fourths  kilos  of  chopped  straw,  seventeen  kilos  of 
faeces  will  be  passed,  in  which  there  will  be  four  kilos  of  solids,  of  which 
30  per  cent  will  be  albuminous  matter,  40  per  cent,  fats,  30  per  cent, 
starch,  and  60  per  cent,  cellulose  having  escaped  digestion.  The  loss 
is,  therefore,  greater  in  a  mixed  diet  than  in  a  horse  fed  on  grain 
alone.  In  the  ruminants  the  digestibility  of  hay  is  much  greater  than 
in  the  horse.  Oxen  fed  with  ten  kilos  of  hay  will  digest  and  absorb 
about  50  per  cent,  of  the  albuminous  matter,  while,  as  already  mentioned, 
if  more  readily  digestible  substances  are  added  to  the  hay  diet,  less  hay 
will  be  digested. 

It  has  been  found  that  in  the  fermentation  of  cellulose  large  quanti- 
ties of  COa  and  CH4  are  formed,  and,  as  the  latter  gas  is  constantly  found 
in  the  intestine,  that  its  source  is  in  the  putrefaction  and  fermentation  in 
the  intestinal  canal  is  readily  conceivable,  and  indicates  a  possible  expla- 
nation of  the  fact  that  about  40  to  60  per  cent,  of  cellulose  disappears 
in  the  intestinal  canal.  This  may  occur  in  the  rumen  of  the  ruminants, 
while  it  certainly  occurs  in  the  caecum  of  the  horse,  although  in  this 
animal  less  cellulose  disappears  than  in  the  ruminant. 

As  regards  the  inorganic  constituents  of  the  food,  the  fact  that  the 
faeces  contain  but  small  amounts  of  soluble  salts  shows  that  they  must 
have  been  largely  absorbed.  Small  amounts  only  of  the  alkalies  are 
found  in  combination  with  chlorine  and  sulphuric  acid,  while  potassium 
and  sodium  are  found  in  combination  as  chlorides  or  sulphates  in  minute 
quantities.  Magnesium  is  also  almost  entirely  absent.  In  the  herbivora 
less  lime  is  absorbed  than  magnesium,  while  in  the  carnivora  but  very 
small  quantities  of  both  lime  and  magnesium  are  absorbed.  Another 
point  of  contrast  between  carnivora  and  herbivora  is  that  in  the  former 
almost  all  the  phosphates  in  the  food  are  absorbed,  while  in  the  herbivora 
they  are  almost  entirely  excreted  in  the  faeces,  unless  they  are  fed  with 
meal,  milk,  or  other  readily  digestible  food. 

Mr.  E.  F.  Ladd  has  tested  the  relative  digestibility  of  the  different 
feeding  stuffs  by  digestion  experiments  performed  with  them,  after 
thorough  comminution,  with  an  artificial  gastric  juice,  formed  of  0.2 
per  cent,  hydrochloric  acid  with  five  grammes  of  pepsin  to  the  liter. 
The  following  tables  give  his  conclusions : — 


COMPARATIVE  DIGESTIBILITY  OF  FOOD-STUFFS. 

CO  CO  CO  tO  tO  to  tO  tO  tp  tO  tO    tOtOI— '»— >l— 'K- 'h-i|— 'I— 'I— 'I— »    I— •>'  I 


439 


3-§?  -§  II  i  S.S.i-i-s'S 


ooenoOtOtO 


ooooeno 
G  i—  H-^CO 


I— '  »— '  OS    i— '  I— ' 

00  00  00  00  OS  00  OS  CO  00  OS  CO 


bOOli—  '  t—  '*'(—  'H-  '1—  ' 


Water. 


tococoocccooot— 'i— coo        rf^entot— '^rcoas-<rO4^co        »-> 


H-1  o  co  co  o  as  to  as  co  bo  bo   bo  to  co  ^j  o  bo  o  as  '*-*  co  as   n-1 
-<r  o  co  i— co  >— o  co  ^r  oc  as   to  ^  en  >-*  4^  en  4*.  as  as  as  co   co 


t~*  P  ~ ' 

^.T  4^.  OO 

co  to  o 


Albuminoids, 
NX  6.25. 


;<r  co  co  j-i  to  to  j-i  ps  p  to  to   •  en  co  to  co  _en  co  co  to  4^  O   Cn  to  en  en  " 


CO  to 

-OiOo 


Crude  Fibre. 


enasasas-<r-<iasenenosas       "    tococoosasentoenenen  co  to  co  4^ "    *    co 

co  -<r  ~4  -<r  pi  co  p  co  to  co  po        •     H-  po  4s>  4^  to  oo  o  to  »4^  co        -<r  oo  o  en  i— '  •     •     t— ' 


•—  '  co  en  'CD  i—  •  ^<r  ^<r  I—1  o       to  to  o  en  co 
cooooit—  rf^oocotoco       to  cc  rf»-  oo  as 


co  co  co 
co  en 
-<r  to  bo 

CO  OO  rfi. 


Nitrogen- 
free 
Extract. 


t-*  1—  »  t-J  CO  CO  4*-  CO  4*-          CO  en 


•  to  to  po  -<r  j-1  as  4^-  en  co  to       {-•  j->  *->  to  to 

•  co  h-L  to  en  to  O  O  *-*  co  bo        J-*  co  co  o  o 
.     to  co  o  co  H-  oo  £  as  co  as        cnenoooos 


Fat,  Ether 
Extract. 


co  h- » j— i  j— » j-j  »— '  *— '  co  to  *— '  i— ' 
H—  O  ~J  en  i— '  ^i  oo 


as  ot  or  i—  '  »-* 


•    en  o  co  en  co  ^r  to  oo  co  i— ' 
i— 'coo       .    Oi^rcoototo4^astoto 


co  co  <r  as  co  •  •  as  h->  co 
i  --  1  •—  as  4^  .  .  H^CHO 


Ash. 


4*.  CO  CO    (-*  i— '  to  CO  k-i  ^-»      t-* 


to  »-» t— '  i-*   i— '  i— 1 1— >  to  i— '  >— ' 

co  CD  bo  to  bo  4^  bo  bo  co  t-o  co   ^r  to  co  en  en  ^i  en  o  bo  bo  bo 
H-'  co  -<r  en  ^i »—  ^j  ^j  H-I  en  ^   co  ^- ^r  o  o  en  o  as -4  i-*  ^r 


Albuminoids. 


co  »—  '  co  -<r  to 


to  bo  bi  bo  "4^.  co  o  co  en  co  bi 
cot—  'i—  *Go-<icotocooot—  >cn 


co  o  "co  i—  '  to  4*-  !—  '  O  as  *—  ' 
^-ascotooocoocoooco 


COtOC04^CO-  •  4i-4^CO 

to  po  en  co  as .  .  p  (-1  co 

4>  co  en  J-»  bo  .  .  ^<r  >-»  o 

ooenrf»-asco  t— '  i— » to 

•  •  o  o  en 


Crude  Fibre. 


to4^coasasosenenasas 
toooas4^^»4^toco 


oocn4iooco  o  co  >—  ' 

rf*.  CO  4*.  O  >—  '  '  Oi  en  »-» 
•   •   --7  CO  CO 


Nitrogen- 
free 
Extract. 


4*-  CO  Cn  en  CO 

CO  OO  4^  tO  CO  CO  CO  •» 


.  en  to  oo  oo  to  co  i—  >  en  4^  co 


ISD  to  to  co  co  to  to  co 

'  bo 


rfi.  <J  CD  Cn  4*.  4=»  OO 

oienooocot—  'os 


Fat,  Ether 
Extract. 


>_i  (_i  j_»  co  to  j-1 1-1   .  po  en  en  t-J  to 

.  o  'en  ^.T  bs  i-*  en  as  CD  en  o 

rf^rf5>coOOi— 'enrf^toco 


en  p  as  en  en .    .    en  4^  7<r 

co  bs  to  bs  bo  .    .    4*.  bo  H-' 
totocooco,    ^    cogg 


Ash. 


440 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


TABLE  No.  II. 
DIGESTED  BY  FLUID  FROM  HOG'S  STOMACH  (LADD). 


i*8 

06 

12 

£4 

1 

£> 

8 

|5 

P| 

HAY  AND  COARSE  FODDERS. 

Si 

S.| 

-g 

*j-2 

0  o 

o  %  £* 

C  g 

r^'3 

C  £>^ 

gg-s 

c-fll 

^Is 

|J 

«-! 

||| 

o|| 

fc 

£3« 

£^ 

£M 

IW 

£<*> 

1 

Clover-hay                 ^ 

1381 

1003 

3  62 

73  75 

63  91 

2 

Same,  exposed,  average,      .     . 

12.19 

9.38 

6.20 

49.23 

33.90 

3 

Same,  exposed,  poorest,  .     .     . 

13.84 

11.31 

7.09 

48.76 

37.31 

26 

Corn-meal    

1087 

831 

1  71 

8398 

7942 

10 

Ensilage,      

731 

446 

2  32 

68  90 

47  98 

TABLE  No.  III. 
DIGESTED  BY  PEPSIN  SOLUTION  (LADD). 


<   <M 

•d  o 

l^a 
|2l 

^&C§ 

44 

HAY  AND  COARSE  FODDERS. 

Per  Cent,  of  Crude 
Albuminoids,  N  X 
6.25. 

Per  Cent,  of  True 
Albuminoids. 

i 

& 

ii 

g 

PerCent.  of  Crude 
Albuminoids  Di- 
gested. 

Per  Cent,  of  True 
Albuminoids  Di- 
gested. 

4 

Clover-hay  . 

1453 

1003 

4  70 

6765 

53  14 

5 

Same,  steamed,     .... 

1434 

670 

5327 

6 

7 
8 

Hay,  ordinary,  mixed,   .     . 
Hay,  poor,  many  daisies,    . 
Fodder-corn,     ..... 

5.94 
5.94 

7.81 

'  5.44 
588 

2.09 
2.51 
289 

35.32 
57.69 
6300 

53.86 
5083 

9 

Soja-hispida 

1068 

956 

2"  57 

75  92 

73  11 

10 

Ensilage,      

731 

456 

282 

61  35 

3925 

11 

By-Products. 
Wheat-bran,     

1587 

1300 

265 

8327 

7961 

13 

Gluten  -meal,     

3287 

551 

8323 

14 

Starch-refuse    . 

21  06 

560 

7343 

'* 

15 

Starch  -feed 

J250 

1268 

489 

6080 

61  36 

16 
17 

18 
19 
20 
21 
21 

Corn-feed,  ground  germ,     .     . 
Corn-feed,  ground  hull,  .     .     . 
Linseed-meal,  old  process,  .     . 
Linseed-meal,  new  process, 
Cotton-seed  rneal,  
Same,  cooked,  
Ship-stuff 

10.75 
7.50 
34.50 
35.37 
43.21 
42.73 
1781 

33.13 
32.19 
40.25 

1681 

4.54 
2.28 
3.61 
7.62 
5.30 
11.19 
234 

57.98 
69.71 
89.52 
78.44 
87.73 
73.81 
87  86 

89.10 
76.33 
86.83 

86  08 

24 

Grams. 
Pea-rneal,     .     

2431 

2019 

275 

8869 

8638 

25 

Crushed  oats 

11  87 

1031 

2  15 

81  8° 

79  14 

26 

Corn  -meal 

1087 

8  31 

1  50 

86  15 

81  95 

27 

Corn-meal    .... 

1041 

764 

285 

7258 

6400 

28 

Same,  cooked,  .... 

987 

761 

3  64 

63  16 

52  17 

31 
29 

Wheat,  Clawson's  winter,    .     . 
Corn-meal,   

14.93 
1225 

8.81 
8  81 

1.93 
357 

87-07 
70-85 

78.09 
59  48 

30 

Same,  heated  

11  81 

8  81 

358 

69-79 

5935 

22 

Corn-meal,    

1237 

941 

3  87 

68-63 

5887 

23 

Same  cooked    .... 

11  25 

5  19 

4  44 

6053 

16  37 

.     32 

Bean,  navy  or  pea,    .... 

25.51 

22.06 

1.13 

95.59 

94.93 

COMPARATIVE  DIGESTIBILITY  OF  FOOD-STUFFS. 


441 


TABLE  No.  IV. 
DIGESTIBLE  CONSTITUENTS  OF  THE  FOOD  IN  PERCENTAGES  (KUHN). 


NOX-NITBOGEN- 

ALBUMEX. 

FAT. 

ous  EXTRACT- 

CELLULOSE. 

IVE  MATTERS. 

NAME  OF  THE 
FOOD. 

3 

d 

| 

3 

| 

3 

3 

3 

d 
§ 

| 

j 

3 

\ 

. 

s 
§ 

*$ 

d 

3  • 
J 

?3 

. 

"3 

i 

I 

0 

a 

i 

'3 

1 

§ 

o 

'c 

'* 
• 

2 

§ 

3 

S 

i 

a 

3 

i 

A 

s 

§ 

3 

s 

I.  Green  Fodders. 

Pasture-grass,    . 

70.6 

79.3 

75.0 

63.4 

68.1 

66.0 

74.5 

84.4 

79.0 

70.3 

75.2 

73.0 

Good     meadow- 

grass,     . 

69.0 

71.7 

70.Q 

60.4 

68.1 

65.0 

74.7 

84.4 

79.0 

65.4 

72.8 

69.0 

Clover,      .     .     . 

77.7 

78.7 

78.0 

63.3 

65.1 

64.0 

78.0 

78.5 

78.0 

66.9 

67.4 

67.0 

Lucern-clover,   . 

78.2 

83.2 

81.0 

37.0 

53.6 

45.0 

61.1 

76.9 

72.0 

31.6 

46.8 

41.0 

Esparcet,  .     .    . 

71.7 

73.3 

73.0 

64.1 

69.2 

67.0 

76.5 

80.0 

78.0 

42.1 

42.3 

42.0 

Lupines,    .     .     . 

73.0 

75.7 

74.0 

15.5 

45.3 

30.0 

57.3 

65.9 

62.0 

67.1 

79.8 

73.0 

Potato-stalks 

(beginning  of 
October), 

420 

24.0 

60.0 

36.0 

Aspen-leaves,     . 

•   • 

•   • 

56.0 

•    • 

•    • 

79.0 

65.0 

•   • 

•    • 

35.0 

II.  Hay. 

Prairie-hay,  .     . 

38.9 

71.0 

57.0 

8.5 

69.7 

46.0 

48.0 

78.8 

63.0 

44.6 

72.4 

58.0 

Second-crop  hay, 

53.0 

68.0 

61.0 

27.0 

57.4 

46.0 

56.7 

75.0 

66.0 

54.3 

74.9 

63.0 

Clover-hay,    .     . 

43.0 

73.3 

60.0 

33.0 

75.3 

59.0 

62.5 

80.1 

69.0 

38.0 

59.2 

47.0 

Lucern-h'ay,  .     . 

72.1 

83.0 

77.0 

29.7 

51.0 

39.0 

52.6 

72.0 

65.0 

33.1 

45.7 

40.0 

73.0 

75.7 

74.0 

15.5 

45.3 

30.0 

57.3 

65.9 

62.0 

67.1 

79.8 

73.0 

Acidified     beet- 

leaves,  .    .     . 

•   • 

•   • 

65.0 

•    • 

60.0 

•    • 

•    • 

54.0 

•   • 

54.0 

III.  Straw. 

Wheat-straw 

r 

260 

270 

400 

52.0 

Rye-straw,     .     . 

2.6 

28.6 

25.0 

21.2 

40.9 

32.0 

28.5 

51.8 

36.0 

46.8 

72.9 

56.0 

Oat-straw,     .     . 

14.4 

50.0 

38.0 

14.0 

51.0 

30.0 

33.2 

47.0 

42.0 

53.0 

67.0 

61.0 

Barley-straw,     . 

12.8 

16.8 

15.0 

32.4 

42.6 

38.0 

50.7 

51.3 

51.0 

49.1 

55.6 

52.0 

Pea-straw,     .    . 

60.3 

60.6 

60.5 

41.6 

50.1 

46.0 

64.0 

64.8 

64.0 

47.2 

65.9 

52.0 

35.4 

39.7 

37.0 

25.4 

35.0 

30.0 

64.5 

65.4 

65.0 

49.2 

52.0 

51.0 

IV.  Cereals. 

Oats       (experi- 

ments      with 

ruminants),    . 

58.0 

81.3 

74.0 

68.4 

99.0 

82.0 

65.0 

79.7 

73.0 

5.5 

32.1 

21.0 

Crushed     barley 

(experiments 

with        rumi- 

nants), .     .     . 

. 

77.0 

100.0 

_ 

87.0 

. 

20.0 

Crushed        corn 

(experiments 

with  hogs),     . 

83.9 

88.1 

85.0 

74.4 

78.5 

76.0 

9.25 

96.3 

94.0 

17.0 

57.4 

34.0 

442 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


TABLE  No.  IV. 
DIGESTIBLE  CONSTITUENTS  OF  THE  FOOD  IN  PERCENTAGES. — (Continued.) 


NON-NITROGEN- 

ALBUMEN. 

FAT. 

OUS  EXTRACT- 

CELLULOSE. 

IVE  MATTERS. 

NAME  OF  THE 

• 

. 

FOOD. 

EJ 

a 

B 

S 

d 

a 

1 

a 

g 

a 

d 

1 

| 

j 

1 

£3 

j 

1 

J 

e 

'2 

| 

« 

fl 

rt 

& 

a 

1 

S 

a 

X 

• 

8 

§ 

s 

i 

s 

s 

S 

1 

55 

Crushed      beans 

(experiments 

with        rumi- 

nants), .     .     . 

80.6 

100.0 

90.0 

86.9 

100.0 

97.0 

90.7 

98.7 

94.0 

25.1 

100.0 

63.0 

Peas        (experi- 

ments      with 

hogs),    .     .     . 

84.4 

91.5 

88.0 

45.0 

69.0 

58.0 

94.7 

98.6 

97.0 

55.1 

88.5 

74.0 

Peas        (experi- 

.  ments       with 

sheep),   .     .     . 

95.5 

97.6 

97.0 

•    • 

•   • 

100.0 

77.0 

100.0 

90.0 

!  '  ' 

•    • 

•   • 

V.  Manufactured 

Products. 

Rape-seed    cake 

(experiments 

with  cows  and 

oxen),     .     .     . 

81.3 

92.4 

85.4 

79.7 

93.6 

88.0 

70.2 

84.9 

78.0 

. 

34.3 

11.0 

Rape-seed    cake 

(experiments 

with  sheep),    . 

65.3 

83.9 

75.9 

59.8 

77.2 

69.0 

66.0 

85.4 

78.0 

5.5 

3.0 

Linseed  cake  (ex- 

periments with 

oxen),     .     .     . 

80.2 

89.9 

87.0 

86.7 

93.9 

91.0 

85.0 

96.3 

91.0 

. 

54.5 

26.0 

Linseed  cake  (ex- 

periments with 
goats  &  sheep), 

80.0 

87.4 

83.0 

86.5 

92.5 

90.0 

60.0 

78.7 

71.0 

29.7 

92.9 

62.0 

Wheat-bran  (ex- 

periments with 

oxen),     .     .     . 

82.9 

93.5 

88.0 

77.6 

81.6 

80.0 

77.7 

81.2 

80.0 

16.9 

32.2 

20.0 

Wheat-bran  (ex- 

periments with 

sheep),    .     .     . 

75.0 

500 

700 

37.0 

Rye-bran      (ex- 

periments with 
pigs),      .     .     . 

65.8 

66.2 

66.0 

57.4 

57.6 

57.5 

74.2 

74.7 

74.5 

6.5 

10.5 

9.0 

Skimmed      sour 

milk     (experi- 

ments       with 

pigs), 

96.0 

. 

95.0 

99.0 

. 

p 

Meat  residue  (ex- 

periments with 

ruminants),     . 

m 

^ 

95.0 

; 

98.0 

f 

. 

4 

, 

.    . 

.   . 

Meat  residue  (ex- 
periments with 
pigs),      .     .     . 

95.1 

98.9 

96.0 

82.3 

90.7 

87.0 

-   - 

COMPARATIVE  DIGESTIBILITY  OF  FOOD-STUFFS. 


443 


TABLE  No.  V. 

DIGESTIBILITY   OF    THE    NUTRITIVE  PRINCIPLES    IN    FOOD-STUFFS    BY  DIF- 
FERENT ANIMALS  (POTT). 


NON  -NITROGEN- 

PKOTEIDS. 

FATS. 

OUS   EXTRACT- 

IVE MATTERS. 

FODDERS. 

' 

• 

g 

| 

g 

| 

jj 

g* 

| 

2 

53 

i    2 

| 

{« 

i 

| 

S3* 

1 

1 

1 

°8 

1 

§ 
« 

1 

1 

i 

S 

£ 

S 

;  i 

S 

s 

i 

s 

& 

A.  THE  RUMINANTS  digest  the  fol- 

lowing percentages  of  nutri- 

tive substances  :  — 

1.  (a)  Green  Foods:  Prairie-grass, 

clover,       lucern,       esparcet, 

vetches,   rye,   lupines,    corn, 

beans,    peas,    spurry,   white 

mustard,  rape-seed,  cabbage, 

beet-leaves. 

(6)  Hay  of   esparcet,  vetches, 
lucern,  and  lupines  

60.0 

81.0 

70.0 

50.0 

75.0 

60.0 

65.0 

79.0 

73.0 

2.  (a)  Green  Foods,  etc.  :  Prairie- 

grass  after  blossoming,  beet- 

leaves,  buckwheat. 

(6)  Prairie-hay,  clover-hay. 

(c)  Straw  of  beans,  peas,  and 

lentils 

40.0 

78.0 

60.0 

32.0 

62.0 

50.0 

54.0 

76.0 

65.0 

3.  Prairie  Grrummet  . 

58.0 

70.0 

64.0 

45.0 

68.0 

54.0 

62.0 

74.0 

67.0 

50.0 

72.0 

60.0 

46.0 

76.0 

60.0 

53.0 

67.0 

60.0 

5.  Straw    of   the    cereals,    rape, 

clover,  lupines,  potatoes,  .     . 

17.0 

48.0 

27.0 

20.0 

49.0 

35.0 

35.0 

60.0 

44.0 

6.  (a)  Roots  and  Bulbs:  All  sorts 

of  beets,  potatoes,  etc. 

(6)  Residue  from  manufacture 

of  spirits,  starch,  and  sugar, 

etc.,  

51.0 

86.0 

65.0 

.    . 

.  . 

•    • 

89.0 

96.0 

93.0 

68.0 

86.0 

78.0 

67.0 

97.0 

82.0 

67.0 

91.0 

86.0 

Malt,    

81.6 

49.0 

87.6 

Brewers'  grains,     .     ,     .^  .     . 

73.0 

* 

84.0 

64.0 

Acorns,    

83.0 

87.5 

91.4 

8.  Hulled  Fruits,  

81.0 

95.0 

91.0 

66.0 

100.0 

86.0 

84.0 

99.0 

92.0 

9.  Fodder  Cakes  :  Rape-seed  cake, 

unshelled    ground-nuts,    un- 

shelled  cotton-seed  and  other 

oil-cakes  and  oil-cake  meals,  . 

74.0 

90.0 

81.0 

69.0 

91.0 

88.0 

46.0 

85.0 

70.0 

444 


PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 


TABLE  No.  V. 

DIGESTIBILITY   OP   THE    NUTRITIVE    PRINCIPLES    IN   FOOD-STUFFS   BY   DIF- 
FERENT ANIMALS. — (Continued). 


FODDERS. 

PROTEIDS. 

FATS. 

NON-NITROGEN- 
OUS EXTRACT- 
IVE MATTERS. 

| 

| 

'3 

i 

| 

g 

1 

1 
£ 

| 
J 
1 

86.0 
50.0 

| 

1 
S 

| 

5 

3 

"3 

i 

1 

a 
'* 

1 

10.  Fodder   Cakes  of  the   various 
nuts    and   seeds,   as    above, 
after  shelling       

80.0 
70.0 

100.0 
89.0 

88.0 
82.0 
95.0 

100.0 

77.0 

90.0 
63.0 
98.0 
76.0 
100.0 
95.0 
69.0 

68.0 
50.0 
76.0 
71  0 

63.0 
71.0 

98.0 
82.0 

86.0 
76.0 

11     Wheat-bran       

12    Meat-powder     

Fish-guano       

900 

Blood-powder      

62.0 

43.0 

89.0 
95.0 
93.0 

53.0 

91.0 
99.0 
96.0 

100.0 
98.0 
47.0 

90.0 

96.0 
95.0 
91.0 
75.0 
100.0 

13.  Milk  and  dairy  residues,     .     . 
14.  Brewed  hops, 

91.0 
26.0 

75.0 
85.0 
84.0 

97.0 
39.0 

80.0 
90.0 
88.0 

94.0 
33.0 

78.0 
88.0 
85.0 
790 

90.0 
52.0 

65.0 
36.0 
74.0 

99.0 
77.0 

77.0 
67.0 
79.0 

B.  HOGS  digest  the  following  per- 
centages   of   nutritive    sub- 
stances :  — 

1.  Crushed  barley,     

2.  Crushed  peas,    

3.  Crushed  corn,     

4.  Crushed  beans,  

5.  Rye-bran,     

91.0 
99.0 

81.0 

66.0 
90.0 
95.0 
72.0 
77.0 
960 

82.0 
79.0 

91.0 
91.0 

58.0 
87.0 

83.0 
95.0 

•    • 

.    . 

880 
82.0 

71.0 

7    Meat-powder     

8.  Blood-meal  

-    • 

•    • 

92.0 

9    Crushed  beetles 

10.  Skimmed  sour  milk,   .... 

80.0 
80.0 

70.0 
92.0 

49.0 
61.0 
67.0 
17.0 

49.0 

90.0 
90.0 

78.0 
96.0 

62.0 
67.0 
71.0 
30.0 

66.0 

99.0 
98.0 
850 
85.0 

76.0 
89.0 
93.0 
73.0 
94.0 
87.0 
56.0 
63.0 
69.0 
24.0 
66.0 
56.0 
94.0 
99.0 

11.  Potatoes    

73.0 

12    Oil-cake 

60.0 
70.0 

77.0 

75.0 
80.0 

91.0 

68.0 
75.0 

86.0 
83.0 
86.0 
94.0 
78.0 
800 

75.0 
60.0 

71.0 

85.0 
70.0 

81.0 

42.0 
31.0 
30.0 
100.0 

80.0 
65.0 

78.0 
70.0 
80.0 
37.0 
63.0 
42.0 
23.0 
29.0 
26.0 
84.0 
13.4 
22.0 

13.  Brewers'  grains  and  malt,   .     . 

C.  HORSES  digest  the  following  per- 
centages   of    nutritive   sub- 
stances :  — 

1.  Oats  

2.  Peas,    

3    Beans       

84.0 

90.0 

6.  Barley,     

7    Prairie-hay  . 

54.0 
51.0 
70.0 

27.0 

66.0 
60.0 
75.0 
44.0 

61.0 
55.0 
72.0 
36.0 
6PO 

14.0 
28.0 
21.0 
67.0 

8    Clover-hay         

9    Lucern-hay        

10.  Wheat-straw  
11    Meadow-grass  

12    Prairie-grass 

54.0 

69.0 

61.0 
990 

13.0 

42.0 

13    Carrots                   .     . 

14   Potatoes            

880 

COMPOSITION   OF  F^CES.  445 

Of  the  feeds  examined  in  per  cent,  of  digestibility  of  the  albumi- 
noids, bean-meal  stands  the  highest,  linseed-meal  (old  process)  next,  and 
pea-meal  but  little  less,  while  the  mixed  hay  of  rather  inferior  quality, 
but  similar  to  much  hay  feed,  stands  lowest.  The  old  process  linseed- 
meal  shows  a  higher  per  cent,  of  digestibility  than  the  new  process  ;  this 
difference  is  due,  very  likely,  to  the  partial  cooking  of  the  meal  by  steam 
during  the  process  of  oil  extraction  and  preparation  of  the  meal  for  feed. 
Cotton-seed  meal,  much  the  richest  substance  examined,  gives  a  high 
co-efficient  for  digestibilit}r.  A  marked  difference  exists  between  the 
first  three  hays,  showing  plainly  the  difference  between  well-cured  hay 
and  that  exposed  to  the  weather. 

Of  the  raw  and  cooked  foods  examined,  in  every  instance  the  higher 
digestion  co-efficients  were  obtained  from  the  raw  foods,  and  an  exami- 
nation of  the  table  of  anatyses  shows  an  actual  loss  in  albuminoids  by 
cooking,  and  a  change  in  the  fat  rendering  it  insoluble  in  ether,  and  un- 
acted upon  by  acids  or  alkalies  of  the  strength  used  for  fibre  determina- 
tions. 

XII.    THE  COMPOSITION  OF  F^CES. 

The  faeces  are  composed  of  the  more  or  less  altered  residue  of  the 
food-stuffs,  to  which  are  added  the  excretory  products  of  the  digestive 
tract.  The  character  of  the  faeces  will  be  governed  by  the  relative 
amounts  of  these  two  groups  of  substances. 

When  no  food  is  given,  as  during  fasting  and  in  the  fetal  state,  the 
faeces  consist  only  of  the  excretory  products  of  the  digestive  tract.  This 
state  of  affairs  will  also  hold  when  the  food  given  is  entirely  digested 
and  absorbed,  as  is  the  case  with  the  dog  fed  on  a  not  too  abundant 
meat  diet. 

The  amount  of  matter  found  in  the  faeces  which  fs  not  derived  from 
the  faeces  may  vary  under  different  circumstances.  In  the  fasting  con- 
dition, according  to  F.  Mu'ller,  the  faeces  contain  4  per  cent,  of  the  total 
amount  of  nitrogen  eliminated,  1.4  per  cent,  of  the  amount  of  carbon,  and 
25  per  cent,  of  tbe  inorganic  matter.  When,  however,  food  is  given,  the 
activity  of  the  intestinal  mucous  membrane  i*  increased,  and  through 
increased  secretion  and  excretion  the  percentage  of  faecal  constituents 
not  derived  from  the  food  is  increased. 

The  faeces  passed  in  the  fasting  condition  furnish,  therefore,  no  index 
as  to  the  degree  of  intestinal  excretion.  This,  however,  may  be  reached 
through  the  examination  of  the  faeces  of  eamivora  fed  on  meat,  when 
the  amount  of  nitrogen  eliminated  will  toe- afeowt  1,2  per  cent,  of  the  total 
amount,  carbon  2.7  per  cent.,  and  inorganic  matters  18.5  per  cent. 

Meconium,  or  the  contents  of  the  foetal  intestinal  canal,  contains 
neutral  fats,  free  fatty  acids,  biliverdin,bilirubin,  unchanged  biliary  acids, 


446  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

and  various  unknown  bodies  which  may  be  extracted  with  ether ;  on  the 
other  hand,  phenol,  indol,  leucin,  and  tyrosin  are  absent,  indicating  the 
absence  of  putrefactive  changes  in  ,the  fetal  canal.  Meconium  also 
contains  sulphur,  lime,  magnesium,  phosphoric  acid,  and  considerable 
amounts  of  alkaline  salts.  The  reaction  is  faintly  acid. 

The  faeces  passed  by  the  carnivofa  during  fasting  closely  resembles 
m.econium,  differing  from  it,  however,  in  that  they  contain  no  unchanged 
biliaiy  acids  and  hydrobilirubin  is  present.  When  fed  with  meat  the 
faeces  of  the  dog  usually  have  an  alkaline  reaction,  and  where  the  meat 
has  not  been  too  freely  given  never  contain  undigested  muscle-fibres. 
The  proof  that  the  faeces  in  carnivora  after  meat  feeding  are  mainly  com- 
posed of  excretory  matter  is  found  in  the  facts  that  while  increasing  the 
amount  of  meat  does  increase  the  amount  of  faeces,  the  increases  are  not 
proportional;  and  that  the  amount  of  food  remaining  unchanged,  the 
amount  of  faeces  varies.  The  amount  of  nitrogen  is  about  6  per  cent., 
while  the  inorganic  matter  is  considerably  larger  in  amount  than  in  meco- 
nium,  but  contains  less  alkaline  salts.  When  large  amounts  of  fats  are 
given  to  dogs  with  meat,  the  faeces  are  dark-brown  externally  and 
grayish  on  the  inside ;  the  daily  amount  passed  is  also  larger  than  where 
meat  alone  constitutes  the  diet. 

The  faeces  in  herbivora  always  have  an  aspect  and  color  closely 
similar  to  the  food  with  which  the  animals  have  been  fed.  Thus,  they 
are  yellow  when  fed  on  hay,  and  green  if  grass  has  been  given,  since 
chlorophyll  is  unchanged  in  the  alimentary  tube;  the  tint  will,  however, 
vary  according  to  the  rapidity  of  their  progression  through  the  intestine 
and  the  quantity  of  bile  poured  out.  The  faeces  of  solipedes  are  extruded 
in  rounded  masses,  flattened  at  the  sides  from  mutual  pressure,  and  are 
yellow,  green,  or  brownish  in  color.  In  oxen  the  faeces  are  of  semi-solid 
consistence,  and  dark-green  or  brown  in  color.  The  faeces  of  sheep  and 
goats  are  passed  in  the  form  of  small,  hard  balls,  very  dark-green  or 
black  in  color.  In  hogs  the  faeces  are  semi-solid,  very  offensive  in  odor ; 
their  color  depends  on  the  nature  of  the  food. 

The  consistency  of  the  faeces  depends  naturally  upon  the  quantity 
of  water  contained  in  them,  which  even  in  the  most  solid  instances  is 
still  considerable.  In  carnivora  the  faeces  have  a  blackish  tint  if  meat 
has  been  given  cooked.  They  become  fatty  or  cla3r-colored  in  cases  of 
obstruction  to  the  flow  of  bile  or  in  diseases  of  the  pancreas.  The  odor 
is  characteristic  of  each  group  of  animals,  and  is  due  primarily  to  indol 
and  sulphuretted  hydrogen.  The  quantity,  both  absolute  and  relative  to 
the  amount  of  food,  is  greater  in  herbivora  than  in  carnivora;  thus, 
horses  empty  their  bowels  on  an  average  every  three  hours,  and  when 
fed  oil  10  kilos  hay  and  2  kilos  oats  will1  pass  about  17  kilos  faeces,  con- 
taining 2.67  kilos  of  solids ;  cattle  evacuate  about  30  kilos  of  faeces  daily, 


COMPOSITION   OF  F^CES.  447 

with  about  4.6  kilos  of  solids ;  dogs,  when  fed  on  a  purely  meat  diet, 
only  every  two  to  four  days,  and  only  a  few  grammes  in  amount.  The 
consistency,  as  mentioned  before,  depends  upon  the  amount  of  water  con- 
tained in  them,  and  is  naturally  governed  by  the  activity  of  secretion,  of 
absorption,. and  the  amount  of  water  drunk.  Thus,  in  man  they  contain, 
on  an  average,  31  per  cent,  of  water ;  in  the  hog,  75  per  cent. ;  in  the  sheep, 
5t>  per  cent. ;  in  the  horse,  77  per  cent,  and  in  the  ox,  70  to  80  per  cent. 

The  reaction  of  the  faeces  may  be  either  alkaline,  neutral,  or  acid, 
depending  upon  the  character  of  the  fermentations  occurring  in  the  con- 
tents of  the  large  intestine.  Thus,  when  alkaline,  as  is  usually  the  case 
in  abundant  albuminous  diet,  the  reaction  is  due  to  ammoniacal  fermen- 
tation, while  an  acid  reaction  is  usually  due  to  the  fermentation  occurring 
in  the  carbohydrate  constituents  of  the  food. 

The  faeces  are  composed  of  excrementitious  substances  no  longer  of 
use  to  the  economy  and  which  must  be  eliminated.  They  contain  indi- 
gestible matters,  such  as  chlorophyll  granules,  gums,  resin,  wax,  animal 
and  vegetable  elastic  tissue,  cellulose,  hulls  of  seeds,  and  epithelial  cells. 
Lactic  acid,  butyric  acid,  and  various  gases,  such  as  hydrogen,  oxygen, 
carbonic  acid,  and  carburetted  hydrogen,  are  present,  while  in  addition 
various  salts  are  found  in  large  amounts,  of  which  the  ammonio-phosphate 
of  magnesium  is  usually  in  excess.  As  putrefactive  products,  leucin, 
ty rosin,  indol,  and  finally  skatol  and  the  volatile  aromatic  acids,  such  as 
valerianic  and  caproic  acids,  are  met  with,  while  cholesterin  and  the 
bile  coloring-matters  and  glycochol  are  also  found,  taurocholic  acid  being 
again  absorbed. 

The  contents  of  the  large  intestine  are  alwa3*s  in  a  more  or  less 
marked  degree  of  putrefaction,  which,  however,  though  hindered,  is  not 
entirely  prevented  by  the  bile. 

In  carnivora  fed  on  bones,  the  faeces  are  dense  and  gray  from  the 
presence  of  lime  salts.  Silicious  salts  constitute  a  large  percentage 
of  the  excrement  of  the  lower  animals ;  thus,  in  the  horse  and  ox  they 
amount  to  from  2J  to  3  per  cent.;  in  the  sheep,  to  6  per  cent.;  while  in 
the  hog  as  much  as  8  per  cent,  of  silicious  salts  are  present.  These 
salts  are  products  derived  from  the  matters  taken  into  the  alimentary 
canal  of  inorganic  nature,  and  from  the  inorganic  matter  of  the  hulls  of 
the  cereals.  A  small  amount  of  soluble  salts  are  present. 

The  following  table  gives  the  percentage  of  salts  found  in  the  faeces 
of  different  animals.  The  percentage  will,  of  course,  vary  according  to 
the  nature  of  the  food.  It  may,  as  a  rule,  be  said  that  in  the  faeces  of  the 
dog  about  20  per  cent,  of  inorganic  matter  is  present  when  on  a  pure  meat 
diet,  and  24  per  cent,  on  a  mixed  diet ;  in  that  of  the  herbivora  58  per 
cent,  is  inorganic,  though  the  faeces  of  the  sucking  calf  will  contain  only 
2.6  per  cent,  of  the  inorganic  matter  contained  in  the  food.  According 


448  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

to  Valentin,  100  grammes  of  faeces  of  the  bog  contains  37.2  grammes, 
ox  15.2  grammes,  horse  13.3  grammes,  sheep  13.5  grammes  of  ash: — 


Sodium  chloride,  . 

Horse. 
0.03 
11.30 

Ox. 
0.23 
2.91 

Hog. 
0.89 
3.60 

Sheep. 
0.14 
8  32 

1.98 

0.98 

3.44 

3.28 

Lime,     .... 
Magnesium,  . 
Oxide  of  iron, 
Phosphoric  acid,    . 
Sulphuric  acid, 

4.63 
.        3.84 
1.44 
.      10.22 
1.83 

5.71 
11.47 
5.22 

8.47 

1.77 

2.03 
2.24 
5.57 
5.39 
0.90 

18.15 
5.45 
2.10 
9.10 
2.69 

Carbonic  acid, 
Silicon,  .... 
Sand       .... 

'.      62.40 

62.54 

0.60 
13.19 
61.37 

traces 
50.11 

Oxide  of  magnesium,     . 

2.13 

.    . 

.    . 

XIII.  THE  MOVEMENTS   OF  THE  INTESTINES. 

The  walls  of  both  small  and  large  intestines  are  supplied  with  un- 
striped  muscular  fibres  arranged  in  circular  and  longitudinal  layers 
which,  through  their  contraction,  serve  to  cause  a  slow,  onward,  pro- 
gressive movement  in  the  contents  of  the  alimentary  tube. 

The  arrangement  of  these  muscular  fibres  differs  in  the  small  and  large 
intestine  and  in  different  animals.  The  longitudinal  layers  lie  beneath 
the  submucous  layer  immediatel}'  below  the  serous  covering,  and,  there- 
fore, give  the  intestine  its  longitudinally  Striated  appearance. 

In  the  small  intestine  these  longitudinal  fibres  form  a  thin,  uniform 
layer,  which  entirely  surrounds  the  intestine,  while  in  the  large  intestine 
they  are  grouped  into  bands,  and,  being  rather  shorter  than  the  intes- 
tine, throw  the  intermediate  parts  into  a  series  of  pouches ;  this  con- 
dition is  seen  in  the  large  intestine  of  man,  the  omnivora,  in  the  caecum 
of  solipedes,  and  in  the  fixed  colon  in  these  animals,  while  in  the  floating 
colon  their  arrangement  is  more  similar  to  that  seen  in  the  small  intes- 
tine, and,  consequent^,  in  those  portions  of  the  alimentary  tract  the 
sacculated  appearance  is  wanting.  Immediately  below  the  longitudinal 
fibres  is  found  the  layer  of  circular  fibres,  which  are  considerably  more 
developed  than  the  longitudinal  fibres. 

The  motions  of  the  intestine  have  been  compared  to  the  move- 
ments of  a  worm,  and  are  termed  peristaltic  contractions.  When  the 
abdomen  of  an  animal  is  opened  after  death  the  walls  of  the  intestine 
are  seen  to  be  in  active  motion,  and  cause  the  intestine  thus  to  undergo 
a  series  of  active  movements  of  the  same  nature,  but  greatly  exaggerated 
in  intensity,  as  the  movements  occurring  during  life.  If  the  intestines 
are  closely  examined,  it  will  be  seen  that  these  movements  consist  in  the 
downward  passage  of  a  constriction  due  to  the  successive  contractions  of 
the  circular  fibres  of  the  small  intestine  from  above  downward,  while  at 
the  same  time  the  longitudinal  fibres  contract  immediately  below  the 


MOVEMENTS   OF   THE   INTESTINES.  449 

ring  of  constriction  so  as  to  shorten  the  intestine  and  to  cause  a  rolling- 
motion  in  the  intestine  itself.  The  contractions  of  the  circular  fibres  of 
the  small  intestine,  as  a  rule,  commence  immediately  below  the  pylorus 
and  progress  downward  toward  the  large  intestine,  so  tending  to  force 
the  contents  of  the  small  intestine  onward  toward  the  ileo-ctecal  valve; 
but  while  the  pylorus  is  ordinarily  the  commencing  point  of  this  series 
of  contractions,  the  wave  of  contraction  frequently  may  seem  to  com- 
mence at  other  points,  and  normally  invariably  moves  downward  toward 
the  large  intestine.  It  is  stated  that  occasionally  the  wave  of  contraction 
moves  in  both  directions,  the  upward  movement  being  then  spoken  of 
as  an  antiperistaltic  movement.  Such  a  contraction  occurs  in  cases  of 
obstruction  of  the  intestines,  but  it  is  extremely  doubtful  as  to  whether 
such  an  antiperistaltic  movement  ever  occurs  during  health. 

It  is  a  peculiarity  of  unstriped  muscular  fibre  that  when  stimulated 
its  contraction  is  preceded  by  a  very  long  latent  period  and  lasjbs  a  con- 
siderable time,  relaxation  taking  place  but  slowly  afterward.  In  .such 
cases  as  the  intestine  and  ureter,  a  stimulation  of  any  one  point  not  only 
causes  contraction  of  the  muscular  fibres  in  that  locality,  but  that  con- 
traction is  transmitted  to  the  parts  below  it,  the  contraction  being  prop- 
agated from  fibre  to  fibre,  so  producing  a  wave  of  contraction  which 
passes  along  both  circular  and  longitudinal  coats  of  such  tubular  struc- 
tures. 

The  peristaltic  movements  of  the  intestine  are,  in  all  probability,  due 
to  the  contact  of  food  with  the  interior,  and  yet,  as  in  the  case  of  the 
stomach,  it  is  probable  that  this  stimulation  is  not  of  a  purely  mechanical 
nature ;  for  while  the  insertion  of  foreign  bodies  into  the  small  intestine 
starts  up  a  wave  of  contraction,  that  contraction  soon  passes  off  as  the 
intestine  becomes  accustomed  to  the  presence  of  the  body.  So,  also,  the 
intestinal  movements  are  frequently  more  energetic  when  the  intestine  is 
comparatively  empty  than  when  distended  with  food. 

The  principal  cause  of  the  movements  of  the  muscular  coat  of  the 
bowels  is  without  doubt  to  be  found  in  the  condition  of  the  blood  circu- 
lating through  the  vessels  in  the  walls  of  the  alimentary  tube.  Closure 
of  the  aorta  causes  active  peristaltic  motion  of  the  intestine.  If  the 
intestinal  tube  be  already  in  motion,  closure  of  the  aorta  increases  the 
vigor  of  the  intestinal  movement.  Closure  of  the  vena  cava,  or  portal 
vein,  and  dyspnoea  likewise  increase  peristalsis.  An  increase  in  the 
amount  of  carbon  dioxide  in  the  blood,  or  a  decrease  in  the  amount  of 
oxygen,  leads  to  powerful  peristaltic  movements,  and  this  condition  will 
probably  explain  the  activity  of  the  intestinal  movements  seen  in  animals 
recently  killed.  In  this  case,  however,  the  exposure  to  the  cold  air  is 
also  concerned  in  the  production  of  this  movement.  The  manner  in 
which  these  changes  in  blood  supply  influence  intestinal  movement  has 

29 


450  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

not  been  thoroughly  cleared  up.  The  closure  of  the  aorta  may  act 
through  the  intermediation  of  the  spinal  cord,  either  by  the  stimulation 
of  motor  or  the  paralysis  of  inhibitory  apparatus  ;  or  it  may  act  directly 
on  peripheral,  intra-muscular,  ganglionic  cells ;  or  directly  on  the  mus- 
cular fibres  themselves.  That  the  central  nervous  system  is  not  solely 
concerned  in  the  production  of  peristalsis  is  proved  by  its  occurrence  in 
an  intestine  removed  from  all  connection  with  the  central  nervous 
system,  and  it  has  been  found  that  ligation  of  the  mesenteric  artery  pro- 
duces in  the  main  the  same  effects  as  ligation  of  the  aorta.  We  have, 
therefore,  to  look  to  the  periphery  for  the  mechanisms  which  maintain 
peristalsis.  It  is  not  permissible  to  assume  that  the  state  of  affairs  here 
is  analogous  to  the  connections  between  nerves  and  striped  muscular  fibre, 
even  although  intestinal  peristalsis  may  be  proved  to  be  influenced  by 
nerve  impulses.  The  state  of  affairs  is  more  analogous  to  the  action  of 
the  pneumogastric  nerve  on  the  heart ;  for  while  the  peristaltic  action 
may  occur  independently  of  the  central  nervous  system,  as  has  been 
proved  by  its  occurrence  in  excised  intestine,  it  also  is  influenced  by 
nervous  impulses  passing  along  the  splanchnic  and  pneumogastric  nerves. 
We  have,  therefore,  to  infer  that  the  movements  are  mainly  due  to  nervous 
impulses  starting  in  the  ganglia  found  in  the  walls  of  the  intestine. — the 
ganglia  of  Auerbach  and  Meissner's  plexus, — and  that  these  ganglia  may 
be  influenced  by  impressions  traveling  along  these  nerves.  When  the 
splanchnic  nerve  is  cut,  the  peristaltic  contractions  are  temporarily 
arrested,  probably  through  the  large  supply  of  arterial  blood  which  then 
passes  through  the  walls  of  the  intestine.  On  the  other  hand,  if  the 
splanchnic  nerve  be  stimulated  while  active  movement,  is  going  on, 
peristalsis  is  arrested,  in  this  case  probably  through  the  consequent 
constriction  of  the  intestinal  blood-vessels.  If  the  pneumogastric  be 
stimulated,  the  intestinal  movements  are  increased,  especially  when  the 
splanchnic  nerve  has  been  cut,  and  it  is  probably  through  the  pneumo- 
gastric that  the  movements  of  the  intestine  are  reflexly  influenced 
through  the  emotions. 

Temperature  is  also  of  influence  on  the  intestinal  movements. 
Contact  of  the  exterior  with  cold  air,  or  the  introduction  of  cold  fluid 
into  the  interior,  accelerates  peristaltic  movements;  so,  also,  the  more 
fluid  the  contents  of  the  intestine,  the  more  active  are  the  intestinal  move- 
ments, thus  perhaps  explaining  the  action  of  various  cathartics  which 
lead  to  the  transudation  of  considerable  quantities  of  fluid  into  the 
interior  of  the  bowels. 

The  movements  of  the  large  intestine  are  the  same  as  occur  in  the 
small  intestine,  but  are  less  marked,  owing  to  the  modified,  sacculated 
shape  of  this  portion  of  the  alimentary  canal.  Just  as  the  peristalsis  of 
the  small  intestine  commences  at  the  pylorus,  the  contractions  of  the  walls 


DEFECATION.  451 

of  the  large  intestine  commence  at  the  ileo-caecal  valve,  which  is  the 
terminal  point  of  the  peristaltic  movements  of  the  small  intestine.  The 
movements  of  the  large  intestine  are  said  not  to  be  influenced  by  stimu- 
lation of  the  splanchnic  nerves. 

XIV.    DEFECATION. 

The  contents  of  the  alimentary  tube,  which  are  forced  onward  by 
the  peristaltic  movements  of  the  walls  of  the  intestine,  are  arrested  at  the 
lower  extremity  of  the  large  intestine  through  the  tonic  contraction  of 
the  sphincters  of  the  anus. 

By  defecation  is  meant  the  mechanisms,  partly  voluntary  and  partly 
reflex,  which  are  concerned  in  the  evacuation  of  the  contents  of  the  lower 
bowel.  The  anus  is  closed  by  two  muscles — an  inner  sphincter  which 
consists  of  unstriped  involuntary  fibres,  and  an  external  sphincter  com- 
posed of  voluntary  red  striped  muscles  ;  both  of  these  muscles  are  in  a 
state  of  tonic  contraction  due  to  the  constant  transmission  of  impulses 
from  a  special  centre  located  in  the  lumbar  portion  of  the  spinal  cord, 
and  which  is  only  inhibited  during  the  act  of  defalcation.  The  contact 
of  the  faeces  with  the  mucous  membrane  of  the  rectum  leads,  as  it  is 
ordinarily  described,  to  the  desire  to  defaecate,  and  inhibits  the  contrac- 
tion of  the  sphincter  muscles.  The  peristaltic  contraction  of  the  larger 
bowel  is  then  sufficient  alone  to  evacuate  the  contents  of  the  rectum, 
while  a  simultaneous  elevation  of  the  anus,  through  the  contraction 
of  the  levator  ani  muscles,  raises  the  floor  of  the  pelvis  and  pulls  the 
anus,  to  a  certain  extent,  up  over  the  descending  faecal  mass,  at  the  same 
time  preventing  distention  of  the  pelvic  fascia.  "As  the  fibres  of  both 
levatores  converge  below  and  become  united  with  the  fibres  of  the  exter- 
nal sphincter,  they  aid  the  latter  during  the  energetic  contractions  of 
the  sphincter."  Defalcation  is  partly  a  voluntary  movement  and  may  be 
aided  voluntarily  through  pressure  produced  by  the  contraction  of  the 
abdominal  muscles.  When  the  contact  of  the  faecal  mass  with  the  mu- 
cous membrane  of  the  upper  portion  of  the  rectum  originates  a  desire  to 
defalcate,  the  impulse  is  transmitted  to  the  brain  and  from  this  to  the 
spinal  cord,  inhibits  the  centre  of  defalcation  in  the  lumbar  portion  of  the 
cord,  and  by  this  means  relaxes  the  anal  sphincter ;  a  deep  inspiration  is 
then  made  and  the  glottis  is  closed  ;  powerful  voluntary  contractions  pf 
the  abdominal  muscles  press  upon  the  abdominal  contents  and  force  the 
intestinal  mass  down  into  the  pelvis,  thus  mechanically  aiding  peristalsis 
in  causing  the  downward  passage  of  the  faeces. 

The  contraction  of  the  anal  sphincters  is  kept  up  through  the  action 
of  a  nervous  centre  situated  in  the  lumbar  spinal  cord.  If  the  connec- 
tion of  this  centre  with  the  sphincter  is  divided  relaxation  of  the  anus 
takes  place,  but  section  of  the  cord  in  the  dorsal  region  only  temporarily 


452  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

inhibits  the  tonic  contraction  of  the  sphincter.  By  the  action  of  the  will 
the  tonic  action  of  the  sphincter  may  be  increased,  or  the  action  of  the 
sphincter  may  be  completely  inhibited.  While  the  abdominal  contrac- 
tions above  alluded  to  aid  in  defaecation,  the  sigmoid  flexure  serves  to 
ward  off  the  pressure  of  the  abdominal  walls;  therefore,  the  contraction 
of  the  abdominal  muscles  is  not  sufficient  alone  to  produce  defaecation, 
but  must  be  accompanied  by  the  peristaltic  action  of  the.  large  intestine 
and  sigmoid  flexure. 

As  a  rule,  the  contraction  of  the  abdominal  muscles  is  voluntary, 
but  the  contact  of  the  faecal  mass  with  the  mucous  membrane  of  the  sig- 
moid flexure  is  itself  sufficient  to  inaugurate  and  normally  complete  the 
act  of  defaecatioru  Therefore,  defaecation  may  be  produced  in  states  of 
entire  unconsciousness. 

Evacuation  of  faeces  occurs  at  various  intervals  in  different  animals — 
in  the  horse,  usually  six  to  seven  times  in  the  twenty-four  hours ;  in  the 
sheep,  four  to  five  times ;  and  in  the  hog,  once  or  twice. 

In  the  act  of  defaecation  in  the  horse,  the  loosely  attached  mucous 
membrane  of  the  lower  part  of  the  rectum  is  also  extruded,  forming  the 
so-called  "rose  of  the  anus,"  and  is  again  retracted  after  the  act  is  com- 
plete ;  the  object  of  this  is,  perhaps,  to  reduce  friction  between  the  mu- 
cous surface  and  the  more  or  less  hard  faecal  masses.  The  horse  is  able 
to  evacuate  its  rectum  while  in  motion  ;  animals,  as  a  rule,  adopt  a  more 
or  less  squatting  position,  with  the  back  highly  arched,  so  as  to  increase 
the  expulsive  action  of  the  abdominal  muscles. 


SECTION   III. 

ABSORPTION. 

WE  have  already  seen  that  the  alimentary  tube  is  developed  as  an 
involution  of  the  external  integument.  Hence,  even  after  having  under- 
gone the  most  perfect  digestion,  food-stuffs  are  practically  still  outside 
of  the  body,  and  can  serve  no  nutritive  purposes  until  they  have  entered 
the  lymph-  or  blood-currents.  This  entrance  of  the  digestive  products 
into  the  circulation  is  termed  absorption,  and,  as  just  indicated,  sub- 
stances reach  the  blood-current  from  the  alimentary  canal  in  one  of  two 
wa}-s :  either  directty  through  the  walls  of  the  minute  blood-vessels  in 
the  mucous  membrane  of  the  stomach  and  intestine,  or  through  the 
mediation  of  the  lymph-channels.  Both  of  these  modes  occur  in  the 
absorption  of  digestive  products. 

1.  VENOUS  ABSORPTION. — The  first  of  these  modes  of  absorption  is 
frequently  termed  venous  absorption,  as  the  entrance  of  substances  into 
the  blood  in  all  probability  occurs  through  the  walls  of  the  minute 
venous  radicals,  where  there  is  not  a  sufficiently  high  pressure  to  inter- 
fere with  the  passage  of  fluids  from  without  to  within  the  vessels  under 
the  ordinary  physical  laws  of  nitration  and  osmosis.  In  fact,  in  the 
very  arrangement  of  the  capillary  blood-vessels  in  the  intestine  we  find 
the  conditions  at  one  time  advantageous  to  the  passage  of  fluid  from 
within  to  without  the  blood-vessels,  and  again  directly  the  reverse  hold- 
ing. Thus,  after  undergoing  subdivision  into  the  minute  arterioles,  we 
find  the  first  capillary  loops,  where,  consequently,  the  pressure  is  highest, 
distributed  around  the  deep  ends  of  the  intestinal  tubules :  the  con- 
ditions are  there  most  favorable  for  the  transudation  of  fluid  from  the 
interior  of  the  vessels  and  the  consequent  formation  of  the  intestinal 
secretion.  The  capillary  loops,  after  leaving  the  deeper  portions  of  the 
intestinal  mucous  membrane,  when  the  blood  has  been  deprived  of  water, 
then  pass  to  the  most  superficial  layers,  and  the  conditions  are  then  most 
favorable  to  absorption.  The  blood  is  more  concentrated,  from  the  loss 
of  water  in  secretion ;  it,  therefore,  from  the  affinity  of  the  albumen  of 
the  blood  for  water,  favors  the  absorption  of  large  quantities  of  water, 
which  may,  of  course,  hold  nutritive  matters  in  suspension.  More 
than  this,  the  blood-current  is  now  becoming  more  accelerated,  and  the 
internal  pressure  on  the  walls  of  the  vessels  reduced,  both  of  which 
conditions  are  favorable  to  absorption. 

(453) 


454  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

The  substances  which  enter  the  blood  by  venous  absorption  are 
probably  all  those  which  are  soluble  in  water,  such  as  salts,  sugar,  soaps, 
and  peptone,  as  we  know  that  all  of  these  will  more  or  less  readily  diffuse 
through  organic  membranes  outside  of  the  body.  The  process  of  osmosis 
is  generally  accepted  as  explaining  the  mode  of  entrance  of  soluble  sub- 
stances 'into  the  blood,  but  many  data  are  still  required  before  this  view 
can  be  acknowledged  as  conclusively  established.  In  the  case  of  grape- 
sugar  the  author  has  found  that  the  osmotic  equivalent  of  sugar  ab- 
sorbed from  the  stomach  of  the  frog  very  closely  corresponds  with  the 
equivalent  of  diffusion  in  ordinary  physical  experiments,  and  some- 
what similar  observations  have  been  made  for  various  salts  and  for 
peptone.  There  is  still,  however,  a  great  deal  of  obscurity  in  the  matter. 
We  have  seen  that  by  the  time  the  blood  has  left  the  secreting  surfaces 
of  the  alimentary  tube  and  reached  the  absorbing  surfaces  it  has  lost  a 
good  deal  of  its  water,  Now,  if  we  assume  that  the  absorption  (of 
sugar,  for  instance)  is  governed  by  purely  physical  laws,  we  must  admit 
that  for  every  gramme  of  sugar  that  is  absorbed  seven  and  one-tenth 
grammes  of  water  (the  osmotic  equivalent  of  sugar)  will  leave  the  blood 
to  enter  the  intestine.  The  blood  will,  therefore,  become  progressively 
concentrated  and  the  intestinal  tube  filled  with  fluid  ;  consequent!}',  every 
substance  which  has  a  high  osmotic  equivalent  will  be  apt  to  prove  a 
cathartic ;  and  it  has,  indeed,  been  found  that  the  higher  the  osmotic 
equivalent  of  the  purgative  salts,  the  more  marked  is  their  cathartic 
action,  though  the  relation  of  cause  and  effect  between  these  facts  has 
been  denied  (Hay). 

Consequently,  though  it  is  probable  that  osmosis  is  largely  con- 
cerned in  the  absorption  of  substances  which  are  soluble  in  water,  the 
process  is  not  a  pure  one,  such  as  might  occur  between  similar  fluids 
separated  by  a  membrane  outside  of  the  body.  In  the  living  animal  the 
phenomena  of  filtration  may  greatty  aid  venous  absorption.  As  we  have 
seen,  the  contents  of  the  venous  radicals  are  subjected  to  but  low  pres- 
sure, and  it  is  quite  conceivable  that  the  pressure  exerted  through  its 
contractions  by  the  intestine  on  its  contents  may  aid  the  passage  of 
fluids  from  the  exterior  to  the  interior  of  the  veins.  Here  also  we  are 
unable  to  conceive  of  an  uncomplicated  process  of  filtration,  for  a  pres- 
sure sufficiently  great  to  force  fluids  through  the  walls  of  a  blood-vessel 
would  undoubtedly  so  compress  that  vessel  as  to  obliterate  its  lumen. 

From  the  above  it  follows  that  although  the  physical  processes  of 
osmosis  and  filtration  underlie  the  absorption  of  salts,  sugar,  and  peptone 
from  the  alimentary  tract,  neither  process  is  entirely  analogous  to  similar 
operations  outside  of  the  body,  it  being  probable  that  the  excess  of  pres- 
sure on  the  intestinal  contents  keeps  down  the  osmotic  equivalent,  and 
again  aids  in  the  resorption  of  the  transuded  water ;  while,  further,  the 


ABSORPTION.  455 

vital  properties  of  the  epithelial  cells  are  in  some  way  concerned  in  the 
absorption  not  only  of  fat,  but  of  sugar,  peptone,  and  salts.  Lannois 
found  that  by  the  injection  of  alcohol  into  exposed  loops  of  intestine  the 
epithelial  cells  were  destroyed,  and  the  absorption  of  oil,  sugar,  peptone, 
and  mineral  salts  was  delayed.  The  tendency  of  opinion  of  late  has 
been  in  favor  of  the  epithelial  cell  as  an  active  factor  in  absorption,  as 
it  is  in  secretion. 

M.  Leubuscher  has  made  some  experiments  which  seem  to  confirm 
this  view.  He  found  in  isolated  loops  of  intestine  that  the  absorption  of 
25  to  50  per  cent,  solutions  of  salt  took  place  just  as  rapidly  as  that  of 


FIG.  167.— SECTION  OF  INTESTINE  OF  DOG  SHOWING  THE  VILI-I.    (Cadiat.) 

The  blood-vessels,  r,  and  the  lacteals,  d,  have  been  injected.    The  blind  ending,  or  simple  loop  of  the  black 
lacteal,  is  seen  to  be  surrounded  by  the  capillary  net-work  of  the  blood-vessels. 

pure  water, — a  phenomenon  which  would  not  take  place  if  the  law  of 
diffusion  were  the  sole  factor  in  the  process.  The  salts  of  sodium  were 
absorbed  more  rapidly  than  the  salts  of  potassium,  and  absorption  was 
not  hastened  by  the  presence  of  bile — contrary  to  the  general  belief. 

Gumelewski  made  a  somewhat  similar  series  of  experiments,  and 
reached  much  the  same  conclusion.  Strong  solutions  of  sulphate  of 
sodium  increase  the  rapidity  of  absorption. 

Hofmeister,  especially,  has  identified  himself  with  the  theor}^  that 
the  absorption  of  peptone  is  not  a  purely  mechanical  process  of  diffusion 
or  filtration,  but  that  it  represents  a  function  of  certain  living,  cells  or 


456 


PHYSIOLOGY   OF   THE  DOMESTIC   ANIMALS. 


leucoc}Ttes,  which  in  the  assimilation  of  albuminoids  fill  a  role  analogous 
to  that  of  the  red  blood-corpuscles  in  respiration.  He  assumes  that  the 
reason  wiry  peptone  cannot  be  recognized  in  the  blood  is  because  it  has 
combined  with  these  lymphatic  cells,  and  is,  through  their  mediation, 
transported  to  different  parts  of  the  body ;  and  he  regards  the  rapid  pro- 
liferation of  the  cells  of  the  adenoid  tissue  of  the  intestinal  mucous  mem- 
brane and  of  the  Peyer's  patches  as  a  morphological  expression  of  the 
chemical  processes  of  assimilation  occurring  in  these  tissues. 

Thus,  it  seems  that  the  process  of  absorption  is  as  much  a  vital  one 
as  that  of  secretion,  and  that  the  epithelial  or  lymphatic  cell  not  only 
aids  the  taking  of  fat  into  the  blood,  but  also  that  of  peptone  (changing  it 
to  albumen),  and  of  sugar  and  salts. 

2.  ABSORPTION  BY  THE  LYMPHATICS. — Absorption  by  the  lymphatics  is 
accomplished  through  the  instrumentality  of  the  villi  of  the  small  intes- 
tine. Each  villus  contains  in  its  axis  the 
commencement  of  a  chyle-vessel,  which  is 
surrounded  by  a  fine  capillary  net-work  (Fig. 
167).  The  chief  purpose  of  this  villous  for- 
mation is  evidently  to  obtain  an  increase  of 
surface  for  absorption  with  economy  of 
space ;  but  each  villus  has,  further,  some 
special  mechanism  which  aids  the  absorption 
of  the  intestinal  contents,  as  is  proved  by 
the  entrance  into  the  chyle-vessels  of 
globules  of  oil  after  having  undergone  emul- 
sification  by  the  bile  and  pancreatic  juice. 

The  fat-globules  first  enter  the  proto- 
plasmic caps  of  the  epithelial  cells,  from 
these  pass  into  the  tissue  of  the  villus,  and 
thence  into  the  central  chyle-duct  (Fig.  168). 
After  an  abundant  fatty  diet,  this  absorption  of  fat  may  be  so  active  as 
to  completely  fill  the  net-work  of  lymphatics  of  the  mesentery  with 
milk-white,  emulsified  oil,  and  even  sometimes  give  the  blood-serum  a 
milky-white  color  (Fig.  169).  It  further  appears  that  the  fat  which  is 
absorbed  in  a  state  of  emulsion  by  these  chyle-vessels  is  greatry  in 
excess  of  the  saponified  fatty  acids  which  may  be  absorbed  by  the 
veins ;  for,  after  a  fat  diet,  nearly  two-thirds  of  the  amount  of  fat  given 
as  food  may  be  recovered  from  the  thoracic  duct. 

As  regards  the  mechanism  of  fat  absorption,  the  most  probable  view 
attributes  the  entrance  of  the  oil-globules  into  the  epithelial  cells  of  the 
villus  to  a  true,  protoplasmic,  selective  power  exerted  *by  the  contents 
of  these  cells,  and  entirely  analogous  to  the  mechanism  of  feedin 
sessed  \>y  the  amoeba  and  other  infusoria. 


FIG.  168.  — DIAGRAM  OF  THE 
RELATION  OF  THE  EPI- 
THELIUM TO  THE  LACTEAL, 
RADICAL,  IN  A  VILLUS, 
AFTER  FUNKE. 

The  protoplasmic  epithelial  cells  are 
supposed  to  be  connected  to  the  absorbent 
vessel  by  adenoid  tissue. 


ABSORPTION. 


457 


Microscopic  examination  of  the  intestinal  epithelium  after  a  full 
meal  which  is  rich  in  fatty  elements  of  food  will  reveal  the  fact  that  the 
epithelium  of  the  villi  is  crowded  with  minute  oil-globules.  These 


E. VEHNIORCKLH.se 

FIG.  169.— LACTEALS  OP  A  DOG  DURING  INTESTINAL  DIGESTION.    (Colin.) 

A,  lacteals  of  mesentery ;  B,  mesenteric  glands ;  C,  efferent  chyle-ducts ;  D,  receptaculum  chyli. 

globules  may  be  found  in  the  substance  of  the  epithelial  cell  itself  and 
in  its  free,  protoplasmic  cap  (Fig.  170). 

When  once  the  absorbed  fat  has  reached  the  central  chyle-vessel  of 
the  villus,  its  onward  progression  through  the  lymphatics  admits  of 


458  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

ready  explanation.  Each  villus  under  the  epithelial  coat  is  supplied 
with  a  layer  of  pale  muscular  fibres,  and  when  these  contract,  the  central 
chyle- vessel  being  full,  the  effect  must  be  to  press  out  the  contents  of 
the  central  vessel  in  the  direction  of  the  thoracic  duct,  at  the  same  time 
emptying  the  capillary  vessels  by  pressure.  When,  now,  the  muscular 
fibres  relax,  the  capillaries  will  again  become  filled,  and  by  the  turgidity 
of  the  net-work  of  blood-vessels  cause  the  central  vessel  to  become 
expanded,  and  so  exert  a  certain  amount  of  suction  in  the  interior  of 
the  villas  since  the  valves  in  the  lymphatics  will  prevent  regurgitation 


FIG.  170.— SECTION  OF  AN  INTESTINAL  VILLUS  OF  A  HORSE.    (Ellcnbergcr.) 

A,  epithelium ;  B,  adenoid  tissue ;  C,  commencement  of  lacteal. 

from  the  mesenteric  vessels.  Each  villns  may  therefore  be  regarded  as  a 
minute  lymphatic  heart,  which  fills  itself  from  the  interior  of  the  villus 
in  dilating,  and  in  contracting  forces  its  contents  into  the  circulation. 

In  addition  to  the  absorption  of  fat,  it  is  evident  that  other  sub- 
stances contained  in  the  intestinal  contents  will  also  mechanically  be 
drawn  into  the  villus  with  the  oil-globules.  Thus,  unchanged  albumen 
ma}^  be  absorbed  in  this  manner  and  has  been  found  in  the  contents  of 
the  chyle-vessels. 


SECTION   IV. 

CHYLE. 

THE  chyle  is  the  cl^me  which  has  been  absorbed  by  the  intestinal 
villi  and  the  thoracic  duct  through  the  mesenteric  lymphatics.  In  the 
receptaculum  chyli  it  is  mixed  with  the  lymph  coming  from  the  lower 
extremities. 

It  may  be  obtained  pure  in  the  ox  from  the  large  trunk  which 
accompanies  the  anterior  mesenteric  artery  (Fig.  171). 


FIG.  171.— COLLECTION  OF  CHYLE  IN  THE  Ox.    (Colin.) 

An  incision  is  made  in  the  right  flank  of  an  animal  in  active  digestion,  and  one  of  the  chyle-v«ss«1§ 
which  accompany  the  mesentery  artery  is  ligated.  When  it  becomes  distended  a  silver  cannula  termi- 
nating in  a  rubber  tube  may  be  readily  inserted. 

It  is  a  milky-white,  or  occasionally  reddish,  opaque  liquid,  of  alka- 
line reaction,  saltish  taste,  and  a  specific  gravity  which  varies  between 
1007  and  1022. 

In  a  fasting  animal  the  chyle  found  in  the  thoracic  duct  and  mesen- 
teric lymphatics  is  pale  and  transparent,  or  perhaps  somewhat  reddish 
in  tint.  During  the  absorption  of  a  meal  containing  fat,  we  have  seen 
that  it  becomes  milky  in  appearance  even  in  the  very  beginnings  of  the 
lymphatic  radicals  in  the  villi. 

In  the  adult  herbivora,  whose  diet  is,  as  a  rule,  comparative!}7"  poor 
in  fatty  matters,  the  chyle  is  scarcely  opalescent,  or  may  be  perfectly 

(459) 


460  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

transparent,  and  of  yellowish  or  reddish  tint.  In  suckling  lierbivora, 
as  in  the  carnivora,  it  is  milky. 

In  its  passage  from  the  intestine  to  the  thoracic  duct  it  undergoes 
important  changes  in  composition.  At  first  it  contains  albumen  in  solu- 
tion, oil-globules  in  suspension,  and  is  not  spontaneously  coagulable. 
After  it  passes  through  the  mesenteric  lymphatic  glands  lymph-cor- 
puscles are  added,  and  it  acquires  the  property  of  undergoing  fibrinous 
coagulation.  It  becomes  poorer  in  albumen  and  fats  in  its  onward 
progress,  and  richer  in  corpuscles  and  fibrin. 

When  taken  from  the  thoracic  duct  after  a  full  meal  of  fat  it  is  a 
white,  milky-looking  fluid,  which  undergoes  spontaneous  coagulation  on 
exposure  to  the  air.  The  nature  6f  the  coagulation  of  the  chyle  is  iden- 
tical with  that  of  the  blood,  to  be  subsequently  studied,  and  is  due  to 
the  addition  in  the  mesenteric  glands  of  immature  blood-corpuscles  and 
fibrin  factors. 

Examined  under  the  microscope,  the  coagulated  chyle  obtained  from 
the  thoracic  duct  contains  fibrin,  a  large  number  of  white  blood-  or 
lymph-corpuscles,  a  few  immature  red  blood-cells,  oil-globules  inclosed  in 
albuminous  envelopes,  and  fatty  granules. 

The  composition  of  chyle  differs  in  different  animals  and  at  dif- 
ferent periods  in  the  same  animal,  dependent  on  the  rapidit}T  and  nature 
of  absorption  taking  place  from  the  intestinal  surface.  In  the  chyle 
obtained  from  horses  fed  with  hay  the  fat  scarcely  exceeds  in  amount 
that  found  in  the  blood,  at  most  not  more  than  1  per  cent.,  while  it  may 
rise  to  3.10  per  cent,  in  horses  fed  with  oats.  It  is  made  up  of  formed 
elements  (lymph-corpuscles  added  as  the  chyle  passes  through  the 
mesenteric  lymphatics)  suspended  in  a  fluid  medium  (serum). 

The  serum  contains  the  following  bodies  in  solution  in  water : — 

1.  Globulin,   alkali    albuminate,   serum-albumen,   and   peptones   in 
small  amount,  rising  during  digestion  to  0.6-0.7  per  cent. 

2.  Cholesterin,  lecithin,  and  fatty  soaps. 

3.  Dextrose,  varying  from  a  mere  trace  to  2  per  cent.,  depending  on 
the  amount  of  carbohydrates  in  the  food. 

4.  Urea  derived  from  the  lymph,  and  alkaline  lactates,  especially  in 
the  lierbivora,  and  after  starchy  food. 

5.  Inorganic  salts  of  the  alkalies  and  alkaline  earths,  iron,  phos- 
phoric acid,  etc.  (Charles). 

As  a  result  of  sixteen  analyses  of  the  chyle  of  the  horse,  Gorup- 
Besanez  gives  the  following  figures  : — 

Water, 871.0    to  967.9    in  1000  parts. 

Albumen,         ....       19.32  "    6053 
Fat, traces  "    36.01 

The  chyle   possesses  the  power  of  converting   starch  into  sugar, 


CHYLE. 


4G1 


probably  clue  to  the  absorption  of  the  amylolytic  ferment  of  the  pancreas 
from  the  intestinal  canal. 

Chyle  of  Man  (Rees). 
Water 90.48  per  cent. 

Solids, 


Fibrin,     :'  .        .        ^ 
Albumen,    ..... 
Eats,  lecithin,  cholesterin,  etc., 
Extractives,        .        . 

Salts,  .        .        .        ».  •     . 


Water, 
Solids, 


Chyle  of  Dog  (Hoppe-SeyUr). 


trace 
7.08 
0.92 
1.0 
0.44 


90.67 
9.02 


Fibrin,         .        .";.-. 

Albumen 

Fats,  lecithin,  cholesterin,  etc., 

Fatty  acid  and  soaps, 

Salts, 


0.11 
2.10 
6.48 
0.23 
0.79 


Chyle  of  Horse  (C.  Schmidt). 


Serum,         *        *        . 

.     96.74 

Clot,    .        .        .        * 

.      3.25 

Water,         .        .        .        ... 

,     88.7 

Solids,      •    .        . 

.     11.2 

Fats,    .        . 

.       0.15 

Soaps,          .-.        .  •      .        . 

.      0.03 

Fibrin,         .       .  * 

.      3.89 

Albumen,  sugar,  and  extractives, 

.      6.59 

Haematin,    ...... 

.      0.20 

Sodium  chloride, 

0.23 

Sodium, 0.13     "      " 

Potassium,  .         .         ...         .         .       0.07     "       " 

Phosphates  and  sulphates,         .        .        .      0.11     "      " 

The  following  table  gives  the  composition  of  the  chyle  from  the 
thoracic  duct  in  the  ruminant  under  different  conditions  (Wurtz)  : — 


O 

X. 

Cow. 

Cow. 

Before 
Rumina- 
tion. 

After 
Rumina- 
tion. 

Fed  with 
Hay  and 
Straw. 

Fed  with 
Straw  and 
Clover. 

Water        

950.89 

929.71 

951.24 

962.21 

1.76 

1.96 

2.82 

0.93 

Albuminoids,     
Fats  
Salts  (soluble  in  alcohol).  . 
Salts  (soluble  in  water),    . 

39.74 
0.81 
2.47 
4.33 

59.64 
2.55 
2.50 
3.61 

38.84 
0.72 
2.77 
3.59 

26.48 
0:49 
1.92 
7.97 

Pure  chyle  from  the  mesenteric  vessels  of  the  ox  before  mixture 
with  the  lymph  has  a  specific  gravity  of  1013  and  contains  in  100  parts 


462  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

0.0019  parts  of  dry  fibrin.  The  serum  contains  4.75  per  cent,  solids 
(albumen,  fats,  salts,  etc.),  and  95.21  per  cent,  of  water. 

The  amount  of  chyle  is  proportional  to  the  activity  of  digestion, 
after  a  hearty  meal  the  mesenteric  vessels  and  thoracic  duct  being  dis- 
tended with  a  milky  emulsion,  while  during  fasting  they  are  collapsed 
and  are  only  seen  with  difficulty. 

The  movement  of  the  chyle  is  dependent  upon  a  number  of  causes. 
In  the  first  place,  as  mentioned  in  the  description  of  the  mechanisms  of 
absorption  of  fat,  the  villi  may  be  regarded  as  lymphatic  hearts,  the  con- 
traction of  their  muscular  fibres  leading  to  an  onward  movement  of  the 
contents  of  the  mesenteric  lacteals,  backward  flow  being  prevented  by 
the  valves  of  these  vessels. 

The  respiratory  movements  are  also  of  influence  in  producing  an 
onward  flow  of  the  contents  of  the  thoracic  duct.  With  each  act  of  ex- 
piration, as  may  be  readily  determined  by  making  a  fistula  of  the  thoracic 
duct  where  it  empties  into  the  veins  at  the  root  of  the  neck,  there  is  an 
acceleration  in  the  flow  of  chyle,  evidently  from  compression  of  the  duct, 
while  in  inspiration  this  flow  is  retarded  or  may  be  even  arrested.  In- 
spiration, therefore,  by  the  production  of  negative  pressure,  favors  the 
flow  of  chyle  frdm  the  lacteals  into  the  thoracic  duct. 

Contraction  of  the  abdominal  muscles,  and  even  intestinal  peristalsis, 
will  further  aid  the  forward  movement  of  the  chyle.  So,  also,  it  has 
been  noticed  that  there  is  a  slight  increase  in  the  rapidity  of  the  flow 
of  chyle  coincident  with  each  systole  of  the  heart.  While  this  factor  is 
comparatively  insignificant,  it  acts  by  the  compression  of  the  thoracic 
duct  where  it  passes  under  the  arch  of  the  aorta. 

Finally,  in  addition  to  these  influences  and  to  the  vis  a  tergo  from 
continuous  absorption  by  the  villi  and  the  propulsion  due  to  their  contrac- 
tion, the  most  important  factors,  there  is  also  a  vis  a  f route  concerned  in 
the  circulation  of  the  chyle.  For,  as  Draper  has  pointed  out,  where  the 
thoracic  duct  empties  into  the  veins,  a  suction  force  is  exerted  on  the 
contents  of  the  lacteals  by  the  passing  current  of  the  venous  blood,  upon 
the  well-known  hydraulic  principle  of  Venturi :  "  If  into  a  tube,  through 
which  a  current  of  water  is  steadily  flowing,  another  tube  opens,  its  more 
distant  end  being  in  communication  with  a  reservoir  of  water,  through 
this  tube  a  current  will  likewise  be  established,  and  the  reservoir  will  be 
emptied  of  its  contents." 


SECTION  V. 

LYMPH. 

As  THE  blood  circulates  through  the  capillaries,  it  is  continually 
losing  a  portion  of  its  fluid  constituents  through  transudation,  carrying 
with  the  water  of  the  blood  various  salts,  gases,  and  organic  matters 
in  solution.  This  fluid,  which  is  termed  the  lymph,  bathes  all  the  ulti- 
mate tissue  elements  and  supplies  them  directly  with  materials  necessary 
for  their  nutrition,  at  the  same  time  removing  the  soluble  effete  matters 
which  result  from  cellular  activity.  This  fluid,  thus  resulting  from  trans- 
udation from  the  blood-vessels,  not  only  fills  all  the  intercellular  chinks 
of  the  different  tissues,  but  also  finds  its  wajr  from  the  extra-vascular 
spaces  and  large  lymph-spaces  (as  the  lacunae  of  the  connective  tissue 
and  great  serous  sacs)  through  the  minute  radicals  of  the  lymphatic 
vessels  to  the  lymphatic  glands,  and  from  there  through  the  large  lym- 
phatic trunks  again  enters  the  blood-vessels  (veins  in  the  neighbor- 
hood of  the  heart). 

From  its  origin  it  is  evident  that  the  lymph  must  have  a  compo- 
sition closely  similar  to  that  of  the  liquor  sanguinis ;  but  since  different 
organs  take  from  the  lymph  different  substances  needed  by  their  nutri- 
tive demands,  and  yield  effete  matters  of  varying  composition,  its  com- 
position must  vary  according  to  the  region  from  which  it  is  taken  and 
the  stage  of  activity  of  the  organs  contributing  to  it.  This  contrast  of 
lymph,  drawn  from  different  localities,  is  most  marked  in  the  lymph 
taken  from  the  tymphatics  of  the  mesentery  during  the  period  of  diges- 
tion when  compared  with  that  drawn  from  other  localities.  Lymph 
drawn  from  the  so-called  lacteals  during  the  digestion  of  fat  is  termed 
chyle,  and  is  of  a  milky  appearance  from  the  large  quantities  of  minute 
fat-globules  which  it  holds  in  suspension.  The  characters  of  the  chyle 
have  been  already  considered. 

Lymph  may  be  obtained  by  inserting  a  cannula  into  the  thoracic  duct  of  an 
anaesthetized  animal  where  it  empties  into  the  junction  of  the  large  veins  at  the 
root  of  the  neck  ;  or  in  large  animals,  such  as  the  horse  and  ox,  it  maybe  collected 
by  a  similar  process  from  the  lymphatics  which  accompany  the  carotid  artery. 

The  amount  of  tymph  which  may  be  obtained  by  such  a  process  varies 
under  different  circumstances.  It  is  increased  by  active  or  passive  move- 
ments, by  venous  obstructions,  and  by  poisoning  with  curare.  It  is 
diminished  by  decrease  in  blood  pressure. 

(463) 


464  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

When  freshly  drawn  from  the  thoracic  duct  of  fasting  animals, 
lymph  is  a  transparent,  slightly  yellowish  fluid ;  when  collected  during 
digestion,  it  is  milky  from  the  fat  in  suspension  derived  from  the  chyle. 
When  examined  under  the  microscope,  lymph  is  seen  to  contain  color- 
less corpuscles,  identical  with  the  colorless  blood-corpuscles,  floating  in 
a  clear  lymph-plasma:  these  corpuscles  are  much  fewer  in  number  in 
lymph  drawn  from  the  lymphatic  radicals,  while  they  are  comparatively 
abundant  in  the  tymph  as  it  issues  from  the  lymphatic  glands.  Although 
the  lymphatic  glands  are  the  principal  manufacturers  of  the  lymph-cor- 
puscles, they  are  not  their  sole  source.  The  lymph-cells  also  originate 
wherever  adenoid  tissue  is  found,  as  in  the  mucous  membrane  of  the 
stomach  and  intestines,  in  the  thymus,  tonsils,  and  spleen. 

The  lymph  of  animals  in  active  digestion  is  milky  from  admixture 
with  the  fatty  clryle :  such  lymph  is  said  to  have  a  molecular  basis  from 
.the  finely  divided  fat-globules  which  it  holds  in  suspension.  These  par- 
ticles often  exhibit  Brownian  movements. 

The  amount  of  lymph  can  only  be  approximately  estimated.  It  has 
been  reckoned  that  for  every  two  hundred  and  twenty  pounds  of  body 
weight  there  is  contained  in  the  body  about  thirteen  and  a  half  pounds 
of  lymph  and  chyle — seven  and  a  half  pounds  being  chyle  and  six 
pounds  lymph.  As  much  as  six  kilos  of  tymph  have  been  collected  in 
two  hours  from  the  lymphatic  trunk  in  the  neck  of  the  horse,  wrhile  in 
twenty-four  hours  ninet3'-five  kilos  of  lymph  and  chyle  have  been  col- 
lected from  the  thoracic  duct  of  the  ox.  The  amount  of  these  two  fluids 
(lymph  and  chyle)  will  evidently  increase  during  digestion.  Active  and 
passive  movements  and  increased  blood  pressure,  as  well  as  obstruction 
of  the  veins,  by  facilitating  transudation  from  the  blood-vessels,  will 
increase  the  amount  of  lymph. 

Lymph  is  a  viscid  fluid,  slightly  less  alkaline  than  blood,  having 
a  specific  gravit}'  that  varies  from  1022  to  1037,  or  occasionally  as  high 
as  1045.  When  removed  from  the  body  it  coagulates  in  from  five  to 
twenty  minutes,  the  process  being  analogous  to  the  coagulation  of  blood- 
plasma,  though  much  slower,  perhaps  on  account  of  its  high  alkalinity. 
The  coagulation  of  lymph  may  be  accelerated  by  the  addition  to  it  of  a 
few  drops  of  defibrinated  blood  b}^  the  addition  thus  accomplished  of 
fibrin  factors  in  larger  amount.  A  soft,  trembling  jelly  is  first  formed, 
which  gradually  contracts,  expressing  out  a  clear  lymph-serum,  in  which 
floats  a  colorless  contracted  coagulum,  composed  of  fibrin  which  is  iden- 
tical with  that  formed  in  blood  coagulation. 

From  1000  parts  of  the  lymph  of  a  foal,  Schmidt  determined  that 
955.17  were  serum,  while  only  44.83  were  coagulum.  After  death  the 
lymph  usually  remains  perfectly  fluid  in  the  lymphatics,  and  does  not 
coagulate  when  the  lymph-current  is  arrested  during  life. 


LYMPH. 


465 


Lymph  is  very  variable  in  its  chemical  composition.  It  may  be 
generally  stated  as  follows  :  — 

Water,        .        .        .        .        .      93  to  98  per  cent.  (Charles). 

Solids,        .        .        .        ...        6  "    2 

Alhumen,  .        .     "    .        .        .3.2  "    0.3     " 

Veuves,  •:    :    :    :.  55  }•**»»«•«••• 

Ash,  .        .      ;  .        ...       ..       .„   0.7  to  0.8 

Sodium  chloride  forms  about  0.6  per  cent.  The  proteids  consist  of 
tibrinogen,  serum-globulin,  and  serum-albumen.  Lymph  yields  only  0.4 
to  0.8  per  one  thousand  of  fibrin,  being  much  less,  therefore,  than  the 
amount  obtainable  from  blood. 

In  the  ash  of  lymph  sodium  chloride  is  very  abundant  and  phos- 
phates scant}'  :  the  lymph-cells,  however,  contain  an  excess  of  potassium 
and  phosphoric  acid,  as  compared  with  the  serum,  the  latter  having  an 
excess  of  sodium.  Urea  is  always  present  (0.019  per  cent,  in  the  cow), 
and  grape-sugar  (0.16  per  cent,  in  the  dog),  though  it  has  been  stated 
that  cli3'le  does  not  take  up  sugar  when  animals  have  been  fed  on  a 
starchy  or  saccharine  diet. 

The  lymph  contains  C02,  N,  and  traces  of  0  when  pure  and  un- 
mixed with  blood.  The  amount  of  C03  is  greater  than  in  arterial  but 
less  than  in  venous  blood.  While  the  quantity  of  N  is  about  the  same  as 
in  the  blood,  the  amount  of  O  is  always  less  than  in  the  blood,  thus 
showing  that  the  tissues  rapidly  appropriate  the  O  of  the  blood. 

The  following  table  gives  a  comparison  of  the  composition  of  the 
lymph  and  blood  :  — 


LYMPH  (Wurz). 


BLOOD  (Nasse). 


Water,   . 

\ 

Ox. 
938.97 
2.05 
50.90 
0.42 
7.46 

Cow. 
955.38 
2.20 
34.76 
0.24 
7.41 

Ox. 
799.59 
3.62 
66.901 
2.045 
7.041 
121.865 

Calf. 
826.44 
5.737 
56.414 
1.610 
8.241 
102.803 

Fibrin,    .         .         .         . 
Albumen  and  extractives, 
Fats,       .... 
Salts,      .... 
Blood-corpuscles,  . 

HESULTS   OF   THE   QUANTITATIVE   ANALYSIS   OF   LYMPH  AND  CHYLE. 
I.   ANALYSES  OP  THE  LYMPH  OF  MAN. 


CONSTITUENTS  IN 
100  PARTS. 

Gubler  and 
Quevenne. 

Marchand 
and 
Colberg. 

Scherer. 

Dannhardt 
and 
Hensen. 

Odeiflus 
and 
Lang. 

I. 

It 

III. 

rv. 

V. 

98.63 
1.37 
0.11 
0.23 

0.15 
0.88 

VI. 

Water    .... 

93.99 
6.01 
0.05 
4.27 
0.38 
0.57 
0.73 

93.48 
6.52 
0.06 
4.28 
0.92 
0.44 
0.82 

96.93 
3.07 
0.52 
0.43 
0.261 
0.31./ 
1.54 

95.76 
4.24 
0.04 
3.47 

0.73 

94.36 
5.64 
0.16 
2.12 
(2.48 
\  0.16 
0.72 

Solid  matters,      .     .     . 
Fibrin,  
Albumen 

Fats 

Extractive  matters, 
Salts      

466 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


II.     ANALYSES    OF   THE   LYMPH    OBTAINED  FROM  THE  LYMPHATICS  OF   THE 

HORSE  (C.  SCHMIDT). 


CONSTITUENTS  IN  1000  PARTS. 

I. 

II. 

Water         

963.93 

955.36 

Solid  matters,      .        .        .        .        ...,,-. 

36.07 

44.64 

Fibrin,        

1 

Albumen,    
Fats  and  fatty  acids,  .         .        .        .-..,  .        . 

28.84 

34.99 

J 

Inorganic  matters,       .         .         .         .         .         . 

7.22 

7.47 

NaCl  .        . 

5^43 

5.67 

Na20,         .        .         .        .        .        .        .      '  . 

1.50 

1.27 

K20,  .   '      .<  '  '    . 

0.03 

0.16 

S03,   .        .        .        .        .        .        .        .        ... 

0.03 

0.09 

P2O5,  combined  with  alkalies,    ..... 
Ca3(P04)2  -     .         .         .         . 
Mg3(P04)2,        . 

0.02 

0.22 

0.02 
0.26 

In   the  serum   from  1000   parts  of  lymph  Schmidt 

found  :  — 

Albumen,    .         .         .         .         ..'... 
Fats  and  fatty  acids,  .         .         ....'.         . 

23.32 

f  30.50 
|   1.17 

4.48 

1.69 

III.    ANALYSES  OF  CHYLE  OF  THE  HORSE,  DOG,  AND  MAN  (HOPPE-SEYLER). 


CONSTITUENTS  IN 
1000  PARTS. 

I 
Chyle  of 
Horse. 

II. 
Chyle  of 
Horse. 

III. 
Blood- 
Serum. 

IV. 

Chyle  of 
Dog. 

V. 
Blood- 
Serum  of 
Dog,  IV. 

VI. 

Chyle  of 
Man. 

Water,    

960.97 

956.19 

930.75 

906.77 

936.01 

904.80 

Solids  

39.03 

43.81 

69.25 

96.23 

63.99 

95.20 

Fibrin     

257 

1  27 

1  11 

Albumen,    ...... 

22.60 

29.85 

56.59 

21.05 

45.24  $ 

70.8 

Fats,    cholesterin,    and 
lecithin,  
Fatty  acids  in  the  form 
of  soaps,      .... 
Other  organic  matters, 
Hsematin,    
Mineral  salts,  .... 
Loss            

Qr09 

0.76 
5.37 
0.05 
7.59 

0.53 

0.28 
2.24 
0.06 
7.49 

1.57  > 
3.855 

7.14 

64.86 
2.34 
7.92 

6.81 
2.91 

8.76 
027 

9.2 
10.8 
'4.4 

NaCl  

5.76 

5.84 

5.74 

Na20  

$  1.17 

0.87 

K20 

A       1.31 

I  013 

014 

SO3  ' 

007 

005 

Oil 

' 

P  O5  

0.01 

0.05 

0.01 

Ca3(P04)2,     .... 
Mg  (P04)2,    . 

I     0.44 
1.02 

0.25 

082 

0.26 
056 

•   • 

.    . 

LYMPH. 


467 


Schmidt  gives  the  following  analysis  of  the  lymph  of  a  cow : — 

Serum,     .        .''.•' 95.52 

Clot,  4.42 


In  100  parts 
Serum. 

Water,     . 

Fibrin,     . 

Other  albumens, 

Fats,     ,  » 

Organic  matter, 

Salts, 

Sodic  chloride, 

Soda, 

Potash,    . 

Sulphuric    and   phosphoric  acids   and 

earthy  phosphates,  .         .        .        .      0.04 


3  20 

0.12 
0.17 
0.74 
0.56 
0.13 
0.01 

In  100  parts 
Clot. 

90.73 
4.86 

3.43 

0.96 
0.60 
0.06 
0.10 

0.23 


The  lymph  further  differs  in  composition  according  to  the  locality 
from  which  it  is  collected.  The  following  table  gives  the  composition 
of  the  lymph  of  the  horse : — 


Lymph 
Collected  from 
the  Femoral 
Vessels 
(Gmelin). 

Lymph 
Collected  from 
the  Cervical 
Vessels  (Leuret 
and  Lassaigne). 

Lvinph 
Collected  from 
the  Vessels  of 
the  Foot 
(Geiger). 

Lymph  from 
the  Vessels  of 
the  Foot  of  an 
Ass  (Rees). 

Water  . 

964.30 

925.00 

983.70 

965.36 

Solids,  

35.70 

75.00 

16.30 

34.64 

Fibrin 

1  90 

330 

040 

1  20 

Albumen,  .... 
Fats  
Extractives,  .... 
Inorganic  matters, 

21.17 
traces 

10'.63 

57.36 
14".34 

6.20 
traces 
2.70 
7.00 

12.00 
traces 
15.69 
5.85 

The  Circulation  of  the  Lymph. — The  tymph  is  continually  moving 
in  the  lymphatic  vessels  in  a  slow  stream  from  the  lymphatic  radicals  to 
the  larger  lymphatic  trunks,  and  thence  into  the  large  veins  in  the  neigh- 
borhood of  the  heart,  motion  being  due  to  the  difference  in  pressures  be- 
tween the  lymphatic  capillaries  and  the  entrance  of  the  lymph-trunks 
into  the  veins. 

Since  the  lymph  originates  as  a  transudation  from  the  blood-vessels 
in  the  interstitial  spaces,  the  pressure  to  which  it  is  subjected  will  be 
nearly  identical  to  the  pressure  in  the  blood-vessels  which  causes  its  pas- 
sage through  the  vascular  walls.  Each  volume  of  lymph  will,  therefore, 
be  forced  onward  by  the  amounts  which  succeed  it  under  a  pressure 
which  is  nearly  equal  to  the  blood  pressure.  On  the  other  hand,  the 
pressure  of  the  lymph  at  the  points  of  entrance  of  the  lymphatics  into 
the  veins  will  be  in  all  cases  slight,  and  sometimes  will  be  even  negative : 
for  during  inspiration  the  expanding  thorax  aspirates  the  blood  from 


468  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

the  large  venous  trunks  into  the  veins  of  the  thorax,  and  by  the  dilata- 
tion of  the  right  auricle  from  thence  into  the  heart.  As  the  lymphatics 
empty  into  the  veins  in  the  neighborhood  of  the  heart,  this  aspiration 
will  also  be  exerted  on  the  lymphatics  and  will  tend  to  produce  a  nega- 
tive pressure.  The  lymph  will,  consequently,  be  subjected  to  a  steadily 
decreasing  pressure  from  the  periphery  to  the  central  vessels,  and  will, 
therefore,  move  from  the  lymphatic  radicals  toward  the  venous  trunks. 
The  onward  motion  of  the  lj*mph  is  also  facilitated  by  muscular  move- 
ments, which,  by  compressing  the  lj  mphatics,  force  their  contents  onward, 
backward  motion  being  prevented  b}^  numerous  valves. 

The  lymphatic  vessels,  also,  possess  the  power  of  rhythmic  contrac- 
tion, through  the  contraction  of  their  muscular  fibres,  and  sometimes 
true  lymph-hearts  aid  the  propulsion  of  the  lymph. 

In  certain  organs  special  mechanisms  are  concerned  in  the  propul- 
sion of  the  lymph.  Thus,  in  the  abdominal  surface  of  the  central  tendon 
of  the  diaphragm  there  are  free  communications  between  the  peritoneal 
cavity  and  the  lymphatics  of  the  diaphragm;  and  as  the  central  tendon 
is  composed  of  two  layers  of  fibrous  tissue  arranged  in  different 
directions,  these  layers  are  alternate^  pressed  together  and  pulled  apart 
in  the  respiratory  movements  of  the  diaphragm.  The  effect  is  to  pump 
lymph  into  the  spaces  between  these  layers.  A  similar  mechanism  exists 
in  the  costal  pleura  and  in  the  fascia  covering  the  muscles.  "  When  a 
muscle  contracts,  lymph  is  forced  out  from  between  the  layers  of  the 
fascia,  while,  when  it  relaxes,  the  lymph  from  the  muscle,  carrying  with 
it  some  of  the  waste  products  of  muscular  action,  passes  out  of  the 
muscle  into  the  fascia,  between  the  now  partially  separated  layers" 
(Landois).  While  the  lymph-glands  offer  considerable  resistance  to  the 
onward  passage  of  the  lymph,  this  is,  to  a  certain  extent,  compensated 
by  the  non-striped  muscular  fibres  which  exist  in  the  capsule  and 
trabeculse  of  the  glands,  these  muscles,  together  with  those  of  the 
lymphatics  and  lymphatic  hearts,  when  present,  being  directly  under  the 
control  of  the  nervous  system. 

The  velocity  of  the  lymph-current  increases  as  the  trunk  increases 
in  size,  from  the  decrease  in  sectional  area.  In  the  large  lymphatic  in 
the  neck  of  the  horse  it  has  been  placed  at  two  hundred  and  thirty  to 
three  hundred  millimeters  per  minute ;  it  must,  therefore,  be  very  slow 
in  the  small  vessels.  The  lateral  pressure  in  the  lymphatics  in  the  neck 
of  the  horse  has  been  estimated  at  from  ten  to  twenty  millimeters  of  a 
weak  soda  solution  (Weiss). 


SECTION    VI. 
THE  BLOOD. 

THE  blood  may  be  regarded  as  the  main  organ  of  nutrition,  since,  on 
the  one  hand,  the  assimilated  food-stuffs  enter  into  it  at  the  point  of 
their  absorption  to  be  carried  to  the  points  where  they  may  be  needed 
by  the  economy ;  and,  on  the  other  hand,  the  results  of  tissue  waste  are 
given  up  to  it  to  be  removed  from  the  economy. 

The  blood  may  be  regarded  as  a  cellular  tissue  with  a  fluid  inter- 
cellular substance  in  perpetual  motion  within  a  system  of  branching 
tubes.  The  blood  is  not  a  homogeneous  solution,  but  is  composed  of 
an  immense  number  of  minute-formed  elements,  the  blood-corpuscles  or 
cells,  suspended  in  a  colorless,  transparent  fluid,  the  blood-plasma.  Of 
the  blood-corpuscles,  the  so-called  red  cells  are  greatly  in  excess,  and  it 
is  to  the  haemoglobin,  or  red  coloring-matter,  which  they  contain  that 
the  red  color  of  the  blood  is  due. 

The  red  hue  of  the  blood  drawn  from  a  living  animal  will  vary  ac- 
cording to  the  locality  from  which  it  is  taken ;  the  blood  taken  from  the 
arteries,  the  left  side  of  the  heart,  or  the  pulmonic  veins  being  of  a  bright, 
scarlet-red  color,  while  that  drawn  from  the  veins,  the  right  side  of  the 
heart,  or  the  pulmonic  artery,  is  dark,  brownish  red.  When  exposed  to 
air  or  to  oxygen  gas,  the  dark  venous  blood  becomes  arterial  in  hue, 
and  this  change  occurs  most  rapidly  when  the  blood  and  gas  are  shaken 
up  together. 

The  specific  gravity  of  defibrinated  human  blood  varies  from  1045 
to  1062,  the  average  being  1055,  though  greater  variations  than  the  above 
are  not  inconsistent  with  health.  Again,  the  specimens  of  blood  first 
drawn  will  have  a  higher  specific  gravity  than  that  examined  after  con- 
siderable hemorrhage,  as  the  water  in  the  blood  will  have  then  increased 
from  the  abstraction  of  fluid  from  the  tissues.  The  cells  are  specifically 
heavier  than  the  plasma,  and  of  the  former  the  red  cells  are  heavier  than 
the  white.  Thus,  if  blood  is  prevented  by  cold  from  coagulation — and 
this  is  best  accomplished  with  horse's  blood — the  blood  will  separate 
into  three  distinct  strata,  the  lowest  being  composed  of  red  corpuscles, 
the  middle  of  white  cells,  and  the  upper  layer  of  the  clear  blood- 
plasma.  The  corpuscles  have  a  density  of  1088-1105  ;  the  plasma,  of 
1027-1028. 

The  reaction  of  the  blood  is  always  distinctly  alkaline,  due  to  sodium 

(469) 


470  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

bicarbonate  and  sodic  phosphate,  most  marked  when  the  blood  is  freshly 
drawn,  and  decreasing  rapidly  in  intensity  until  coagulation  occurs. 

Blood  has  a  peculiar  odor  which  varies  in  different  animal  species, 
and  in  certain  animals,  as  in  the  cat,  dog,  sheep,  and  goat,  is  charac- 
teristic of  the  species.  This  odor  is  due  to  the  presence  of  certain  vola- 
tile, fatty  bodies  contained  in  the  blood-plasma,  and  may  be  readily 
developed  by  treating  the  blood  with  sulphuric  acid. 

The  temperature  of  the  blood  varies  in  different  animals,  and  depends 
upon  the  oxidation  processes  continually  occurring  in  the  tissues.  In 
man  and  the  domestic  mammals  the  temperature  varies  from  37.5°  to 
38°  C.  In  birds  it  is  always  higher  than  in  mammals,  and  may  rise  as 
high  as  44.03°  C.  even  in  a  state  of  health.  The  arterial  blood  is,  as  a 
rule,  warmer  than  venous  blood,  as  the  conditions  for  radiation  of  heat 
are  more  favorable  in  the  latter  than  in  the  former.  The  temperature  of 
the  blood  of  the  hepatic  and  portal  veins  is  warmer  than  other  venous 
blood,  and  the  blood  of  the  right  side  of  the  heart  is  warmer  than  that 
of  the  left  heart. 

The  quantity  of  blood  varies  in  different  animals  and  in  the  same 
species  of  animal  at  different  periods  of  life.  Various  methods  have  been 
proposed  for  determining  the  amount  of  blood  contained  in  the  body. 
The  method  which  is  now  generall}'  adopted  as  giving  the  most  reliable 
results  is  to  bleed  an  animal  to  death  and  measure  the  amount  of  blood 
collected.  The  blood-vessels  are  then  washed  out  with  dilute  saline  solu- 
tion until  the  fluid  which  issues  from  the  veins  comes  out  entirely  color- 
less, and  the  various  washings  are  collected  and  mixed.  A  known 
quantity  of  blood  is.  then  diluted  with  saline  solution  until  it  acquires 
the  same  tint  as  a  measured  quantit}7  of  the  washings  collected  from  the 
veins.  From  the  data  so  obtained  the  amount  of  coloring  matter  in  the 
washings  m&y  be  estimated.  The  entire  body  is  then  minced,  washed 
free  from  blood  with  saline  solution,  filtered,  and  the  amount  of  coloring 
matter  in  the  washings  estimated  as  before.  The  quantit}*  of  blood  in 
the  two  washings,  together  with  the  blood  first  drawn,  give  the  total 
amount  in  the  body. 

Estimated  in  this  wa}- ,  the  total  amount  of  blood  in  the  human  body 
has  been  fixed  at  y1^  of  the  body  weight ;  in  the  rabbit  at  y1^  of  the  body 
weight ;  dog,  y1^  of  the  body  weight ;  cat,  ^r ;  frog,  TTg  ;  mouse,  -^ ;  the 
guinea-pig,  y1^ ;  bird,  yV-^a  ;  fishes,  y^-yV  No  reliable  estimates 
exist  as  to  the  amount  of  blood  in  the  larger  domestic  animals.  Colin 
states  that  the  amount  of  blood  in  the  ox  amounts  only  to  ^  of  the 
body  weight,  but  this  is  probably  a  low  estimate.  In  animals  bled  to  death 
the  amount  of  blood  retained  in  the  bod}r  depends  upon  the  amount  of 
adipose  tissue  :  the  fatter  the  animal,  the  more  blood  remains  in  the  bod}' 
after  slaughtering.  In  thin  cattle  the  amount  of  blood  which  escapes 


BLOOD. 


471 


has  been  estimated  at  4.7  per  cent,  of  the  body  weight;  in  fat  animals, 
at  3.9  per  cent.  In  the  horse  the  amount  of  blood  has  been  estimated  at 
•fg  of  the  body  weight. 

The  following  tables  represent  the  general  composition  of  the  blood 
in  different  domestic  animals  : — 

In  One  Hundred  Parts  Venous  Blood  (Hoppe- Seyler  and  Fudakowski). 

Horse.  Dog. 

Corpuscles,  .        ; 32.62  38.34 

Plasma,      ".,.-.      .        .....     67.38  61.66 

One  Hundred  Parts  Plasma. 

Solids, 9.16  7.87 

Water,.    ..'..'.        .        .         .     90.84  92.13 

Fibrin, 1.01  0.18 

Albumen,      .        .' 7.76  6.10 

Fats, 0.12  0.21 

Extractives, *     .        .      0.40  0.39 

Soluble  salts,        .        .        .        .        .        .      0.64  0.82 

Insoluble  salts,     .....        .        .0.17  0.17 

One  Hundred  Parts  Corpuscles. 

Water, 56.50  .    .    . 

Solids,   .  43.50          .    .    . 

In  One  Hundred  Parts  Defibrinated  Venous  Blood  of  Ox  (Bunge). 

Corpuscles.  Serum. 

31.87  68.13 


Water,    .        .        . 

Solids,    . 

Albumen, 

Haemoglobin, 

Other  organic  matters,  . 

Inorganic  matters, 

Potassium, 

Sodium, 

Lime, 

Magnesium, 

Iron  oxide, 

Chlorine, 

Phosphoric  acid, 


Water,    . 

Fibrin,    . 

Fat, 

Corpuscles,    . 

Albumen, 

Alkaline  phosphates, 
"         sulphates, 
"          carbonates, 

Sodium  chloride,  . 

Iron  oxide,     . 

Calcium, 

Phosphoric  acid,    . 

Sulphuric  acid, 


19.12 
12.75 

3.42 

8.94 

0.24 

0.15 

0.0238 

0.0667 

6.0005 

6.0521 
0.0224 

Ox. 

799.59 
3.62 
2.04 

121.86 
66.90 
0.468 
1.181 
1.071 
4.321 
0.731 
0.098 
0.123 
0.018 


62.22 
5.91 
4.99 

0.38 

0.54 

0.0173 

0.2964 

0.0070 

0.0031 

0.0007 

0.2532 

0.0181 

Calf. 

826.71 
5.76 
1.61 

102.50 
56.41 
0.957 
0.269 
1.263 
4.864 
0.631 
0.130 
0.109 
0.018 


1.  THE  RED  BLOOD-CORPUSCLES. — Human  red  blood-corpuscles  re- 
semble biconcave  lenses :  their  diameter  varies  between  0.0064  and 
0.0086  millimeters. 


472 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


In  man  and  all  mammalia,  with  the  exception  of  the  camel  tribe, 
they  are  circular  and  devoid  of  a  nucleus ;  in  birds,  reptiles,  and  most 
fish,  they  are  oval,  biconvex,  and  nucleated ;  in  the  camel,  the  red 
blood -cells  are  oval,  but  are  not  nucleated.  From  the  fact  that  the 
edges  of  the  red  blood-cells  are  convex  and  the  centre  concave,  these 
different  parts  refract  light  differently,  and  when  examined  under  the 
microscope,  if  the  edges  are  sharply  denned,  the  centres  appear  dark, 
and  vice  versa  (Fig.  172). 

There  is  no  constant  relation  between  the  size  of  an  animal  and  the 
size  of  its  blood-disks ;  thus,  among  mammals,  although  the  red  blood- 
corpuscles  of  the  elephant  are  the  largest,  those'  of  the  mouse  are  by  no 
means  the  smallest,  being,  in  fact,  three  times  as  large  as  those  of  the 
musk-deer  (Fig.  173). 


FIG.  172.— RED  BLOOD-CORPUSCLES.    (Landois.) 

A,  human  red  blood-corpnscles:  1,  seen  on  the  flat;  2,  on  edge:  3,  rouleaux  of  colored  corpuscles 
slightly  separated.  B,  colored  amphibian  blood-corpuscles:  1,  seen  on  the  flat,  and,  2,  on  edge.  C,  ideal 
transverse  section  of  a  human  red  blood-corpuscle  magnified  five  thousand  times  linear:  no,  diameter; 
c  d,  thickness. 

In  the  various  domestic  animals  their  diameter  is  placed  as  follows 
in  fractions  of  a  millimeter :  horse,  0.004-0.005  ;  ox,  0.003-0.005  ;  dog, 
0.005-0.007;  sheep,  0.002-0.004;  goat,  0.002;  hog,  0.003-0.004  milli- 
meters. Frequentl}',  particularly  in  growing  animals  and  after  profuse 
hemorrhage  or  exhausting  disease,  red  blood-corpuscles  smaller  than  the 
above  will  be  found.  These  are  probably  to  be  regarded  as  young,  grow- 
ing blood-cells.  The  number  of  the  red  blood-cells  is  almost  infinite;  in 
one  cubic  centimeter  of  blood  in  man,  five  million  red  blood-disks  have 
been  estimated  to  be  present ;  in  the  goat,  nine  to  ten  millions  ;  in  the  lamb, 
thirteen  to  fourteen  millions ;  in  birds,  one  to  four  millions  ;  in  the  fish, 
one-quarter  to  two  millions ;  in  the  frog,  half  a  million ;  and  in  the  pro- 
teus,  thirty-six  thousand.  In  fact,  30  to  40  per  cent,  of  the  entire  mass 
of  the  blood  is  composed  of  red  blood-corpuscles ;  thus,  in  the  horse, 


BLOOD. 


473 


63. 7  per  cent,  of  the  blood  is  constituted  by  the  plasma,  and  36.3  per 
cent,  blood-corpuscles.  The  red  corpuscles,  as  already  mentioned,  are 
heavier  than  the  other  constituents  of  the  blood,  and  are  the  cause  of 


FIG.  173.— BLOOD-CORPUSCLES  OF  DIFFERENT  ANIMALS.    (Thanh offer.) 

1,  proteus  :  2,  rana  esculenta :  a,  upper  view  :  b,  white  blood-corpuscle :  c.,  side  view  of  red  blood-cor- 
puscle: 3,  triton ;  4,  snake:  5,  camel;  6,  turtle;  7,  salamander:  8,  carp;  9,  cobitis  fossilis;  10,  cuckoo; 
11,  chicken;  12,  canary-bird;  13.  lion:  14,  elephant;  15,  man:  a,  upper  view;  1>.  crenated  form;  c,  color- 
less corpuscle ;  16,  horse,  the  cells  arranged  in  rouleaux  ;  17,  hippopotamus,  upper  view. 

the  color  and  opacity  of  the  blood ;  their  specific  gravity  may  be  placed 
at  about  1090.  If  water  is  added  to  blood,  it  appears  darker  in  reflected 
light,  but  is  more  transparent.  This  depends  upon  the  change  in  shape 


FIG.  174.— RED  BLOOD-CORPUSCLES,  SHOWING  VARIOUS  CHANGES  IN  SHAPE.    (Landois.) 

«,  6,  normal  human  red  corpuscle,  with  the  central  depression  more  or  less  in  focus :  c,  d,  e,  mulberry 
forms:  <j,  h,  crenated  corpuscles;  A%  pale,  decolorized  corpuscles;  t,  stroma;  /,  a  frog's  corpuscle,  partly 
shriveled,  owing  to  the  action  of  a  strong  saline  solution. 

of  the  red  blood-cells :  as  they  imbibe  water  they  swell  up,  and  so  reflect 
less  light,  and  at  the  same  time  the  co-efficient  of  refraction  differs  less 
than  normal  from  that  of  the  blood-serum.  On  the  other  hand,  if  salt 


474 


PHYSIOLOGY   OF   THE  DOMESTIC   ANIMALS. 


solution  is  added  to  blood  instead  of  water,  the  corpuscles  shrivel  up  and 
therefore  favor  the  reflection  of  light  and  prevent  its  transmission ; 
hence  the  blood  is  now  less  transparent,  but  appears  lighter  in  reflected 
light  (Fig.  174). 

The  red  blood-corpuscles  are  almost  fluid  in  consistence,  and 
resemble,  therefore,  suspended  drops  of  jell}'.  This  characteristic  is 
frequently  seen  when  the  circulation  in  the  capillaries,  as  in  the  mesen- 
tery of  the  guinea-pig,  is  examined  under  the  microscope.  The  red 
blood-cells  will  often  be  observed  to  change  their  shape  by  pressure 
from  a  disk  to  an  elongated  rod,  and  sometimes  such  a  distorted  cor- 
puscle will  catch  at  the  point  of 
bifurcation  of  a  capillary,  where  it 
may  hang  like  a  pair  of  saddle-bags, 
part  in  one  branch  of  the  capillary, 
and  the  other  half  in  the  opposite. 
Even  in  animals  with  nucleated  red 
blood-cells,  like  the  frog,  similar 
change  in  shape  may  be  seen  ;  the 
red  blood-cells  may  even  be  seen  to 
pass  out  through  the  walls  of  the 
blood-vessels,  becoming  in  the 
process  drawn  out  into  a  fine  thread. 
The  red  blood-corpuscles  are 
composed  of  the  "  stroma"  and  "  hae- 
moglobin." 

Early  observers  regarded  the  red 
blood-corpuscle  as  a  vesicular  body 
in  which  a  cell-membrane  inclosed 
fluid  contents ;  at  present  it  is  be- 
lieved to  be  composed  of  a  semi-fluid 
net-work  or  frame-work,  the  stroma, 
denser  at  the  periphery  than  at  the 
centre,  in  the  meshes  of  which  are  inclosed  the  other  constituents  of  the 
cell.  The  stroma  may  be  demonstrated  by  alternately  freezing  and 
thawing  the  blood,  which  then  loses  its  opacity  and  becomes  a  clear, 
lake-colored  fluid,  the  haemoglobin  having  left  the  corpuscles  to  pass  into 
solution  in  the  plasma,  and  the  stromata  remaining  as  colorless  bodies, 
which  sometimes  retain  the  original  form  of  the  blood-cell,  but  usually 
are  either  more  globular  or  more  shriveled  than  normal.  The  stroma  is 
colorless  and  highly  elastic  and  is  albuminous  in  nature ;  it  is  insoluble 
in  serum,  dilute  salt  or  sugar  solutions,  and  water  below  60°  C.,  but  it 
is  soluble  in  serum  containing  alcohol,  ether,  or  chloroform,  in  caustic 
alkalies,  and  in  solutions  of  alkaline  salts  of  the  bile  acids. 


FIG.    175.— H^MOG^OBIN    CRYSTALS 
THE  Ox.     (Ellenberger.) 


OF 


BLOOD. 


475 


The  most  important  constituent  of  the  red  blood-corpuscles,  both  in 
quantity  and  function,  is  the  "  haemoglobin."  Haemoglobin,  or  the  blood 
coloring-matter,  is  a  complicated,  crystallizable  albuminoid  body 
containing  iron,  and  forms  about  90  per  cent,  of  the  red  blood-cells. 
When  separated  from  the  corpuscles,  haemoglobin  readily  crystallizes  out 

.4,  a 

o 


FIG.  176.— BLOOD-CRYSTALS  OF  MAN  AND  DIFFERENT  ANIMALS.     (Thanhoffer  and  Prey.) 

1,  haemoglobin  crystals ;  Mo,  squirrel ;  Tr,  guinea-pig ;  U,  ground-mole :  L.  horse:  Em,  man;  H, 
marmot;  Ma,  cat;  T,  cow;  mu,  from  the  venous  blood  of  a  cat.  2,  hsematin  crystals ;  E,  man;  V&, 
sparrow ;  M,  cat.  3,  haematoidin  crystals  from  an  old  blood  extravasation  of  man. 

of  its  solutions  in  serum  when  concentrated.  These  crystals  have  dif- 
ferent forms  in  different  species  of  animals,  depending,  apparently,  on 
varying  amounts  of  water  of  crystallization.  In  the  domestic  animals  they 
belong  to  the  rhombic  system  ;  those  of  the  squirrel  are  hexagonal.  The 


476  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

crystals  are  doubly  refractive  and  soluble  in  water  and  weak  alkaline 
solutions,  those  obtained  from  horses'  blood  being  more  soluble  than  the 
haemoglobin  of  the  dog  or  cat  (Figs.  175  and  176). 

Haemoglobin  solutions  decompose  after  s.tanding  a  few  daj^s,  es- 
pecially when  concentrated  and  exposed  to  a  warm  temperature,  and  the 
red  color  is  then  replaced  by  a  dirty-brown  hue,  which  appears  greenish 
in  transmitted  light.  Concentrated  alkalies,  various  metallic  salts,  and 
acids  facilitate  this  decomposition,  which  consists  of  the  breaking  up  of 
the  haemoglobin  into  certain  albuminoids  and  a  coloring  matter,  haematin, 
which  is  often  found  in  old  blood  extravasations.  Haemoglobin  crystals 
may  be  obtained  in  various  ways  from  the  blood  of  the  dog,  horse, 
guinea-pig,  or  cat.  All  the  agents  which  deprive  the  red  corpuscles  of 
their  coloring  matter,  so  rendering  the  blood  lake-colored,  may  serve  to 
form  oxyhaemoglobin  crystals ;  such  as  repeated  freezing  and  thawing, elec- 
tricity, a  temperature  of  60°  C.,  powdered  salts,  ether  in  vapor  or  sub- 
stance, chloroform,  and  the  bile  salts.  The  simplest  way  is  to  defibrinate 
dog's  blood,  remove  as  much  serum  as  possible,  and  then  shake  the  blood 
with  a  little  ether.  As  soon  as  the  ether  has  partially  evaporated  the 
crystals  commence  to  form. 

The  composition  of  haemoglobin  is  as  follows  : — 


16.1^21.6^0.5. 


The  following  has  been  given  as  its  empirical  formula,  assuming 
that  the  molecule  contains  one  atom  of  iron  : — 

C60oH960N164FeS8Om. 

Haemoglobin  readily  forms  a  loose  chemical  union  with  oxygen, 
called  -  oxyhaemoglobin.  It  may  be  formed  by  shaking  a  solution  of 
haemoglobin  with  oxygen.  The  oxygen  is  again  readily  removed  from 
this  compound  by  exposure  to  a  vacuum  or  by  various  reducing  agents, 
such  as  ammon.  sulph.,  iron  salts,  or  metallic  iron.  That  this  union  of 
oxygen  with  haemoglobin  is  of  a  chemical  nature  is  proven,  in  the  first 
place,  by  the  constancy  of  the  equivalent  of  combination :  Thus,  one 
gramme  of  haemoglobin  will  unite  with  0.0024  gramme  oxygen ;  this 
would  place  the  molecular  weight  of  haemoglobin  at  about  13,000. 

In  the  second  place,  the  difference  in  optical  characteristics  of 
haemoglobin  and  oxyhaemoglobin  point  to  difference  in  chemical  consti- 
tution. Thus,  reduced  haemoglobin  is  characterized  by  an  absorption- 
band  in  the  yellow  portion  of  the  spectrum,  while  solutions  of 
oxyhaemoglobin  show  two  absorption-bands,  one  at  the  line  D  (sodium 
line),  and  the  other  at  E  of  the  solar  spectrum,  while  the  portion  of  the 
spectrum  which  with  reduced  haemoglobin  is  dark,  with  oxyhaemoglobin 
is  clear  (Fig.  177). 


BLOOD. 


477 


In  the  animal  body  haemoglobin  is  never  saturated  with  oxygen, 
even  in  arterial  blood,  while  oxy haemoglobin  is  never  absent  from  venous 
blood ;  consequently,  physiologically,  we  have  to  deal  with  an  association 


of  haemoglobin  with  oxy haemoglobin,  the.  relative  proportions  of  each 
varying  in  different  localities  and  under  different  circumstances. 
Further  characteristics  of  these  bodies  will  be  studied  in  the  chapter  on 
Respiration. 


478  PHYSIOLOGY  OF  THE   DOMESTIC  ANIMALS. 

Compounds  similar  to  oxyhsemoglobin  are  formed  between  haemo- 
globin and  carbon  monoxide  and  cyanogen.  These  two  gases  displace  the 
oxygen  from  oxyhaemoglobin,  and  form  compounds  which  cannot  again 
be  broken  up  with  oxygen.  These  compounds,  as  well  as  those  formed 
with  nitrous  oxide  and  sulphuretted  hydrogen,  are  more  stable  in  nature 
than  the  oxyhsemoglobin. 

Haemoglobin  is  chemically  an  even  more  complex  body  than  albumen, 
since  the  latter,  together  with  haematin,  are  decomposition  products  of 
haemoglobin.  This  decomposition  especially  occurs  under  the  action  of 
acids,  though  it  also  takes  place  when  solutions  of  haemoglobin  are 
exposed  to  a  moderately  warm  temperature.  Out  of  one  hundred  parts 
haemoglobin,  about  four  parts  haematin  and  ninety-six  parts  albumen 
may  be  separated. 

The  inorganic  constituents  of  the  red  blood-corpuscles  differ  very 
essentially  from  those  found  in  the  blood-plasma.  While  the  latter  is 
rich  in  chlorine  and  sodium,  only  traces  are  to  be  found  in  the  blood- 
corpuscles,  where,  however,  potassium  and  phosphates  are  present  in 
large  amounts,  though  they  are  almost  entirely  absent  from  the  serum. 
The  fact  that  we  have  here  such  a  marked  separate  distribution  of  soluble 
salts,  without  any  apparent  tendency  to  their  equal  distribution,  shows 
that  there  must  be  some  force  present  which  interferes  with  the  working 
of  the  laws  of  diffusion  and  inhibition. 

The  following  table  shows  the  contrast  between  the  inorganic  con- 
stituents of  the  corpuscles  and  blood-plasma  (Schmidt) : — 

1000  parts  of  Moist  Corpuscles  yield—  1000  parts  of  Plasma  yield- 

Mineral   matters    (exclusive  Mineral  matters,  .      .  8.550 


of  iron), 
Chlorine, 

Sulphuric  anhydride, 
PHOSPHORUS  PENTOXIDE, 
POTASSIUM,   . 
Sodium, 

Calcium  phosphate, 
Magnesium,  . 


8.120  CHLORINE, 

1.686  Sulphuric  anhydride, 

0.066  Phosphorus  pentoxide, 

1.134  Potassium, 

3.328  SODIUM.     . 

1.052  Calcium  phosphate,  . 

0  114  Magnesium  phosphate, 
0.073 


3.640 

0.115 
0.119 
0.323 
3.341 
0.311 
0.222 


Too  much  importance  must  not,  however,  be  laid  upon  this  peculiar 
distribution  of  the  inorganic  constituents  of  the  red  blood-corpuscles 
and  plasma,  as  given  above  for  human  blood,  since  it  does  not  by  tiny 
means  hold  in  the  case  of  other  animals,  for  in  most  animals  the  sodium 
salts  in  the  corpuscles  actually  preponderate  over  the  potassium  salts. 
The  following  table  illustrates  this : — 

BLOOD-OKLL.S.  LIQUOK  SANGUINIS. 

K. 

Man, 
Dog, 
Cat,  . 
Sheep, 
Goat, 


K. 

Na. 

Cl. 

K. 

Na. 

Cl. 

40.89 

9.71 

21.00 

5.19 

37.74 

40.68 

6.07 

36.17 

24.88 

3.25 

39.68 

37.31 

7.85 

35.02 

27.59 

5.17 

37.64 

41.70 

14.57 

38.07 

27.21 

6.56 

38.56 

40.89 

37.41 

14.98 

31.73 

^3.55 

37.89 

40.41 

BLOOD.  479 

2.  THE  WHITE  BLOOD-CORPUSCLES. — The  white  blood-cells  are  nucle- 
ated masses  of  free  protoplasm  destitute  of  any  membrane,  granular  in 
appearance,  and  of  the  same  nature  as  lymph  and  pus,  or  connective- 
tissue  corpuscles.  When  in  globular  form  these  cells  have  a  diameter 
of  about  0.01  millimeter ;  like  other  forms  of  free  protoplasm,  such  as 
the  amoeba,  they  are  capable  of  assuming  the  most  diverse  shapes.  Even 
after  being  drawn  from  the  body,  if  a  drop  of  blood  is  kept  at  the  body 
temperature  011  a  warm  stage  under  the  microscope,  the  white  blood- 


FIG.  178.— HUMAN  LEUCOCYTES  SHOWING  AMOEBOID  MOVEMENTS.    (Landois.) 

cells  may  be  seen  to  change  their  shape  and  position,  arid  even  take  fine 
granules,  such  as  carmine,  into  their  interior.  In  other  words,  they 
behave  precisely  like  the  amreba  (Fig.  178). 

The  white  blood-cells  are  found  in  much  smaller  numbers  in  the 
blood  than  the  red  cells ;  their  relative  proportions  vary  according  to  the 
nutritive  condition  of  the  animal,  the  locality  from  which  the  blood  is 
taken,  and  various  other  circumstances.  As  an  average,  it  may  be  stated 
that  there  are  about  three  hundred  to  three  hundred  and  fifty  times  as 
many  red  cells  as  white. 


480  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

The  white  corpuscles  are  much  lighter  than  the  red,  as  is  shown  by 
their  being  found  in  greatest  number  near  the  upper  surface  of  a  blood- 
clot,  and  by  the  fact  that  when  horses'  blood  coagulates  the  white  blood- 
cells  form  a  distinct  layer  on  the  surface  of  the  red  corpuscles. 

The  white  blood-cells  possess  great  adhesiveness,  even  while  in  the 
blood-current.  This  adhesiveness  of  the  white  cells  may  also  be  seen 
in  blood  drawn  from  the  body.  If  a  drop  of  blood  is  covered  with  a 
cover-slip  and  a  drop  of  -J  per  cent,  salt  solution  passed  under  the  cover 
by  dropping  a  little  of  the  solution  at  one  side. and  drawing  it  through 
by  placing  a  piece  of  bibulous  paper  at  the  opposite  edge,  the  red  blood- 
cells  may  be  seen  by  the  microscope  to  rapidly  pass  from  one  side  of  the 
field  to  the  other,  while  the  white  cells  remain  adherent  to  the  cover-slip. 
They,  therefore,  have  a  tendency  to  cling  to  the  walls  of  the  blood-vessel 
in  which  they  may  be  circulating,  and,  since  the  white  cells  have  an  almost 
fluid  consistence,  they  readily  pass  through  the  walls  of  the  capillaries 
into  the  surrounding  tissue.  This  especially  occurs  in  inflamed  tissues, 
when  the  slow  blood-current  and  high  pressure  favors  this  transudation  ; 
in  fact,  according  to  many  pathologists,  nearly  all  pus-cells  are  supposed 
to  originate  in  such  a  transudation  of  the  white  blood-cells. 

After  passing  through  the  walls  of  the  capillaries  in  normal  circum- 
stances the  white  blood-cells  directly  enter  the  lymph-spaces  in  which 
originate  the  Lymphatic  vessels,  from  which  they  may  again  enter  the 
blood-current.  It  does  not,  however,  follow  that  all  lymph-corpuscles 
which  are  thrown  into  the  venous  current  have  originally  been  derived 
from  white  blood-cells  which  have  passed  from  the  blood  through  the 
walls  of  the  capillaries  into  the  lymph.  We  have  already  seen  that 
man}T  lymph-cells  originate  in  the  lymphatic  glands,  are  developed  in 
the  blood  into  red  blood-cells,  and  as  such  are  again  broken  down.  This 
change  of  the  white  into  red  blood-cells  appears  principally  to  take  place 
in  the  red  marrow  of  bones  and  in  the  spleen.  In  these  organs  capillary 
arterioles  do  not  pass  directly  into  the  venous  radicals,  but  into  large 
spaces,  or  lacunse,  from  which,  after  passing  through  a  sieve-like  cellular 
net-work,  the  modified  blood-cells  enter  at  once  into  large  venous  capil- 
laries. The  passage  of  the  blood  into  these  great  expansions  naturally 
produces  a  great  slowing  of  the  current,  and  it  is  quite  conceivable  that 
time  will  then  be  given  for  profound  changes  in  the  blood-cells ;  part  of 
the  protoplasm  of  the  white  cells  is  changed  into  haemoglobin,  the 
nucleus  appears  to  be  extruded  and  ultimately  dissolved  in  the  blood- 
serum,  and  a  red  blood-cell  is  thus  developed. 

The  white  blood-cells  have  a  very  complex  chemical  composition ; 
various  albuminoids  enter  into  their  composition,  as  well  as  carbo- 
hydrates, fats,  lecithin,  cholesterin,  phosphates,  and  calcium,  while  the 
cell-nucleus  appears  to  consist  mainly  of  a  phosphorized  bod}^,  nuclein. 


BLOOD.  481 

Albuminoids  of  various  sorts  form  the  great  mass  of  the  white 
blood-corpuscles.  These  correspond  mainly  to  the  albuminoids  which 
are  found  in  the  blood-plasma,  which,  together  with  the  paraglobulin, 
or  fibrino-plastic  substance,  will  be  described  in  the  consideration  of  the 
coagulation  of  the  blood. 

The  protoplasm  of  the  colorless  blood-cells  undergoes  partial  coagu- 
lation at  40°  C.  It  swells  and  becomes  transparent  when  treated  with 
acetic  acid,  the  nuclei  becoming  more  distinct.  With  10  per  cent,  salt 
solution  the  protoplasm  swells  and  becomes  dissolved  (leaving  the  nuclei 
intact),  the  solution  being  coagulable  with  heat  and  the  mineral  acids 
and  precipitated  by  dilution  with  water.  The  proteid  constituents  of 
the  white  blood-cells  are  thus  largely  of  a  globulin-like  nature. 

Of  the  carbohydrates,  gtycogen  occupies  the  first  rank  in  importance. 
When  treated  with  a  solution  of  iodine  (one  gramme)  in  iodide  of  potas- 
sium (two  grammes  in  one  hundred  c.c.  water)  many  of  the  white  blood- 
cells  assume  a  reddish,  mahogany  color,  while  in  others  the  body  of  the 
cell  stains  deep  j^ellow,  numerous  granules  taking  on  the  mahogany 
tint  which  is  characteristic  of  gtycogen.  From  the  importance  which 
glycogen  has  been  found  to  possess  for  muscular  contraction,  it  may  be 
assumed  that  the  contractility  of  the  white  blood-corpuscles  is  developed 
at  the  expense  of  the  glycogen. 

Variable  amounts  of  fat  are  also  found  in  the  protoplasm  of  the 
white  blood-corpuscles  in  the  form  of  highly  refractive  granules.  The 
importance  of  this  fat  for  the  life  processes  of  the  blood-cells  is  as  jret 
undetermined.  Whether  it  is  formed  as  a  result  of  the  breaking  down 
of  the  cell-protoplasm,  or  whether  it  exists  as  a  result  of  absorption 
processes,  is  not  certain,  though  the  following  experiment  seems  to 
indicate  the  former  origin. 

If  a  piece  of  dry  pith  is  inserted  into  the  abdominal  cavity  of  a  liv- 
ing animal,  the  pores  of  the  pith  are  soon  found  to  be  filled  with  blood- 
serum  and  white  blood-cells ;  the  latter  pass  into  the  interior  of  the  pith, 
and  if,  after  remaining  in  the  abdominal  cavity  for  twenty-four  hours, 
the  pith  is  examined  under  the  microscope,  the  external  layers  will  be 
found  to  be  occupied  by  perfectly  normal,  living,  white  blood-cells,  wrhile 
those  which  are  found  in  the  central  portions  have  assumed  a  spherical 
form  and  undergone  such  extensive  fatty  degeneration  that  the  pith 
seems  to  be  impregnated  with  fat-globules. 

Lecithin. — A  phosphorized  body  which  has  already  been  described 
as  a  constituent  of  nearly  all  developing  cells  is  also  found  as  a  constant 
constituent  of  the  white  blood-cells.  As  regards  the  origin  of  this  sub- 
stance, there  is  also  the  greatest  uncertainty,  though  there  is  some 
evidence  in  favor  of  the  view  that  it  exists  as  a  preliminary  stage  to 
the  formation  of  fat.  Lecithin  is  capable  of  a  high  degree  of  aqueous 

31 


482  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

inhibition,  when  it  becomes  a  very  adhesive,  gummy  substance,  to  which 
probably  the  adhesive  properties  of  the  white  blood-cells  are  due. 

Cholesterin  is  also  a  constant  constituent  of  normal  white  blood- 
cells.  It  is  not  known  whether  the  cholesterin  is  dissolved  or  suspended 
in  the  protoplasm  of  the  white  blood-corpuscles. 

In  addition  to  the  above  substances  which  are  contained  in  the  liv- 
ing white  blood-corpuscles,  there  exists  in  breaking  up  corpuscles  the 
fibrin  ferment  which  originates  in  the  death  of  the  protoplasm.  This 
substance,  which  possesses  the  power  of  converting  soluble  into  insoluble 
fibrin,  may  be  regarded  as  a  complicated  organic  body,  and  possesses, 
even  when  in  most  minute  quantity,  the  power  of  decomposing  the 
peroxide  of  hydrogen,  probably  with  the  assistance  of  the  elements  of 
water,  and  of  producing  the  modified  forms  of  fibrinogen.  That  this  fer- 
ment is  set  free  by  the  breaking  down  of  tl^e  protoplasm  of  the  white 
cells,  and  is  not  contained  dissolved  in  the  plasma  of  the  blood,  is  ren- 
dered probable  by  the  following  experiment : — 

If  the  mesenteiy  of  the  guinea-pig  be  examined  under  the  micro- 
scope and  a  crystal  of  common  salt  placed  near  a  small  blood-vessel,  as 
the  salt  melts  the  inner  wall  of  the  vessel  will  be  found  to  be  gradually 
covered  with  numerous  white  blood-cells  until  the  lumen  of  the  vessel  is 
finally  obstructed  by  a  plug  of  white  blood-cells.  At  first  the  margin  of 
each  separate  cell  is  distinct,  but  soon  they  become  indistinct  and  the 
vessel  is  then  filled  with  a  mass  of  fibrin,  white  thrombus,  which  exactly 
resembles  the  colorless  coagulum  which  forms  in  clotting  blood-plasma. 

Nuclein  is  the  most  important  constituent  of  the  cell-nucleus.  Nu- 
clein  is  insoluble  in  water  and  dilute  acids,  but  readily  soluble  in  dilute 
potash  solutions  ;  when  treated  with  hydrochloric  acid  it  is  changed 
into  a  stiff  jelly.  Nuclein  is  completely  indifferent  to  the  action  of  the 
digestive  juices. 

As  every  increase  in  the  white  blood-cells  is  preceded  by  a  growth 
of  the  nucleus,  it  is  possible  that  the  nuclein  plays  an  important  role 
in  the  life  of  the  white  blood-corpuscles. 

In  addition  to  the  white  and  red  blood-corpuscles,  microscopic  ex- 
amination of  the  blood  will  often  reveal  the  presence  of  granular  nucleated 
bodies,  which  are  described  as  blood-plates  or  haematoblasts.  These 
bodies  vary  considerably  in  size,  being  usually  about  one-third  the  size 
of  a  red  blood-cell,  and,  like  them,  biconcave  in  shape,  have  about  the 
same  specific  gravity  as  the  white  blood-cells,  and  possess  the  power 
of  amoeboid  movement.  They  occur  as  pale,  colorless,  oval,  round, 
or  lenticular  disks,  of  variable  size,  averaging  about  3  (J..  By  Hayem 
the}1-  are  supposed  to  represent  an  early  stage  of  development  of  the  red 
blood-corpuscles.  They  are  about  forty  times  as  numerous  as  the 
leucocytes,  and  may  be  recognized  in  the  circulating  blood  in  the  mesen- 


BLOOD. 


483 


tery  of  the  guinea-pig  or  in  the  wing  of  the  bat.  They  are  precipitated 
in  enormous  numbers  upon  threads  suspended  in  fresh  blood.  They  are 
believed  by  Bizzozero  to  be  the  agents  which  immediately  induce  coagu- 
lation and  take  part  in  the  formation  of  fibrin.  They  become  colorless 
and  disintegrate  during  the  act  of  coagulation  (Fig.  179). 

3.  BLOOD-PLASMA  AND  BLOOD  COAGULATION. — Blood-plasma  is  blood 
less  blood-corpuscles.  It  may  readily  be  obtained  for  study  by  pre- 
venting the  coagulation  of  horses'  blood  by  cold,  when  both  the  red  and 
white  blood-corpuscles  settle  to  the  bottom  and  leave  the  pure  plasma, 
forming  a  clear,  amber-colored  fluid  above. 

Plasma  is  a  somewhat  viscid  fluid  of  alkaline  reaction.  Its  specific 
gravity  is  about  1027  or  1028.  It  contains  about  90  per  cent,  water, 
with  from  7  to  9  per  cent,  of  various  albuminoids,  with  small  amounts 


FIG.  179.— "  BLOOD-PLATES  "   AND   THEIR  DERIVATIVES,  AFTER  BIZZOZERO 
AND  LAKER.    (Landois.) 

1,  surface  view  of  red  blood-corpuscles ;  2,  side  view;  3,  unchanged  blood-plates;  4,  a  lymph-cor- 
puscle, surrounded  with  blood-plates;  5,  blood-plates  variously  altered;  6,  a  lymph-corpuscle  with  two 
heaps  effused  blood-plates  and  threads  of  fibrin;  7,  group  of  blood-plates  fused  or  run  together;  8,  a  simi- 
lar heap  of  partially  dissolved  blood-plates  with  threads  of  fibrin. 

of  urea,  kreatin,  kreatinin,  and  other  nitrogenous  organic  bodies,  as  well 
as  sugar,  fat,  cholesterin,  and  mineral  bodies,  of  which  compounds  of 
sodium  with  chlorine  and  carbon  dioxide  are  in  excess.  If  horses' 
plasma,  prepared  as  above,  is  allowed  to  become  warmed  a  few  degrees 
above  the  freezing  point,  it  completely  solidifies  into  a  solid  mass  :  the 
plasma  is  then  said  to  be  coagulated.  This  process  of  coagulation  com- 
mences at  the  edges,  in  contact  with  the  walls  of  the  vessel  which  con- 
tains it,  and  on  the  free  surface  of  the  fluid,  and  rapidty  extends  through- 
out the  entire  mass  until  a  firm  jelly  results,  which  is  quite  as  transparent 
as  the  original  fluid.  Coagulation  is  due  to  certain  albuminoids  becoming 
transformed  from  the  fluid  to  the  solid  state,  resulting  in  the  formation 
of  fibrin.  Shortly  after  the  formation  of  the  coagulum,  a  depression 
forms  in  the  upper  surface  of  the  clot,  in  which  a  clear  fluid,  the  serum, 


484  PHYSIOLOGY  OF  THE   DOMESTIC  ANIMALS. 

collects  ;  the  clot  then  gradually  shrinks  away  from  the  sides  of  the  vessel 
and  contracts  in  every  direction,  and  as  the  coagulum  decreases  in  bulk 
the  fluid  serum  increases,  until,  finally,  the  now  opaque,  small,  firm  clot 
swims  in  a  large  amount  of  clear,  yellowish  serum. 

When  horses'  blood  is  not  artificially  cooled,  and  in  blood  of  other 
mammals,  the  process  of  coagulation  follows  a  somewhat  different  course. 
Here  also  it  is  only  the  fibrin  which  coagulates,  and  not  the  blood  in  toto; 
but  the  process  takes  place  so  rapidly  that  the  corpuscles  do  not  have 
time  to  settle,  but  remain  entangled  in  the  fibrin,  and  the  coagulum, 
instead  of  being  colorless,  is  of  a  deep-red  color  from  the  contained  red 
blood-corpuscles,  the  whole  forming  a  red,  gelatinous  mass, — the  crassa- 
mentum,  or  clot.  Here,  also,  the  process  of  coagulation  commences  at  the 
free  surface  of  the  blood  and  at  the  surfaces  in  contact  with  the  walls  of 
the  vessel  by  the  formation  of  a  delicate  pellicle,  which  rapidly  thickens 
until  in  from  seven  to  fourteen  minutes  the  entire  mass  of  blood  is  trans- 
formed into  a  stiff  jelly ;  and  here,  also,  after  the  formation  of  the  clot, 
there  is  a  gradually  progressive  contraction,  with  exudation  of  serum, 
until  finally  there  results  a  small,  red,  firm  coagulum,  floating  in  the 
yellowish  serum. 

Blood  of  different  species  of  animals  varies  in  the  rapidity  with  which 
coagulation  takes  place.  In  the  following  series  coagulation  occurs  in 
gradually  increasing  rapidity  from  the  first  to  the  last, — horse,  cat, 
dog,  ox,  pig,  goat,  sheep, — the  time  varying  from  twenty-five  to  one 
and  a  half  minutes.  Normal  horses'  blood  always  clots  so  slowly 
that  the  corpuscles  have  time  partially  to  settle  to  the  bottom 
of  the  vessel  which  contains  it.  Immediately  before  coagulation,  there- 
fore, the  horse's  blood  forms  different-colored  layers,  the  upper  and 
smallest  being  yellowish,  while  the  lower  is  red.  When  coagulation 
takes  place  the  same  arrangement  holds,  and  the  clot  of  horses'  blood 
has,  therefore,  a  yellowish  upper  surface,  the  so-called  buffy  coat,  forming 
what  used  to  be  called  an  inflammatory  clot  (crusta  phlogistic  a}.  Every- 
thing, therefore,  which  accelerates  the  settling  of  the  red  blood-cells, 
or  which  delays  coagulation,  will  tend  to  develop  the  buffy  coat  on 
the  clot. 

In  addition  to  cooling,  coagulation  nuiy  be  retarded  by  pumping  out 
the  oxygen  from  the  blood,  by  saturation  with  carbon  dioxide  (explaining 
the  tardy  coagulation  of  the  blood  in  animals  dying  from  suffocation,  and 
why  coagulation  occurs  sooner  in  venous  than  arterial  blood),  addition 
of  certain  salts,  such  as  sulphate,  borate,  and  carbonate  of  sodium, 
chloride  of  sodium,  sulphate  of  magnesium,  nitrate,  acetate,  and  car- 
bonate of  potassium,  and  chloride  of  potassium,  through  the  addition 
of  small  amounts  of  caustic  potash  or  ammonia,  sugar  and  gum  solutions, 
or  by  acidulation  with  dilute  acetic  or  nitric  acids.  By  exact  neutraliza- 


BLOOD.  485 

tion  of  acidified  blood  with  ammonia,  or  through  the  prolonged  action  of 
ozone,  the  coagulabilit}'  of  the  blood  may  be  completely  removed. 

The  intravenous  injection  of  0.3  gramme  peptone  in  0.5  per  cent,  salt 
solution  for  each  kilo  of  body  weight  in  the  dog  likewise  prevents  the 
coagulation  of  the  blood. 

Warming  of  the  blood  above  its  normal  temperature  accelerates  co- 
agulation :  so,  also,  the  more  extensive  the  contact  of  the  blood  with 
foreign  bodies  and  with  the  atmosphere,  the  more  rapid  the  coagulation. 

If  blood,  as  it  escapes  from  a  blood-vessel,  is  stirred  or  whipped 
with  glass  rods  or  twigs,  coagulation  occurs  somewhat  more  rapidly 
than  normally ;  but  instead  of  the  entire  blood  being  transformed  into  a 
jelh',  the  substance — fibrin — on  whose  solidification  blood  coagulation 
depends  separates  in  the  form  of  fibrous  lumps  and  shreds  adhering  to 
the  body  with  which  the  blood  is  whipped.  The  blood  is  then  said  to  be 
defibrinated,  and  the  fluid  in  which  the  corpuscles  remain  suspended  is 
termed  serum,  instead  of  plasma.  Plasma  is,  consequent!}-,  the  fluid 
constituent  of  blood  which  still  contains  uncoagulated  fibrin  elements ; 
serum  is  plasma  minus  the  fibrin  elements.  Serum  may  be  obtained  as 
a  clear  fluid  by  allowing  the  corpuscles  to  settle  or  by  separating  them 
with  the  centrifugal  machine ;  or,  as  already  stated,  it  exudes  from  the 
clot  when  blood  is  allowed  spontaneously  to  coagulate. 

The  coagulation  of  the  blood  consists  in  the  formation  of  fibrin,  an 
albuminous  body  which  results  from  the  action  of  a  ferment-like  body 
on  the  albuminous  constituents  of  the  plasma,  the  process  being  similar 
to  the  spontaneous  conversion  of  soluble  into  coagulated  casein  in  milk 
from  the  action  of  the  casein  ferment. 

The  theory  as  to  the  formation  of  fibrin  which  has  met  with  most 
general  acceptance,  though  we  shall  find  that  it  requires  some  slight 
modification,  is  that  coagulation  results  when  two  albuminous  bodies 
contained  in  blood-plasma,  the  fibrinogen  and  fibrino-plastic  substances, 
unite  under  the  influence  of  the  fibrin  ferment.  The  conditions  governing 
this  chemical  process  may  be  made  clear  by  the  following  experimental 
facts  (Foster): — 

If  the  blood,  as  it  flows  from  a  divided  vessel,  is  received  in  a  beaker 
containing  about  one-third  the  volume  of  blood  of  a  saturated  solution 
of  a  neutral  salt,  such  as  magnesium  sulphate,  coagulation  will  be 
prevented,  the  corpuscles  will  settle  in  time  to  the  bottom  of  the  vessel, 
the  fluid  plasma — mixed,  of  course,  with  the  salt  solution — forming  a 
transparent  la\^er  above  them.  If  some  of  this  plasma  be  drawn  off 
with  a  pipette  and  diluted  with  eight  or  ten  times  its  bulk  of  water, 
coagulation  will  be  produced.  The  neutral  salt  has,  therefore,  merely 
prevented  coagulation  by  its  presence,  and  has  not  destroyed  the  sub- 
stance or  substances  from  which  fibrin  is  formed.  If  to  some  of  the 


486  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

undiluted  blood-plasma,  in  which  coagulation  has  been  prevented  by  cold 
or  a  neutral  salt,  an  excess  of  sodium  chloride  in  bulk  be  added,  a  sticky, 
white  precipitate  will  be  formed,  and  if  it  is  filtered  off'  it  will  be  found 
that  the  plasma,  even  if  warmed  or  diluted  with  water,  has  now  lost  its 
power  of  coagulation.  If  the  precipitate  collected  in  the  filter  be 
washed  with  a  saturated  solution  of  sodium  chloride,  in  which  it  is 
insoluble,  and  then  dissolved  in  a  small  amount  of  distilled  water 
(enough  salt  will  cling  to  the  precipitate  to  make  it  a  dilute  saline 
solution)  and  filtered,  the  clear  filtrate  will  rapidly  solidify  in  the  same 
manner  as  the  blood-plasma  prevented  by  cold  from  coagulation  when 
gently  warmed.  This  substance  is  termed  plasmine,  and  it  is  evident 
that  the  coagulation  of  the  blood  is  due  to  the  conversion  of  plasmine 
into  fibrin.  Plasmine  is  not,  however,  a  simple  body,  but  a  mixture  of 
two  proteids,  as  is  shown  by  the  following  facts  : — 

If  sodium  chloride  in  bulk  be  added  to  the  serum  which  separated 
from  clotted  blood,  a  precipitate  will  be  formed  which  in  its  general 
characters  resembles  plasmine,  but  its  solution  will  not  coagulate  spon- 
taneously. This  body  is  termed  paraglobulin  or  fibrinoplastin. 

If  sodium  chloride  be  added  in  bulk  to  some  hydrocele  fluid,  a 
similar  precipitate  will  also  be  formed,  which  also,  when  in  solution,  will 
not  coagulate  spontaneously.  This  substance  is  termed  fibrinogen.  If 
a  solution  of  fibrinogen  be  added  to  a  solution  of  paraglobulin,  coagula- 
tion occurs  in  a  manner  precisely  similar  to  that  observed  in  blood-plasma 
or  in  solutions  of  plasmine.  So,  also,  the  addition  of  blood-serum  to 
hydrocele  fluid  will  likewise  cause  coagulation.  These  facts  would  seem 
to  indicate  that  plasmine  is  a  mixture  of  paraglobulin  and  fibrinogen. 
Another  factor  is,  however,  also  concerned. 

Both  paraglobulin  and  fibrinogen  may  be  precipitated  from  serum 
and  hydrocele  fluid  by  C02,  and  yet  the  solutions  of  these  precipitates 
when  mixed  together  will  not  coagulate. 

If  some  defibrinated  blood  be  poured  into  about  twenty  times  its 
volume  of  strong  alcohol,  all  the  proteids  will  be  coagulated.  If,  after 
standing  some  weeks  in  alcohol,  the  precipitate  be  filtered  off  and  ex- 
tracted with  water,  a  few  drops  of  this  solution  added  to  the  above  mix- 
ture of  paraglobulin  and  fibrinogen  obtained  by  C02,  coagulation  will 
rapidly  result.  If,  however,  the  watery  extract  be  first  boiled,  no 
clotting  will  result.  This  points  to  the  presence  of  a  ferment.  Conse- 
quently we  say  coagulation  results  from  the  union  of  paraglobulin  and 
fibrinogen  in  the  presence  of  the  blood  ferment. 

It  has,  however,  been  found  that  fibrin  may  result  from  the  addition 
of  the  fibrin  ferment  to  pure  fibrinogen,  without  in  any  way  requiring 
the  assistance  or  presence  of  fibrinoplastin.  Nevertheless,  the  amount 
of  fibrin  so  formed  is  considerably  less  than  would  result  from  the  coag- 


BLOOD.  487 

illation  of  the  same  amount  of  fibrinogen  if  fibrinoplastin  were  present. 
It  would,  therefore,  appear  that  the  fibrinoplastin  in  some  way  assists  in 
converting  the  soluble  fibrinogen  into  the  insoluble  fibrin,  without  itself 
directly  taking  part  in  the  formation  of  the  latter.  This  view  is  sup- 
ported by  the  fact  that  while  blood-serum  is  entirely  free  from  fibriu- 
ogen  it  contains  nearly  as  much  fibrinoplastin  as  uncoagulated  blood. 

Fibrinoplastin  perhaps  acts  in  the  same  way  as  certain  salts  (NaCl, 
CaCl2)  and  lecithin,  which,  when  added  in  very  small  amounts  to  coag- 
ulable  fluids,  appear  to  increase  the  amount  of  fibrin  formed. 

The  above-mentioned  fibrin  factors  do  not  exist  ready  formed  in 
the  circulating  blood  of  living  animals,  but  originate  in  the  breaking 
down  of  the  white  blood-cells  in  man  and  other  mammals,  and  of  the  red 
nucleated  blood-cells  of  birds  and  amphibia.  As  to  how  far  the  haemato- 
blasts  are  concerned  in  this  process  is  still  the  subject  of  controversy; 
it  is,  however,  absolutely  certain  that  immense  numbers  of  the  white 
blood-corpuscles  disappear  during  coagulation. 

Fibrinogen  belongs  to  the  group  of  globulins,  i.e.,  albuminous  bodies  which 
are  insoluble  in  water,  but  soluble  in  dilute  saline  solutions,  in  which  again  they 
are  rendered  insoluble  through  the  action  of  acids  and  alkalies. 

Fibrinogen  may  be  prepared  by  collecting  horses'  blood  in  one-fourth  its 
volume  of  a  saturated  solution  of  magnesium  sulphate,  stirring  and  filtering, 
separating  the  corpuscles  from  the  plasma  by  the  use  of  the  centrifugal  machine, 
and  adding  to  the  latter  an  equal  volume  of  a  saturated  salt  solution.  The  pre- 
cipitate is  then  collected,  dried  by  pressing  between  layers  of  filter-paper,  dis- 
solved in  an  8  per  cent,  salt  solution,  again  precipitated  with  an  equal  volume  of 
saturated  salt  solution,  again  drying  and  dissolving,  and  repeating  the  process  until 
a  precipitate  is  obtained,  which,  after  drying  with  filter-paper,  still  retains  enough 
salt  adhering  to  it  to  render  it  soluble  in  distilled  water,  and  which  should  con- 
tain no  trace  of  serum-albumen  or  paraglobulin.  The  removal  of  the  paraglobu- 
lin  depends  upon  the  fact  that  fibrinogen  is  very  much  more  readily  precipitated 
l>y  15-20  per  cent,  salt  solution  than  is  paraglobulin.  So*  obtained,  fibrinogen,  in 
1-5  per  cent,  salt  solution,  coagulates  at  52°-55°  C.  It  also  may  be  obtained, 
mixed  with  fibrinoplastin,  from  hydrocele  or  pericardial  fluid,  by  dilution  with 
10-15  volumes  of  water,  or  by  the  passage  of  a  stream  of  CO2. 

The  jibrinoplastic  substance,  or  paraglobulin,  is  obtained  as  a  white  precipi- 
tate when  perfectly  clear  and  colorless  blood-serum  is  faintly  acidulated  with 
acetic  acid,  and  then  diluted  with  fifteen  or  twenty  times  its  volume  of  distilled 
water.  The  precipitate  is  then  collected  on  a  filter  and  washed  with  distilled 
water.  Out  of  100  c.c.  ox-serum  0.7-0.9  gramme  paraglobulin  may  be  obtained 
by  this  process,  though  it  is  almost  impossible  to  free  it  entirely  from  fibrin 
ferment. 

The  freshly  precipitated  paraglobulin  is  perfectly  white,  is  insoluble  in  water, 
but  is  soluble  in  dilute  solutions  of  sodium  bicarbonate,  sodium  phosphate,  sodium 
chloride,  and  other  neutral  salts  of  the  alkalies.  These  solutions  coagulate  on 
heating  like  ordinary  albumen  (between  60°  and  80°  C.),  and  when  diluted  with 
distilled  water  again  precipitate  the  paraglobulin. 

If  paraglobulin  is  added  to  certain  serous  fluids,  such  as  hydrocele  fluid,  peri- 
cardial fluid,  and  serous  effusions,  coagulation  is  instantly  produced  through  the 
action  of  the  fibrin  ferment,  which  always  contaminates  it. 

There  is  less  paraglobulin  in  horses'  blood  than  in  oxen's  blood — 0.3  to  0.5 
per  cent,  in  the  serum  of  the  former  to  0.7  to  0.8  per  cent,  in  the  latter. 

Paraglobulin,  as  well  as  fibrinogen,  originates  in  the  breaking  down  of 
white  blood-corpuscles. 

The  fibrin  ferment  has  never  been  obtained  pure.  Its  aqueous  solutions  may 
be  prepared  by  adding  15-20  volumes  of  absolute  alcohol  to  the  pure  serum  of 


488  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

horses',  oxen's,  or  dogs'  blood,  allowing  the  coagulated  albuminoids  to  remain  for 
at  least  two  weeks  under  alcohol  until  they  become  completely  insoluble,  filtering, 
drying  over  sulphuric  acid,  and  dissolving  in  water ;  traces  of  albumen  which 
still  cling  to  the  ferment  may  be  removed  by  the  cautious  addition  of  acetic  acid, 
or  CO2.  The  ferment  is  not  contained  in  living  blood,  but  is  a  product  of  break- 
ing down  white  blood-corpuscles.  Its  amount  appears  to  have  no  influence  on 
the  quantity  of  fibrin  formed,  but  only  on  the  rapidity  of  the  process.  Its  activity 
increases  up  to  the  temperature  of  the  body,  and  the  heat  of  boiling  water  destroys 
it ;  it  may  be  preserved  indefinitely,  without  losing  its  activity,  at  0°  C 

The  serous  transudations,  especially  of  the  horse,  since  they  contain  both 
fibrinogen  and  fibrinoplastin,  but  no  ferment,  coagulate  at  once  on  the  addition  of 
a  drop  of  ferment  solution  ;  these  fluids  are,  therefore,  admirable  tests  for  the  pres- 
ence of  the  ferment.  The  same  also  holds  for  the  still  fluid  blood  which  remains 
in  the  blood-vessels  after  death. 

Fibrin  is  an  albuminous  body  which,  in  its  percentage,  composition,  and  be- 
havior to  most  reagents,  does  not  difler  from  other  albuminoids.  It  may  readily 
be  obtained  by  whipping  blood  as  it  flows  from  a  vessel,  and  then  washing  the 
coagulum  in  water  until  all  the  red  blood-corpuscles  are  removed.  It  then  forms 
a  snow-white  fibrous  mass  of  the  greatest  elasticity,  this  latter  property  depend- 
ing on  the  water  contained  in  its  molecular  interspaces,  for  dry  fibrin  is  as  brittle 
as  glass. 

Fresh,  spontaneously  coagulated  fibrin  contains  within  its  meshes  large  quan- 
tities of  blood-serum,  which  are  pressed  out  in  the  contraction  of  the  fibrin. 

The  fibrin  formed  by  the  slow  coagulation  of  the  plasma  of  horses'  blood 
possesses  a  less  marked  fibrous  structure  than  the  fibrin  obtained  by  whipping 
blood,  or  even  by  the  coagulation  of  other  mammalian  blood.  It  is  rather  more 
of  an  almost  amorphous  jelly,  which  will  fracture  along  any  line. 

In  hydrochloric  acid  of  from  0.1-0.5  per  cent.,  and  in  dilute  phosphoric, 
acetic,  and  lactic  acid  solutions,  fibrin  swells  up  to  a  transparent  jelly,  but  with- 
out, to  any  great  extent,  passing  into  solution,  unless  kept  for  some  time  at  an 
elevated  temperature,  when  it  is  nearly  all  converted  into  syntonin  and  passes  into 
solution.  On  neutralization  it  is  precipitated,  the  precipitate  being  insoluble  in 
water,  but  readily  soluble  in  very  dilute  acids  and  alkalies.  Boiled  fibrin  is 
entirely  insoluble  in  dilute  acids  and  alkalies,  but  is  partially  soluble  in  the  con- 
centrated acids. 

The  cause  of  the  constant  fluidity  of  the  blood  in  the  living  organism 
is  found  in  the  influence  of  the  normal  vascular  wall  on  the  blood  con- 
tained in  the  vessels.  That  the  fibrin  factors  are  not  found  in  the  living 
blood  is  not  a  sufficient  explanation,  for  it  offers  no  reason  why  these 
substances  develop  in  blood  outside  of  the  body. 

Coagulation  occurs  as  soon  as  contact  with  the  living  blood-vessels 
ceases,  or  when,  through  various  causes,  the  walls  of  the  blood-vessels 
lose  their  normal  properties,  from  which  we  might  infer  that  something 
in  the  vascular  walls  prevents  the  development  of  the  fibrin  factors ;  for 
injections  of  fibrinoplastin  and  the  fibrin  ferment,  or  transfusion  of  u  lake- 
colored"  blood,  have,  as  an  immediate  consequence,  the  abundant  forma- 
tion of  blood-clots  even  in  perfectly  normal  vessels. 

It  is  not  necessary  for  the  blood  to  be  in  constant  motion  in  the 
vessels  to  prevent  coagulation,  for  the  circulation  may  be  arrested  in 
any  part,  provided  the  stoppage  does  not  entail  any  injury  to  the  walls 
of  the  vessels,  and  the  blood  still  remain  fluid.  But  if  any  circumscribed 
injury  be  made  to  the  walls  of  a  blood-vessel,  as  by  the  application  of  a 
ligature,  even  though  it  be  subsequently  removed,  a  deposit  of  fibrin 
will  occur  at  that  point. 


BLOOD.  489 

4.  THE  BLOOD-SERUM. — Blood-plasma  freed  from  fibrin  constitutes 
blood-serutn,  and,  as  already  stated,  may  be  obtained  by  allowing  blood 
to  coagulate  in  a  glass  cylinder,  when  the  gradual  contraction  of  the 
fibrin  in  the  clot  presses  out  the  serum. 

Serum  is  an  alkaline,  transparent  fluid,  of  a  specific  gravity  of  from 
1026  to  1029,  amber-yellow  in  the  horse's  blood,  and  almost  colorless  in 
that  of  the  other  domestic  animals.  In  carnivora  and  omnivora,  as  well 
as  in  nursing  herbivora,  the  serum  is  often  milky  from  the  contained  fat- 
globules,  which  gradually  rise  to  the  top  to  form  a  Ia3*er  of  cream  ;  this, 
however,  only  occurs  at,  or  shortly  after,  the  period  of  fat  absorption. 

In  round  numbers  the  composition  of  serum  is  as  follows  : — 

Water,     ...        . .-'.-.        .        .        .          90  per  cent. 

Proteids, 8  to  9    "       " 

Fats,  extractives,  and  salts,  .        .        .        .     2  to  1    "      " 

The  Albuminoids  of  the  Serum. — The  following  albuminoids  are 
found  in  serum  :  Paraglobulin,  alkali  albuminate,  serum-albumen,  and  fre- 
quently peptone. 

Paraglobulin  has  already  been  considered  under  blood  coagulation  ; 
in  coagulation  all  the  fibrinogen  becomes  solidified,  while  a  considerable 
amount  of  paraglobulin  still  remains  in  the  serum.  The  amount  remain- 
ing in  solution  in  the  serum  has  been  estimated  at  from  1.7  per  cent,  in 
the  rabbit  to  4.5  per  cent,  in  the  horse. 

Alkali  albumen  (sodium  albumen,  serum-casein)  is  precipitated  by 
exact  neutralization  with  acetic  acid.  It  is  insoluble  in  distilled  water, 
but  readily  soluble  in  dilute  acid  and  alkalies. 

Serum-albumen  exists  in  larger  amount  than  all  the  other  albumi- 
noids, the  serum  containing  from  6  to  8  per  cent.  As  already  mentioned, 
it  differs  from  egg-albumen  in  rotating  polarized  light  56°  to  the  left, 
while  egg-albumen  rotates  it  but  35.5°,  and  in  its  behavior  to  ether  and 
acids.  After  removing  paraglobulin  and  alkali  albuminate,  serum-albu- 
men may  be  completely  coagulated  after  acidulation  and  dilution  by  heat 
(70°-75°  C.). 

The  quantitative  proportions  between  serum-albumen  and  para- 
globulin vary  in  different  animal  species.  The  proportion,  while  not 
even  constant  in  any  given  species,  varies  about  as  follows,  paraglobulin 
being  represented  by  the  numerator  of  the  fraction,  serum-albumen  by 
the  denominator  :  Horse  ^Vrj  QX  ff.A*»  ^an  T.sVn  Dog  T.J3,  Rabbit  5^. 

Peptone  differs  from  other  albuminoids  in  that  it  is  not  coagulated 
by  heat  or  acetic  acid  and  potassium  ferrocyanide,  but  is  precipitated  by 
tannic  acid,  corrosive  sublimate,  absolute  alcohol  in  great  excess,  phos- 
phowolframic  acid,  phosphomolybdic  acid,  and  iodide  of  mercury  and 
potassium. 


490  PHYSIOLOGY  OF   THE  DOMESTIC   ANIMALS. 

Its  other  characteristics  have  been  described  under  the  head  of 
Gastric  Digestion. 

To  detect  the  presence  of  peptone  in  blood-serum,  all  the  other  albuminoids 
must  first  be  removed.  This  may  readily  be  accomplished  by  adding  a  solution 
of  acetate  of  iron,  to  which  a  few  drops  of  sulphate  of  iron  solution  have  been 
added.  The  serum  must  first  be  diluted  with  five  to  eight  volumes  of  water,  heated 
on  the  water-bath,  and  the  iron  solution  and  then  caustic  soda  added,  until  only 
a  faint  acid  reaction  remains.  A  thick,  brown  precipitate  then  falls,  and  the 
supernatant  fluid  is  free  from  iron  and  all  albuminoids  but  peptone,  the  presence 
of  which  may  be  recognized,  after  filtration,  by  the  biuret  reaction. 

Peptone  is  only  found  in  the  serum  during  and  shortly  after  albu- 
men absorption. 

Other  Organic  Constituents  of  the  Serum. — Sugar  may  be  detected, 
after  removal  of  albuminoids,  by  the  copper  test.  Sugar  is  a  constant 
constituent  of  the  serum  of  blood.  Its  origin  and  importance  will  be 
discussed  later.  Ox-blood  contains  0.543  pro  mille  sugar,  sheep's  blood 
0.521  pro  mille,  dogs'  blood  0.787  pro  mille. 

Fat  has  already  been  mentioned.  It  is  found  only  in  scanty  amount, 
except  after  a  meal,  being  in  largest  amounts  in  the  serum  from  suckling 
animals.  Stearin,  palmitin,  and  olein,  with  their  respective  soaps,  are 
the  principal  representatives.  The  odor  of  serum  is  probably  due  to  a 
volatile  body  of  the  fatty  acid  series.  The  yellow  color  of  serum  is  due 
to  the  presence  of  a  special  pigment. 

Lecithin  is  a  constant  constituent  of  the  ethereal  extract  of  blood- 
serum.  A  large  proportion  of  the  phosphoric  acid  of  the  serum  is  con- 
tained in  this  bod}-.  Its  origin  and  uses  are  not  well  understood. 
Perhaps,  since  it  is  the  carrier  of  phosphorus,  it  is  of  special  importance 
in  the  nutritive  processes  of  bone. 

Cholesterin  is  also  found  in  the  ethereal  extract  of  blood-serum,  from 
which  it  coagulates  in  white,  pearly  flakes. 

Further,  small  amounts  of  urea  are  found  in  serum,  as  well  as 
kreatin,  kreatinin,  and  other  products  of  the  retrograde  metamorphosis 
of  tissues,  which  will  subsequently  claim  attention. 

The  Inorganic  Constituents  of  Blood-Serum. — Serum  }^ields  about 
0.75  per  cent,  of  ash,  in  which  the  following  bases  are  found:  Na,  K, 
Ca,  Mg,  Si,  and  Fe  and  P2O5H2,  H2SO4,  C02,  and  Cl.  K  and  Fe  are  in 
extremely  minute  quantit}^;  Mg  and  Cain  somewhat  larger  quantit}^, 
though  out  of  proportion  to  the  richness  of  the  organism  in  these  bodies. 

The  Gases  of  the  Blood. — Oxygen,  carbon  dioxide,  and  nitrogen  are 
found  in  the  blood  in  conditions  of  loose  chemical  union  with  certain 
blood  constituents  (haemoglobin)  and  in  solution  in  the  blood-plasma, 
which,  like  other  fluids,  is  capable  of  dissolving  a  certain  amount  of 
different  gases.  Their  consideration  will  be  reserved  for  the  chapter  on 
Respiration. 


SECTION    VII. 
THE  CIRCULATION  OF  THE  BLOOD. 

IT  has  been  seen  that  digestion  is  the  preparation  of  food  for  ab- 
sorption ;  absorption  is  the  process  by  which  the  results  of  digestion 
reach  the  interior  of  the  blood-vessels ;  but  that  the  blood,  which  by 
means  of  absorption  has  thus  received  the  nutritive  principles  of  the  food, 
may  satisfactorily  meet  the  nutritive  wants  of  the  different  tissues  of 
the  body,  it  must  be  in  constant  motion.  The  circulation  of  the  blood  is, 
therefore,  that  function  by  means  of  which  the  nutritive  materials  sup- 
plied by  absorption  are  distributed  to  the  economy  after  being  subjected 
to  aeration,  and  by  which  the  refuse  and  effete  materials  are  carried  where 
they  may  be  excreted. 

1.  GENERAL  VIEW  OF  THE  ORGANS  OF  CIRCULATION. — Circulation  is  an 
organic  function,  being  present  in  both  the  animal  and  vegetable  king- 
doms. 

In  the  simplest  forms  of  life,  both  animal  and  vegetable,  in  which 
absorption  takes  place  by  imbibition  from  the  entire  external  surface, 
no  special  circulatory  apparatus  is  required.  It  is  only  when  certain 
tissues  become  specialized  organs  for  absorption  and  others  for  aeration 
that  a  necessity  arises  for  some  apparatus  by  which  the  materials  ab- 
sorbed are  convej-ed  from  the  point  of  absorption  to  the  respiratory 
organs  and  to  the  S3'stem  at  large.  The  development  of  the  circulatory- 
organs  is,  therefore,  proportional  to  the  degree  in  which  absorption  and 
respiration  are  limited  to  special  tissues. 

As  might  be  expected  from  the  definition  of  the  circulation,  in 
the  lowest  animals,  as  in  plants,  in  which  absorption  takes  place  from 
the  entire  external  surface,  there  exists  no  apparatus  for  carrying 
on  a  circulation  of  fluid,  the  contractile  vesicles  seen  in  many  of  the 
protozoa  having,  probably,  rather  a  respiratory  than  a  circulatory 
function ;  it  is  only  when  the  digestive  organs  become  highl}:  specialized 
that  a  circulator}'  apparatus  appears.  Thus,  in  the  coelenterata  the 
somatic  cavity  is  in  free  communication  with  the  digestive  cavit}-  and 
with  the  exterior,  and  the  fluid  which  it  contains,  representing  the  blood 
of  higher  orders,  is  moved  b}r  the  contractions  of  the  entire  body  and  by 
the  vibration  of  cilia  lining  the  somatic  cavity,  there  being  no  indication 
of  either  a  heart  or  a  vascular  system.  In  the  turbellaria,  trematoda, 
and  cestoidea  the  lacunae  of  the  mesoderm  and  the  interstitial  fluid  of 

(491) 


492 


PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 


its  tissues  are  the  representatives  of  a  blood-vascular  system — a  condi- 
tion closely  analogous  to  what  occurs  as  the  first  indication  of  a  circula- 
tion in  plants.  In  annelida,  as  is  also  the  case  in  the  rotifea,  we  find  a 
perivisceral  cavity  lying  between  the  splanclmopleure  and  the  somato- 
pleure,  communicating  with  the  segmental  organs,  as  the  water-vascular 
system.  In  the  former  group  there  is  also  to  be  found  a  system  of  canals 
(the  pseudo-haemal  system),  in  some  instances  communicating  with  the 
perivisceral  cavity,  with  contractile  and  often  ciliated  walls,  and  con- 
taining a  clear,  sometimes  corpusculated  fluid,  which  may  be  either  red 
or  green  from  the  presence  of  a  substance  which  resembles  haemoglobin 
and  which  is  evidently  of  a  respiratory  value.  These  canals  always  com- 
municate at  some  point  b}^  a  tubular  stem  with  the  exterior.  In  the 
lowest  forms  of  the  arthropoda  the  same  general  conditions  noted  in 
the  turbellaria  are  to  be  found,  viz.,  a  perivisceral  cavity  and  an  inter- 


si.  A 


IAA 


FIG.  180.— DIAGRAMS  TO  SHOW  THE  ARRANGEMENT  OP  THE  GREAT  BLOOD- 
VESSELS IN  WORMS  AND  LOWER  CRUSTACEANS.    (Jeffrey  Bell.} 

A,  earthworm :  D.  dorsal  vessel.  B,  crayfish:  A  A,  anterior  aorta ;  PA,  posterior  aorta ;  H,  heart; 
AT  and  HP,  transverse  vessels  which  supply  the  anterior  regions  of  the  body  and  the  viscera;  ST.A, 
sternal  artery  ;  SI.A  and  IAA,  abdominal  artery. 

stitial  fluid,  in  which,  however,  colorless  cells  may  be  detected.  In  the 
lower  Crustacea  and  in  many  insecta  we  find  a  single  elongated,  some- 
times segmented,  contractile  vessel,  the  dorsal  vessel,  provided  with 
lateral  valvular  openings  by  which  the  blood  enters  from  an  inclosing 
venous  space  or  sinus  (Fig.180).  In  the  anodon  (Fig.  181,  C)  the  spaces 
or  sinuses  are  much  more  developed,  and  no  traces  of  a  ventral  vessel 
are  now  to  be  seen  ;  the  dorsal  is,  however,  shown  by  the  heart,  with  its 
anterior  and  posterior  aortae,  while  the  terminal  parts  of  the  transverse 
vessels  become  enlarged  to  form  the  auricles  of  the  heart.  In  the  higher 
Crustacea,  as  in  the  lobster,  there  is  a  single,  well-developed,  muscular, 
systemic  dorsal  heart  surrounded  by  a  venous  sinus  and  giving  off  a 
number  of  arteries,  which  pass  into  capillaries ;  but  the  venous  system 
still  remains  more  or  less  lacunar.  In  the  mollusca,  also,  the  same  gradual 


CIRCULATION   OF  THE  BLOOD. 


493 


differentiation  of  the  blood-vascular  system  is  observable.  In  some  of 
the  lowest  forms,  as  in  polyzoa,  neither  a  contractile  heart  nor  even 
vessels  can  be  detected ;  circulation  in  them,  as  in  lower  forms,  being 
carried  on  by  mere  imbibition.  In  the  tunicata  the  heart,  whose 
position  closely  resembles  its  ventral  situation  in  the  vertebrata,  has 
no  valves  between  its  dilated  chambers,  and  the  blood  is  propelled  by 
opposite  peristaltic  movements,  first  in  one  direction  and  then  in 
another  ;  hence,  here  the  heart  is  sometimes  systemic  and  sometimes 
respirator}'.  The  most  perfect  form  of  circulation  found  in  tha 
mollusca  exists  in  the  cephalopoda.  In  them  there  is  a  systemic 
ventricle  provided  with  valve's  at  its  orifice,  with  systemic  arteries,  the 
blood  being  returned  into  a  large  venous  sinus,  from  which  it  passes  to 
the  gills  through  contractile  vesicles,  the  branchial  hearts,  which  serve 
to  propel  the  blood  through  the  gills ;  from  there  it  passes  again  into 

H 

PA 


DA 


BR 

FIG.  181.— DIAGRAMS  OF  THE  GREAT  BLOOD-VESSELS  IN  THE  FRESH- WATER 
MUSSEL  AND  THE  FISH.    (Jeffrey  Bell.) 

C,  fresh-water  mussel :    H,  heart :    AA.  anterior,  and  PA.  posterior  aortse ;    A,  auricle.     D,  fish :   H, 
heart ;  BR,  branchial  vessels ;  DA,  dorsal  aorta. 

contractile  venous  sinuses,  which,  therefore,  act  as  auricles,  and  is  then 
driven  to  the  heart. 

Thus  we  find  that  in  the  invertebrata  the  circulatory  apparatus,  even 
in  the  highest  forms,  contrasted  with  what  we  shall  find  in  the  vertebrata, 
does  not  consist  of  a  continuous  series  of  tubes,  but  that  the  blood 
passes  from  such  vessels  into  spaces  (lacunae  or  perivisceral  spaces) 
without  distinct  walls.  Connected  with  the  vessels  we  often  find  several 
pulsating  cavities  more  analogous  to  the  lymphatic  or  venous  hearts 
found  in  the  vertebrata  than  to  a  true  respiratory  or  systemic  heart. 
When  a  heart  is  present  in  the  invertebrates,  it  is  single,  is,  as  a  rule, 
placed  on  the  dorsal  aspect  of  the  body,  contrasted  with  its  ventral 
position  in  vertebrates,  and  is  of  a  systemic  and  not  respiratory  function. 
In  the  invertebrata  there  is  no  trace  of  a  portal  system,  the  liver  being 
supplied  by  the  systemic  arteries. 


494 


PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 


FIG.  182.  —  DIAGRAM  OF  THE 
CIRCULATION  IN  THE  FISH. 
(Eeclard.) 


A,  dorsal  artery,  or  aorta;  C,  sys- 
temic organs  ;  O,  auricle  ;  V,  ventricle  ; 
B,  branchiae. 


In  the  vertebrata,  amphioxus,  the  lowest  form  of  fish,  has  a  system 
of  blood-vessels  with  contractile  walls,  but  no  distinct  heart,  while  in  all 
the  other  vertebrates  there  is  a  heart  with,  at  fewest,  three  chambers 
(sinus  venosus,  atrium,  ventricle),  arteries,  capillaries,  and  veins,  and  a 

system  of  lymphatics  connected  with  the 
veins.  In  many  of  the  lower  forms  of  verte- 
brates we  still  find  large  venous  sinuses,  but 
in  the  higher  forms  these  are  for  the  most 
pavt  replaced  by  definite  vessels  with  mus- 
cular walls.  Important  peculiarities,  how- 
ever, exist  in  the  vascular  systems  of  the 
vertebrata  dependent  upon  the  character  of 
their  respiration,  whether  pulmonated  or 
air-breathing,  or  branchiated  or  water- 
breathing  ;  and  further,  as  to  whether  their 
blood  is  warm  or  cold.  Mammalia  and  birds 
are  included  in  the  group  of  warm-blooded 
pulmonated  vertebrata  ;  reptilia  and  amphibia 

in  the  group  of  cold-blooded  pulmonated  animals  ;  and  fish  constitute 
the  group  of  cold-blooded  branchiated  vertebrata. 

In  all  of  these  animals  the  character  of  the  circulatory  apparatus 
depends  upon  the  manner  in  which  the  blood  is  oxy- 
genated ;  therefore,  in  those  animals  (certain  of  the 
amphibia)  which  commence  life  as  branchiated  ani- 
mals and  subsequently  become  pulmonated,  we  find 
that  their  circulatory  apparatus  becomes  modified 
accordingly,  and  presents  two  different  styles  corre- 
sponding to  the  stage  of  their  existence.  In  all  forms 
of  vertebrata  a  portal  system  is  present — that  is, 
the  liver  receives  a  special  supply  of  venous  blood 
derived  from  the  sj'stemic  capillaries  of  the  abdominal 
organs. 


FIG.  184.—  PLAN  OF 
CIRCULATION  IN 
THE  FISH.  (Car- 
penter.) 

A,  auricle;  B.  ventricle; 
C,  branchial    artery  ;     D, 

{Pniting  in  FTthe^aorta"! 

G,  venacava. 


FIG.  183.—  DIAGRAM  OF  THE  ARTERIAL  CIRCULATION  IN  FISHES, 

AFTER  WlEDERSHEIM.      (Jeffrey  Sell.) 


In  fishes  (see  Fig.  181,  Z)),the  lowest  forms  of  vertebrates,  the  heart 
consists  of  a  single  auricle  with  the  sinus  venosus,  which  is  always  present, 
and  a  single  ventricle,  the  former  receiving  the  dark  venous  blood  from  the 


CIRCULATION   OF  THE  BLOOD. 


495 


bod}'  and  transmitting  it  through  an  opening,  guarded  by  a  valve,  to  the 
ventricle,  from  which  the  blood  is  propelled  to  the  bulbus  arteriosus,  and 
then  through  four  or  five  branching  vessels  supported  on  the  cartilaginous 
branchial  arches  to  the  gills  (Figs.  182  and  183).  After  being  subjected  to 


FIG.    185.— ClRCFLATORY    APPARATUS    IN 

THE  FISH.    (Owen.) 

A,  bulhus  arteriosus:  B,  branchial  arteries:  b, 
branchial  veins :  H,  ventricle ;  h,  auricle ;  L  L,  portal 
vein:  V  V,  vena  cardinalis:  »*,  jugular  veins ;  I,  in- 
testine; A'  A',  aorta;  K,  kidney. 

The  lower  figure  shows  an  enlarged  diagram  of  a 
branchial  arch,  the  lettering  being  the  same  as  above, 
be  being  the  branchial  cavity. 


FIG.  186.— HEART  OF  TORTOISE.  (B6clard.) 

1,  right  auricle:  2,  single  ventricle:  3,  left  auricle: 
4,  right  aorta ;  5,  left  aorta ;  6,  pulmonary  artery  dividing 
into  two  branches ;  7,  venae  cavae. 


FIG.  187.— HEART  OF  FROG.    (Livon.) 

I,  anterior  view ;  II,  posterior  view.  A  A,  aortas ; 
Vc,  superior  venae  cavae  :  Or,  auricles  :  V,  ventricle :  Ba, 
aortic  bulb ;  SV,  venous  sinus :  Vci,  inferior  venae  cavae  ; 
Vh,  hepatic  veins ;  Vp,  pulmonary  veins. 


aeration  in  the  capillaries  of  the  gills,  .the  blood  is  then  collected  by  the 
branchial  veins,  which,  uniting  into  a  single  arterial  trunk  situated  on 
the  dorsal  aspect  of  the  alimentary  canal,  and  corresponding  to  the 
aorta  of  higher  vertebrates,  serves  by  a  sj^stem  of  branching  vessels  to 


496  PHYSIOLOGY  OF   THE  DOMESTIC   ANIMALS. 

distribute  the  arterial  blood  to  the  S3^stem  at  large  ;  whence  it  is  again 
returned  by  the  venous  system,  after  passing  through  the  systemic 
capillaries  to  the  auricle  (Fig.  184).  In  fishes,  therefore,  the  respira- 
tory apparatus  forms  a  part  of  the  general  systemic  circulation,  the 
heart  being,  therefore,  a  branchial  and  not  a  systemic  organ,  and  the  cir- 
culation being  simple  instead  of  imperfectly  double,  as  in  the  reptilia,  or 
perfectly  double,  as  in  the  warm-blooded  vertebrata.  In  the  fish,  a 
portal  S3rstem,  composed,  as  in  all  vertebrates,  of  veins  from  the  digestive 
apparatus,  conducts  the  blood  from  the  abdominal  organs  through  the 
kidneys  and  liver ;  hence,  in  the  fish,  both  these  glands  receive  venous 
blood  (Fig.  185). 

In  the  reptilia  the  heart  consists  of  two  auricles  and  one  ventricle 
(Figs.  186  and  187).     The  right  auricle  receives  venous  blood  from  the 


FIG.  188.— DIAGRAM  OF  THE  CIRCULATION 

IN  REPTILIA.    (Beclard.)  FIG.  189.— DIAGRAM  OF  THE  CIRCULATION 
P,  lungs;    O,  left  auricle;    V,  ventricle,  whence  the  IN  THE  REPTILIA.      (Carpenter.} 

blood  is  driven  through  the  systemic  circulation  to  enter  A,  ventricle;  B,  left  auricle ;  C,  right  auricle :  D,  pulmo- 
the  right  auricle,  O',  after  being  collected  by  the  veins.  nary  circulation;  E,  systemic  circulation. 

system  at  large;  the  left  auricle  receives  arterial  blood  from  the  lungs; 
both  discharge  their  contents  into  the  single  ventricle,  which  thus  re- 
ceives a  mixture  of  venous  and  arterial  blood.  From  the  ventricle  the 
blood  is  driven  partly  through  the  lungs  and  partly  to  the  general 
S3rstem,  so  both  lungs  and  system  receive  a  partially  aerated  blood, 
forming  an  incomplete  double  circulation  (Fig.  188  and  189).  In 
the  reptilia,  as  a  rule,  there  is  a  distinct  arterial  and  distinct  pul- 
monary trunk  arising  from  the  ventricle,  but  in  the  amphibia  there  is 
only  a  single  trunk,  of  which  the  pulmonary  arteries  are  branches,  rising 
from  the  ventricle.  In  the  crocodile  there  exists  a  partial  ventricular 
septum,  so  placed  that  it  serves  to  direct  the  dark  venous  blood  entering 
from  the  right  auricle  chiefly  into  the  pulmonary  arteries,  whilst  the 
arterial  blood  coming  from  the  left  auricle  is  sent  out  into  the  systemic 


CIRCULATION   OF   THE   BLOOD. 


497 


arteries,  thus  closely  approaching  the  double  circulation  of  birds  and 
mammals  (Fig.  190).  A  portal  circulation  is  also  present  in  the  cold- 
blooded pulmonated  vertebrata,  and,  as  in  the  fishes,  is  connected  with 
the  renal  veins. 

In  birds  the  heart,  as  in  man,  consists  of  four  cavities,  two  auricles 
and  two  ventricles,  and  the  general  distribution  of  the  circulation 
is  the  same,  i.e.,  the  right  auricle  collects  the  blood  from  the  sys- 
temic veins  and  transmits  it  to  the  right  ventricle,  which,  by  means  of  the 
pulmonary  artery,  forces  the  blood  through  the  lungs.  From  the  lungs  the 
oxygenated  blood  is  carried  by  the  pulmonary  veins  to  the  left  auricle, 
from  there  to  the  left  ventricle,  and  thence,  by  means  of  the  aorta  and  its 
branches,  to  the  system  at  large.  There  is,  therefore,  in  birds  a  perfect 
double  circulation — a  pulmonary  and  a  systemic  circulation  (Fig.  191). 


FIG.   190.  —  HEART    OF    THE    CROCODILE. 

(Perrier.) 

a  a,  venae  cavae  :  b,  right  anricle ;  r.  right  ventricle ; 
<L  left  ventricle  :  e,  pulmonary  veins  :  /,  left  auricle  ;  It  hf. 
aortae :  i.  second  arch  of  the  aortae.  in  which  arterial  and 
venous  blood  is  mixed ;  g,  pulmonary  arteries. 


FIG.  191.— DIAGRAM  OF  THE  CIRCULATION 
IN  BIRDS  AND  MAMMALS.     (Carpenter.) 

A,  heart ;  B,  vena  cava ;  C,  right  auricle ;  D,  right 
ventricle ;  E,  pulmonary  arte^1- ;  F,  pnlmonic  capillaries  ; 
G,  left  auricle;  H,  left  ventricle ;  i,  aorta;  J,  systemic 
capillaries. 


The  portal  system  is  also  present  in  birds,  and,  as  in  the  lower  verte- 
brates, receives  branches  from  the  kidneys  and  from  the  lower  limbs. 

The  circulation  in  mammals,  of  which  man  may  be  taken  as  a  type, 
deserves  to  be  treated  at  somewhat  greater  length  ;than  the  circulation  in 
inferior  organisms.  As  in  other  vertebrates,  with  the  exception  of  the 
openings, of  the  larger  lymphatics,  the  blood  is  contained  in  a  com- 
pletely closed  S3rstem  of  vessels,  whose  course  and  general  arrangement 
we  will  first  trace  in  outline. 

The  circulation  is  carried  on  through  a  S3Tstem  of  tubes  of  different 
functions  and  different  properties.  These  are :  (1)  the  central  organ,  the 
heart,  a  hollow  muscle,  which  serves  as  both  a  pump  and  a  reservoir, 
divided  into  four  cavities,  two  auricles  or  receivers  of  blood,  and  two 
ventricles  or  pumps  (Fig.  192)  ;  (2)  the  arteries,  a  system  of  muscular 

32 


498 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


and  elastic  tubes  coming  off  from  the  heart,  which  gradually  subdi- 
vide, like  the  trunk  of  a  tree,  into  branches,  and  which  serve  to  carry 
oxygenated  blood  to  the  tissues;  (3)  the  veins,  another  S3Tstem  of  branch- 
ing tubes,  also  elastic  and  muscular,  but  less  so  than  the  arteries,  which 
conduct  to  the  heart  the  blood  collected  from  (4)  the  capillaries,  a 
system  of  fine  tubes  situated  between  the  arteries  and  the  veins. 

In  man,  as  in  other  mammals,  we  have  to  deal  with  a  double  circu- 
lation— the  s}^stemic  circulation  and  the  pulmonic.  Their  general  out- 
line may  be  given  as  follows :  Starting  from  the  heart,  the  arterial 
blood  leaves  the  left  ventricle  through  the  aorta,  which  immediately 
gives  off  two  vessels,  the  coronary  arteries,  for  nourishing  the  tissues 


I 


FIG.  192.— DIAGRAM  OF  MAMMALIAN  HEART.    (B6clard.) 

a,  left  ventricle;  6,  right  ventricle;  c,  left  auricle;  Bright  auricle:  /,  aorta;  g  g,  pnlmonary 
arteries ;  h,  inferior  rena  cava ;  i,  superior  vena  cava;  k,  orifice  of  the  superior  vena  cava  ;  I,  orifice  or 
the  inferior  vena  cava;  m,  orifice  of  the  coronary  vein  ;  o,  left  pulmonary  veins;  p,  right  pulmonary- 
veins;  r,  orifices  of  the  right  pulmonary  veins;  s,  orifice  of  the  left  pulmonary  veins. 

of  the  heart  itself;  the  aorta  then  "divides  into  branches,  which  them- 
selves become  successively  subdivided  to  supply  arterial  blood  to  the 
head,  trunk,  limbs,  and  all  the  organs  of  the  body,  the  vessels 
becoming  finally  so  minute  as  to  allow  merely  the  passage  of  a  single 
blood-corpuscle,  forming  then  the  so-called  capillary  vessels.  From  the 
capillaries  the  blood  is  again  collected  by  converging  venous  radicals, 
which  finally  are  united  to  form  two  main  venous  trunks — the  vena 
cava  superior,  bringing  the  blood  from  the  head  and  upper  extremities, 
and  the  vena  cava  inferior,  collecting  the  blood  from  the  trunk  and 
lower  limbs.  Both  of  these  large  veins  empty  into  the  right  auricle,  com- 


CIRCULATION   OF   THE   BLOOD. 


499 


pleting  the  circuit  of  the  greater  or  systemic  circulation.  From  the  right 
auricle  the  blood  is  emptied  into  the  right  ventricle,  from  which  it  is 
forced  by  the  heart's  contractions  into  a  single  large  trunk,  the  pul- 
monary artery.  This  artery,  which,  however,  contains  venous  blood, 
soon  divides  into  two  trunks,  one  going  to  each  lung,  each  of  which 
divides  and  subdivides  in  the  lung-tissue  to  form  a  second  capillary  net- 
work, in  which  the  dark  venous  blood  is  subjected  to  the  influence  of 
the  air  contained  in  the  air-cells,  gives  up  its  carbon  dioxide  and 
certain  organic  impurities,  and  absorbs 
oxygen,  becoming  again  bright-red  arterial 
blood.  It  is  then  collected  by  the  pul- 
monary veins  and  carried  to  the  left 
auricle,  thus  completing  the  lesser  or 
pulmonary  circulation,  and  bringing  us 
back  to  the  point  from  which  we  started 
(Fig.  194). 

2.  THE  ACTION  OF  THE  HEART. — The 
circulation  of  the  blood  consists  in  the  con- 
tinuous movement  of  the  blood  in  a  series 
of  ramifying  tubules  or  blood-vessels,  and 


FIG.  193.-HEART  OF  DTTGONG,  SHOWING  THE  SKP- 

A  RATION    OF    THE     RIGHT  AND    LEFT,   OR  PUL- 
MONARY  AND  SYSTEMIC  HEARTS.     (Pei'rier.) 


FIG.  194.—  SCHEME  OF  THE  CIRCU- 
LATION IN  MAMMALS.    (Landois.) 

a.  right  auricle  ;  A,  right  ventricle  ;  b,  left 
auricle  :  B.  left  ventricle  :  1,  pulmonary  artery  ; 
2,  aorta,  with  semi  lunar  valves  ;  L,  area  of  pul- 
monarv  circulation  ;  K,  area  of  systemic  circu- 


*  ;   <  Id,  i  minnteric  arr 

q,  portal  vein;  L,  liver;  h,  hepatic  vein. 


owes  its  maintenance  largely  to  the  motor  power  derived  from  the 
contractions  of  the  heart.  The  circulatory  apparatus  consists,  there- 
fore, of  the  heart,  the  arteries,  the  veins,  and  midway  between  the 
latter  the  capillaries.  The  conditions  which  govern  the  movement  of 
the  blood-current  in  these  different  parts  of  the  circulatory  apparatus 
will  be  studied  in  turn. 

The  heart  is  a  muscular  reservoir,  divided,  as  already  indicated,  in 


500 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


mammals  into  four  cavities,  two  auricles  and  two  ventricles.  In  its 
function  it  acts  as  a  force-pump,  and  by  the  contraction  of  its  walls 
empties  the  contents  of  its  cavities  into  the  arterial  branches  in  connec- 
tion with  them,  and  therefore  is  the  starting  point  of  the  circulation.  Its 
action  as  a  pump  is  therefore  mainly  physical,  the  effect  produced  by  its 
contractions  being  governed  by  their  frequency,  force,  and  character, 
and  the  quantity  of  blood  ejected  at  each  beat.  Its  physical  properties, 
as  indicated  by  the  above  considerations,  are  governed  by  a  number 
of  vital  conditions,  which  modify  the  various  characters  of  cardiac 
pulsation.  These  will  later  demand  attention. 

The  heart  consists  of  interlacing  muscular  fibres,  which  are  midway 
between  the  striped  and  nnstriped  muscular  tissues.  They  are 
extremely  short,  transversely  striated,  are  devoid  of  sarcolemma,  and 
are  usually  bifurcated  at  their  extremities  and  anastomose  with  each 


FIG.  195.— ARRANGEMENT  OF  MUSCULAR   FIBRES  IN   THE  AURICLES  AND 
GREAT  VEINS.    (Landois.) 

I,  muscular  fibres  on  the  left  auricle,  showing  the  outer  transverse  and  inner  longitudinal  fibres,  and 
the  circular  fibres  on  the  pulmonary  veins,  v.p.      V,  the  left  ventricle  (Reid). 

II,  arrangement  of  the  striped  muscular  fibres  on  the  superior  vena  cava  (Elischer).    a,  opening  of 
vena  azygos ;  v,  auricle. 

other.  In  the  tubular  heart  of  the  embryo,  microscopic  inspection 
shows  that  the  muscular  fibres  may  at  first  be  resolved  into  an  outer 
circular  and  an  inner  longitudinal  layer  of  fibres.  And,  from  the 
fact  that  at  first  the  heart  consists  of  but  one  chamber,  it  is  clear 
that  a  part  of  the  fibres  at  least  must  be  common  to  the  two 
auricles  and  a  part  also  to  the  two  ventricles.  While,  however,  this  is 
true,  the  muscular  fibres  of  the  auricles  are  completely  separated  from 
those  of  the  ventricles  by  the  fibro-cartilaginous  rings  of  the  auriculo- 
ventricular  orifices.  In  adult  animals  the  fundamental  circular  arrange- 
ment of  the  embryonic  fibres  partly  remains,  while  in  the  ventricles,  as 
the  septum  becomes  formed,  the  fibres  become  twisted  into  the  form 
of  spiral  loops.  The  arrangement  of  the  muscular  fibres  in  the  differ- 
ent cavities  of  the  heart  serves  to  a  considerable  degree  to  explain  the 


CIRCULATION  OF  THE  BLOOD. 


501 


physiological  characteristics  of  the  different  cardiac  cavities,  this  physio- 
logical difference  depending  upon  the  anatomical  structure  of  the  different 
parts  of  the  heart,  as  has  been  clearly  traced  out  by  Landois  whose 
description  of  this  subject  has  been  mainly  followed.  In  the  auricles 
the  fibrous  auriculo-ventricular  rings  serve  to  separate  the  auricular 
muscular  fibres  from  the  ventricles,  and,  therefore,  serves  to  explain  the 
fact  that  the  auricles  are  enabled  to  contract  independently  of  the  ven- 
tricles. 

In  the  auricles  the  muscular  fibres  are  arranged  in  an  external  trans- 
verse layer  continuous  over  both  auricles  and  an  internal  longitudinal 
layer.  This  double  arrangement  of  the  fibres  enables  them  in  their 
contraction  to  produce  a  uniform  diminution  of  the  auricular  cavities 
(Fig.  195). 


FIG.  196.— COURSE  OF  THE  VENTRICULAR  MUSCULAR  FIBRES.    {Landois.) 

A,  on  the  anterior  surface ;    B,  view  of  the  apex  with  the  vortex  (Henle) ;    C,  scheme  of  the  course  of  the  fibres 
within  the  ventricular  wall;  D,  fibres  passing  into  a  papillary  muscle  (C.  Ludwig). 

At  the  openings  of  the  large  veins  into  the  auricles  there  is  a  special 
development  of  circular  bands  of  striped  muscular  fibre.  The  contrac- 
tion of  these  bands  enables  the  veins  to  empt}7  themselves  into  the 
auricle  and  also  serves  to  prevent,  to  a  certain  degree,  backward  reflux 
of  the  blood  from  the  auricles  into  the  veins  when  the  auricles  contract, 
even  though  no  valves  are  present  in  these  vessels.  In  the  ventricles  the 
fibres  are  arranged  in  a  number  of  separate  Ia3*ers  so  as  to  form  figure  of 
8  loops.  First,  there  is  an  outer  longitudinal  layer  which  is  in  the 
form  of  single  bundles  on  the  right  ventricle  and  forms  a  complete  layer 


502  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

on  the  left  ventricle,  constituting  about  one-eighth  of  the  thickness  of  the 
ventricular  wall  (Fig.  196).  "  A  second  longitudinal  layer  of  fibres  lies  on 
the  inner  surface  of  the  ventricles,  distinctly  visible  at  the  orifices,  and 
within  the  vertically  placed  papillary  muscles,  while  elsewhere  it  is 
replaced  by  the  irregularly  arranged  trabeculae  carnse.  Between  these 
two  layers  there  lies  the  thickest  la}^er,  consisting  of  more  or  less  trans- 
versely arranged  bundles,  which  may  be  broken  up  into  single  layers 
more  or  less  circularly  disposed.  The  deep  lymphatic  vessels  run  between 
the  layers,  while  the  blood-vessels  lie  within  the  substance  of  the  layers, 
and  are  surrounded  by  the  primitive  bundles  of  muscular  fibres  (Henle). 
All  three  layers  are  not  completely  independent  of  each  other :  on  the 
contrary,  the  fibres  which  run  obliquely  form  a  gradual  transition  between 
the  transverse  layers  arid  the  inner  and  outer  longitudinal  layers.  It  is 
not,  however,  quite  correct  to  assume  that  the  outer  longitudinal  layer 
gradually  passes  into  the  transverse,  and  this  again  into  the  inner  longi- 
tudinal layers  (as  is  shown  schematically  in  0,  Fig.  196),  because,  as  Henle 
pointed  out,  the  transverse  fibres  are  relatively  far  greater  in  amount. 
In  general,  the  outer  longitudinal  fibres  are  so  arranged  as  to  cross  the 
inner  longitudinal  layer  at  an  acute  angle.  The  transverse  layers,  lying 
between  these  two,  form  gradual  transitions  between  these  directions. 
At  the  apex  of  the  left  ventricle  the  outer  longitudinal  fibres  bend  or 
curve  so  as  to  meet  at  the  so-called  vortex  (Wirbel),  B,  and  where 
they  enter  the  muscular  substances,  and,  taking  an  upward  and  inward 
direction,  reach  the  papillary  muscles  (Lower),  D,  although  it  is  a 
mistake  to  say  that  all  the  bundles  which  ascend  to  the  papillary  muscles 
rise  from  the  vertical  fibres  of  the  outer  surface  ;  many  seem  to  rise  inde- 
pendently within  the  ventricular  walls. 

"According  to  Henle,  all  the  external  longitudinal  fibres  do  not  rise 
from  the  fibrous  rings,  but  the  roots  of  the  arteries." 

The  Movements^/  the  Heart. — The  movements  of  the  heart  can  be 
most  readily  studied  in  their  simplest  form  in  the  frog. 

The  batrachian  heart,  as  seen  in  Fig..  187,  is  an  egg-shaped  mass  slightly  flat- 
tened at  the  sides  and  marked  by  a  furrow  which  crosses  the  heart  nearly  at  right 
angles  to  its  axis,  dividing  the  heart  (in  an  anterior  view)  into  an  upper  globular 
part,  the  two  auricles,  and  a  lower  conical,  the  single  ventricle  ;  the  anterior  sur- 
face of  the  ventricle  is  also  marked  by  a  slight  groove  inclining  from  above  down- 
ward toward  the  right  of  the  heart.  Anteriorly,  the  ventricle  is  seen  to  be  con- 
tinuous with  a  cylindrical  prominence,  the  bulbus  arteriosus,  which  crosses  over 
the  right  auricle  and  divides  into  the  right  and  left  aortse.  In  viewing  the  pos- 
terior part,  the  right  auricle  is  seen  to  be  continuous  with  a  bulbar  expansion  of 
the  inferior  vena  cava,  which  receives  the  name  of  the  sinus  venosus,  the  line  of 
junction  of  the  sinus  with  the  auricle  being  marked  by  a  slight  furrow.  The  two 
auricles  are  separated  from  each  other  by  an  antero-posterior  septum,  incomplete 
at  its  lower  margin,  where  the  two  auricles  communicate  through  a  crescentic 
opening  ;  the  opening  of  the  sinus  into  the  auricle  is  marked  by  an  Eustachian 
valve,  which  hangs  downward  and  toward  the  right. 

The  auriculo- ventricular  valve  consists  of  an  anterior  and  posterior  segment, 
each  of  which  is  continuous  at  its  edge  with  the  inter-auricular  septum. 


CIRCULATION   OF  THE  BLOOD.  503 

To  expose  the  heart  of  a  chloralized  frog,  the  integument  is  divided  over  the 
sternum  and  the  anterior  wall  of  the  upper  part  of  the  visceral  cavity,  which  is 
then  to  be  carefully  opened  so  as  to  expose  the  pericardium,  taking  care  not  to 
wound  the  large  abdominal  vein.  The  pericardium  is  then  carefully  slit  up  and 
the  pulsating  heart  exposed.  A  large  glass  rod  is  now  thrust  down  the  oesophagus 
of  the  animal  so  as  thoroughly  to  distend  the  parts  and  bring  the  heart  more 
prominently  forward. 

On  directing  attention  to  the  series  of  movements  which  constitute  a 
cardiac  revolution,  taking  first  the  anterior  view  alone,  the  wave  of  con- 
traction is  distinctly  seen  to  commence  in  the  auricles.  The  auricles  be- 
come distended  and  full  of  blood  ;  they  suddenly  contract  and  transfer 
their  contents  into  the  empty  and  relaxed  ventricle,  which  is  now  gorged 
with  blood,  but  it  is  not  until  the  auricular  contraction  is  complete  that 
the  ventricle,  in  its  turn,  contracts  and  discharges  the  blood  into  the 
relaxed  bulbus  arteriosus,  which  becomes  distended  and  finally  forwards, 
in  its  turn,  its  contents  to  the  arterial  sj'stem.  From  the  fact  that  while 
the  ventricle  contracts  the  auricles  are  already  filling,  and  that  the  ven- 
tricle does  not  contract  until  the  auricular  contracting  is  complete,  it 
would  appear,  on  superficial  examination,  as  if  there  were  a  constant  inter- 
change of  contents  between  the  ventricle  and  auricles.  But  on  lifting  up 
the  ventricle  and  dividing  the  little  band  which  connects  its  posterior  sur- 
face with  the  pericardium,  so  as  to  expose  the  posterior  portions  of  the 
heart,  the  true  sequence  of  contraction  is  immediately  evident.  The 
wave  of  muscular  contraction  distinctly  originates  in  the  sinus  venosus, 
extends  to  the  auricles,  and  it  is  not  until  their  contraction  is  complete 
that  the  ventricle  contracts ;  but  by  this  time  the  sinus  is  again  already 
full  and  the  auricles  filling.  Therefore,  while  the  ventricular  contraction 
is  determined  by  that  of  the  auricles,  and  the  auricular  by  that  of  the 
sinus,  the  contraction  of  the  latter  originates  independently  of  an y  previ- 
ous movement. 

This  sequence  of  contraction  may  be  graphically  represented  by  resting  a 
lever  of  the  second  class  on  the  contracting  heart  in  such  a  manner  that  its  point 
will   describe   its    movements  on    the 
smoked  surface  of  a  revolving  drum, 
as  show/i  in  the  accompanying  tracing 
(Fig.  197)  :— 

In  this  curve  the  first  slight  ascent 
represents  the  contraction  of  the 
auricles,  and  its  subsidence  represents 
the  interval  between  its  contraction 
and  that  of  the  ventricle,  thus  showing 
that  the  one  is  complete  before  the 
other  commences.  The  next  more  de- 
cided ascent  is  due  to  the  vigorous  con-  FlG\  I9J'TTRA^TNG  DRAWN  BY  A  LEVER 

.  *  /»  .,  i  *     •    t  T   *i         i  -/Vrx*lMEL)     UIRKCTIjY    TO     THE     APEX.     OF 

traction  of  the  ventricle  and  the  descent  THE  FROG'S  HEART.    (Sanderson. ) 

tO    its   relaxation        We    learn    from  this  x  contraction  of  auricles;  B,  contraction  of  ventricle; 

that  the  auricles  have  completed  their     c,  relaxation  of  ventricle, 
systole  before  the  ventricle  contracts. 

Passing  now  to  the  movements  of  the  heart  as  seen  in  mammals  the  thorax  is 
to  be  opened  in  a  rabbit,  rendered  insensible  by  chloral,  by  dividing  the  integu- 
ment from  the  larynx  to  the  end  of  the  xiphoid  cartilage  and  then  removing  the 


504  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

sternum  by  cutting  through  the  costal  cartilages  on  each  side  with  a  pair  of  strong 
scissors.  If  the  operation  is  performed  carefully  very  little  hemorrhage  will 
occur.  On  dilating  the  opening  in  the  thorax  thus  formed,  and  maintaining  the 
opening  by  means  of  hooks  fastened  to  weighted  cords,  the  movements  of  the 
heart  are  readily  followed.  We  have,  however,  by  thus  opening  the  thoracic 
cavity  interfered  with  respiration,  and  to  permit  of  a  reliable  study  of  the  cardiac 
movements  the  animal's  life  must  be  prolonged  by  artificial  respiration. 

Having  now  the  heart  and  great  vessels  well  exposed,  and  the  normal  con- 
ditions as  regards  respiration  imitated  as  nearly  as  possible,  the  sequence  of  events 
which  make  up  a  cardiac  revolution  may  be  readily  followed. 

Starting  in  the  distended  venous  trunks  at  the  base  of  the  heart,  as 
seen  in  the  mammal,  the  wave  of  contraction  extends  rapidly  to  the  auri- 
cles, now  filled  with  blood,  which  contract  with  a  sudden,  sharp  systole, 
discharging  their  contents  into  the  flaccid  ventricles,  the  auricular  append- 
ages becoming  pale  and  the  whole  auricle  being  drawn  down  toward  the 
auriculo-ventricular  ring.  During  the  systole  of  the  auricles,  the  ventricles 
become  more  and  more  gorged  with  blood,  but  when  felt  are  still  soft 
and  flaccid.  Immediately,  however,  upon  the  completion  of  the  auricular 
contraction,  the  ventricles  harden  and  become  globular,  or,  in  other  words, 
shorten  and  thicken.  Examined  more  closely,  it  is  seen  that  during 
repose  the  ventricles  form  an  imperfect  cone,  its  base  being  a  transverse 
ellipse,  but  during  systole  they  form  a  more  perfect  cone,  shortened  in 
its  long  axis,  and  having  a  circle  for  a  base,  the  greatest  contraction  hav- 
ing taken  place  in  its  longitudinal  and  transverse  axes,  while  the  antero- 
posterior  diameter  of  the  base  of  the  cone  has  been  little  altered,  although 
the  circumference  of  the  base  has  been  actually  increased  (Foster).  At 
the  moment  of  ventricular  systole  the  heart  rotates  on  its  axis  to  the 
right,  so  as  to  expose  more  of  the  left  ventricle,  while  the  apex  seems  to 
approach  the  base.  The  rotation  of  the  heart  is  due  to  the  contraction  of 
the  muscular  fibres  which  pass  from  the  sternal  surface  of  the  auriculo- 
ventricular  rings  obliquely  downward  and  to  the  left ;  when  they  shorten 
they  raise  the  apex  and  bring  more  of  the  posterior  surface  of  the  ven- 
tricles in  relation  with  the  chest-walls.  At  this  moment  the  aorta  and 
pulmonary  artery  are  seen  to  expand  and  lengthen,  thus  compensating 
for  the  shortening  in  the  long  axis  of  the  ventricle.  Then,  as  diastole 
commences,  the  ventricles  flatten  and  elongate,  the  great  arteries  con- 
tract and  shorten,  the  heart  rotates  back  to  the  left,  and  the  cardiac  revo- 
lution is  completed. 

It  has  been  stated  that  in  the  systole  the  apex  seemed  to  be  drawn 
up  toward  the  base.  This,  however,  is  not  exactly  correct. 

In  the  conditions  in  which  we  have  been  studying  the  heart  its  nor- 
mal supports  have  been  more  or  less  interfered  with,  and  although  we 
have  not  thereby  lessened  the  value  of  the  conception  obtained  of  the 
sequence  of  contractions,  we  ma}'  perhaps  extend  our  knowledge  as  to 
the  degree  and  character  of  the  locomotion  performed  by  different  parts 
of  the  heart  in  its  contraction. 


CIRCULATION   OF   THE   BLOOD.  505 

This  may  be  accomplished  by  the  following  experiment : — 

A  large  dog  should  be  rendered  unconscious  by  a  subcutaneous  injection  of 
morphine,  fastened  securely  on  his  back,  and  a  long,  slender,  steel  needle  then 
passed  perpendicularly  through  the  walls  of  his  chest  into  his  heart  at  the  point 
of  greatest  intensity  of  the  cardiac  impulse.  Then,  following  the  line  of  the  ven- 
tricle up  to  the  aorta,  three  more  steel  needles  should  be  inserted,  one  in  each 
succeeding  intercostal  space  above  the  first,  and  then  again  one  on  each  side  of 
the  second  needle,  about  one  inch  from  it  and  in  the  same  interspace.  -Then  it  will 
be  seen  that,  although  each  of  these  needles  moves  at  each  contraction  of  the  heart, 
the  movements  described  by  their  free  ends  widely  differ. 

No.  1,  inserted  in  the  apex,  merely  quivers  at  each  pulsation  without  describ- 
ing any  definite  motion  dependent  upon  the  cardiac  contraction,  though  it  is  seen 
tolbllow  the  ascent  and  descent  of  the  diaphragm. 

Nos.  2,  3,  4,  inserted  in  the  intercostal  spaces  above,  describe  an  instantaneous 
upward  movement  at  each  contraction,  the  degree  of  excursion  of  their  free  ends 
being  directly  dependent  upon  their  distance  from  No.  1.  The  fulcrum  on  which 
each  needle  moves  is  its  point  of  transfixion  of  the  chest-wall ;  therefore,  an  up- 
ward movement  of  the  free  end  of  the  needle  indicates  a  downward  movement  of 
the  body  in  which  the  other  end  is  inserted.  Finally,  Nos.  5  and  6  oscillate  more 
or  less  horizontally,  their  free  ends  receding  from  each  other  as  well  as  from 
No.  1  at  each  contraction  of  the  ventricle. 

From  these  facts  we  learn  that  the  apex,  the  point  at  which  the  car- 
diac impulse  is  felt,  is  itself  nearly  motionless,  while  the  base  of  the 
heart  at  each  ventricular  systole  approaches  the  apex,  and  that  the  other 
parts  of  the  ventricle  are  drawn  toward  the  apex  in  a  degree  propor- 
tionate to  their  distance  from  it,  while,  as  seen  in  the  exposed  heart,  the 
shortening  of  the  ventricles  is  compensated  by  the  elongation  of  the 
great  vessels  at  the  base.  The  impulse,  therefore,  is  the  hardening  of  the 
ventricle,  transmitted  through  the  stationary  portion  which  is  in  contact 
with  the  chest-walls,  through  the  chest-wall  to  the  finger.  It  is  improper 
to  speak  of  the  impulse  as  a  blow,  as  the  apex  never  leaves  the  chest- 
wall.  But  while  this  is  so,  there  is,  nevertheless,  a  certain  amount  of 
motion  in  the  apex  which  results  in  the  elevation  of  the  chest-wall  at 
the  point  of  cardiac  impulse.  If  an  excised  heart  is  placed  on  a  hori- 
zontal surface,  the  base  of  the  ventricles  in  a  state  of  diastole  takes  on 
the  form  of  an  ellipse  with  its  largest  diameter  horizontal,  while  the 
apex  falls  until  it  is  in  contact  with  the  supporting  surface.  When  the 
ventricle  passes  into  systole  the  base  of  the  heart  passes  from  an  ellip- 
tical to  a  circular  form,  and  since  the  apex  takes  a  position  in  a  line  with 
the  central  point  of  the  base  of  the  heart  it  leaves  the  surface  on  which 
it  rested  and  tilts  forward,  at  the  same  time  approaching  the  base  from 
the  reduction  in  the  length  of  the  ventricles.  The  state  of  affairs  is 
somewhat  similar  while  the  heart  is  in  its  normal  position  in  the 
thorax.  There  the  base  of  the  heart  takes  on  an  elliptical  form  from 
contact  with  the  chest-walls,  while  the  apex  tends  to  fall  away  from  the 
chest.  In  systole,  the  base,  assuming  a  circular  form,  must  cause  the  apex 
to  move  forward,  and,  so  producing  stronger  pressure  on  the  ribs,  cause 
the  elevation  which  constitutes  the  cardiac  impulse,  the  base  descending 
in  systole  as  already  described. 


506 


PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 


Ludwig  and  Hesse  have  shown  that  the  shape  which  the  heart 
assumes  after  death  does  not  represent  its  shape  during  life,  either  during 
systole  or  diastole.  They  obtained  the  diastolic  shape  of  the  ventricle 
by  making  a  plaster  cast  of  the  heart  dilated  under  the  pressure  of  a 
column  of  defibrinated  blood  equal  to  that  of  the  mean  arterial  pressure 
(150  mm.  of  mercury  in  the  dog).  The  systolic  shape  was  obtained  by 
immersing  the  heart,  immediately  after  death,  in  a  hot  (50°C.)  saturated 
solution  of  potassic  bichromate,  when  the  heart  gives  a  single  contraction 
and  remains  in  systole,  the  proteids  being  coagulated  from  heart  rigor. 
A  plaster  cast  is  then  made  as  before.  They  found  that  in  diastole  the 
shape  of  the  ventricle  is  nearly  hemispherical,  with  the  posterior  surface 


in  iv  v 

FIG.  198.— PROJECTIONS  OF  A  DOG'S  HEART,  AFTER  LUDWIG  AND  HESSE.    (Landois.) 

I,  posterior  surface.  II.  left  lateral  surface.  Ill,  anterior  surface.  IV,  A.  aorta :  PA,  pulmonary 
arterv :  M,  mitral,  and  T,  tricnspid  orifices.  V.  projection  of  the  base  in  systole  and  diastole:  RV,  right, 
and  LV,  left  ventricles.  The  shaded  outlines  represent  the  projections  of  the  heart  in  diastole,  the  dotted 
line  the  outline  of  the  heart  in  systole. 

flatter  than  the  anterior,  the  greatest  diameter  being  the  transverse 
diameter  of  the  base,  and  the  shortest  from  the  apex  to  the  base.  In 
systole  the  ventricle  becomes  more  conical  from  the  greater  contraction 
of  the  basal  diameters,  the  curvatures  of  the  anterior  and  posterior 
surfaces  being  now  nearly  equal,  and  while  the  vertical  diameter  of  the 
right  ventricle  shortens  the  left  remains  unchanged.  In  the  systole,  the 
area  of  the  base  of  the  heart  is  diminished  nearly  one-half,  thus,  by 
diminishing  the  auriculo-ventricular  openings,  greatly  assisting  the  ven- 
tricular valves  (Fig.  198). 

The  transmission  of  the  ventricular  contraction  may  be  represented 
graphically  by  the  cardiograph  (Fig.  199). 


CIRCULATION   OF   THE  BLOOD. 


507 


Sanderson's  cardiograph  consists  of  a  hollow  disk,  the  rim  and  back  of 
which  are  of  brass,  while  the  front  is  of  thin  rubber.  To  the  back  is  fastened  a 
flat  steel  spring,  bent  twice  at  right  angles  in  the  same 
direction,  so  that  the  free  end,  which  is  provided  with 
an  ivory  button,  hangs  directly  over  the  centre  of  the 
rubber  membrane.  The  ivory  button  is  on  one  extrem- 
ity of  a  small  screw  which  perforates  the  free  end  of  the 
lever,  while  the  other  end  of  the  screw  rests  on  the 
rubber  membrane,  the  rubber  being  protected  from  the 
point  of  the  screw  by  a  light  metal  plate.  The  instru- 
ment is  further  provided  with  three  adjusting  screws,  by 
which  it  rests  on  the  chest-wall.  The  cavity  of  the 
tympanum  communicates  by  a  rubber  tube  with  the 
interior  of  a  somewhat  similar  drum,  the  rubber  surface 
of  which  is  in  communication  with  a  long,  light  lever 'of 
the  second  order  (Fig.  200). 

On  placing  the  ivory  button  of  the  cardiograph 
over  the  point  of  cardiac  impulse,  and  regulating  the 
adjusting  screws  so  that  the  instrument  is  parallel  to 
the  chest-walls  and  the  screw-point  of  the  button  in 
contact  with  rubber  membrane,  each  movement  of  ascent 
of  the  button  creates  pressure  on  the  rubber  membrane, 
with  a  consequent  diminution  of  the  capacity  of  the 
tympanum.  Then,  since  the  drum  is  in  air-tight  com- 
munication with  a  second  similar  one,  each  diminution 
in  the  capacity  of  the  first  causes  a  proportionate  increase 
in  the  contents  of  the  second,  a  bulging  of  its  rubber 
face,  and  a  consequent  elevation  of  the  lever  with  which 
it  is  connected.  Then,  on  causing  this  lever  to  record 
its  movements  on  the  smoked  surface  of  a  revolving 
drum,  an  exact  record  of  the  movement  of  the  surface  is 
obtained  with  which  the  button  is  in  contact. 

This  instrument,  applied  to  the  study  of  the  im- 
pulse of  a  healthy  human  heart,  shows  that  each  systole 
of  the  ventricle,  when  the  button  is  precisely  over  the 
apex,  is  marked  by  a  sudden  ascent  of  the  lever,  and  the 
end  of  the  systole  by  a  marked  but  more  gradual  descent 
(Fig.  201). 

By  shifting  the  cardiograph  toward  the  sternum,  ^    m 

so  that  the  button  is  no  longer  over  the  point  of  im- 
pulse, a  tracing  of  an  entirely  different  character  is 
obtained  (Fig.  202). 

Although  the  ventricular  systole  is  indicated  by  an 
elevation  of  the  lever,  this  ascent  is  immediately  followed 
by  a  sudden  fall  below  the  position  of  rest  of  the  lever,  <( 


FIG.  199.— SANDERSON'S  CARDIOGRAPH. 


FIG.  200.  —  M  AREY'S  TYM- 
PANUM AND  LEVER. 
(Sanderson.) 

A,  bearings  in  which  the  steel 
axis  of  the  lever  works.  It  may  be 
raised  or  depressed  by  the  adjusting 
lever,  the  long  arm  of  which  extend* 
downward  and  backward  from  A; 
B.  tympanum  :  F,  tube  by  which  the 
cavity  of  the  tympanum  communi- 
cates with  the  cardiograph. 


508 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


thus  indicating  that  there  has  been  an  actual  recession  of  the  chest,  and 
representing  graphically  the  condition  known  in  clinical  language  as  the 
"negative  impulse." 


FIG.  201.— TRACING  OBTAINED  WITH  THE  CARDIOGRAPH  WHEN  THE  BUTTON 

is  PLACED  AT  APEX  BEAT  OF  THE  HUMAN  HEART.    (/Sanderson.) 

Each  ascent  in  the  curve  coincides  with  the  ventricular  systole. 

To  recapitulate,  it  may  be  stated  that  a  single  pulsation  of  the  heart 
may  be  divided  into  three  phases : — 1st.  The  auricles  contract,  while  the 


FIG.  202.— CARDIOGRAPH  TRACING  OBTAINED  WHEN  THE  BUTTON  is  PLACED 

TO  ONE  SIDE  OP  APEX  BEAT.    (Sanderson.) 

The  line  of  descent  coincides  with  the  ventricular  systole. 

ventricles  are  relaxed,  con  traction  and  relaxation  occurring  synchronously 
on    both   sides   of  the   heart.     2d.    The  ventricles   contract,  while  the 

«-• 


FIG.  203.— HEART-BONES  OF  A  Cow,  NATURAL  SIZE.    (Mutter.) 

a,  larger,  b,  smaller  heart-bone ;  c,  anterior,  d,  posterior  extremity. 

auricles  are  relaxed.     3d.  Both  auricles  and  ventricles  are  in  a  state  of 
relaxation,  the    auricles  being  near  the  end  and  the  ventricles  at  the 

commencement  of  their  diastole ;  this 
phase  is  termed  the  pause,  the  con- 
dition of  ventricular  contraction  being 
described  as  systole,  of  relaxation  as 
diastole.  The  duration  of  a  cardiac 
revolution,  consisting  of  diastole,  sys- 
tole, and  pause,  is  equal  to  the  interval 
of  time  ^tween  two  pulsations  felt  in 

THE  HEART-BONES.  ONE-HALF  THE    nT1\r  nrtprv 
NATURAL  SIZE.    (Milller.)  •>   a     er-> ' 

a,  larger  heart-bone ;    b,  smaller  heart-bone :    c,                    The    ActlOH    of   the      VdlveS    OJ     the 
root  of  the  aorta ;    d,  right  coronary  artery  ;    e,  rigrht 
semi-lunar  valve ;/,  central  part  of  the  mitral  valve.      Heart. The     direction     of    tllC     CUrreilt 

of    circulating    blood    through   the    heart   is    rendered    possible    solely 
through  the  integrity  of  the  cardiac  valves.     These  A'alves,  as  already 


CIRCULATION   OF  THE  BLOOD. 


509 


mentioned,  are  situated  between  the  two  auricles  and  ventricles,  and  at 
the  origin  of  the  pulmonary  artery  and  aorta.  Their  mechanical  action 
is  different,  the  two  auriculo-ventricular  Aralves  operating  upon  the  same 
principle,  and  the  two  valves  at  the  starting  point  of  the  large  arteries 
being  similar  in  function  and  operation.  Both  the  auriculo-ventricular 
valves  at  their  bases  constitute  complete  cylinders  which  originate  in  the 
auriculo-ventricular  ring,  which  is  often  cartilaginous,  and  even,  in  some 
animals,  as  in  the  bird,  furnished  with  a  bone. 

In  the  heart  of  the  ox  are  found  two  bony  structures  at  the  origin  of  the  aorta, 
to  the  larger  of  which  are  fastened  the  right  leaflet  of  the  aortic  semi-lunar  valve 
and  the  central  portion  of  the  mitral  valve,  while  the  smaller  is  in  connection  with 
the  left  semi-lunar  valve  of  the  aorta  (Figs.  203  and  204). 


IK- 


FIG.  205.— HEART  OF  THE  HORSE,  SEEN  FROM  THE  RIGHT  SIDE,  THE  RIGHT 
AURICLE  AND  RIGHT  VENTRICLE  BEING  LAID  OPEN.    (Miiller.) 

Hb, Hb,  pericardium  slit  open  and  drawn  to  the  sides ;  r  V.  right  auricle :  rK.  right  ventricle :  IK,  left 
ventricle ;  1,  inferior,  or  posterior,  vena  cava,  with  probe  inserted  in  it :  2,  superior,  or  anterior,  vena 
cava:  3,  azygos  vein;  4,  pulmonary  veins:  5,  posterior  aorta;  6,  anterior  aorta:  7,  right  auricular 
appendage  :  ft.  Lower's  ridge  :  9,  orifice  of  the  coronary  vein  ;  10,  oval  foramen  :  11,  right  coronary  artery  ; 
12,  longitudinal  fissure,  with  13,  its  artery,  and  14,  its  vein:  15,  columnar  carnse;  16  16,  papillary 
muscles ;  17  17,  chordae  tendinae ;  and  18,  a  leaflet  of  the  tricuspid  valve. 

The  cylindrical  form  of  these  valves  exists  only  a  short  distance  from 
this  ring,  and  then  the  valve  divides  into  a  number  of  different  segments, 
which,  in  the  right  ventricle,  are  three  in  number,  hence  the  name  of 
tricuspid  valves,  and  in  the  left  are  two,  hence  the  name  of  mitral  valves. 


510 


PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 


The  leaflets  of  these  valves  again  subdivide  into  numerous  tendinous 
filaments  which  are  inserted  in  the  papillary  muscles  of  the  heart  (Figs. 
205  and  206).  The  tendinous  threads  which  arise  in  the  papillary  muscles 
and  are  inserted  in  the  valve  are  not  in  connection  solely  with  the  free 
border  of  the  latter,  but  the  entire  surface  of  the  valve,  which  is  directed 
toward  the  walls  of  the  ventricle,  offers  points  of  insertion  for  these 
tendons  (Figs.  207  and  208). 

Numerous  theories  have  been  proposed  to  explain  the  manner  in 
which  the  auriculo-ventricular  valves  prevent,  in  the  systole  of  the  ven- 


FIG.  206.— HEART  OF  THE  HORSE,  SEEN   FROM  THE  LEFT  SIDE,  THE  LEFT 
AURICLE  AND  LEFT  VENTRICLE  BEING  LAID  OPEN.    (Muller.) 

I V,  left  auricle :  IK,  left  ventric'e;  r K,  right  ventricle;  1,  trabeculae  in  left  auricle;  2,  coronary 
fissure,  with  its  artery  and  vein ;  3,  pulmonary  artery  ;  4,  anterior  aorta ;  5,  posterior  aorta  :  6,  left  longi- 
tudinal furrow  ;  7.  left  coronary  artery;  8,  coronary 'vein ;  9,  columnar  carnae  ;  10  10',  papillary  muscles; 
11  11',  chordae  tendinae;  12  12',  mitral  valve. 

tricle,  regurgitation  of  blood  into  the  auricles.     These  may  be  classified 
into  two  different  groups. 

According  to  the  one,  the  occlusion  is  purely  passive,  and  is  pro- 
duced by  the  pressure  of  the  blood  behind  the  valves,  causing  their 
ascent,  and  so  occluding  the  orifice  between  the  ventricles  and  auricles. 
In  this  view  of  their  action,  the  papillary  muscles  have  for  their  sole 
function  the  regulation  of  the  situation  of  the  valves,  and,  consequently, 


CIRCULATION   OF  THE  BLOOD. 


511 


the  degree  of  occlusion,  and  to  prevent  the  valves  being  everted  into  the 
auricles.  According  to  the  other  view,  which  seems  to  be  supported  by 
the  largest  amount  of  proof,  the  papillary  muscles  play  an  active  role 
in  the  occlusion  of  the  auriculo-ventricular  orifices.  This  view  has  been 
strongly  supported  by  Ku'ss,  who  describes  their  operation  as  follows : 
"  If  the  finger  be  introduced  into  the  auriculo-ventricular  region  at  the 
moment  of  the  systole  of  the  ventricle,  we  find  that  the  kind  of  funnel 


FIG.  207.— HEART  OF  A  Cow,  WITH  THE   RIGHT  VENTRICLE    LAID  OPEN, 
ONE-FOURTH  THE  NATURAL  SIZE.    (Miillei:) 

a,  posterior  aorta;  at,  anterior  aorta;  b  b,  spaces  in  the  lateral  wall  of  the  right  ventricle  ;  p  pt  pH, 
papillary  muscles  ;  q  q>,  columns;  carnae  ;  L,  pulmonary  artery  laid  open ;  O,  opening  into  right  auricle; 
S,  ventricular  septum;  W,  lateral  wall  of  ventricle;  1,  2,  and  3,  leaflets  of  the  tricuspid  valve;  4,  chorda 
tendinse ;  5,  6,  7,  cusps  of  semi-lunar  valve ;  8,  sinus  of  Valsalva. 

which  hangs  from  the  auricle  to  the  ventricle  is  continued ;  it  even 
appears  to  lengthen  itself  out,  and  the  finger,  as  it  were,  is  drawn  into 
the  interior  of  the  ventricle.  In  fact,  the  first  result  of  the  contraction 
of  the  papillary  muscle  is  the  lengthening  of  the  auricular  cone,  the 
edges  of  which  are  afterward  brought  near  each  other.  While  this 
hollow  cone  descends  into  the  ventricle,  the  sides  of  the  latter  contract 
and  approach  the  cone  in  such  a  manner  that  the  auriculo-ventricular 


512 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


apparatus  acts  as  a  sort  of  hollow  piston,  which  penetrates  the  ventricle 
and  comes  into  close  contact  with  its  walls,  and  thus  the  ventricle  (Figs. 
207  and  208)  empties  itself  completely,  the  -contact  becoming  perfect 
between  its  sides  and  the  auricular  prolongation. 

"  The  result  of  this  mechanism,  which  is  so  simple,  and  tyet  so  gen- 
erally misunderstood,  is  that  no  reflux  of  blood  into  the  auricle  can  take 
place ;  the  auricle,  even  by  means  of  the  mechanism  which  we  have  de- 
scribed, exercises  a  sort  of  suction  upon  the  venous  blood,  its  cavity  being 


FIG.  208.— HEART  OF  A  Cow,  WITH  LEFT  AURICLE  AND  VENTRICLE  LAID 
OPEN.     (Miiller.) 

a,  root  of  the  aorta ;  6,  spaces  in  the  wall  of  the  auricle :  c  c,  orifices  of  the  pulmonary  veins  :  1 1,  pul- 
monary veins ;  p p,  papillary  muscles;  <f  ql,  columnae  carnae;  t,  auricular  trabeculse : "A,  orifice  of  the 
aorta ;  K,  left  ventricle ;  S,  septum ;  V,  left  auricle ;  W,  lateral  wall  of  left  ventricle ;  1,  2,  leaflets  of  the 
mitral  valve. 

continued  so  far  into  the  ventricle.  We  see,  also,  that  when  the  ventricular 
systole  is  complete,  the  lengthened  tube,  the  hollow  cone  which  unites 
the  ventricle  and  the  auricle,  is  full  of  blood,  and  that  a  slight  and  rapid 
contraction  of  the  auricle  is  sufficient  to  drive  this  blood  into  the  ven- 
tricle and  fill  it. 

"  Nearly  all  the  standard  works  admit  without  discussion  the  theory 
of  the  occlusion  of  the  auriculo-ventricular  orifices  by  the  simple  inech- 


CIRCULATION  OF  THE  BLOOD. 


513 


anism  of  a  plug  or  valve,  just  as  in  the  case  of  the  arterial  orifices  (see 
farther  on),  but  without  remarking  the  entire  difference  of  structure 
which  distinguishes  the  auriculo-ventricuiar  valves  from  the  semi-lunar 
valves  of  the  aorta  and  of  the  pulmonary  artery.  This  theory  has  be- 
come, up  to  a  certain  point,  the  property  of  Chauveau  and  Faivre,  on 
account  of  the  interesting  experiments  which  they  have  so  often  made 
upon  horses  killed  instantaneously  by  section  of  the  bulb,  and  in  which 
artificial  respiration  was  kept  up.  '  If,  under  these  circumstances,  the 
finger  is  introduced  into  one  of  the  auricles,  and  the  auriculo-ventricuiar 
orifices  explored,  the  tricuspid  valves  will, at  the  moment  that  the  ventricles 
begin  to  contract,  be  felt  to  straighten,  push  their  borders,  and  stretch  in 
such  a  manner  as  to  become  convex,  and  form  a  concave  dome  above 
the  ventricular  cavity.'  This  method  of  proof  does  not  always  furnish 


FIG.  209.  — DIAGRAM  OF  THK  AURICULO- 
VENTRICULAR  APPARATUS  DURING 
VENTRICULAR  SYSTOLE,  AFTER  Kiiss. 
(Beaunis.) 

\.  During  the  first  part  of  systole.  2.  At  the  com- 
pletion of  systole.  AV,  valvular  cone ;  O,  auricle ;  \t 
ventricle ;  A,  aorta  or  pulmonary  artery. 


FIG.   210. —DIAGRAM  OF  THE  ATJRICULO- 
VENTRICUL.AR    APPARATUS     DURING 
VENTRICULAR  DIASTOLE,  AFTER  Kiiss. 
(Beaunis.) 
V,  vena  cava:  O,  auricle;  V  ventricle;  A,  artery; 

1,  valvular  cone ;  2,  arterial  infundibulum. 


such  decided  results,  and  many  observers,  among  others  Spring  and 
Onimus,  have  met  with  one  entirely  different.  The  latter  found  the 
auriculo-ventricuiar  orifices  effaced  by  the  contraction  of  the  muscular 
fibres,  which,  at  this  level,  really  form  a  sphincter  (this  is  the  case  in  the 
heart  of  birds,  but  not  of  the  mammalia).  The  papillary  muscles,  being 
now  contracted,  lower  the  valves,  and  these,  supporting  themselves 
against  the  sides  of  the  ventricles,  have  the  effect  of  driving  the  blood 
ingulfed  between  them  and  the  corresponding  sides  into  the  arterial 
orifices.  Such  is,  in  short,  the  working  of  the  auriculo-ventricuiar  mem- 
branes. This  is  the  only  theory  which  accounts  for  the  existence  and 
arrangement  of  the  papillary  muscles.'7 

The  action  of  the  semi-lunar  valves  is  more  simple.    The  semi-lunar 
valves  are  composed  of  three  free  folds  of  serous  membrane,  which  during 

83 


514  PHYSIOLOGY  OF  THE   DOMESTIC  ANIMALS. 

the  systole  of  the  ventricle  are  forced  back  by  the  escaping  current 
of  blood  against  the  walls  of  the  pulmonary  artery  and  aorta;  they, 
therefore,  offer  no  obstacle  to  the  escape  of  blood  from  the  cavities  of  the 
ventricles.  At  the  end  of  ,the  contraction  of  the  ventricles  relaxation 
commences,  the  ventricles  dilate,  and  there  is,  therefore,  a  tendency  for 
the  blood  to  return  into  their  cavities  from  the  aorta  and  pulmonary 
artery.  This  backward  current  carries  the  blood  behind  the  free  margins 
of  these  valves  and,  distending  the  pockets  behind  them,  flattens  out  the 
valves,  causing  them  to  come  into  complete  contact  and  thus  completely 
obstruct  the  orifice  of  these  arteries  into  the  ventricles  (Fig.  211).  This 
closure  of  the  semi-lunar  valves  is  rendered  more  perfect  by  the  fact  that 
the  three  leaflets  do  not  originate  from  the  walls  of  the  artery  on  the 
same  plane,  but  their  origins  form  a  spiral  line  around  the  base  of 

these  arteries  ;  consequently,  the 
leaflets  descend  one  over  the 
other,  and,  to  a  certain  extent, 
overlap  each  other,  and  thus 
completely  prevent  regurgitation 
of  tlie  arterial  blood  into  the 
ventricles. 

The  Sounds  of  the  Heart.— 
When  the  ear  is  applied  to  the 
walls  of  the  thorax  over  the 
heart,  two  sounds  are  recog- 

FIG.    211.-BASE  OF  THE  HEART  OF  THE  HORS^,      ™^  ^"^    ^^    ^    intensity, 

BOTH  AURICLES  BEING  REMOVED.    (Miillcr.)      jn  pitch,  and  in  duration.    These 

rV,  right  auricle ;  IV,  left  auricle;    rK,  right  ventricle  ;  IK,  _  Y  .. 

left  ventricle;  1,  coronary  furrow ;  2,  right,  3,  left  auricnlo-ven-  SOlinClS  are  described  aS  tllC 
tricular  orifices;  4,  origin  of  the  aorta;  5,  aortic  semi-lunar 

valves-  86>auriSar  Vtam"1™01""7  artory;    7,  its  semi-lunar  first     and    SCCOnd    SOUnds    of  tllC 

heart.    The  first  of  these  sounds 

is  dull  and  prolonged,  and  coincides  with  the  systole  of  the  ventricle  ;  the 
second  sound  is  shorter,  sharper,  and  of  higher  pitch,  and  occurs  at  the 
end  of  the  systole,  or  at  the  commencement  of  ventricular  relaxation. 
The  musical  interval  between  these  two  sounds  corresponds  about  to  a 
fourth;  the  pitch  of  both  sounds  varies,  but  this  interval  is  usually 
preserved.  The  first  sound  is  heard  with  greatest  distinctness  at  the 
spot  where  the  impulse  is  felt,  and  is  not  dependent  upon  the  cardiac 
impulse,  from  the  fact  that  it  exists  after  the  removal  of  the  chest-walls. 
As  it  coincides  with  the  contraction  of  the  ventricle,  it  also,  of  course, 
coincides  with  the  closure  of  the  auripulo-ventricular  valves,  and  is 
largely  due  to  the  action  of  these  valves. 

The  character  ol  the  first  sound  of  the  heart  is  not,  however,  purely 
valvular  in  nature,  and  is  not  what 'would  be  expected  from  the  sudden 
closure  of  a  membranous  valve.  That  it  is,  however,  largely  due  to  the 


CIRCULATION   OF  THE  BLOOD. 


515 


action  of  these  valves  is  proved  by  the  alteration  in  its  character  which 
occurs  when  either  the  mitral  or  bicuspid  valves  are  diseased,  when  this 
sound  becomes  obscure,  altered,  or  replaced  by  murmurs. 

While  the  valves  in  their  closure  are  the  principal  factors  in  the  pro- 
duction of  the  first  sound  of  the  heart,  its  characters  are  dependent  upon 
the  presence  of  several  other  factors.  It  will  be  found  that  whenever 
a  muscle  contracts  a  sound  is  produced  which  depends  for  its  pitch  upon 
the  number  of  contractions  occurring  per  second.  At  the  moment  of 
closure  of  the  auriculo-ventricular  valves  the  blood  is  forced  out  from 
the  ventricles  into  the  great  arteries.  The  rushing  sound  of  this  moving 
column  of  blood  is,  therefore,  another  factor  in  the  production  of  the  first 
sound  of  the  heart. 

To  recapitulate :  It  may  be  stated  that  the  first  sound  of  the  heart  is 
produced  by  the  sudden  tightening  of  the  auriculo-ventricular  valves, 
whatever  view  be  accepted  as  to  the  nature  of  their  action,  to  the  sound 
of  muscular  contraction,  and  to  the  rushing  of  the  current  of  blood  from 
the  ventricles  into  the  pulmonary  artery  and  aorta.  In  support  of  this  view, 
it  may  be  mentioned  that  when  the  muscular  contraction  of  the  heart 
becomes  greatly  weakened  from  any  depressing  cause,  as  in  severe  fevers, 
the  first  sound  of  the  heart  becomes  distinctly  sharper  and  more  purely 
valvular  in  nature,  evidently  due  to  the  diminished  intensity  of  the  con- 
traction of  the  cardiac  muscle. 

The  second  sound  of  the  heart  is  short  and  sharp,  and  is  due  to  the 
sudden  closure  of  the  semi-lunar  valves,  which  by  their  rapid  increase  in 
tension,  like  every  other  elastic  membrane,  produce  a  sound.  In  living 
animals,  the  second  sound  of  the  heart  is  best  heard  over  the  root  of  the 
large  vessels.  When  the  semi-lunar  valves  are  destroyed,  as  by  inserting 
a  hook  into  these  valves,  the  second  sound  disappears.  The  relative 
lengths  of  the  auricular  and  ventricular  systole  and  diastole,  the  time  of 
the  occurrence  of  the  impulse,  and  the  different  sounds  of  the  heart  may 
be  diagrammatical^  represented  by  a  line  divided  into  five  parts,  which 
represent  the  length  of  a  cardiac  revolution : — 

1         |        2        |        3        I        4        |        5 


1                 1                 1 

Auricle     .     . 

v  Systole. 

Diastole  or  repose. 

Ventricle  .     . 

Eepose. 

Systole.                        Repose. 

Sounds      .    . 

Silence. 

1st  Sound. 

2d  Sound. 

Shock  .     .    . 

Impulse. 

We  may  now  extend,  somewhat,  the  sketch  which  has  already  been 
given  as  to  the  movement  of  the  blood  through  the  pulsating  heart. 


516  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

During  the  diastole  of  the  auricles  the  blood  streams  into  them  from  the 
large  venous  trunks  which  are  in  connection  with  the  base  of  the  heart, 
the  propelling  force  being  the  pressure  of  the  blood  in  the  veins  and  the 
aspiration  exerted  by  the  lungs.  Soon  the  elastic  tension  of  the  walls 
of  the  dilated  auricles  becomes  sufficiently  great  to  balance  the  forces 
which  cause  the  entrance  of  blood  into  the  auricles;  but  before  the 
entrance  of  blood  into  the  auricles  is  entirely  arrested,  the  ventricles, 
which  had,  np  to  this  point,  been  in  systole,  and  thus  prevented  entrance 
of  blood  from  the  auricles,  now  relax,  the  auriculo-ventricular  valves 
are  forced  open  by  the  pressure  of  blood  in  the  auricles,  and  the  ven- 
tricles dilate,  not  only  through  the  aspiration  of  the  lungs,  but  in  virtue 
of  the  elasticity  of  their  own  walls. 

The  auricles  now  pass  into  systole,  and  by  the  pressure  of  the  con- 
traction of  their  muscular  walls  force  the  blood  from  the  auricles  through 
the  auriculo-ventricular  openings  into  the  relaxed  and  dilating  ventricles. 
The  blood  passes  from  the  auricles  into  the  ventricles,  and  not  back  into 
the  veins,  because  this  is  the  direction  in  which  the  moving  blood-cur- 
rent meets  with  the  least  resistance.  We  have  seen  that  by  the  opening 
of  the  auriculo-ventrieular  valves  the  bottom  falls  out  of  the  auricles  and 
the  dilatation  of  the  empty  ventricles  exerts  a  negative  pressure  on  the 
contents  of  the  auricles.  At  the  same  time  the  contraction  of  the  mus- 
cular fibres  of  the  auricles  serves  somewhat  to  constrict  the  openings  of 
the  veins,  and  the  pressure  of  the  blood  in  the  venae  cavae,  supported  by 
the  valves  in  the  inferior  vena  cava,  offer  a  sufficient  resistance  to  prevent 
regurgitation  into  the  veins. 

The  blood  continues  to  flow  from  the  auricles  into  the  ventricles 
until  the  propelling  force  of  the  contracting  auricles  is  balanced  by  the 
elastic  tension  of  the  dilated  ventricles  or  by  commencing  ventricular 
systole,  exit  of  blood  from  the  ventricles  being  prevented  by  the  closed 
semi-lunar  valves  at  the  openings  of  the  aorta  and  pulmonary  arter}^.  The 
ventricles  now  being  filled,  systole  commences,  the  closure  of  the  auriculo- 
ventricular  valves  prevents  regurgitation  into  the  auricles,  and,  the  force 
of  the  ventricular  contraction  being  greater  than  the  pressure  of  the  blood 
in  the  aorta  and  pulmonary  artery,  the  semi-lunar  valves  are  forced  open, 
and  the  ventricles  empty  themselves  completely  into  these  vessels.  The 
ventricles  then  relax,  regurgitation  from  the  great  arteries  being  pre- 
vented by  the  closure  of  the  semi-lunar  valves,  the  ventricles  fill  them- 
selves from  the  auricles,  and  the  process  goes  on  as  before. 

3.  THE  HYDRAULIC  PRINCIPLES  OF  THE  CIRCULATION! — The  physical 
principles  concerned  in  the  movements  of  the-  blood  through  the  arteries 
of  the  animal  body  are  largely  governed  by  the  purely  physical  laws  of 
hydraulics.  Before,  therefore,  we  attempt  to  explain  the  movements 
of  the  blood,  a  glance  at  the  most  important  of  the  physical  principles  of 


CIBCULATION  OF  THE  BLOOD.  517 

hydraulics  or  hydrodynamics  will  greatly  facilitate  the  explanation  of  the 
circulation. 

Every  fluid  particle  under  the  action  of  the  law  of  gravitation  falls 
like  a  solid  body  to  the  earth.  When,  however,  a  large  mass  of  fluid  is 
freely  acted  on  by  gravity  the  slight  cohesion  exerted  by  the  molecules 
of  liquid  on  each  other  leads  to  their  separation  one  from  the  other. 

Every  fluid,  therefore,  in  falling  tends  to  separate  into  drops.  This 
tendency  to  break  up  into  drops  may  be  prevented  either  by  delaying 
the  flow  of  the  liquid,  as  by  causing  it  to  descend  an  inclined  plane,  or 
permitting  the  liquid  to  flow  within  a  vessel  in  which  the  tendency  of 
the  particles  to  separate  will  lead  to  the  production  of  a  vacuum,  and 
atmospheric  pressure  will,  consequently  ,  serve  to  strengthen  the  cohesive 
forces.  Consequently,  in  a  stream  of  liquid  falling  into  a  tube  each  par- 
ticle is  not  only  acted  on  by  gravity,  but  also  by  the  pressure  of  the  mass 
of  fluid  behind  it.  If,  therefore,  an  aperture  be  made  in  the  bottom  of  any 
vessel,  any  particle  of  liquid  on  the  surface  of  the  fluid  contained  in  that 
vessel,  if  we  could  imagine  that  it  would  fall  freely  without  reference  to 
the  particles  below,  would  have  a  velocity  on  reaching  the  orifice  equal 
to  that  of  any  other  body  falling  through  the  distance  between  the  level 
of  the  liquid  and  the  orifice.  If  the  liquid  in  such  a  vessel  be  maintained 
at  the  same  level,  the  particles  will  follow  one  another  with  the  same 
velocity  and  will  issue  in  the  form  of  a  stream  ;  while,  from  the  principle 
of  transmission  of  pressures  in  liquids  equally  in  all  directions,  a  liquid 
would  issue  from  an  orifice  in  the  side  with  the  same  velocity  as  from  an 
aperture  in  the  bottom  of  the  vessel,  provided  the  depth  were  the  same. 

The  velocity  of  efflux,  therefore,  as  formulated  by  Torricelli,  is  the 
velocity  which  a  freely  falling  body  would  have  on  reaching  the  orifice 
after  having  started  from  a  state  of  rest  at  the  surface.  It  is  expressed 
by  the  formula  — 


V  =  l2^h,  in  which  g  =  32.16  ft. 

It  further  follows  that  while  the  velocitj'  of  efflux  depends  on  the 
depth  of  the  orifice  below  the  surface  and  not  on  the  nature  of  the  liquid, 
the  velocities  of  the  efflux,  from  the  laws  of  falling  bodies,  are  directly 
proportional  to  the  square  roots  of  the  depths  of  the  orifices,  while  the 
quantity  of  fluid  which  issues  from  the  orifices  of  different  areas  is  very 
nearly  proportional  to  the  size  of  the  orifice,  provided  the  level  remains 
constant.  It  is  evident,  however,  that  the  mass  of  liquid  in  such  an  ex- 
periment at  the  side  of  the  column  vertically  over  the  orifice  of  exit  offers 
by  friction  more  or  less  resistance  to  the  line  of  movement. 

And  while  the  molecules  vertically  over  the  centre  of  the  orifice 
pass  directly  down  and  out  by  the  orifice,  the  molecules  of  fluid  at  the 
side  of  this  moving  column  not  only  offer  resistance  to  this  downward 


518 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


FIG.  212. 


motion  through  attraction,  but  also  through  their  own  mobility  tend  to 
pass  in  an  oblique  line  into  the  moving  column.  In  fact,  every  particle 
above  the  orifice  endeavors  to  pass  out  of  the  vessel,  and  in  so  doing 
exerts  pressure  on  every  particle  near  it.  The  result  may  be  made  clear 
by  the  diagram  (Fig.  212). 

Every  particle  above  A  B  endeavors  to  pass  out  of  the  vessel,  and 
in  so  doing  exerts  a  pressure  on  those  near  it.  Thosje  that  issue  near 
A  and  B  exert  pressures  in  the  direction  M  M  and 
N  N,  those  in  the  centre  of  the  orifice  in  the  direction 
II  Q,  those  in  the  intermediate  parts  in  the  directions 
P  Q,  P  Q.  In  consequence  of  the  fluid  in  the  space 
P  Q,  P  is  unable  to  escape,  and  that  which  does  escape, 
instead  of  assuming  a  cylindrical  form,  contracts  and 
takes  the  form  of  a  truncated  cone.  It  is  found  that 
the  escaping  jet  continues  to  contract  until  at  a  distance 
from  the  orifice  about  equal  to  the  diameter  of  the  orifice. 
This  part  of  the  jet  is  called  the  vena  contracta.  It  is  found  that  the  area 
of  its  smallest  section  is  about  five-eighths  or  0.62  of  that  of  the  orifice. 
Accordingly,  the  actual  value  of  the  escape  is  only  about  0.62  of  its 
theoretical  amount.  If  a  cylindrical  tube  (termed  ajutage),  with  a 
length  two  or  three  times  its  diameter,  be  made  the  channel  of  exit  of 
the  fluid,  the  amount  discharged  per  second  may  be  increased  to  about 
0.82  of  the  theoretical  amount.  A  contracted  vein  is  formed  within  the 
tube,  just  as  it  would  do  if  issuing  freely  into 
the  air;  but  from  the  adhesion  of  the  water 
to  the  interior  of  this  tube,  the  section  of  the 
column  flowing  from  the  tube  is  greater  than 
that  of  the  contracted  vein  (Fig.  213).  (The 
contraction  of  the  moving  column  of  fluid 
within  the  tube  causes  a  partial  vacuum,  and  if 
a  side  tube,  dipping  into  mercury,  be  connected 
with  the  ajutage  at  this  point  the  mercury  will 
rise  in  the  vertical  tube,  demonstrating  the 
existence  of  the  vacuum.  This  fact  is  made 
use  of  in  Bunsen's  filter  pump.)  If  a  conical 
tube  be  fitted  to  the  orifice  of  exit,  with  the 

smaller  end  in  connection  with  the  vessel,  the  efflux  may  be  still  further 
increased,  and  fall  very  little  short  of  the  theoretical  amount. 

Flow  of  Liquids  Through  Rigid  Tubes. — If  the  ajutage  inserted 
in  the  side  of  the  vessel  has  more  than  a  certain  length,  the  amount  of 
fluid  escaping  is  very  considerably  reduced.  This  fact  rests  upon  the 
hydraulic  friction  produced  between  the  moving  liquid  and  the  walls  of 
the  tube  in  liquids  which  exert  a  certain  amount  of  adhesion  against  the 


FIG.  213. 


CIBCULATION  OF  THE  BLOOD. 


519 


walls  of  the  tube  ;  for  the  movement  of  the  portion  of  liquid  in  contact 
with  the  walls  of  the  tube  is  delayed  by  adhesion,  and  the  movement  of 
the  central  column  is  delayed  by  friction  with  the  external  layers.  It  is 
evident  that  the  resistance  due  to  friction  along  the  sides  of  the  tube 
will  depend  upon  the  length  of  the  tube.  This  may  be  illustrated  by 
the  accompanying  diagram. 

If  a  horizontal  tube  be  connected  with  a  reservoir  of  liquid  and  a 
number  of  vertical  side  arms  be  connected  with  the  horizontal  tube,  the 
liquid  will  rise  in  the  branch  tubes  to  different  heights  inversely  as  the 
distance  of  the  vertical  tube  from  the  reservoir,  for  the  propelling  force 
in  the  horizontal  tube  will  diminish  from  point  to  point  on  account  of 
the  uniformly  acting  resistance  (Fig.  214).  The  vertical  tubes  will,  there- 
fore, enable  us  to  measure  the  pressure  exerted  by  the  fluid  upon  the 
walls  of  the  tube  through  which  it  is  flowing,  and  shows  us  that  the  pres- 
sure at  an 3^  point  of  such  a  tube  will  be  less  the  greater  the  distance  from 


FIG.  214.— ESTIMATION  OF  PRESSURE  OF  LIQUID  IN  A  HORIZONTAL,  OUTFLOW-TUBE 
CONNECTED  WITH  A  CYLINDRICAL,  VESSEL  FILLED  WITH  WATER.    (Landois.) 

a  b,  outflow-tube,  along  which  are  placed  at  intervals  vertical  tubes  I.  II,  and  III  to  estimate  the  pressure.    The 
line  D,  Dl,  D2,  D3,  D4  indicates  the  rapidly  decreasing  pressure. 

the  propelling  force.  Further,  the  resistance  increases  with  the  velocity 
of  the  current ;  for  it  is  evident  that,  the  resistance  being  mainly  depend- 
ent upon  friction,  if  the  column  of  fluid  is  at  rest  there  is,  consequent^, 
no  friction  and  no  resistance,  while  the  greater  the  rapidity  of  motion 
the  greater  will  be  the  friction,  and,  consequent!}^,  the  greater  the  resist- 
ance. It  follows  from  this  that  the  smaller  the  tube  the  greater  will  be 
the  resistance,  for  the  smaller  the  tube  the  greater  will  be  the  velocity 
of  motion.  It  may,  therefore,  be  said  that  in  a  moving  column  of  liquid 
"  the  resistance  is  directly  proportional  to  the  length  of  the  tube  and  is 
inversely  proportional  to  its  cross-section,  and  increases  with  the  speed 
of  the  stream." 

It  has  been  mentioned  that  the  friction  of  the  central  moving  column 
on  the  outer  layer  is  a  source  of  resistance,  consequently  increase  in  the 
cohesive  nature  of  the  fluid  will  increase  the  retardation  of  the  central 


520 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


column  and  accordingly  increase  the  resistance,  while  heat,  by  diminish- 
ing the  cohesion  of  the  liquid,  will  lessen  the  resistance. 

A  similar  state  of  affairs  holds  in  tubes  of  varying  calibre.  In  tubes 
of  unequal  calibre,  as  already  pointed  out,  the  velocity  of  the  current 
will  vary ;  that  is,  it  will  be  slower  in  the  wide  part  of  the  tube  and 
more  rapid  in  the  narrower  parts  of  the  tube.  And  as  the  resistance 
is  greater  in  narrow  tubes,  the  propelling  force  will  diminish  more 
rapidly  than  in  wide  tubes.  "  When  a  small  tube  passes  suddenly 
into  a  tube  of  larger  diameter  there  is  a  sudden  increase  of  pressure  at 
the  surface  of  junction,  accompanied  by  a  diminution  in  the  speed  of 
movement  through  the  wider  tube.  The  molecules  of  which  the  fluid 
consists  cannot  suddenly  change  the  swift  movement  into  a  slower  one, 
and  on  account  of  their  inertia  the  pressure  exerted  by  them  on  one 
another  develops  the  increased  force.  On  the  other  hand,  the  rapid 
transition  from  a  slow  to  a  quick  movement  at  a  place  where  a  wide  tube 


FIG.  215.— DIAGRAM  ILLUSTRATING  THE  VARIATIONS  OF  PRESSURE  IN  AN 
OUTFLOW-TUBE  OF  VARYING  CALIBRE.     (Rollet.) 

passes  into  a  narrow  one  diminishes  the  pressure.  The  effect,  however, 
in  a  system  of  tubes  of  a  series  of  wider  parts  is  to  diminish  the  total 
resistance  "  (Robertson)  (Fig.  215). 

Bending  the  tube  adds  a  new  resistance,  the  fluid  pressing  more 
strongly  on  the  convex  than  on  the  concave  side  of  the  bend,  and,  there- 
fore, producing  greater  resistance  to  movement  on  the  convex  side. 
Consequently,  resistance  is  increased  behind  the  bend  and  diminished 
in  front  of  it,  with  a  consequent  increase  in  the  velocity  of  the  current  at 
this  point.  When  a  tube  through  which  liquid  is  passing  divides  into 
two  or  more  branches,  still  further  resistance  is  added  by  not  only  in- 
creasing the  surface,  but  by  the  production  of  angles  and  bends.  The 
total  calibre  of  the  branches  which  originate  from  a  single  tube  may  be 
either  greater  or  less,  and  so  the  surface  of  contact  between  the  walls  of 
the  tube  and  the  fluid  are  either  increased  or  decreased. 

The  most  interesting  case  corresponds  to  that  seen  in  the  develop- 


CIRCULATION   OF  THE  BLOOD. 


521 


FIG.  216.  —DIAGRAM  OF  VARIATIONS  IN 
PRESSURE  IN  BRANCHING  TUBES. 
(Wundt.) 


The  changes  in 
represented 


re  in  the  tube  A,  B,  C,  D  are 
the  broken  line  A,  B,  c,  D,  E. 


ment  of  the  circulatory  system  of  animals,  where  a  vessel  divides  into 
several  branches  of  greater  total  calibre  than  the  parent  stem,  and  where, 
after  repeated  subdivision,  the  branches  again  unite  to  form  a  single  tube 
whose  calibre  is  about  the  same  as  that  of  the  original  tube. 

A  simple  representation  of  such  a  series  of  branching  tubes  is  given 
in  Fig.  216. 

In  such  a  series  the  pressures  are  seen  in  the  broken  line  A,  B,  c,  D,  E. 
At  B,  taking  into  consideration  only  the  increase  in  calibre,  a  sudden 
increase  in  pressure  occurs.  On  the 
other  hand, considering  only  the  occur- 
rence of  bends  and  angles  in  the  tube, 
the  pressure  would  suddenly  sink. 
These  two  causes,  however,  oppose 
each  other,  and  the  most  ordinary  rep- 
resentation of  the  case  would  be 
indicated  by  a  slower  sinking  in  the 
line  of  pressure  than  in  the  single 
parent  stem.  The  condition  is,  how- 
ever, different  where  the  branches  again  unite  to  form  a  single  trunk; 
here  the  pressure  must  fall,  because  the  bed  of  the  stream  becomes 
contracted,  while  at  the  same  time  an  angle  is  also  met  with.  Both 
these  facts,  therefore,  work  in  the  same  direction,  and  the  pressure 
undergoes  a  sudden  fall  which  would  be  greater  than  that  produced 
by  mere  contraction  of  the  stem. 

It  follows  from  the  above  that  in  a  symmetrical  system  of  tubes  the 
pressure  does  not  symmetricall}*  increase  and  decrease,  but  will  be  greater 
in  any  portion  in  the  centre  of  the  system  of  the  tubes  (at  M,  Fig.  216) 
than  the  mean  of  pressure  at  any 
two  points  equally  distant  in  front 
or  behind  this  point.     It  ma}r,  there- 
fore, happen  that  in  a  complicated 
system   of  branching  tubes  the  re- 
sistance is  not  greater  than  in  a  single 
tube,  or  may  even  be  smaller,  since 
the   increase  in   the   diameter   may 

diminish  the  resistance  more  than  the  branching  increases  it.  If  the 
resistance  is  the  same,  it  is  evident,  also,  that  the  rapidity  is  the  same 
in  both  cases,  and  as  a  consequence  more  fluid  will  flow  out  of  such  a 
branching  system  of  tubes  when  the  resistance  is  smaller  than  would 
escape  from  a  single  tube  (Fig.  217). 

The  angle  formed  by  the  branches  with  the  original  stem  seems  to 
produce  no  marked  influence  on  the  resistance  and  velocity  of  movement. 

The  above  relationship  between  resistance  and  velocity  of  movement 


FIG.  217.— DIAGRAM  OF  SYSTEM  OF  BRANCH- 
ING TUBES.    (Wundt.) 


522  PHYSIOLOGY  OP  THE  DOMESTIC  ANIMALS. 

and  diameter  of  the  tube  only  holds  as  long  as  the  calibre  of  the  tubes 
does  not  fall  below  a  certain  diameter. 

In  capillary  tubes  the  conditions  are  so  far  similar  in  that  the  resist- 
ance is  proportional  to  the  length  of  the  tube.  It  has  been  found,  how- 
ever, that  the  discharge  is  not  proportional  to  the  calibre  of  the  tube,  but 
to  the  fourth  power  of  the  diameter.  This  is  evidently  to  be  explained  by 
the  greater  prominence  attributed  to  the  adhesion  of  the  fluid  to  the 
wails  of  the  tube,  and  will;  therefore,  differ  greatly  in  different  liquids. 

The,  Flow  of  Liquids  Through  Elastic  Tubes.  —  When  a  constant 
stream  passes  through  an  elastic  tube  the  conditions  are  precisely  the 
same  as  have  been  described  as  governing  the  movement  of  liquids 
through  rigid  tubes.  When,  however,  the  current  is  intermittent,  the 
elasticity  of  the  tube  then  comes  into  play,  and  decidedly  modifies  the 
conditions  of  movement. 

If  a  quantity  of  liquid  be  forcibly  injected  into  an  elastic  tube 
already  distended  with  fluid,  the  first  part  of  the  tube  suddenly  dilates 
to  accommodate  the  quantity  of  fluid  propelled  into  it. 

This  impulse  communicates  a  movement  of  undulation  to  the  par- 
ticles of  fluid,  which  is  rapidly  transmitted  to  all  the  particles  of  fluid 
within  the  tube.  In  other  words,  a  wave  movement  is  rapidly  propa- 
gated throughout  the  entire  length  of  the  tube.  If  the  elastic  tube 
be  imagined  to  be  closed  at  its  further  end,  the  wave  will  be  reflected 
from  the  point  of  occlusion,  and  will  be  conducted  to  and  fro  in  the  tube, 
gradually  decreasing  in  intensity  until  it  at  length  disappears.  This 
propagation  of  the  wave  should  not  be  confounded  with  the  forward  move- 
ment of  the  fluid.  For  when  the  fluid  itself  moves  the  movement  of 
each  particle  is  in  the  line  of  the  axis  of  the  tube,  but  in  a  wave  move- 
ment the  motion  of  the  particles  is  simply  one  of  undulation  at  right 
angles  to  the  line  of  movement,  and  not  of  forward  movement. 

In  a  rigid  tube,  a  movement  of  progression  alone  exists.  In  a 
closed  elastic  tube,  filled  with  liquid,  into  which  more  fluid  is  suddenly 
injected,  the  wave  movement  alone  exists. 

If  the  peripheral  end  of  the  elastic  tube  be  open  and  more  fluid  be 
injected,  both  movements  co-exist ;  that  is,  there  is  a  forward  progression 
of  the  particles  of  the  liquid  added  to  the  wave  movement  already  de- 
scribed. When  the  wave  movement  passes  in  the  same  direction  as  the 
current,  it  is  called  a  positive  wave;  when  in  the  opposite  direction,  it  is 
called  a  negative  wave.  The  speed  of  propagation  of  the  wave  is  pro- 
portional to  the  elastic  force/ of  the  walls  of  the  tube,  while  the  height 
of  the  wave  depends  upon  their  extensibility. 

It  is  evident  from  the  above  that  the  movement  of  liquids  in  open 
tubes  will  vary  according  to  whether  their  walls  are  rigid  or  elastic.  If 
in  a  rigid  tube  a  definite  amount  of  liquid  be  injected,  no  more  or  no  less 


CIKCULATION   OF  THE  BLOOD.  523 

can  escape  from  the  open  end.  If  the  calibre  of  a  rigid  tube  be  dimin- 
ished, the  increased  resistance  will  react  on  the  propelling  power,  and 
will  likewise  prevent  injection  of  more  than  can  escape  by  the  open  end. 

Thus,  suppose  a  rigid  tube  be  connected  with  a  pump  which  throws 
any  definite  quantit}',  say  one  ounce,  of  water  at  each  stroke,  the  rigid 
tube  being  supposed  to  be  already  distended  with  liquid.  At  each 
stroke  of  the  pump,  therefore,  one  ounce  of  liquid  will  escape  from  the 
free  end.  Suppose,  now,  the  free  end  of  the  rigid  tube  be  so  decreased 
in  calibre  as  to  allow  only  one-half  the  previous  quantity  to  escape,  this 
resistance  will,  therefore,  react  on  the  pump  and  prevent  its  throwing 
more  than  one-half  the  quantity  into  the  tube. 

If,  on  the  other  hand,  the  walls  of  the  tube  be  elastic,  the  conditions 
Will  vary  according  as  the  resistance  is  increased  or  diminished. 

If  an  elastic  tube  of  the  same  length  and  diameter  as  the  rigid 
tube  already  experimented  with  be  connected  with  a  pump  throwing 
the  same  quantity  of  liquid  at  each  stroke,  it  is  evident  that  the  con- 
ditions will  be  the  same  as  in  the  rigid  tube ;  that  is,  the  same  amount 
of  fluid  will  escape  from  the  free  end  as  enters  at  the  opposite  end 
from  the  pump,  and  the  time  of  injection  and  escape  of  liquid  will 
coincide. 

If,  now,  the  distal  end  of  the  elastic  tube  be  contracted  so  as  to 
diminish  the  outflow,  the  pump  still  throwing  the  same  amount  of 
fluid,  it  is  evident  that  if  we  say  only  one-half  of  the  amount  injected 
can  escape  from  the  free  end  of  the  tube  the  other  half  will  collect 
in  the  tube  and  overdistend  its  walls. 

In  the  intervals  of  action  of  the  pump,  the  elasticity  of  the  walls 
of  the  tube  will  lead  to  their  contraction,  and  this  recoil  will  act  as  a 
propelling  power  on  the  contents  of  the  tube,  and  lead  to  its  escape 
from  the  end  of  the  tube.  The  stream,  now,  instead  of  being  inter- 
rupted and  in  jerks,  will  tend  to  become  continuous.  Thus,  elastic  tubes 
have  the  power  of  transforming  an  intermittent  into  a  continuous  flow. 
The  fluid  thus  contained  in  a  series  of  elastic  tubes  is  subjected  to  two 
pressures,  one  derived  from  the  propelling  force  and  the  other  exerted 
by  the  elastic  walls,  due  to  the  overdistention  of  the  tubes.  In  tubes 
with  elastic  walls,  the  velocity  of  the  current  is  diminished  before  the 
quantity  of  fluid  discharges  is  increased. 

In  the  mechanics  of  the  circulation  the  former  of  these  forces  is 
spoken  of  as  blood  pressure  upon  the  walls  of  the  vessels,  and  is  due  to 
the  propelling  power  of  the  heart;  while  the  second,  the  force  exerted 
by  the  walls  of  the  arteries  upon  the  blood,  due  to  the  recoil  of  these 
vessels,  is  spoken  of  as  arterial  tension. 

4.  THE  CIRCULATION  IN  THE  ARTERIES. — The  principal  cause  of 
the  movement  of  the  blood  in  the  arterial  system  is  the  intermittent 


524  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

contraction  of  the  ventricles.  At  each  systole  of  the  ventricles  the  heart 
completely  empties  itself,  and,  consequently,  throws  into  the  blood- 
vessels the  amount  of  blood  capable  of  being  contained  in  its  cavity, 
while  at  the  same  time  an  equal  quantity  of  blood  enters  the  heart  from 
the  veins.  This  injection  of  new  amounts  of  blood  into  the  arterial 
system,  as  a  consequence,  occurs  intermittently,  as  may  be  readily 
recognized  by  opening  the  artery  of  an  animal,  when  it  will  be  found 
that  the  blood  will  issue  in  spurts,  each  spurt  corresponding  to  a  con- 
traction of  the  ventricles.  It  will,  however,  be  remarked  that  there  is 
also  an  escape  of  blood  during  the  pauses  of  the  contractions  of  the 
heart,  and  that  the  farther  from  the  heart  a  blood-vessel  be  opened  the 
less  will  be  the  apparent  effect  of  ventricular  contraction  in  increas- 
ing the  velocity  with  which  the  blood  flows  from  the  divided  vessel.  In 
other  words,  the  blood  within  the  blood-vessels  is  subjected  to  a  con- 
siderable tension,  derived  from  the  elasticity  of  the  vascular  walls,  and 
this  tension  itself  serves  partly  to  assist  in  the  onward  movement  of  the 
blood.  When  a  vessel  divides,  except  in  rare  instances,  the  sum  of  the 
calibre  of  the  branches  is,  as  a  rule,  greater  than  that  of  the  parent  stem. 
In  nearly  all  cases,  however,  the  capacity  of  the  branches  is  consider- 
ably greater  than  the  original  vessels  before  division,  even  though  the 
sum  of  the  diameters  of  the  branches  be  but  little  greater  than  that  of 
the  parent  stem.  The  arterial  system  may  thus  be  regarded  as  a  cone 
whose  apex  joins  the  left  ventricle,  and  whose  base  is  represented  by  the 
capillary  S3^stem.  The  venous  system,  on  the  other  hand,  may  be  repre- 
sented by  an  inverted  cone,  whose  base  is  formed  by  the  capillaries,  and 
whose  apex  is  in  communication  with  the  right  auricle. 

In  the  arteries  the  conditions  of  the  movements  of  the  blood  are 
largely  governed  by  the  physical  characteristics  of  the  walls  of  the  blood- 
vessels. The  arteries  consist  of  three  coats — an  inner  serous  coat  or 
endothelium,  the  middle  elastic  and  muscular  coat,  and  an  outer  fibrous 
coat.  It  is  to  the  middle  coat  that  the  physical  characters  of  the  circu- 
lation are  largely  due.  The  proportion  of  muscular  fibre  to  elastic  tissue 
varies  considerably  in  different  parts  of  the  arterial  system.  In  the 
large  arteries  directly  in  the  neighborhood  of  the  heart  the  middle  coat 
is  composed  almost  solely  of  yellow  elastic  tissue,  while  the  muscular 
fibres  are  present  in  small  amount.  As  the  capillary  system  is  ap- 
proached, or,  in  other  words,  as  the  arteries  become  smaller  and  smaller 
by  repeated  subdivisions,  the  elastic  coat  diminishes  in  amount,  while  the 
muscular  coat  increases.  The  relative  proportions  of  these  two  elements 
of  the  middle  coat  are,  therefore,  inversely  as  the  diameter  of  the  vessel. 

The  action  of  these  two  elements  is  to  a  certain  extent  antagonistic, 
although  they  both  combined  serve  to  assist  in  the  onward  movement  of 
the  blood. 


CIRCULATION  OF  THE  BLOOD.  525 

The  direction  of  the  muscular  fibres  of  the  arteries  is  circular,  while 
longitudinal  fibres  are  absent.  As  a  consequence,  the  contraction  of  the 
muscular  coat  of  an  artery  tends  to  obliterate  its  calibre.  On  the  other 
hand,  the  elastic  element  tends  to  keep  the  artery  open.  When,  there- 
fore, an  artery  is  reduced  in  calibre  by  contraction  of  its  muscular  fibres, 
when  the  muscular  coat  becomes  relaxed,  the  elastic  coat  dilates  it. 
There  is  no  active  dilating  mechanism  in  the  walls  of  the  blood-vessels. 
The  combined  action  of  these  two  forces,  the  expanding  force  of  the 
elastic  coat  and  the  contracting  force  of  the  muscular  coat,  would  serve 
to  cause  the  arteries  to  assume  the  form  of  hollow  ribbons  with  flattened 
sides,  or  flattened  cylinders.  This  shape  is  found  in  the  arteries  of  an 
animal  when  examined  after  death.  In  the  act  of  dying  the  arteries 
empty  themselves  by  the  contraction  of  the  muscular  coat,  forcing  their 
entire  contents  over  into  the  venous  system ;  they,  therefore,  become 
completely  emptied,  and  are  then  flattened  cylinders ;  this  condition 
holds  until  one  of  the  larger  arteries  be  opened;  air  then  enters  the 
arteries,  the  muscular  force  having  been  lost  through  death;  the  arteries 
then  dilate  through  the  action  of  the  elastic  tissue  which  is  longer  pre- 
served, and  they  now  become  hollow  C3Tlinders  filled  with  air.  It  is  thus 
seen  that  the  larger  arteries  are  highly  elastic  tubes,  and  the  influence  of 
the  elasticity  of  the  walls  of  a  tube  on  a  moving  column  of  fluid  has  been 
already  alluded  to.  In  other  words,  the  elastic  tissue  in  the  walls  of  the 
large  arteries  tends  to  overcome  the  intermittent  action  of  the  heart  and 
to  render  the  flow  of  blood  in  the  arteries  continuous.  In  the  smaller 
arteries  the  elastic  tissue  is  reduced  in  amount  and  often  becomes  en- 
tirely absent,  but,  on  the  other  hand,  the  proportion  of  muscular  tissue  is 
increased.  Muscular  tissue  is  itself  a  highly  elastic  tissue,  consequently 
the  smaller  arteries  are  not  only  elastic  but  are  also  supplied  with  con- 
tractile walls,  and  as  a  consequence  their  calibre  may  be  reduced,  thus 
permitting  variations  in  the  supply  of  blood  to  different  localities. 

The  conditions  for  permitting  a  satisfactory  interchange  between 
the  blood  and  different  organs  are,  therefore,  fulfilled.  For  we  have  not 
only  a  constant  flow  of  blood  through  all  parts  of  the  body,  but  this  flow 
is  susceptible  of  general  and  local  alterations ;  general  alterations,  be- 
cause the  heart  itself  is  capable,  as  already  indicated,  of  being  modified 
in  its  activity ;  and,  second,  because  we  see  that  the  smaller  arteries  are 
supplied  with  tissue  which,  by  regulating  the  calibre  of  the  blood-vessels, 
is  capable  of  regulating  the  amount  of  blood  supplied  to  different  organs. 
The  mechanism  by  which  this  supply  is  governed  will  be  alluded  to 
directly. 

Blood  Pressure. — In  the  arteries  in  their  normal  state  the  elastic 
coat  is  in  a  condition  of  distention  beyond  its  point  of  equilibrium.  In 
other  words,  the  arteries  are  vessels  overfilled  with  fluid.  The  contents 


526  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

of  the  vessels  must,  consequently,  produce  pressure  on  the  walls  of  the 
blood-vessels  to  a  sufficient  degree  to  prevent  the  regaining  by  tM  elastic 
tissue  of  its  position  of  equilibrium.  Such  a  tension  as  already  described 
is  one  of  the  important  factors  in  blood  pressure.  By  blood  pressure  is 
meant  the  pressure  which  the  blood  exerts  on  the  walls  of  the  vessels. 
By  arterial  tension  is  meant  the  pressure  which  the  walls  of  the  vessels 
exert  on  their  contents.  It  is  thus  seen  that  these  two  terms  are  mutually 
convertible.  The  pressure  which  the  blood  exerts  on  the  walls  of  the 
vessels  is,  of  course,  dependent  upon  the  energy  of  the  contraction  of  the 
heart  and  the  resistance  which  the  capillaries  offer  to  the  onward  motion 
of  the  blood.  The  pressure  which  the  elastic  walls  of  the  arteries  exert 
on  their  contents  will,  of  course,  again  depend  upon  the  amount  of  blood 
contained  in  the  arteries  and  their  consequent  distention,  and  while  this, 
again,  as  we  shall  see,  is  capable  of  being  modified  by  different  causes,  it 
is  mainty  dependent  upon  the  activity  of  the  heart.  Blood  pressure  is 
measured  by  estimating  the  pressure  which  the  blood  exerts  on  the  vas- 
cular walls. 

It  has  been  mentioned  that  when  an  opening  is  made  in  the  walls  of  an 
artery  the  blood  escapes  therefrom  in  jets,,  and  it  is  found  that  the  larger 
the  artery,  and,  consequently,  the  nearer  the  opening  is  to  the  heart,  the 
higher  will  be  the  jet  of  blood  and  the  more  intermittent  will  be  the 
flow ;  this  indicates  that  the  blood  pressure  is,  therefore,  greater  in  the 
large  vessels  than  in  the  small  arterioles,  and  is  only  what  is  to  be 
expected  from  the  conditions  which  are  necessary  for  the  maintenance  of 
the  circulation.  It  has  been  stated  that  the  arteries  subdivided  into 
smaller  and  smaller  vessels',  and,  consequently,  the  friction  proportionally 
increases  with  the  minuteness  of  the  vessel.  It  is,  therefore,  evident, 
further,  that  the  pressure  in  the  large  arteries  must  be  higher  than  in  the 
arterioles,  and  in  all  arteries  higher  than  in  the  veins. 

The  hlood  pressure  may  be  directly  measured  in  any  accessible  artery  by 
directly  connecting  a  manometer  with  the  interior  of  the  vessel  (Fig.  218).  Such 
an  instrument,  in  its  simplest  form,  consists  of  a  U  -shaped  tube  containing  mercury  * 
in  its  lower  part,  the  distal  end  being  free  to  the  atmosphere,  and  the  proximal 
end  connected  directly  with  the  interior  of  the  blood-vessel.  If  the  pressure  in 
the  blood-vessel  is  greater  than  the  atmospheric  pressure,  it  is  evident  that  the 
mercury  will  be  depressed  in  the  proximal  arm  and  rise  in  the  distal  arm,  until 
the  difference  in  height  between  the  columns  of  mercury  in  the  two  arms  equals 
the  pressure  exerted  by  the  fluid.  Such  an  experiment  is  termed  a  blood-pressure 
experiment,  and  is  readily  performed  on  any  of  our  domestic  animals. 

To  make  a  blood-pressure  experiment,  the  animal  should  be  securely 
fastened  and  the  artery  exposed  through  an  incision.  In  the  dog,  in  which  such 
experiments  may  be  most  conveniently  performed,  the  arteries  usually  experi- 
mented on  are  the  carotid  or  the  femoral.  To  expose  the  carotid  artery,  the' hair 
is  removed  from  the  front  part  of  the  neck,  and  an  incision,  about  two  inches  in 
length,  made  in  the  middle  of  the  neck,  at  the  anterior  border  of  the  sterno-mas- 
toid  muscle  :  the  platysma  and  subcutaneous  fascia  are  then  broken  through  with 
forceps  or  blunt  hooks,  and  the  sterno-mastoid  muscle  pushed  to  the  outside,  and 
the  artery  is  readily  found  lying  beneath  it,  the  pneumogastric  nerve  running  in 
the  same  sheath.  The  bundle  containing  the  pneumogastric,  the  sympathetic,  and 


CIRCULATION  OF  THE  BLOOD. 


527 


carotid  arteries  is  then  raised  on  a  blunt  hook,  the  connective  tissue  gently  torn 
away  with  two  pairs  of  forceps,  and  the  artery  freed  from  the  surrounding  nerves 
and  fibrous  tissue.  After  the  blood-vessel  is  so  isolated  for  a  distance  of  about 
an  inch,  it  is  firmly  ligated  at  the  extremity  of  the  free  portion  nearest  to  the 
head,  and  a  thread  is  then  tied  in  a  loop-knot  around  the  artery  at  the  end  of  its 
freed  extremity  nearest  to  the  heart.  A  small  cut  is  then  made  in  the  interme- 
diate portion  with  a  pair  of  scissors,  and  a  slightly  constricted  glass  tube  inserted 
into  the  interior  of  the  artery  and  bound  fast  with  a  thread.  This  glass  tube  is 
then  to  be  filled  by  a  pipette  with  a  saturated  solution  of  sodium  bicarbonate,  to 
prevent  coagulation  of  the  blood,  and  the  cannula  then  connected  by  thick  rubber 
tubing,  also  filled  with  the  same  solution,  with  the  proximal  arm  of  the  manome- 
ter. Care  should  be  taken  that  all  air-bubbles  are  removed  from  the  cannula, 
rubber  tube,  and  proximal  arm  of  the  manometer,  so  that  the  entire  tubing,  from 
the  level  of  the  mercury  to  the  interior  of  the  carotid,  is  completely  filled  with 
soda  solution.  If,  now,  the  slip-knot  previously  tied  around  the  carotid  is 


FIG.  218.— MERCURIAL  MANOMETER  FOR  MEASURING  AND  RECORDING  THE 
BLOCTO  PRESSURE.    (Yeo.) 

a,  proximate  limb  of  the  manometer;  b,  union  of  the  two  limbs  of  the  manometer:  e,  the  rod  floating 
in  the  mercury  carries  the  writing  point;  d,  stop-cock  through  which  the  sodium  bicarbonate  can  be 
introduced  between  the  blood  and  the  mercury  of  the  manometer. 

loosened,  thus  establishing  communication  between  the  interior  of  the  artery  and 
the  manometer,  the  blood  at  once  rushes  from  the  artery  into  the  connecting  tube, 
and  so  causes  the  level  of  mercury  to  be  depressed  in  the  proximal  arm  and  rise 
in  the  distal  arm.  This  rise  of  mercury  occurs  very  rapidly,  in  jerks  correspond- 
ing to  the  beats  of  the  heart,  and  soon  reaches  its  maximum.  When  this  point  is 
attained,  the  mercury  does  not  remain  level,  but  undergoes  rapid  oscillations, 
each  rise  corresponding  to  the  systole  of  the  ventricle,  each  fall  correspond- 
ing to  the  diastole.  If  a  float,  swimming  on  the  top  of  the  mercury,  in  the 
distal  arm  of  the  manometer  be  allowed  to  record  its  up-and-down  movements 
on  a  moving  surface,  as,  for  example,  the  revolving  drum  of  the  kymographion 
(Fig.  219),  a  series  of  curves  will  be  produced,  in  which  each  ascent  cor- 
responds to  the  contraction  of  the  ventricle,  each  descent  to  its  diastole  (Fig. 
220).  In  the  experiment,  as  above  described,  it  is  evident  that  a  considerable 
quantity  of  blood  will  leave  the  arterial  system  and  fill  the  tube  of  the  manometer. 


528 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


To  avoid  this  loss  of  blood,  it  is  therefore  advisable  to  inject  the  sodium  carbo- 
nate solution  into  the  tube  of  the  manometer  until  the  column  of  mercury  has 
been  elevated  to  the  height  which  will  probably  correspond  to  that  of  the  mean 
arterial  pressure. 

Comparative  experiments  made  in  the  above-described  manner  will 
show  that  the  blood  pressure  is  considerably  higher  in  the  arteries  than 
in  the  veins,  and  greater  in  the  large  arteries  than  in  the  arterial 
branches  (Fig.  221)  ;  so,  also,  the  pressure  may  be  demonstrated  to  be 
higher  in  the  small  veins  than  in  the  large  veins  at  their  opening  into 
the  heart.  Experiment  will  further  show  that  in  the  veins  the  pressure  is 
almost  constant,  overlooking  the  insignificant  variations  which  are  due  to 
respiration ;  so,  also,  the  pressure  will  be  found  to  be  almost  constant  in 


FIG.  219.— LUDWIG'S  KYMOGRAPHION,  AFTER  HERMANN.    (Yco.) 

The  ordinary  form  of  rotating,  blackened  cylinder  (R),  which  is  moved  by  the  clock-work  in  the  box 
(A)  by  means  of  the  disk  (D)  pressing  on  the  wheel  (•»),  which  can  be  raised  or  lowered  by  the  screw  (L) 
BO  as  to  rub  on  a  part  of  the  disk  more  or  less  near  the  centre,  and 'thus  rotate  at  different  rates.  The 
cylinder  may  be  raised  by  the  screw  (»)  which  is  turned  by  the  handle  (U). 

the  small  arteries,  while  in  the  large  arteries  considerable  variations, 
corresponding  in  their  increase  to  the  systole  and  their  decrease  to  the 
diastole,  are  invariably  found.  It  is  evident  that  the  mean  between  the 
maximum  and  minimum  pressures  in  the  arteries,  as  indicated  by  these 
oscillations,  will  represent  the  force  which  is  concerned  in  the  propul- 
sion of  the  blood.  Although  theoretically  and  practically  the  pressure 
decreases  as  the  distance  increases  from  the  heart,  yet  in  any  artery 
which  is  not  too  small  to  be  subjected  to  such  manometrical  experiments 
it  will  be  found  that  the  pressure  will  be  slightly  affected,  not  more  than 
one-tenth  lower  than  the  mean  pressure  in  the  aorta.  This  fact  indicates 
that  the  blood  in  moving  through  the  arteries  has  to  overcome  but  slight 


CIRCULATION   OF   THE   BLOOD. 


529 


FIG.  220.— BLOOD-PRESSURE  CURVE,  DRAWN  BY  MERCURIAL  MANOMETER.    (Yeo.) 

0to  x  =  zero  line,  y  to  yl  =  curve  with  large  respiratory  waves  and  small  waves  of  heart  impulse.    A  scale 
is  introduced  to  show  height  of  pressure  in  millimeters  of  mercury. 


FIG.  221.— DIAGRAM  SHOWING  THE  RELATIVE  HEIGHTS  OF  BLOOD  PRESSURE 
IN  THE  DIFFERENT  REGIONS  OF  THE  VESSELS.    ( Yeo.) 

H,  heart;  A.  arteries:  a.  arterioles :  r,  capillaries:  V.  small  veins;  r,  large  veins:  H  V,  being  the 
zero  line,  the  pressure  is  indicated  bv  the  elevation  of  the  curve.  The  numbers  to  the  left  give  the 
pressures  (approximately)  in  millimeters  of  mercury. 

34 


530 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


resistance,  evidently  to  be*  explained  by  the  fact  that  as  the  arteries 
divide  their  total  calibre  increases.  If  the  mean  pressure  in  the  artery 
is  measured  at  different  times  it  will  be  found  to  be  subject  to  very  great 
variations,  from  causes  which  will  subsequently  receive  attention. 

The  average  blood  pressure  of  mammals  is  by  no  means  dependent 
upon  the  animal's  size.  In  all  cases  the  arterial  blood  pressure  may  be 
stated  as  exceeding  the  atmospheric  pressure  and  varying  between  one 
hundred  and  two  hundred  millimeters  of  mercury. 

The  following  table  gives  various  estimates  of  the  mean  arterial 
pressure  in  different  animals  (Volkmann)  : — 


Animal.                                         Mean  Pressure  in  mm.  of  Mercury. 

Horse,  . 

321  mm.  (Ludwig)     in  the  carotid  artery 

Horse,  . 

214 

" 

" 

Horse,  . 

150 

(Spengler) 

brachial 

Horse  (old), 

140 

" 

" 

Sheep,  . 

206 

(Ludwig) 

carotid 

Sheep,   . 

169 

" 

" 

Sheep,  . 

156 

(Blake) 

brachial 

Sheep  (old), 

86 

" 

*< 

Calf,       . 

177 

(Ludwig) 

carotid 

Calf,      . 

165 

(Spengler) 

" 

Calf,      . 

153 

« 

brachial 

Calf,       . 

133 

(Ludwig) 

" 

Dog  (large), 

172 

<            n 

carotid 

Dog,      , 

157 

(Blake) 

brachial 

Dog,       . 

166 

(Spengler) 

carotid 

Dog,       . 

143 

(Ludwig) 

brachial 

Dog  (young) 

104 

" 

Goat,      . 

135 

" 

Cat, 

150 

" 

Rabbit,  . 

90 

" 

Goose,  . 

162 

(Blake) 

carotid 

Stork,    . 

161 

M 

Pigeon, 

157 

brachial 

The  facts  thus  reached  experimentally  as  to  the  gradual  decrease  in 
pressure  from  the  arteries  to  the  commencement  of  the  veins  and  from 
there  to  the  larger  venous  trunks  completely  explains  the  constant  cur- 
rent of  blood  from  the  arteries  to  the  veins.  The  blood,  therefore,  moves 
in  a  circle  from  the  heart  to  the  arteries,  through  the  capillaries  to  the 
veins,  and  from  the  veins  to  the  heart,  to  again  enter  the  arterial  system. 

The  Velocity  of  the  Blood. — From  the  fact  that  the  arteries  as  they 
pass  into  the  capillaries  increase  immensely  in  area,  and  as  the  capillaries 
pass  into  the  veins  a  corresponding  decrease  is  found,  it  is  to  be  expected 
that  the  velocity  of  the  blood-current  will  be  greatest  in  the  vessels  near 
the  heart.  As  the  blood  leaves  the  heart  to  pass  into  the  aorta  the 
velocity  of  the  current  is  at  its  maximum  ;  it  then  gradually  decreases  as 
the  capillaries  are  reached,  then  undergoes  a  sudden  retardation,  and  again, 
as  the  blood  is  collected  from  the  capillaries  in  the  veins,  the  current 
moves  with  an  increasing  velocity  as  the  right  side  of  the  heart  is  ap- 
proached. No  absolute  figures  can  be  given  as  representing  the  normal 


CIRCULATION    OF   THE   BLOOD.  531 

velocity  at  any  point  in  the  blood-vessel  system,  since  measurements 
show  that  at  any  one  point  the  velocity  is  subject  to  very  great  varia- 
tions. 

The  velocit}*  and  pressure  of  the  blood  at  any  given  point  do  not 
correspond,  and  may  even  be  in  inverse  ratio ;  thus  many  causes,  such 
as  obstruction  of  any  part  of  the  vascular  system,  will  increase  the  blood 
pressure  at  that  point  and  decrease  the  velocity.  As  a  rule,  the  pressure 
at  any  point  depends  upon  the  distance  of  that  point  from  the  heart, 
whether  in  the  arterial  or  venous  S3rstem,  while  the  velocity  depends  upon 
the  capacity  of  the  vessels  at  that  point. 

Where  the  area  of  the  circulatory  system  is  very  large,  as  in  the 
capillaries,  the  blood  circulates  slowly,  just  as  the  current  of  a  stream 
becomes  retarded  as  it  widens  into  a  lake. 

Various  methods  have  been  employed  for  calculating  the  rapidity  of 
the  circulation  in  different  blood-vessels.  The  following  represents  the 
estimations  as  to  the  flow  in  the  arteries,  capillaries,  and  veins  of  the 
horse  (Volkmann): — 

Carotid  artery, 300  mm.  per  second 

Maxillary  artery, 165 

Metatarsal  artery,  .        .        .        .        .56 

Capillaries, 0.5  to  0.8 

Jugular  vein,  ......     100 

Vena  cava,      .        .        .        .        .         .110 

Chauveau  estimates  the  velocity  of  the  blood-flow  in  the  carotid  of 
the  horse  as  varying  from  520  to  150  mm.  per  second,  the  highest  velocity 
coexisting  with  the  systole  of  the  ventricle  and  the  lowest  with  its  dias- 
tole. In  the  larger  veins  respiration  also  produces  considerable  varia- 
tion in  the  velocity  of  the  flow,  the  velocity  being  increased  in  inspira- 
tion and  decreased  in  expiration.  The  velocity  of  the  circulation  through 
any  one  vessel  may  be  modified  by  a  number  of  causes ;  provided  the 
artery  maintains  its  calibre  unchanged,  the  velocity  would  evidently  be 
dependent  upon  the  propelling  force.  Therefore,  an  increase  in  the 
energy  of  the  heart's  contraction,  the  calibre  of  the  arteries  remaining 
unchanged,  will  produce  an  accelerated  flow  through  those  vessels,  while 
a  decrease  in  the  heart's  energy  will  correspondingly  retard  the  arterial 
current.  On  the  other  hand,  the  heart's  energy  remaining  the  same,  a 
dilatation  of  the  artery  will  cause  a  slowing  of  the  current,  and  a  reduc- 
tion in  the  calibre  of  the  artery  will  cause  the  current  to  become  acceler- 
ated. So,  also,  if  the  resistance  to  be  overcome  in  the  circulation  of  the 
blood  be  reduced,  as  by  the  relaxation  of  the  capillaries,  the  energy  of  the 
heart's  contraction  and  the  calibre  of  the  artery  remaining  the  same,  the 
velocity  of  the  blood-current  will  be  increased  ;  while,  again,  an  increase 
in  the  resistance,  the  other  conditions  being  unchanged,  will  retard  the 
blood-flow. 


532  PHYSIOLOGY   OF   THE  DOMESTIC   ANIMALS. 

Various  attempts  have  been  made  to  calculate  the  time  required  by 
the  blood  for  making  one  complete  circuit  of  the  body.  The  method 
which  is  generally  accepted  as  giving  reliable  results  is  what  is  known 
as  the  "  transfusion  method  "  of  Hering,  and  consists  in  injecting  into 
one  of  the  jugular  veins  toward  the  heart  a  solution  of  some  salt,  the 
presence  of  which  in  the  blood  may  be  readily  recognized  by  chemical 
tests,  and  in  finding  how  soon  after  the  injection  the  salt  appears  in 
the  blood  coming  from  the  head  in  the  corresponding  vein  on  the 
opposite  side  of  the  neck.  As  determined  by  Vierordt,  the  duration  of 
the  circulation  in  different  animals  is  as  follows  : — 

Horse,         .  31.5  seconds.  Goose,  .       10.86  seconds. 

Dog.  .  16.7      "  Duck,  .       10.64      " 

Rabbit,       .  7.79    "  Buzzard,  .         6.73      " 

Hedgehog,          7.61    "  Fowl,  .        5.17 
Cat,    . 


By  comparing  these  numbers  with  the  frequency  of  the  pulse  in 
these  animals,  the  deduction  has  been  made  that  the  circulation  is 
accomplished  in  21  heart-beats.  From  this  the  amount  of  blood  thrown 
out  at  each  contraction  of  the  ventricle  may  be  calculated  :  for  if  the 
entire  amount  of  blood  passes  through  the  heart  in  27  pulsations,  one 
pulsation  will  throw  out  gV  the  total  amount  of  blood  in  the  body,  and 
placing  this  amount  at,  for  example,  ^  of  the  body  weight  in  a  man 
weighing  65.8  kilos,  the  ventricles  at  each  pulsation  will  discharge  187.5 
grammes,  the  amount,  of  course,  being  the  same  for  both  ventricles..  If 
we  assume  that  these  data  are  approximately  correct,  the  work  done  by 
the  heart  may  be  calculated.  One  kilogramme-meter  is  a  force  which  in 
the  unit  of  time  can  raise  one  kilo  one  meter  high.  If,  therefore,  the 
left  ventricle  expels  0.188  gramme  of  blood  against  the  pressure  of  blood 
in  the  aorta  (250  milligrammes  of  mercury  or  3.21  meters  of  blood),  the 
work  done  at  each  systole  is  0.188  X  3.21  =  0.604  kilogramme-meter. 
If  the  number  of  beats  is  75  per  minute,  then  the  work  done  in  twenty- 
four  hours  =  (0.604  X  75  X  60  X  24)  =  65,230.  kilogramme-meters, 
while  the  work  done  by  the  right  ventricle,  since  the  pressure  in  the 
pulmonary  artery  is  only  one-third  that  of  the  aorta,  will  be  one-third 
this  amount,  or  21,740.  kilogramme-meters:  and  both  ventricles  together 
will  do  a  work  of  86,907.  kilogramme-meters  in  the  twenty -four  hours. 
Since  part  of  this  work  is  converted  into  heat,  the  contractions  of  the 
heart  assist  in  maintaining  the  body  temperature. 

In  the  case  of  the  ox  it  has  been  estimated  that  0.75  liter  of  blood 
is  driven  from  the  left  ventricle  at  each  systole,  and  since  the  pulse 
in  this  animal  averages  50  per  minute  37.50  liters  of  blood  will  pass 
through  the  heart  in  each  minute,  or  900  liters  in  twenty-four  hours. 
The  specific  gravity  of  the  blood  being  1045,  18,810  pounds  of  blood,  or 


CIRCULATION   OF   THE   BLOOD.  533 

fifteen  times  the  body  weight,  will  be  set  in  motion  b}^  the  contractions 
of  each  ventricle,  or  37,620  pounds  in  all,  Jf  it  be  admitted  that  the 
amount  of  blood  in  the  ox  is  ^  of  the  body  weight,  or  52.18  pounds, 
and  each  systole  propels  0.75  liter,  or  1J  pounds  of  blood,  thirty-five  con- 
tractions of  the  heart  would  be  needed  to  drive  the  entire  amount  once 
around  the  body ;  or,  the  pulse-rate  being  50  per  minute,  the  circulation 
would  be  completed  in  forty-two  seconds.  It  is  evident  that  these  figures 
are  in  opposition  to  the  estimates  obtained  by  Bering's  method,  which, 
according  to  Vierordt,  places  the  duration  of  the  circulation  as  equal  to 
the  time  required  by  the  heart  for  making  twenty-seven  pulsations.* 

The  Pulse. — As  the  left  ventricle  empties  itself  into  the  aorta  it  is 
compelled  to  overcome  the  pressure  of  the  blood  already  contained  in 
the  arterial  system  and  two  phenomena  result — an  acceleration  of  the 
current  of  blood  toward  the  capillaries  and  the  dilatation  of  the  aorta  to 
accommodate  the  additional  amount  of  blood  thrown  in  by  the  ventricle. 

In  the  description  of  the  physical  principles  concerned  in  the  pas- 
sage of  fluid  through  an  overfilled  system  of  tubes  with  elastic  walls, 
it  was  stated  that  at  each  introduction  of  fluid  a  wave  was  produced 
which  rapidly  traversed  the  walls  of  the  tube,  its  velocity  of  movement 
being  proportional  to  the  tension  of  the  walls  of  the  tube,  while  its  cause 
was  found  not  in  the  passage  of  the  fluid,  but  in  an  up-and-down  oscilla- 
tion of  the  walls  of  the  vessels.  Such  a  wave  of  oscillation  as  seen  in 
the  arterial  system  is  described  as  the  pulse.  The  pulse  is,  therefore, 
the  diastole  of  the  arteries.  In  the  arteries  which  are  close  to  the  heart 
this  diastole  is  almost  synchronous  to  the  systole  of  the  ventricle,  but  as 
the  distance  from  the  heart  increases  a  sensible  interval  may  be  recog- 
nized between  the  contraction  of  the  ventricle  and  the  appearance  of  the 
pulse-wave.  This  time  is  required  for  the  transmission  of  the  wave 
through  the  walls  of  the  vessels.  To  determine  the  time  required  for  the 
transmission  of  this  wave  it  is  only  necessary  to  estimate  the  interval  of 
time  elapsing  between  the  contraction  of  the  heart  and  the  appearance  of 
the  pulse-wave  in  any  locality.  This  time,  together  with  the  distance 
of  the  point  examined  from  the  heart,  will  enable  us  to  calculate  the  rate 
of  movement  of  the  pulse-wave.  It  has  been  found  that  the  transmission 

*It  is  probable  that  the  data  on  which  the  above  calculations  are  made  are  not  even 
approximately  correct,  though  they  may  perhaps  serve  to  give  a  general  idea  of  the  subject. 
For  experimental  proof  as  to  the  different  sources  of  error  in  Bering's  method  and  the 
mode  of  calculating  the  amount  of  blood  thrown  out  in  the  contractions  of  the  ventricles, 
see  papers  by  the  author— "A  New  Method  for  Determining  the  Amount  of  Blood  Thrown 
Into  the  Arterial  System  by  Each  Ventricular  Systole,"  Philadelphia  Medical  Times, 
Jan.  26, 1884,  and  "The  Time  Required  by  the  Blood  for  Making  One  Complete  Circuit  of 
the  Body,"  Transactions  of  the  College  of  Physicians,  Philadelphia,  1884,  and  American 
Journal  of  the.  Medical  Sciences,  April,  1884.  Also  W.  H.  Howell  and  F.  Donaldson, 
"  Proceedings  of  the  Royal  Society,"  No.  226, 1883  and  1884,  p.  139,  and  Stolnikow,  Archiv 
fur  Anat.  u.  Physiologic,  1886. 


534  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

of  the  undulation  is  not  uniform  in  all  segments  of  the  arterial  system. 
It  progressively  diminishes  from  the  centre  to  the  periphery,  and  in- 
creases with  the  resistance  and  thickness  of  the  arterial  walls.  It  is, 
therefore,  more  rapid  in  the  arteries  of  the  inferior  extremities. 

It  has  been  found  that  in  man  in  the  arterial  system  of  the  upper 
extremities  the  pulse-wave  travels  with  a  velocity  of  5.8  meters  per  sec- 
ond. In  the  arterial  system  of  the  leg  the  velocity  of  movement  is  about 
6.4  per  second.  In  }roung  individuals  before  maturity,  and  when,  there- 
fore, the  arteries  are  more  extensible  and,  consequently,  less  elastic,  the 
velocity  of  the  pulse-wave  is  diminished,  it  then  being  only  about  four 
meters  per  second.  So,  also,  the  causes  which  reduced  the  blood-pres- 
sure will  also  reduce  the  rapidity  of  movement  of  the  pulse-wave.  It 
must  not  be  forgotten  that  the  time  of  appearance  of  the  pulse-wave  in 
any  point  of  the  arterial  system  by  no  means  indicates  that  the  blood 
thrown  out  from  the  left  ventricle  would  in  that  interval  reach  the  point 
at  which  the  pulse-wave  is  perceived  ;  for  by  comparing  the  velocities 
of  movement  of  the  blood,  even  in  the  vessels  where  the  velocity  of 
movement  is  highest,  and  the  velocity  of  movement  of  the  pulse-wave,  it 
will  be  found  that  the  latter  moves  with  many  times  the  higher  velocity. 
The  onward  current  of  the  blood  in  the  arteries  at  points  at  a  distance 
removed  from  the  heart  is  due  to  the  blood  being  mechanically  pushed 
forward  by  the  increased  quantities  thrown  into  the  vascular  system  by 
the  contraction  of  the  ventricle. 

When  the  finger  is  applied  over  a  superficial  artery  resting  upon 
some  firm  surface,  as  on  a  bone,  a  series  of  impulses  are  felt  which  coin- 
cide in  number  with  the  contractions  of  the  heart.  They  are  not,  how- 
ever, synchronous  with  the  heart's  contraction,  but  each  dilatation  of 
the  artery  will  occur  at  an  appreciable  interval  after  the  heart's  con- 
traction, the  length  of  that  interval  corresponding  with  the  distance 
of  the  point  examined  from  the  heart.  This  intermittent  expansion  is 
called  the  pulse,  and  corresponds  to  the  intermittent  outflow  of  the  blood 
from  a  severed  artery,  and  is  present  in  the  arteries  only,  being  absent, 
except  under  certain  circumstances,  from  the  capillaries  and  veins. 

The  practical  phenomena  concerned  in  the  production  of  the  different 
degrees  of  the  pulse-wave  may  be  reproduced  by  forcing  fluid  intermit- 
tent^ through  a  tube  with  elastic  walls,  in  which  a  variable  resistance 
may  be  introduced,  and  by  so  arranging  movable  levers  in  contact  with 
the  walls  of  the  tube  as  to  enable  them  to  record  their  movements  on  a 
revolving  surface. 

The  following  diagram,  after  Marey  (Fig.  222),  represents  the  curves  produced 
by  a  series  of  levers  placed  at  intervals  of  twenty  centimeters  along  an  elastic 
tube,  into  which  fluid  is  forced  by  the  intermittent  strokes  of  a  pump.  With  each 
stroke  of  the  pump  each  lever  rises  and  then  falls,  thus  describing  a  curve  and 
indicating  an  expansion  of  the  tube,  which  travels  along  its  walls  in  the  form  of 


CIRCULATION   OF   THE   BLOOD. 


535 


a  wave.     The  rise  of  each  lever  is  abrupt  ;  its  fall  is  more  gradual,  and  usually 
marked  by  secondary  fluctuations. 

If  two  levers,  separated  by  a  considerable  length  of  tube,  be  allowed  to 
record  their  movements  on  a  rapidly  traveling  surface,  it  will  be  found  that  on 
working  the  pump  the  movements  described  by  the  levers  will  not  be  synchronous  ; 
in  other  words,  an  appreciable  interval  of  time  will  be  required  for  the  trans- 
mission of  the  wave  through  the  length  of  tube  separating  the  two  levers.  In 


,WV\AA/W\A/\/VWW 


50V 


FIG.  222.— PULSE- WAVES  DESCRIBED  BY  LEVERS  PLACED  AT  INTERVALS  OF 
TWENTY  CENTIMETERS  ON  AN  ELASTIC  TUBE,  INTO  WHICH  FLUID  is 
FORCED  BY  THE  SUDDEN  STROKE  OF  A  PUMP,  (foster.) 

The  pulse-wave  is  traveling  from  left  to  right;  A,  primary,  and  B  C  secondary  waves.  The  intervals 
between  the  dotted  lines  each  correspond  to  1-50  second,  determined  by  the  tuning-fork  curve  V,  and 
permit  measurement  of  the  velocity  of  the  wave.  A'A'  are  reflected  waves  from  the  closed  end  of  the  tube. 

such  an  apparatus  the  statement  already  made  as  to  the  conditions  governing  the 
rapidity  of  transmission  of  the  wave-impulse  may  be  readily  demonstrated.  The 
more  rigid  the  tube,  the  more  rapid  the  movement  of  the  wave  ;  the  more  exten- 
sible the  tube,  the  slower  the  wave  travels.  It  will  also  be  noticed  that  the 
nearer  the  levers  are  to  the  pump,  the  greater  will  be  their  excursion,  indicating  a 
greater  expansion  of  the  tube  at  that  point,  while  in  very  long  tubes  the  wave 
gradually  decreases  in  intensity  until  it  often  becomes  scarcely  distinguishable. 


536 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


The  same  condition  applies  in  the  arterial  system  of  animals  :  the  nearer  the  artery 
to  the  heart,  the  greater  will  be  its  expansion  on  the  systole  of  the  ventricle  and 
the  stronger  will  be  the  pulse,  while  the  greater  the  distance  the  less  will  be  the 
expansion  and  the  weaker,  consequently,  will  be  the  pulse. 

It  has  been  mentioned  that  the  descending  limb  of  the  curve  described  by 
such  levers  is  ordinarily  broken  into  a  number  of  secondary  undulations.  These 
may  be  due  to  various  causes.  When  by  the  injection  of  a  mass  of  fluid  the 
walls  of  the  tube  are  distended,  as  they  regain  their  position  of  equilibrium  inertia 
carries  them  still  farther,  until  the  point  of  equilibrium  has  been  passed  ;  a  recoil 
then  takes  place,  and  so  on.  In  other  words,  each  point  of  the  tube  is  the  seat  of 
a  series  of  oscillations  following  each  succeeding  wave,  and  which  are  due  simply 
to  the  inertia  of  the  walls  of  the  tube. 


FIG.  223.— MAREY'S  SPHYGMOQRAPH.    (Yeo.) 

The  frame  B,  B,  B,  is  fastened  to  the  wrist  by  the  straps  at  B,  B,  and  the  rest  of  the  instrument  lies  on 
the  forearm.  The  end  of  the  screw,  V,  rests  on  the  spring,  R,  the  button  of  which  liee  on  the  radial  artery. 
Any  motion  of  the  button  at  R  is  communicated  to  V,  which  moves  the  lever  L  up  and  down.  When  in 
position,  the  blackened  slip  of  glass  is  made  to  move  evenly  by  the  clock-work,  H,  so  that  the  writing 
point  draws  a  record  of  the  movements  of  the  lever. 

Again,  in  the  artificial  scheme  of  the  circulation,  if  the  resistance  be  consider- 
able, or  if  the  end  of  the  tube  be  completely  obstructed,  the  wave  will  be 
reflected  from  the  distal  end  of  the  tube,  and  will  again  cause  a  secondary  wave. 
If  a  lever  (the  sphygrnograph,  Fig.  223)  be  so  placed  on  an  artery  in  a  living 
animal  as  to  record  the  movements  of  its  walls,  various  breaks  will  also  be  seen 
in  the  descending  limb  of  the  pulse-curve  (Fig.  224).  The  most  important  of 
these  is  the  so-called  dicrotic  wave,  which  is  more  or  less  marked  in  every  pulse r 
although  it  may  be  so  exaggerated  as  to  produce  the  impression  of  a  double 
impulse,  or  may,  on  the  other  hand,  be  scarcely  perceptible.  Anything  which 
reduces  the  tension  in  the  arterial  system  will  facilitate  the  development  of  the 
dicrotic  wave.  Anything  which  increases  the  rigidity  of  the  arteries  reduces  the 
degree  of  the  dicrotic  wave.  It  is,  therefore,  evident  that  the  dicrotic  wave  is 


FIG.  224.— TRACING  DRAWN  BY  MAREY'S  SPHYGMOGRAPH.    (Yeo.) 

mainly  a  wave  of  oscillation,  due  to  the  inertia  of  the  walls  of  the  vessels,  possibly 
being  reinforced  by  a  wave  of  expansion  reflected  from  the  closure  of  the  aortic 
valves.  When  the  conditions  are  especially  favorable  for  producing  such  waves 
of  oscillation,  or,  in  other  words,  when  the  walls  of  the  arteries  are  especially 
relaxed,  we  will  then  sometimes  find  that  the  pulse-curve  in  its  descent  will  be 
marked  by  two  breaks,  the  first  of  which  is  then  spoken  of  as  the  pre-dicrotic 
and  the  second  as  the  dicrotic  wave. 

5.  THE  CIRCULATION  IN  THE  CAPILLARIES. — The  capillaries  consist 
of  minute  tubules  whose  walls  are  constituted  by  a  single  layer  of  trans- 
parent, thin,  nucleated,  endothelial  cells  joined  to  each  other  by  their 


CIRCULATION   OF   THE   BLOOD. 


537 


margins.  These  tubules  divide  and  reunite  to  form  net-works  which 
differ  in  shape  and  arrangement  in  different  organs  and  tissues.  Their 
diameter  varies  considerably,  but  is  as  a  rule  about  that  of  the  single  red 
blood-corpuscle.  In  the  lungs  and  brain,  the  capillaries  are  smaller  than 
those  of  the  skin ;  in  the  retina  and  muscle,  are  smaller  than  in  bone, 


FIG.  225.— SMALL  PORTION  OF  FROG'S  LIVER,  VERY  HIGHLY  MAGNIFIED, 
AFTER  HUXLEY.    (Yeo.) 

A,  wall  of  capillary  vessels ;  B,  tissue  lying  between  the  capillaries ;  C,  epithelial  cells  of  the  skin, 
only  shown  in  part  of  specimen  where  the  surface  is  in  focus ;  D,  nuclei  of  the  epithelial  cells ;  E,  pigment- 
cells,  contracted ;  F,  red  blood-corpuscles :  G,  H,  red  corpuscles  squeezing  their  way  through  a  narrow 
capillary,  showing  their  elasticity ;  I,  white  blood-cells. 

marrow,  river,  and  the  choroid  tunic  of  the  eye.  In  all  probability  the 
walls  of  the  capillaries  are  not  contractile,  although  they  are  capable  of 
undergoing  variations  in  diameter,  this  change  in  all  probability  being 
of  a  passive  nature,  owing  to  similar  phenomena  taking  place  in  the 
small  arteries  and  veins.  Thus,  the  pulse  which  is  evident  in  inflamed 


538  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

organs  is  not  due  to  rhythmic  contractions  of  the  walls  of  the  capillaries, 
but  to  the  paralysis  of  the  walls  of  the  minute  arterioles  and  the  conse- 
quent conduction  of  the  impulse  from  the  heart. 

The  circulation  of  the  blood  through  the  capillaries  admits  of  ready 
study  in  the  transparent  tissues  of  different  organs,  such  as  the  web  of  a 
frog's  foot,  the  lung  of  the  frog,  or  the  mesentery  of  the  guinea-pig. 
When  such  tissue  is  subjected  to  microscopic  examination  in  an  animal 
rendered  motionless  by  the  injection  of  curare,  the  blood  may  be  seen 
passing  in  a  continuous  stream  from  the  smaller  arterioles  through  the 
capillaries  to  the  veins  (Fig.  225).  The  arterioles  are  readily  recognized 
by  the  greater  velocity  of  the  flow  within  them  and  by  the  fact  that 
occasionally  faint  pulsations  synchronous  with  the  contractions  of  the 
heart  may  be  recognized.  Under  ordinary  circumstances  when  the 
circulation  through  the  capillaries  is  examined  it  will  be  found  that  the 
corpuscles  pass  in  single  file  with  a  velocity  usually  of  about  0.5T  mm. 
a  second.  The  calibre  of  the  capillaries  is,  however,  the  seat  of  frequent 
changes  whose  mechanism  will  be  subsequently  studied.  Often  we  shall 
find  that  the  capillaries  dilate,  and  we  have  then  a  stream  of  corpuscles 
moving  several  abreast  through  them,  and  even  while  undergoing 
inspection  the  capillaries  may  be  seen  to  become  smaller  in  diameter 
and  occasionally  in  certain  places  so  narrow  as  to  refuse  the  passage 
of  a  single  corpuscle;  the  blood  then  becomes  blocked  up  behind  this 
contraction,  and  then  we  have  channels  dilating  behind  this  obstruction 
and  carrying  off  the  stagnated  blood. 

The  mean  blood  pressure  in  the  capillaries  has  been  placed  at  about 
thirty-five  millimeters  of  mercury,  but  it  is  evident  that  this  pressure 
must  be  subject  to  very  great  variations. 

When  a  microscopic  examination  is  made  of  a  frog's  foot  it  is  seen 
that  the  file  of  nucleated  corpuscles  move  with  their  axes  parallel  with 
the  stream,  rotating  sometimes  on  their  axes,  and  occasionally  we  find 
an  evidence  of  the  flexibility  of  the  red  blood-cells  by  noticing  that 
sometimes  one  of  these  cells,  striking  the  bifurcation  of  a  capillary, 
will  become  doubled  on  itself,  part  lying  in  one  branch  and  part  in 
another,  until  finally  driven  along  by  the  cells  coming  behind  it. 

The  white  blood-cells  will  be  found  to  be  moving  with  a  much  lower 
velocity  than  the  red  blood-corpuscles  (one-tenth  or  one-twelfth  as  fast), 
rolling  slowly  along  in  contact  with  the  walls  of  the  capillaries  outside 
of  the  central,  rapidly  moving  blood-current.  Such  a  layer  is  termed  the 
inert  layer,  and  in  nearly  all  cases  it  will  be  found  that,  while  the  red 
blood-cells  move  in  a  rapid  stream  through  the  centre  of  the  vessel,  a 
clear  space  between  this  central  column  and  the  walls  of  the  capillaries 
may  be  recognized,  in  which  inert  layer,  as  already  mentioned,  the  white 
cells  may  be  nearly  always  found.  The  presence  of  the  white  blood-cells 


CIKCULATION   OF  THE  BLOOD.  539 

in  this  peripheral  layer  is  due  to  two  causes.  The  white  blood-cells  are 
much  more  adhesive  than  the  red,  and  therefore  tend  to  cling  to  the 
sides  of  the  capillaries.  In  addition  to  this,  the  white  blood-cells  are 
lighter  in  specific  gravity  than  the  red,  and  it  has  been  noticed  that  when 
a  fluid  holding  particles  in  suspension  of  two  different  densities  is  forced 
through  a  capillary  tube,  the  heavier  particles  will  always  pass  through 
the  rapidly  moving  axial  current,  while  the  lighter  particles  will  be  in  a 
current  by  the  sides  of  the  tube,  where  the  friction  is  greatest  and  where 
motion  is  therefore  slowest. 

When  the  circulation  is  studied  in  the  vessels  of  the  mesentery  of 
a  warm-blooded  animal,  or  where  inflammation  is  produced  in  the  tissues 
of  the  web  of  a  frog's  foot  by  mechanical  irritation,  the  corpuscles  may 
frequently  be  observed  to  pass  through  the  walls  of  the  vessel  in  great 
numbers  (diapedesis).  At  first  the  colorless  cells  are  found  to  move 
more  and  more  slowly;  several  accumulate  and  adhere  to  the  wall  and 
ultimately  pass  out  through  it,  during  the  act  of  passing  being  finely 
drawn  out  into  slender,  protoplasmic  threads.  It  is  doubtful  whether 
actual  stomata  or  openings  exist  between  the  cells  which  compose  the 
vascular  walls,  or  whether  they  simply  pass  through  the  cement  substance 
between  the  endothelial  cells. 

6.  THE  CIRCULATION  IN  THE  VEINS. — The  veins  are  much  less  elastic 
than  the  arteries,  and  so  do  not  remain  open,  even  in  a  dead  body,  after 
the  blood  has  been  withdrawn;  otherwise  they  resemble  the  arteries  in 
structure,  although  the  muscular  element  in  them  is  unequally  distributed. 
The  veins  are,  nevertheless,  contractile,  although  unequally  so,  and  may 
often  be  noticed  to  reduce  in  diameter  when  the  part  is  exposed  to  the 
cold  or  to  various  other  irritations.  The  veins  are  very  dilatable,  and 
are  in  capacity  much  greater  than  that  of  the  arterial  system :  the  veins 
are,  in  fact,  capable  of  containing  the  entire  blood  of  the  body. 

When  a  vein  is  cut  the  flow  from  the  divided  extremity  occurs 
usually  from  the  distal  end;  that  is,  the  one  nearest  the  capillaries,  alone. 
It  is  continuous  and  of  comparatively  slight  velocity.  The  pressure  of 
the  blood  within  the  veins,  as  determined  by  connecting  a  manometer 
with  them,  is  always  much  lower  than  in  the  arteries,  and  decreases  as 
the  heart  is  approached,  where  during  inspiration  even  a  negative 
pressure  may  be  noticed.  This  is  proved  by  the  constant  entrance  of 
the  lymph,  which  is  itself  moved  under  an  extremely  low  pressure,  into 
the  large,  venous  trunks  at  the  root  of  the  neck.  In  the  sheep  the  mean 
pressure  in  the  brachial  vein  has  been  found  to  be  four  millimeters  of 
mercury ;  in  the  crural,  eleven  and  four-tenths  millimeters  ;  in  the  axillary 
the  pressure  is  usually  negative,  becoming  one  millimeter  negative 
during  inspiration,  and  three  to  five  millimeters  during  strong  inspira- 
tion, and  becoming  positive  only  during  forced  expiration.  No  pulse  is 


540  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

to  be  detected  in  the  veins,  except  in  cases  where  the  small  arterioles 
and  capillaries  are  greatly  dilated,  as  in  the  case  of  the  secreting  glands, 
and  where  the  arterial  pulse  may  be  directly  transmitted  to  the  veins. 
The  forces  which  occasion  the  movement  of  the  blood  in  the  veins  con- 
sist in  the  propulsion  of  the  blood  by  the  heart  through  the  capillaries, 
a  vis  a  tergo  ;  a  vis  a  f route,  found  in  the  aspiratory  power  of  the  lungs 
in  inspiration  and  of  the  heart  in  diastole,  aided  by  the  compression  of 
the  venous  trunks  in  the  contraction  of  various  muscular  masses,  by 
which  the  blood  is  forced  on  toward  the  heart. 

The  velocity  of  movement  in  the  veins  is  much  less  than  in  the 
arteries,  and  it  is  greater  in  the  large  veins  than  in  the  small,  from  the 
reduction  in  the  total  capacity  of  the  venous  system. 

In  the  dog  the  velocity  of  movement  has  been  stated  to  be  about 
two  hundred  millimeters  per  second.  The  veins  are  generally  furnished 
with  valves  arranged  in  such  a  manner  that  when  any  increase  of  pres- 
sure takes  place  they  become  closed  and  obliterate  the  lumen  of  the  ves- 
sel and  prevent  the  blood  from  returning  to  the  capillaries.  The  valves 
are  formed  by  free  folds  of  the  inner  endothelial  coat  arranged  in  the 
form  of  either  single,  double,  or  triple  cusps.  They  serve  to  support  the 
blood-column  in  the  large  veins,  and  here  these  vessels  are  furnished 
with  especially  thick  coats.  Where  local  pressures  are  not  apt  to  un- 
dergo sudden  modification,  we  find  that  valves  are  not  present ;  they  are,, 
therefore,  absent  in  the  veins  of  the  brain  and  lungs. 

The  portal  vein  differs  from  other  venous  trunks  in  that  the  blood 
circulating  in  it  passes,  not  into  a  larger  trunk  or  directly  into  the  heart, 
but  through  a  second  capillary  net-work  in  the  liver.  The  forces,  how- 
ever, which  move  the  blood  in  the  portal  vein  are  the  same  as  in  other 
veins. 

7.  THE  INFLUENCE  OF  THE  NERVOUS  SYSTEM  ON  THE  CIRCULATION. — 
The  quantity  of  blood  supplied  to  any  organ  is  not  a  fixed  quantity,  but 
is  governed  by  the  demands  of  the  organ.  To  accomplish  this,  it  isr 
evidently,  necessary  that  the  influence  which  produces  and  maintains  the 
circulation  cannot  be  a  fixed  and  constant  force,  but  must  be  capable  of 
modification.  The  modifications  in  the  organs  of  circulation  may  be  of 
two  different  kinds — modifications  in  the  force  and  frequency  of  the 
heart's  pulsation  or  modifications  in  the  calibre  of  the  peripheral  vessels, 
which  latter,  evidently,  may  be  either  general  or  local.  Both  of  these 
variations  are  dependent  upon  the  influence  of  the  nervous  system. 

The  Intrinsic  Nervous  System  of  the  Heart. — The  conditions  upon 
which  the  action  of  the  heart  depends,  and  the  means  by  which  it  may 
be  modified,  will  now  be  considered.  That  the  heart  contains  within 
itself  the  conditions  necessary  for  its  rhythmical  movement  was  known 
to  Galen,  but  that  the  main  factor  of  its  motor  apparatus  consists  of 


CIRCULATION   OF   THE   BLOOD.  541 

small  automatic  nervous  centres  situated  in  the  walls  of  the  heart  was 
first  pointed  out  by  Remak.  These  cardiac  ganglia  are  three  in  number 
and  are  of  different  functions ;  two  are  motor  ganglia,  one  an  inhibitory 
ganglion.  The  motor  ganglia  are  the  ganglia  of  Remak,  situated  at  the 
opening  of  the  inferior  vena  cava;  the  ganglion  of  Bidder  is  situated  in 
the  left  auriculo-ventricular  septum.  These  ganglia  are  entirely  independ- 
ent of  the  will,  and,  under  the  excitation  of  the  temperature  and  chemical 
composition  of  the  blood,  communicate  to  the  muscular  fibres  of  the 
heart  their  motor  impulse.  The  inhibitory  ganglion  is  that  of  Ludwig, 
situated  in  the  inter-auricular  septum.  The  function  of  this  ganglion  is 
to  regulate  the  transmission  of  motor  impulses,  produced  by  the  motor 
ganglia,  to  the  fibres  of  the  heart.  It  fulfills  this  end,  however,  not  by 
acting  directly  on  the  muscular  structure  of  the  heart,  but  through  the 
mediation  of  the  motor  ganglia ;  by  this  means  it  compels  the  motor 
ganglia  to  dispense  the  power  which  they  develop  during  excitation 
rhythmically  and  moderately.  As  regards  the  manner  in  which  these 
ganglia  produce  the  rhythmical  contraction  of  the  heart,  little  is  known, 
but  that  they  are  the  prime  factors  in  producing  the  rhythm  of  the  car- 
diac revolutions,  with  its  various  modifications,  is  capable  of  experimental 
demonstration. 

If  the  heart  be  removed  from  a  frog  and  placed  in  a  watch-glass 
containing  a  dilute  saline  solution,  it  will  be  seen  that  it  still  continues 
to  pulsate  in  as  exact  rhythm  and  as  vigorously  as  when  in  its  normal 
condition.  Under  favorable  circumstances  it  might  be  kept  pulsating 
for  many  hours.  This  is  not,  however,  the  case  with  the  frog  alone ;  the 
heart  of  almost  any  cold-blooded  animal  will  beat  outside  of  the  body, 
and  a  similar  observation  has  even  been  made  on  the  heart  of  man.  But, 
to  return  to  the  share  of  the  motor  ganglia  in  producing  cardiac  pulsa- 
tion :  As  before  stated,  one  motor  ganglion  is  situated  at  the  opening  of 
the  inferior  vena  cava,  and  the  other  in  the  auriculo-ventricular  septum. 
If  the  apex  of  the  ventricle  be  cut  off  from  the  base  of  the  heart  with  a 
pair  of  sharp  scissors,  dividing  the  ventricle  at  about  its  lower  third, 
instantly  the  apex  ceases  to  pulsate,  while  the  remainder  of  the  heart 
still  goes  on  contracting  as  before.  The  apex  has  been  cut  off  from  its 
motor  ganglia.  It  may  be  said  that  the  section  of  the  heart  has  destroyed 
the  irritability  of  the  muscular  fibres  of  the  apex,  but  if  the  apex  be 
irritated  with  a  weak  induction  current  it  responds ;  it  will  again  pulsate, 
to  again,  however,  become  quiescent  on  removal  of  the  irritation.  It 
has,  however,  been  stated  by  Meruncowicz  that  the  apex  fragment  will 
again  commence  to  pulsate  if  kept  supplied  with  defibrinated  blood  or 
artificial  serum ;  so,  also,  after  an  hour  or  more  the  apex  will  usually 
again  spontaneous^  commence  to  pulsate. 

Further,  if  in  a  narcotized  frog  the  ventricle  is  compressed  trans- 


542  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

versely  with  the  blades  of  a  pair  of  forceps  in  the  line  of  incision  of 
the  former  experiment,  the  apex  will  cease  to  pulsate,  though  still 
supplied  with  its  normal  excitant  and  nutriment ;  it  has  been  separated 
from  its  motor  ganglion.  If  the  apex  be  irritated  it  will  beat,  to  again 
become  motionless  on  removal  of  the  irritation.  This  condition  of 
affairs  will  remain  for  an  indefinite  length  of  time,  even  for  as  much  as 
three  weeks — the  apex  of  the  ventricle  motionless  and  gorged  with 
blood  and  the  rest  of  the  heart  contracting  normally.  If,  however,  the 
intra-cardiac  pressure  be  increased  by  clamping  the  aorta,  the  apex  will 
commence  to  beat,  but  independently  of  the  rest  of  the  heart  and  at  a 
slower  rate.  This  being  so,  if  we  can  be  positive  that  there  are  no 
ganglia  present  in  the  apex,  it  must  be  concluded  that  the  heart-muscle 
may  contract  independently  of  any  nervous  mechanism.  It  must  not 
be  forgotten,  however,  that  it  has  not  been  definitely  proved  that  there 
are  no  ganglia  in  the  apex,  only  they  have  never  been  found.  The  posi- 
tion then  is  this : — 

A  fragment  of  cardiac  muscle  containing  a  motor  ganglion  will 
pulsate  when  removed  from  the  body,  and  without  any  artificial  stimulus. 
A  fragment  of  muscular  fibre  unconnected  with  a  motor  ganglion  will 
remain  quiescent  until  it  receives  some  external  stimulus.  By  cutting  a 
heart  in  halves  it  will  be  seen  that  one  part  pulsates  while  the  other  does 
not.  If  this  subdivision  be  carried  still  further,  gradually  cutting  the 
heart  into  fragments  until  they  become  microscopic  in  size,  and  some  of 
them  be  placed  under  the  microscope,  it  will  be  seen  that  some  fragments 
are  rhythmically  contracting  and  others  are  motionless ;  if  the  sub- 
division be  carried  still  further,  until  the  ultimate  fibres  of  the  heart  are 
isolated,  in  nearly  all  the  contracting  fibres  will  be  found  ganglionic 
nerve-cells,  while  none  are  to  be  found  in  those  which  are  motionless. 

The  action  of  the  inhibitory  ganglion  may  be  seen  by  exposing  the 
heart  of  a  frog  in  the  usual  way,  and  distending  the  oesophagus  with  a 
short  glass  rod  in  order  to  bring  the  parts  exposed  into  more  prominent 
view. 

The  apex  of  the  ventricle  should  be  seized  with  a  pair  of  forceps 
and  drawn  forward  and  to  the  right,  after  dividing  the  little  connecting 
band  between  the  posterior  surface  of  the  ventricle  and  the  pericardium. 
With  the  aid  of  a  delicate  aneurism  needle,  a  silk  ligature  is  to  be  passed 
between  the  vena  cava  inferior  and  the  ventricle  and  between  the  vena 
cava  superior  and  the  right  auricle  in  such  a  position  that  when  tight- 
ened it  will  grasp  the  line  of  junction,  which  is  marked  by  a  slight 
groove,  of  the  sinus  venosus  and  right  auricle.  After  seeing  that  the 
heart  is  pulsating  rhythmically,  the  ligature  should  be  suddenly  tightened, 
and  it  will  be  found  that  after  a  few  beats  the  heart  will  stop  in  diastole, 
while  the  sinus  will  continue  to  pulsate  as  before.  After  a  few  moments 


CIRCULATION  OF  THE  BLOOD.  543 

the  ventricle  will  again  pulsate,  but  its  rhythm  will  be  no  longer  syn- 
chronous with  that  of  the  sinus. 

In  another  frog,  prepared  in  the  same  manner,  the  heart  may  be 
separated  from  the  sinus  venosus  with  a  pair  of  scissors,  following  the 
line  of  the  ligature  in  the  preceding  experiment,  and  the  result  will  be  the 
same.  Cut  off  the  ventricle,  including  the  auriculo-ventricular  groove, 
from  the  auricle  be  fore  it  starts  spontaneously  to  pulsate,  the  ventricle 
immediately  begins  to  beat ;  the  same  result  might  have  been  obtained 
after  ligature  as  in  the  first  experiment. 

Or,  if  this  line  be  irritated  with  an  induction  current,  taking  care  to 
include  the  sinus  in  the  current,  the  same  result  will  follow.  But  in  a 
frog  in  which  T^Tr  of  a  grain  of  atropine  has  been  injected  irritation  with 
the  electric  current  will  have  no  effect ;  while  if  the  first  experiment  is 
repeated,  by  ligating  this  line,  the  heart  will  stop  as  before. 

What  inference  can  be  drawn  from  these  experiments  ?  It  has  been 
stated  that  the  ganglion  of  Remak,  a  motor  ganglion,  is  situated  at  the 
opening  of  the  inferior  vena  cava,  that  is,  in  the  sinus  venosus ;  also  that 
the  inhibitory  ganglion  of  Ludwig  is  in  the  interauricular  septum,  and  the 
motor  ganglion  of  Bidder  in  the  left  auriculo-ventricular  septum.  We 
may  assume  that  Remak's  ganglion  is  an  automatic  motor  centre,  i.e., 
"a  ganglionic  centre  in  which  energy  tends  to  accumulate  and  discharge 
itself  in  the  form  of  motion  at  regular  intervals,  the  length  of  which  varies 
with  the  resistance  to  the  discharge  and  with  the  rapidity  of  the  accumu- 
lation," the  physiological  grounds  for  this  assumption  being  as  follows: 
The  succession  of  acts  which  make  up  a  cardiac  revolution  distinctly 
start  in  the  sinus ;  this  is  the  only  portion  of  the  heart  that  contracts 
independently,  and  electric  excitation  of  this  centre  induces  increased 
frequency  of  contraction  of  the  whole  organ.  By  separating  the  heart 
from  the  sinus  venosus,  either  by  ligature  or  by  amputation  with  the 
scissors,  we  not  only  remove  the  heart  from  its  main  motor  centre,  but 
also  irritate  the  inhibitory  centre,  and  so  cause  arrest  of  the  pulsation 
of  the  heart,  while  the  sinus  containing  the  motor  centre  goes  on  con- 
tracting as  before.  After  a  few  minutes,  however,  the  inhibitory  effect 
induced  through  irritation  passes  off,  and  then  the  motor  ganglion  at  the 
base  of  the  ventricle  starts  the  heart  again.  So,  when,  without  waiting 
for  the  inhibition  to  pass  off,  we  remove  the  ventricle  from  the  auricles, 
the  motor  ventricular  ganglion  is  released  from  its  inhibition  and  starts 
the  heart  again.  The  effect  is  somewhat  different,  however,  when  we 
irritate  this  line  with  electricity ;  then  the  stoppage  is  due  alone  to  the 
inhibitory  action  of  the  ganglion,  and  when  this  passes  off  the  heart 
pulsates.  So,  when  this  inhibitory  ganglion  is  paralyzed  with  atropine, 
electric  irritation  is  powerless  to  stop  the  heart,  while  ligature  by  re- 
moval of  the  heart  from  its  main  motor  centre  prevents  pulsation. 


544 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


From  these  experiments  it  has  been  found  that  a  heart  will  contract 
rhythmically  outside  of  the  body,  that  this  function  is  probably  due  to 


FIG.  226.— SIMPLEST  FORM  OP  MANOMETER  FOR  FROG'S  HEART.    (Sanderson.) 

(For  description,  see  text.) 

the  presence  of  motor  ganglia,  and  that  the  heart  may  be  slowed  or 
stopped   either   through   inhibition   from   irritation   of    the   inhibitory 


CIRCULATION   OF   THE   BLOOD. 


545 


SM — - 


GP-Y-i 


ganglion  or  removal  of  the  heart  from  the  influence  of  the  main  motor 
ganglion. 

To  carry  this  subject  still  further,  a  more  delicate  means  of  experimentation 
must  he  used.  Poisons  must  be  employed  as  instruments  of  investigation. 
Pharmacology  has  indeed  in  this  line  almost  run  ahead  of  physiology,  for  it  has 
been  through  the  study  of  the  action  of  poisons  on  the  heart  that  our  complete  ideas 
of  cardiac  physiology  have  been  derived. 

Fig.  226  represents  an  apparatus  devised  by  Dr.  Coats,  of  Glasgow,  and 
Professor  Ludwig,  of  Leipsic.  It  consists  of  a  reservoir,  A,  with  a  stop-cock, 
15,  containing  fresh  serum ;  a  rubber  tube,  C,  leading  from  this,  and  acannula,  D, 
which  is  to  be  inserted  into  the  vena  cava  inferior ;  another  cannula,  D',  to  be 
inserted  in  the  aorta,  connected  by  tubing  with  a  mercurial  manometer,  E,  i.e.,  a 
fine  U -shaped  tube  partly  filled 
with  mercury,  and  supporting  on 
one  limb  of  the  column  a  piston 
with  a  long,  delicate  wire  rod,  G, 
above  it. 

The  brain  and  spinal  cord  of 
a  frog  should  be  destroyed  by 
introducing  a  needle  into  the  cere- 
bro-spinal  canal,  the  heart  freely 
exposed,  and  one  of  the  pneumo- 
gastric  nerves  carefully  dissected 
out.  To  find  the  vagus  nerve, 
follow  up  the  diverging  aortae  to 
where  they  cross  the  cartilaginous 
tips  of  the  posterior  horns  of  the 
hyoid  bone  :  from  each  of  these  tips 
the  petro-hyoid  muscles  are  seen 
passing  upward  and  backward  to- 
ward the  occipital  region.  The 
lower  border  of  these  nearly  par- 
allel fibres  is  the  guide  to  the  vagus, 
which  is  found  lying  beneath  its 
inner  edge.  Following  these 
muscles  back  from  their  insertion 
in  the  hyoid  bone  to  their  origin  in 
the  petrous  bone,  they  are  seen  to 
be  crossed  first  by  the  hypoglossal 
nerve,  ascending  inward  to  the 
muscles  of  the  tongue  Nearer  FlQ  ^.-DIAGRAM  OP  THE  COURSE  OF  THE 
the  middle  line  and  following  the  VAGUS  NERVE  IN  THE  FROG.  (Stirling.) 

same  course  as  the  hypoglossal 
is  seen  the  glosso-pharyngeal,  and 
crossing  over  the  top  of  the  in- 
ferior horn  of  the  hyoid  bone  is 
the  laryngeal  nerve  (Fig.  227). 

Place  a  thread  loosely  around  the  nerve,  so  that  it  can  be  easily  found  when 
required.  The  next  step  is  to  insert  the  cannula,  D,  into  the  inferior  vena  cava, 
and  secure  it  with  a  thread ;  the  cannula,  D',  is  then  inserted  into  one  aorta,  the 
other  being  ligated.  All  the  other  organs  may  be  removed,  leaving  only  the 
thorax,  heart,  and  a  large  fragment  of  skin,  S,  to  cover  the  heart  and  nerve,  to  pre- 
vent drying.  The  oesophagus  is  now  distended  with  a  large  glass  rod,  firmly 
clamped  to  an  upright  stand.  The  next  step  is  to  connect  the  vena  cava  by 
means  of  its  cannula  with  the  reservoir  containing  serum.  Open  the  stop-cock 
for  a  moment,  and  allow  the  serum  to  pass  through  the  heart  and  apex  of  the 
arterial  cannula,  to  wash  out  all  the  blood  from  the  heart.  The  arterial  cannula 
is  then  connected  with  the  manometer,  and  the  serum  allowed  to  flow  through  the 
heart  into  the  manometer  until  the  air  in  the  proximal  is  entirely  expelled  through 
at  F.  Then  the  apparatus  is  ready  for  use.  The  heart  should  be  filled  so  full  that 
a  little  tension  exists,  even  during  the  diastole.  It  will  be  noticed  that  at  each 

35 


H,  heart;  LU,  lung;  BR,  brachial  plextis;  HY,  hypoglossal 
nerve ;  V,  vagus ;  L,  laryngeal  nerve ;  GP,  glosso-pharyngeal 
nerve ;  SM,  submental  muscle ;  GH,  genio-hyoid  muscle ;  HG, 
hyoglossal  muscle ;  HB,  hyoid  bone ;  PH,  petro-hyoid  muscle  : 
OH,  omo-hyoid  muscle ;  SH,  sterno-hyoid  muscle. 


546 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


FIG.  228.—  PULSE  TRACING  OF  THE  FROG'S 
HEART.    (Sanderson.) 


pulsation  of  the  heart  the  column  of  mercury  sinks  in  one  arm  of  the  manometer, 
while  it  rises  a  corresponding  distance  in  the  other,  carrying  with  it  the  piston, 
which  by  means  of  its  pen  traces  a  line  composed  of  a  succession  of  curves  on 
the  smoked  surface  of  the  revolving  drum.  The  ascending  limb  of  each  curve 
corresponds  to  the  systole  of  the  ventricle,  and  the  descending  curve  to  its 
diastole  (Fig.  228).  By  irritating  the  vagus  with  a  weak  induction  current  the 
heart  stops  in  diastole,  a  result  similar  to  that  obtained  in  the  previous  experiment 
when  the  line  of  junction  of  the  auricle  and  sinus  venosus  was  irritated.  This 
identical  result,  however,  has  not  been  produced  by  the  same  mechanism,  as  may 

be  seen  if  to  the  serum  in  the  reservoir 
a  few  drops  of  dilute  solution  of  nico- 
tine be  added ;  if  the  vagus  now  be 
irritated,  no  arrest  of  the  heart  occurs. 
The  vagus  has  been  paralyzed  by  nico- 
tine ;  it  no  longer  is  able  to  restrain 
the  heart,  which  beats  faster  than  be- 
fore. (When  the  nicotine  is  first  given 
the  heart  is  slowed,  and  then  quick- 
ened, the  slowing  being  due  to  the  first 
effects  of  the  nicotine  on  the  vagus, 
irritating  it  before  it  paralyzes  it.) 

It  would  seem  that  nicotine  and  atropine  have  the  same  action.  But  it  will 
be  remembered  that  after  atropine  poisoning  it  is  impossible  to  stop  the  heart 
through  electric  irritation  of  the  sinus  venosus. 

But  if  the  sinus  venosus  be  irritated  in  the  heart  which  has  received  the 
nicotine,  it  will  stop.  Therefore,  nicotine  and  atropine  must  act  on  different 
inhibitory  organisms. 

If  in  a  frog  which  has  been  placed  under  the  influence  of  nicotine  the  heart 
be  removed  and  placed  on  a  watch-glass,  it  will  pulsate  regularly.  If  a  drop  of 
saline  solution  containing  a  little  of  the  alkaloid  muscarine  be  placed  on  the  heart, 

it  ceases  to  beat  entirely,  and  will  remain  motion- 
less. But  if  while  at  rest  a  drop  of  a  solution  of 
atropine  be  placed  in  the  heart,  it  will  commence 
to  beat  again. 

If  in  two  fresh  frogs  a  drop  of  muscarine 
solution  be  placed  on  the  "hearts,  immediately  they 
begin  to  beat  more  and  more  slowly,  and  at  last 
stop  in  diastole.  If  into  one  frog  nicotine  be  in- 
jected no  effect  will  be  observed  ;  the  heart  still 
remains  motionless  in  diastole  ;  but  the  injection 
of  atropine  into  the  other  frog  whose  heart  was 
stopped  by  muscarine  will  cause  it  to  commence 
to  beat,  and  it  will  pulsate  as  strongly  and  rhythm- 
ically as  before  the  operation.  If,  however,  the 
atropine  be  injected  first,  and  then  the  muscarine 
be  applied,  the  heart  will  not  be  stopped. 

It  has  now  been  stated  that  both  nicotine 
and  atropine  render  the  heart  insusceptible  to 
irritation  of  the  vagus,  but  that  irritation  of  the 
sinus  venosus  will  stop  the  heart  in  nicotine 
poisoning,  but  not  in  atropine  poisoning  There- 
fore some  part  of  the  cardiac  inhibitory  apparatus 
escapes  in  nicotine  poisoning  which  is  paralyzed 
by  atropine. 

In  the  above  diagrammatic  sketch  of  the  arrangement  of  the  cardiac 
ganglionic  apparatus,  proposed  by  Schmiedeberg  (Fig.  229,  M),  is  the  main  motor 
ganglion  acting  on  the  muscular  fibres  of  the  heart  by  means  of  radiating  fibres. 
It  is  regulated  by  an  intermediate  apparatus  represented  by  the  dotted  lines,  on 
the  one  side  by  the  inhibitory  ganglion,  I,  connected  again  with  an  intermediate 
apparatus  with  the  vagus  nerve,  and  on  the  other  side  by  the  accelerator  ganglion, 
Q,  connected  in  the  same  manner  with  the  accelerator  nerves.  According  ro 
this  arrangement,  nicotine  is  supposed  to  paralyze  the  fibres  intermediate  between 
the  inhibitory  ganglion  and  the  vagus  nerve,  while  atropine  paralyzes  this  portion. 


FIG.  229.  —  DIAGRAM  OF  THE 
HYPOTHETICAL,  NERVOUS 
APPARATUS  OF  THE  H.EART. 
(Lauder-Brunton. ) 


M,    motor    ganglio 


I,    inhibitory 


ganglion  ;  Q,  accelerator  ganglion ;  V,  in- 
hibitory extra-cardiac  nerves  :  S,  acceler- 
ator extra-cardiac  nerves.  The  interme- 
diate apparatus  of  Schmiedeberg  is 
represented  by  the  dotted  lines. 


CIRCULATION   OF   THE   BLOOD.  547 

the  inhibitory  ganglion  and  the  apparatus  intermediate  between  the  ganglion,  I, 
and  the  motor  ganglion.  On  the  other  hand,  muscarine  slows  the  heart  or  stops 
it  in  diastole,  similar  to  irritation  of  the  vagus,  while  its  effects  are  not  interfered 
with  by  either  the  previous  or  subsequent  injection  of  nicotine  :  therefore,  mus- 
carine must  act  on  some  apparatus  more  central  than  that  affected  by  nicotine, 
and  as  the  effects  are  gradually  developed,  it  is  supposed  to  act  by  irritating  the 
ganglion,  I.  Again,  we  have  seen  that  muscarine  will  have  no  effect  after  the  in- 
jection of  atropine,  and  that  atropine  will  cause  a  heart  stopped  by  muscarine  to 
recommence  beating ;  therefore,  atropine  acts  on  a  more  central  apparatus  than 
muscarine:  in  other  words,  on  the  apparatus  intermediate  between  I  and  M.  The 
effects  of  atropine  may  be  removed  by  physostygma  and  is  antagonistic  to 
nicotine.  These  points  are  valuable  in  determining  the  antidotal  effects  of 
poisons. 

The  action  of  the  accelerator  apparatus  has  not  been  so  thoroughly  well 
worked  up,  but  the  action  of  poisons,  as  of  veratrine,  renders  it  necessary  to 
assume  a  similar  arrangement. 

There  is  one  more  point  in  the  action  of  these  cardiac  ganglia ;  that 
is,  the  influence  of  heat  and  cold  on  the  heart. 

The  simplest  method  of  studying  the  action  of  heat  on  the  cardiac 
pulse  is  that  of  Lauder-Brunton  (Fig.  230).  His  arrangement  consists 
of  a  plate  of  glass  about  three  inches  by  four  inches,  at  one  end  of 
which  a  cork  is  cemented  projecting  about  half  an  inch  beyond  the  edge 


7 


FIG.  230.— LAUDER-BRUNTON'S  ARRANGEMENT  FOR  STUDYING  THE  EFFECT 
OF  HEAT  AND  COLD  ON  THE  HEART  OF  THE  FROG. 

of  the  glass  plate.  To  this  is  fastened  a  long,  light  lever  freely  moving 
on  a  pivot,  and  projecting  about  one  and  one-half  inches  beyond  one  end 
of  the  plate  and  about  four  inches  beyond  the  other  end ;  the  lever  is 
counterpoised  by  fastening  a  small  pair  of  forceps  on  the  short  end  of 
the  lever ;  by  altering  the  angle  of  the  forceps,  the  lever  can  be  balanced 
to  a  nicety.  A  frog's  heart  may  be  placed  on  the  plate  close  up  to  the 
pivot  and  lying  so  that  the  lever  is  lifted  at  each  pulsation  of  the  ven- 
tricle, the  lever  being  balanced  so  as  to  make  slight  pressure  by  altering 
the  position  of  the  pair  of  forceps.  If  the  glass  plate  is  placed  on  some 
pounded  ice  the  heart  will  beat  gradually  more  and  more  slowly,  until  at 
length  it  will  come  to  rest  in  diastole,  thus  indicating  irritation  of  some 
portion  of,  the  inhibitory  apparatus.  If  the  plate  be  removed  from  the 
ice,  the  heart  will  commence  again,  and  by  gradually  heating  it  over  a 
spirit-lamp  the  heart  will  pulsate  faster  and  faster,  the  extent  of  the 
contractions  increasing  up  to  20°  C.,  until  at  length  it  will  stand  at  rest 
in  what  is  called  u  heat-tetanus  ;  "  if,  however,  the  temperature  is  lowered 
the  heart  will  again  commence  to  beat,  but  if  the  temperature  is  raised 


548 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


still  higher  than  before  when  the  heart  stopped  from  heat,  the  condition 
of  heat-tetanus  will  pass  into  that  of  "  heat-rigor,"  and  no  application 
of  cold  will  have  the  slightest  effect  toward  again  starting  the  heart. 

The  influence  of  heat  and  cold  on  the  amount  of  work  done  by  the 
heart  is  an  extremely  complicated  subject.  We  can  only  state  here  that 
within  certain  limits  the  mechanical  work  done  by  the  heart  increases 
with  an  increase  of  temperature,  but  that  very  soon  the  contractions 
increase  in  number  in  much  greater  proportion  than  the  mechanical 
effect ;  hence,  though  the  amount  of  work  done  at  a  comparatively  high 
temperature  is  greater  than  can  be  accomplished  at  a  low  temperature, 
the  effect  of  each  individual  contraction  is  much  less. 

The  frequency  of  the  normal  rate  of  contraction  of  the  heart  varies 
greatly  in  different  animals,  as  shown  in  the  following  table  compiled  by 

Colin  :— 

Frequency  of  the  Pulse  per  Minute. 
In  the  elephant, 
camel, 


25  to 

28  to 


28 
32 


giraffe, . 

horse,    .        .                                  i                 .  86  to    40 

ox,                                                    .                 .  45  to    50 

mule,     .                                         .                .  46  to   50 

tapir,     .                                                            .  44 

ass,        .        .        .        .        .        .        .        .  46  to    50 

pig,        .        .        .        .        .    -  .        .        .  70  to    80 

lion,      .        .        .        .        .        .        .        .40 

lioness, .        .  68 

tiger, 64 

sheep, 70  to   80 

goat .  70  to    80 

leopard, 60 

female  wolf, 96 

hyena, 55 

dog,       . .  90  to  100 

cat,        .  -       .     •   .        .         .        .        »        .  120  to  140 

rabbit, 120  to  150 

marmot, 90  to  175 

mouse,  .........  120 

goose,  ........  110 

chicken,        .......  140 

pigeon, .  136  to  138 

snake, 24 

carp,      . 20 

frog 80 

salamander, 77 

The  following  table  shows  the  variation  and  frequency  of  the  pulse 
per  minute  in  the  horse  and  ox  at  different  ages  : — 

Horse.  Ox. 

Newborn,  ....  100-120  Newborn,    ....  92-132 

Fourteen  days  old,  .  80-  96  Fourteen  days  old,  .  68 

One-fourth  year  old,  68-  76  One-fourth  year  old,  .  . 

One-half  year  old,     .  64-  72  One-half  year  old,    .  50-  68 

One  year  old, ...  48-  56  One  year  old,       .     .  50-68 

Two  to  three  years,  .  40-  48  Young  cow,     ...  64 

Four  years  of  age,    .  38-50  Four-year-old  ox,     .  56 

Aged, 32-40      Aged, 45-50 


CIRCULATION   OF   THE   BLOOD. 


549 


The  frequency  of  the  pulse  in  man  and  animals  depends  upon  the 
age,  sex.  state  of  nutrition,  size,  and  various  other  conditions. 

In  man  the  normal  rate  of  the  pulsations  of  the  heart  is  about  72 
per  minute ;  in  the  female,  about  80,  though  great  variations  may  be  met 
with  in  perfectly  normal  individuals.  Up  to  fifty  years  of  age  the  rate 
of  the  pulse  is  in  inverse  ratio  to  the  age,  as  is  shown  in  the  following 

table  :— 

Beats  per  Minute. 
Newly  born  infant, 
One  year, . 
Two  years, 
Three   " 
Four     " 
Five      " 
Ten     '" 

The  pulse-rate  is  increased  by  muscular  exercise  in  creating  a 
greater  demand  for  arterial  blood,  by  increasing  blood  pressure,  by  in- 
creased temperature  (fever),  in  digestion,  by  various  mental  disturbances, 
and  in  extreme  debility.  It  is  more  frequent  in  the  erect  than  in  the 
recumbent  position,  and  varies  inversely  with  the  barometric  pressure. 


ant 

,    130-140 
120-130 
105 
100 
97 

Ten  to  fifteen  years, 
Fifteen  to  twenty, 
Twenty  to  twenty-f 
Twenty-five  to  fifty, 
Sixty 

.     .     78 
.     .     70 
ve,  .     70 
.     .     70 

74 

90-  94 
about  90 

Eighty,     .... 
Eighty  to  ninety,  . 

.     .     79 

over  80 

FIG.  231.— TRACING  OBTAINED  FROM  THE  FROG'S  HEART  ON  STIMULATION 
OF  THE  PNEUMOGASTRIC  NERVE.    (Foster.) 

The  current  entered  the  nerve  at  a,  and  was  shut  off  at  b.  The  latent  period  is  indicated  by  the  fact 
that  one  pulsation  occurred  after  the  stimulation  entered  the  nerve.  It  is  further  evident  that  the  inhi- 
bition persisted  some  time  after  the  stimulation  ceased. 

In  addition  to  the  intrinsic  nervous  system  of  the  heart,  the  pulsa- 
tions of  this  organ  are  also  governed  by  impulses  coming  from  the 
central  nervous  system.  These  are  of  two  different  kinds, — inhibitory 
and  accelerating. 

The  Inhibitory  Nerves  of  the  Heart. — It  was  discovered  in  1848 
that  stimulation  of  the  pneumogastric  nerve  or  of  its  divided  periph- 
eral extremity  had  the  effect,  in  the  dog,  of  retarding  the  pulsations 
of  the  heart,  and,  when  the  stimulation  was  sufficiently  strong,  of  entirely 
arresting  the  heart  in  diastole.  This  effect  is  not  produced  immedi- 
ately on  the  application  of  the  electric  current  to  the  nerve,  but  is  pre- 
ceded by  a  latent  period  amounting  to  about  one-tenth  of  a  second ;  so, 
also,  the  effect  lasts  a  certain  time  after  the  shutting  off  of  the  current, 
if  the  application  has  not  been  too  prolonged  (Fig.  231).  On  the  other 


550 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


hand,  if  the  current  is  very  strong,  the  heart  may  be  completely  arrested 
and  yet  start  again  during  the  passage  of  the  current.  With  weak  cur- 
rents no  actual  arrest  of  the  heart  takes  place,  but  the  pauses  between 
the  beats  are  prolonged  during  the  earlier  part  of  the  application  of  the 
current,  and  the  pulse  is  thus  rendered  slow.  If  the  pneumogastric  be 
stimulated  in  a  dog  during  a  blood-pressure  experiment  some  such  curve 
as  represented  in  the  diagram  will  be  produced  (Fig.  232). 

The  blood  pressure  is  seen  to  undergo  a  rapid  fall  shortly  after  the 
application  of  the  current,  from  the  fact  that  on  the  cessation  of  the 
pulsation  of  the  heart  the  arteries,  through  their  contractility,  empty 
themselves  into  the  venous  system.  As  the  heart  again  commences  to 
pulsate  it  throws  its  contents  into  the  arterial  system,  which  has  been 
already  largely  depleted  of  blood,  and,  as  a  consequence,  the  walls  of  the 
arteries  are  rapidly  stretched,  and  we  have  a  correspondingly  rapid 


FIG.  232.— MANOMETER  TRACING  FROM  THE  CAROTID  OF  A  RABBIT  ON  STIM- 
ULATION OF  THE  PNEUMOGASTRIC  NERVE.    (Foster.) 

The  current  entered  the  nerve  at  a  and  was  shut  off  at  b. 

increase  in  pressure,  and  therefore  a  rapid  rise  in  the  mercury  in  the 
manometer.  When  the  heart  is  only  slowed  b}^  stimulation  of  the 
pneumogastric,  and  not  completely  arrested,  the  mercury  in  the  manom- 
eter undergoes  extensive  oscillations,  partly  due  to  inertia,  which 
exaggerates  these  movements,  and  partly  due  to  the  same  cause  already 
mentioned.  In  other  words,  between  the  pulsations  of  the  heart,  which 
succeed  each  other  slowly,  the  arterial  system  has  time  to  partially  empty 
itself  into  the  veins. 

Inhibition  of  the  heart  may  not  only  be  produced  by  direct  stimu- 
lation of  the  pneumogastric,  but  also  may  be  produced  reflexly.  If  one 
pneumogastric  nerve  be  divided,  and  the  central  end,  in  connection  with 
the  brain,  be  stimulated  with  the  induction  current,  the  heart  will  be 
arrested  or  slowed  as  before.  If  the  abdomen  of  a  frog  be  opened,  and 
the  intestine  struck  sharply,  as  with  the  handle  of  a  scalpel,  the  heart 


CIRCULATION    OF   THE   BLOOD.  551 

will  be  likewise  arrested  in  diastole.  If  the  mesenteric  nerve  be  stimu- 
lated by  an  induction  current  the  heart  will  also  be  brought  to  a  sudden 
standstill.  If  both  pneumogastric  nerves  be  divided,  the  anterior  roots 
of  both  spinal  accessory  nerves  be  torn  out,  or  the  medulla  oblongata 
destroyed,  the  preceding  experiments  will  all  fail.  This  indicates  that  in 
the  first  case  the  impulse  was  conducted  through  the  central  stump  of 
the  divided  pneumogastric  to  the  brain,  and  there,  from  a  collection  of 
nerve-cells  in  the  medulla  oblongata,  which  is  termed  the  cardio-inhibi- 
tory  centre,  is  transmitted  through  the  spinal  accessory  nerve  to  the 
pneumogastric  plexus,  and  through  the  undivided  vagus  to  the  heart. 
If  the  spinal  accessory  nerve  be  pulled  out  by  the  roots,  the  cardio- 
inhibitory  fibres  of  the  pneumogastric  undergo  degeneration,  and  four  or 
five  days  after  the  operation  stimulation  of  the  vagus  fails  to  slow  the 
heart.  In  the  other  instance,  where  irritation  of  the  intestinal  surface 
or  mesenteric  nerves  produces  inhibition,  the  impulse  is  conducted 
through  the  mesenteric  and  s^^mpathetic  chain  to  the  spinal  cord,  from 
there  to  the  cardio-inhibitory  centre,  and  from  there  to  the  heart.  It  is 
probable  that  the  syncope  occasionally  produced  by  severe  pain,  emotions, 
or  sometimes  from  drinking  ice-water  when  overheated  is  produced  in 
the  same  manner,  the  heart  being  arrested  or  slowed  through  reflex 
inhibition. 

It  is  thus  observed  that  the  pneumogastric  nerve  possesses  a  function 
directly  opposed  to  that  of  most  other  nerves.  When  a  motor  nerve  is 
stimulated  it  produces  contraction  of  the  muscles  to  which  it  is  dis- 
tributed. Stimulation  of  the  pneumogastric,  on  the  other  hand,  produces 
relaxation  of  the  heart-muscle.  The  manner  by  which  this  effect  is 
produced  is  in  all  probability  through  the  inhibition  of  the  motor  ganglia 
of  the  heart. 

The  cardio-inhibitory  centre  in  the  medulla  is  in  constant  action, 
through  reflex  stimuli  conducted  to  it  through  the  abdominal  and  cervical 
sympathetic,  and  might  be  compared  to  the  action  of  a  brake  on  a 
moving  machine.  When  both  pneumogastric  nerves  are  divided,  the 
heart  in  the  dog,  and  to  a  less  extent  in  the  rabbit,  beats  very  much 
faster,  so  that  this  inhibitory  centre  is  constantly  restraining  the  action 
of  the  motor  ganglia.  The  cardio-inhibitory  centre  may  be  directly 
stimulated  by  sudden  anaemia  of  the  medulla,  as  by  sudden  ligation  of 
both  carotids;  by  sudden  venous  hyperaemia,  as  by  ligation  of  all  the 
veins  of -the  neck;  or  by  increased  venosity  of  the  blood,  as  by  dyspnoea 
or  causing  an  animal  to  inhale  CO,.  It  may  also  be  reflexly  stimulated, 
as  already  indicated. 

The  Accelerator  Nerves  of  the  Heart. — The  action  of  the  heart 
may  not  only  be  retarded  or  arrested  through  the  stimulation  of  the 
pneumogastric,  but  in  the  mammal,  even  after  division  of  both  pneumo- 


552 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


gastrics,  it  may  be  accelerated  by  stimulation  of  the  cervical  sympathetic, 
stimulation  of  the  cervical  spinal  cord,  or  in  a  more  marked  degree  by 
stimulation  of  the  communicating  filament  between  the  spinal  cord  and 
the  inferior  cervical  and  the  first  dorsal  ganglia  of  the  S3rmpathetic. 
These  latter  fibres  are  described  as  the  accelerator  nerves  of  the  heart, 
and  when  stimulated  produce  an  increase  in  the  rate  of  the  heart's  pulse, 
but  with  a  decreased  force,  the  loss  in  power  being,  however,  compensated 
by  the  increase  in  rapidity.  As  a  consequence,  after  stimulation  of  these 

nerves  the  blood  pressure  remains  unchanged. 
The  course  of  these  nerves  is  different  in  the 
rabbit  and  the  dog. 

The  diagrams  (Figs.  233  and  234)  indicate 
their  most  usual  course. 

These  accelerator  fibres  originate  from 
centres  in  the  medulla  oblongata  and  spinal 
cord,  though  their  exact  location  has  not  been 
determined.  It  is  by  means  of  stimulation  of 
these  fibres,  therefore,  that  stimulation  of  either 
the  cervical  spinal  cord  or  cervical  sympa- 
thetic produces  increase  in  the  rate  of  the 
heart's  pulsation.  When  the  cervical  spinal 
cord  is  stimulated  a  great  increase  in  blood 
pressure  follows  from  stimulation  of  vaso-motor 
nerves,  but  that  the  increased  rate  of  the 
heart's  contractions  is  not  due  to  the  high 
blood  pressure  alone  is  proved  by  the  occur- 
rence of  acceleration  of  the  pulse  when  the 
cervical  cord  is  stimulated,  even  after  section 
of  the  splanchnic  nerves,  when  increased  blood 
pressure  is  prevented.  These  nerves  are  not 
in  constant  activity  ;  in  other  words,  they  do 
not  antagonize  the  pneumogastrics,  and  when 
divided  the  heart  does  not  beat  slower.  A 
long  latent  period  also  characterizes  these 
nerves,  and  it  takes  considerable  time,  as  much  as  ten  seconds,  from 
the  commencement  of  stimulation  before  the  maximum  acceleration  of 
the  heart  is  reached ;  while,  again,  it  is  only  slowly  and  gradually  that 
the  normal  heart-rate  is  regained  even  at  the  cessation  of  stimulation. 

8.  THE  INFLUENCE  OF  THE  NERVOUS  SYSTEM  ON  THE  ARTERIES. — 
Anatomical  examination  of  the  walls  of  the  minute  arteries  shows  that 
these  vessels  are  not  only  supplied  with  circular  muscular  fibres,  but  are 
also  supplied  with  nerve-fibres  which  come  both  from  the  sympathetic  and 
cerebro-spinal  nervous  system,  and  numerous  ganglia  have  also  been 


FIG.  233.  —  SCHEME  OF  THE 
COURSE  OF  THE  CARDIAC 
ACCELERATOR  FIBRES. 
(Landois. ) 

P,  pens ;  MO,  medulla  oblongata ; 
V,  inhibitory  centre  for  heart ;  A,  accel- 
erator centre  :  VAG,  vagus ;  SL,  supe- 
rior, IL  inferior  laryngeal  nerves ;  SC, 
superior  cardiac  fibres ;  H,  heart ;  C,  cere- 
bral impulse;  S,  cervical  sympathetic; 
a,  a,  accelerator  fibres. 


CIRCULATION   OF   THE   BLOOD.  553 

detected.  Anatomical  data,  therefore,  support  the  view — which  would 
otherwise  be  rendered  probable,  as,  for  example,  in  the  production  of 
blushing  from  emotions — that  the  calibre  of  the  minute  arterioles  is  under 
the  control  of  the  central  nervous  system.  Numerous  experiments  still 
further  demonstrate  the  truth  of  this  statement.  When  the  web  of  a 
frog's  foot  is  examined  under  the  microscope  it  will  be  found  that  the 
smaller  arterioles  are  constant!}'  varying  in  calibre,  sometimes  being  so 
contracted — evidently  due  to  the  contraction  of  their  muscular  fibres — 
as  to  almost  shut  off  blood  from  the  part  supplied  by  the  contracted 


FIG.  234.— CARDIAC  PLEXUS  AND  STELLATE  GANGLION  OF  THE  CAT.  (Landois.) 

R.  right;  L.  left:  X  1^-  1.  vagus:  2'.  cervical  sympathetic,  and  in  the  annulus  of  vieussens ;  2, 
communicating  branches  from  the  middle  cervical  ganglion  and  the  stellate  ganglion  ;  2",  thoracic  sym- 
pathetic; 3,  recurrent  laryngeal ;  4,  depressor  nerve:  5,  middle  cervical  ganglion;  5',  communication 
between  5  and  the  vagus :  6,  stellate  (first  thoracic)  ganglion  ;  7,  communicating  branches  with  the  vagus ; 
8,  accelerator  nerve ;  8,  8',  8",  roots  of  the  accelerator  nerve;  9,  branch  of  the  stellate  ganglion. 

vessel,  at  other  times  so  dilated  as  to  cause  the  tissues  supplied  by  the- 
vessel  to  become  gorged  with  arterial  blood.  If  the  web  of  the  frog's 
foot  be  examined  and  an  arteriole  picked  out  which  appears  to  be  midway 
between  the  states  of  extreme  relaxation  and  extreme  dilatation,  and  a 
weak  induction  current  be  then  applied  to  the  sciatic  nerve,  the  arterioles 
will  all,  as  a  rule,  be  found  to  become  immediately  contracted.  If  the 
effects  of  stimulation  be  allowed  to  pass  off,  and  then,  instead  of  stimu- 
lating the  sciatic,  this  nerve  be  divided,  directly  opposite  results  will 


554  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

ensue.  The  arterioles  will  now  all  dilate,  and,  as  a  consequence,  the  parts 
will  become  filled  with  blood. 

Similar  effects  may  be  seen  in  warm-blooded  animals.  If  the  sympa- 
thetic nerve  be  divided  in  the  neck  of  a  rabbit,  it  will  be  found  that  the 
vessels  in  the  lobe  of  the  ear  on  that  side  will  have  greatly  increased  in 
calibre,  will  appear  not  only  larger,  but  numerous  vessels  which  before 
were  invisible  will  now  be  readily  seen.  The  entire  tissue  of  the  ear  will 
be  much  redder  than  before,  much  warmer  in  temperature,  and  distinct 
throbbing  of  the  pulse  may  be  readity  perceived.  Here  division  of  the 
sympathetic  has  produced  dilatation  of  the  auricular  arterioles.  If,  on 
the  other  hand,  the  cervical  sympathetic  be  stimulated  with  an  induction 
current  in  the  rabbit,  directly  opposite  results  will  be  produced.  The 
auricular  vessels  will  now  all  contract,  and  the  tissues  of  the  ear  will 
become  pale  and  free  from  blood. 

So,  also,  if  the  sciatic  nerve  be  divided  in  a  mammal,  a  corresponding 
dilatation  occurs  in  the  small  arterioles  of  the  foot  and  leg,  and  may  be 
readily  determined  through  inspection  of  the  balls  of  the  toes,  especially 
as  seen  in  the  cat,  where  they  are  hairless  and  not  pigmented.  So,  also, 
the  temperature  of  the  foot  on  the  side  on  which  division  of  the  sciatic 
nerve  has  been  performed  will  be  considerably  elevated.  Further,  if  the 
splanchnic  nerves  be  divided,  the  vessels  of  the  abdomen  all  undergo 
extensive  dilatation.  If  the  lingual  nerve  be  divided,  the  vessels  on  the 
corresponding  side  of  the  tongue  dilate,  while  in  all  cases  in  which 
a  nerve  supplying  a  muscle  is  cut  a  great  increase  in  the  flow  of  blood 
from  the  muscle  may  be  made  out.  It  is,  therefore,  evident  that  the 
blood-vessels  of  certain  parts  of  the  body  are  kept  in  a  state  of  tonic 
contraction  through  impulses  traveling  along  certain  nerves.  Section  of 
these  nerves  has  been  found  to  produce  dilatation  in  the  corresponding 
vascular  areas  :  therefore  it  is  evident  that  the  arteries  before  the  division 
of  their  vascular  nerves  were  in  a  state  of  constriction  through  contraction 
of  their  muscular  fibres,  and  that  this  state  of  contraction  was  due  to 
impulses  coming  along  the  vascular  nerves  or  vaso-motor  nerves  of  that 
part.  Section  of  these  nerves,  therefore,  produces  paralysis  of  the 
muscular  fibres,  and  the  muscular  tissue  is  no  longer  able  to  resist  the 
pressure  of  the  blood,  and,  as  a  consequence,  these  vessels  passively 
dilate. 

It  has  been  found  that  the  vascular  condition  of  the  specific  parts 
of  the  body  are  governed  by  impulses  coining  along  specific  nerves,  and 
that  these  nerves  may  be  either  of  the  sympathetic  or  cerebro-spinal 
systems.  If  the  spinal  cord  is  divided  in  the  lumbar  region  it  will  be 
found  that  the  blood-vessels  of  all  the  parts  below  will  be  paralyzed  and 
gorged  with  blood.  If  the  spinal  cord,  or  even  the  lateral  columns  alone, 
be  divided  in  the  cervical  region,  the  blood-vessels  of  the  entire  body 


CIRCULATION   OF  THE  BLOOD.  555 

become  dilated.  This,  therefore,  indicates  that  some  portion  of  the 
brain  higher  up  than  the  cervical  spinal  cord  is  the  centre  from  which 
originate  all  the  impulses  which  travel  along  the  different  vaso-motor 
nerves  to  innervate  the  muscular  fibres  of  the  different  arterioles  of  the 
body.  When  the  path  of  communication  between  any  vascular  area  and 
•the  medulla  oblongata  is  broken,  the  vessels  of  that  part  are  deprived  of 
the  nervous  impulse  coming  from  the  medulla,  they  lose  tone,  their  mus- 
cular fibres  relax,  and  their  arteries  dilate.  When  the  entire  body  is  cut 
off  from  the  medulla  all  the  vessels,  therefore,  dilate.  It  has  been  stated 
that  stimulation  of  one  of  the  vaso-motor  nerves — such  an  example  being 
the  sympathetic,  the  sciatic,  or  splanchnic — leads  to  contraction  of  the 
arterioles  in  the  corresponding  vascular  area.  In  other  words,  the 
electric  stimulation  has  been  added  to  that  coming  constantly  from  the 
medulla,  and  has  therefore  increased  the  contraction  of  the  muscular 
fibres  of  the  arteries.  So,  also,  if  the  spinal  cord  be  itself  stimulated, 
the  blood-vessels  in  all  the  parts  below  become  still  further  contracted, 
while  by  directly  stimulating  the  medulla  oblongata  all  the  blood-vessels 
of  the  body  contract.  These  facts  indicate  that  the  normal  degree  of 
constriction  of  the  arterioles  of  the  body,  or  what  is  termed  vascular 
tonus,  is  maintained  by  a  series  of  impulses  constantly  coming  from 
a  collection  of  cells  in  the  medulla  oblongata,  called  the  vaso-motor 
centre.  These  impulses  reach  the  arteries  after  passing  through  the 
lateral  columns  of  the  cord,  during  which  passage  they  make  connection 
with  the  subordinate  vaso-motor  centres  of  the  cord,  either  through  the 
anterior  spinal  roots  directly  or  by  passing  through  the  rami  commu- 
nicantes  to  the  sympathetic. 

The  vaso-motor  centre  has  been  located  in  the  floor  of  the  fourth 
ventricle,  its  lower  limit  being  a  horizontal  line  about  four  or  five  milli- 
meters above  the  point  of  the  calamus  scriptorius  and  the  upper  limit 
about  four  millimeters  higher  up,  or  one  or  two  millimeters  below  the 
corpora  quadrigemina.  The  vaso-motor  centre,  as  already  stated,  may 
be  directly  stimulated,  and  so  lead  to  increased  vascular  contraction 
throughout  the  entire  body.  Increased  venosity  of  the  blood  and  vari- 
ous poisons,  such  as  strychnine,  likewise  directly  stimulate  the  vaso- 
motor  centre,  and  so  cause  increased  blood  pressure  ;  so,  after  death,  the 
venous  character  of  the  blood,  through  stimulation  of  the  vaso-motor 
centre,  leads  to  firm  contraction  of  the  arteries  and  a  consequent  empty- 
ing of  these  vessels  into  the  veins.  It  nmy  also  be  reflexly  stimulated. 
Irritation  of  any  sensory  nerve  will  reflexly  act  on  the  vaso-motor  centre 
and  lead  to  arterial  contraction,  especially  of  the  vessels  of  the  abdomen. 
On  the  other  hand,  the  vaso-motor  centre  may  be  inhibited. 

If  the  small  nervous  filament  which  is  formed  in  the  rabbit  by  the 
union  of  branches  from  the  pneumogastric  and  superior  laryngeal  nerves 


556 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


be  stimulated,  it  will  be  found  that  the  blood  pressure  will  steadily  fall 
until  it  may  be  not  more  than  one-third  of  the  normal  height  (Fig.  235;. 
During  the  production  of  this  decrease  of  blood  pressure  no  change 
occurs  in  the  rate  of  pulsation  of  the  heart.  It  must  be,  therefore,  due  to 
the  diminution  of  the  resistance  in  the  peripheral  vascular  system.  If  the 
splanchnic  nerves  be  divided  previous  to  this  experiment,  no  subsequent 
decrease  in  pressure  will  take  place.  The  conclusion  from  this  is  evi- 
dent. When  this  nerve,  which  has  been  termed  the  "  depressor  of  Lud- 
wig  and  Cyon  "  (the  superior  cardiac  branch  of  the  vagus),  is  stimulated 
the  impulses  pass  to  the  vaso-motor  centre  in  the  medulla,  and  there  so 
alter  the  impulses  coming  from  it  that  it  is  unable  to  maintain  the  nor- 
mal degree  of  contraction  of  the  abdominal  vessels,  through  the  failure  of 
the  influence  which  it  normally  exerts  on  these  vessels  through  the 
splanchnic  nerves.  The  abdominal  vessels,  consequently,  dilate  and 


JUUUUUUUUUUUUUUU^ 

FIG.  235.— BLOOD-PRESSURE  TRACING  OBTAINED  BY  STIMULATING  THE  DE- 
PRESSOR NERVE  IN  A  BABBIT.     (Foster.) 

The  current  entered  the  nerve  at  C  and  was  shut  off  at  O.    The  intervals  on  the  line  T  represent  seconds. 

draw  off  so  much  blood  from  the  general  arterial  system  that  the 
blood  pressure  may  be  reduced  two-thirds  or  more.  On  the  other  hand, 
if  in  an  animal  placed  under  curare  the  central  end  of  the  divided 
sciatic  nerve  be  stimulated,  directly  opposite  effects  will  be  produced. 
Without  any  change  in  the  heart's  rate  of  pulsation  the  pressure  will 
gradually  rise  until  it  may  be  one-third  higher  than  before  the  experi- 
ment :  here,  again,  the  increased  pressure  being,  evidently,  due  to  constric- 
tion of  the  local  arterioles,  for  previous  division  of  the  splanchnic  nerves 
will  largely  interfere  with  the  production  of  an  increased  blood  pressure. 
These  variations  in  blood  pressure  are  of  the  greatest  importance  in 
governing  the  general  character  of  the  circulation. 

The  effects  of  local  and  general  variations  in  vascular  tone  have 
been  admirably  formulated  by  Foster  : — 

Let  us  suppose  that  any  artery,  A,  is  in  a  condition  of  normal  tone — 


CIRCULATION   OF   THE   BLOOD.  557 

is  midway  between  extreme  constriction  and  dilation.  The  flow  through 
A  is  determined  by  the  resistance  in  A  and  in  the  vascular  tract  which  it 
supplies,  in  relation  to  the  mean  arterial  pressure,  which  again  is  depend- 
ent on  the  way  in  which  the  heart  is  beating  and  on  the  peripheral  re- 
sistance of  all  the  small  arteries  and  capillaries,  A  included.  If,  while 
the  heart  and  the  rest  of  the  arteries  remain  unchanged,  A  be  constricted, 
the  peripheral  resistance  in  A  will  increase,  and  this  increase  of  resist- 
ance will  lead  to  an  increase  of  the  general  arterial  pressure.  This  in- 
crease of  pressure  will  tend  to  cause  the  blood  in  the  body  at  large  to 
flow  more  rapidly  from  the  arteries  into  the  veins.  The  constriction  of 
A,  however,  will  prevent  any  increase  of  the  flow  through  it — in  fact,  will 
make  the  flow  through  it  less  than  before.  Hence,  the  whole  increase  of 
the  discharge  from  the  arterial  into  the  venous  system  must  take  place 
through  channels  other  than  A.  Thus,  as  the  result  of  the  constriction 
of  any  artery  there  occur  (1)  diminished  flow  through  the  artery  itself, 
(2)  increased  general  arterial  pressure,  leading  to  (3)  increased  flow 
through  the  other  arteries.  If,  on  the  other  hand,  A  be  dilated,  while 
the  heart  and  other  arteries  remain  unchanged,  the  peripheral  resistance 
in  A  is  diminished.  This  leads  to  a  lowering  of  the  general  arterial  pres- 
sure, which,  in  turn,  causes  the  blood  to  flow  less  rapidly  from  the  arteries 
into  the  veins.  The  dilation  of  A,  however,  permits,  even  with  the  low- 
ered pressure,  more  blood  to  pass  through  it  than  before.  Hence,  the 
diminished  flow  tells  all  the  more  on  the  rest  of  the  arteries.  Thus,  as 
the  result  of  the  dilation  of  any  artery,  there  occur  (1)  increased  flow  of 
blood  through  the  artery  itself,  (2)  diminished  general  pressure,  and  (3) 
diminished  flow  through  the  other  arteries.  Where  the  artery  thus  con- 
stricted or  dilated  is  small,  the  local  effect,  the  diminution  or  increase  of 
flow  through  itself,  is  much  more  marked  than  the  general  effects,  the 
change  in  blood  pressure  and  the  flow  through  other  arteries.  When, 
however,  the  area  the  arteries  of  which  are  affected  is  large,  the  general 
effects  are  very  striking.  Thus,  if  while  a  tracing  of  the  blood  pressure 
is  being  taken  by  means  of  a  manometer  connected  with  the  carotid 
artery  the  splanchnic  nerve  be  divided,  a  conspicuous  but  steady  fall  of 
pressure  is  observed  very  similar  to  that  which  is  seen  in  Fig.  235.  The 
section  of  the  splanchnic  nerves  causes  the  mesenteric  and  other  abdomi- 
nal arteries  to  dilate,  and  these  being  very  numerous  a  large  amount  of 
peripheral  resistance  is  taken  away,  and  the  blood  pressure  falls  accord- 
ingly ;  a  large  increase  of  flow  into  the  portal  veins  takes  place,  and  the 
supply  of  blood  to  the  face,  arms,  and  legs  is  proportionally  diminished. 
It  will  be  observed  that  the  dilation  of  the  arteries  is  not  instantaneous, 
but  somewhat  gradual,  the  pressure  sinking,  not  abruptly,  but  with  a 
gentle  curve. 

Arterial  tone,  then,  both  general  and  local,  is  a  powerful  instrument 


558  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

for  determining  the  flow  of  blood  to  the  various  organs  and  tissues  of 
the  body,  and  thus  becomes  a  means  of  indirectly  influencing  their  func- 
tional activity. 

In  certain  instances  stimulation  of  spinal  nerves  will  not  only  pro- 
duce contraction  of  the  arterioles  of  different  parts  of  the  bod}^  through 
reflex  stimulation  of  the  vaso-motor  centre,  but  will  also  produce  dilata- 
tion of  the  arterioles  in  the  vascular  area  supplied  by  that  nerve  ;  thus, 
for  example,  if  in  a  rabbit  under  the  influence  of  curare  the  central  stump 
of  the  great  auricular  nerve  be  stimulated  with  an  induction  current,  the 
blood  pressure  will  be  increased  through  constriction  of  the  general  vas- 
cular areas,  while  inspection  of  the  ear  will  show  that  its  vessels  have 
become  largely  dilated.  So,  also,  as  already  described  under  the  section 
on  Digestion,  when  the  chorda  tympani  nerve  is  stimulated,  we  not  only 
have  increased  secretion  of  saliva,  but  we  have,  also,  an  increase  of  the 
supply  of  blood  to  the  glands.  Such  nerves  as  the  chorda  tympani  and 
the  great  auricular,  with  numerous  others,  are  spoken  of  as  vaso-dilator 
nerves,  from  the  fact  that  their  stimulation  leads  not  to  contraction  of 
arterioles,  but  to  an  increase  in  their  calibre  ;  they,  therefore,  are  of  op- 
posite function  to  the  vaso-motor  nerves.  The  vaso-dilator  nerves,  as  a 
rule,  come  from  the  cerebro-spinal  system;  the  vaso-constrictor  nerves 
are,  as  a  rule,  branches  of  the  sympathetic  S3^stem.  The  explanation  of 
the  functions  of  the  vaso-dilator  system  of  nerves  is  somewhat  simplified 
by  the  following  observation  :  It  has  been  stated  that  when  the  sciatic 
nerve  of  a  frog  is  divided,  the  vessels  of  the  parts  supplied  by  that  nerve 
dilate.  Such  dilatation  is,  however,  usually  transient.  Twenty-four  hours 
after  the  section  of  the  nerve  the  vessels  ma}'  be  found  to  have  quite 
regained  their  normal  calibre,  even  if  still  cut  off  from  the  central  nerv- 
ous sj'stem.  Such  a  fact,  which  must,  of  course,  be  due  to  the  regained 
power  of  contraction  of  the  circular  muscular  fibres,  can  only  be  ex- 
plained through  the  assumption  that  the  walls  of  the  vessels  are  supplied 
with  nervous  ganglia  which  are  themselves  capable  of  originating  im- 
pulses sufficient  to  produce  varying  degrees  of  contraction  of  the  circular 
muscular  fibres  of  the  arterioles.  Normally,  the  impulses  originated  by 
these  peripheral  ganglionic  cells  are  dominated  by  the  influences  coming 
from  the  central  vaso-motor  centre.  When  the  vaso-motor  nerve  of  a 
part  is  divided  these  centres  are  suddenly  deprived  of  this  dominating 
influence,  the  muscular  fibres  are  paralyzed,  and  the  arteries  dilate.  When 
the  shock  of  the  operation  has  passed  off,  the  peripheral  ganglionic  cells 
themselves  acquire  the  power  of  governing  the  degree  of  contraction  of 
the  muscular  fibres  of  the  arteries  and  the  vessels  then  regain  their  nor- 
mal tone.  When  stimulation  of  the  auricular  nerve  or  of  the  chorda 
tympani  produces  dilatation  of  the  vessels  of  the  parts  supplied  by  these 
nerves,  the  effect  may  be  explained  by  assuming  that  the  impulses  com- 


CIRCULATION   OF   THE   BLOOD.  559 

ing  along  these  vaso-dilator  nerves  inhibit  the  local  ganglia  in  the  walls 
of  these  vessels  and  thus  lead  to  relaxation  of  the  muscular  fibres  of  the 
vessels  and  to  their  consequent  dilatation.  Their  modus  operandi  may 
thus  be  regarded  as  similar  to  that  of  the  pneumogastric  nerves,  since 
r  in  both  cases  the  motor  ganglia  are  inhibited  and  the  muscular  fibres  in 
the  walls  of  the  organs  of  circulation  relax  (Fig.  236). 


FIG.  236.— DIAGRAMMATIC  PLAN  OF  THE  CARDIAC-NERVE  MECHANISM,  AFTER 
CARPENTER.    (Yeo.) 

The  direction  of  the  impulses  is  indicated  by  the  arrows.    Both  right  and  left  sides  of  the  cut  are  used 
to  show  one  complete  lateral  half  of  the  fibres. 

Finally,  to  recapitulate,  the  pulse  and  blood  pressure  may  be  modi- 
fied \)y  the  following  causes  ( Laud  er-B  run  ton)  : — 

We  have  now  to  follow  the  blood  in  its  course  through  the  body  and 
consider  the  changes  which  it  undergoes  in  the  different  organs  and  tis- 
sues. It  was  seen  that  the  circulation  might  be  divided  into  two  sys- 
tems, the  greater  and  lesser.  The  changes  which  the  blood  undergoes  in 
the  latter,  the  pulmonary  system,  will  be  considered  first. 


560 


PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 


S  a  £                       *s     ^          ,•£-.••* 

'g                                    -g-2    *"                               -     ^         -g  >  a             § 
^•S                               £     £         Jg-3 

..11    .       if-          ii  H:i  U 

Ji.si      |             gS.il               t     1    |      .s^g      -|| 
§|8l                 .illl              !    *    I  *8tl9-   If 

i£§:  4|       h*i«          i-i^  §<3^i>  cs 

III!  II     Hi-         ii  *  1          ii 

°^|°      S8               S-38*  |                 *£     .1     1     -|S?I°     S-a 

nil  ii     .jin*      ii  iai>  11  ii  ii 

Sill   Sc         f-a  I*         II   l|l  lH'1-a  ^ 

•3>,:.S      rS.                    5g:    §     gg                   St,       "1^      8>>g      ^g      *| 

u  *£  >  *         ^  :  ||       ^  ^||  -^  !^  1s 

^^1^1        ££  i  U       ^1^!l  |1^  1-^  H 

ag^=|-a=            S|=|o-a.          g^  g||.tt    §.||=  -_|    §^ 
a  S»    «    £               S«         5               5-5  SM    H    5«t^       M    £ 

o           ' 

5        -c 

M                           O      r/> 

1     I  *  ^  : 

£               >   e^        2     . 
g             *S^        g     '                || 

-  •  ™^'                ^*f~      .                       —  v  — 

.    ^ 

'•    •  !     :  i  : 

.         a,                          •          J      • 

rl                                        rJ~l 

®                                    .            ^                                                              JH      OS 

•    -i 

.     OQ  «*H                       «T 

pj  o            o> 

HJ                  ."S  ^*          £2                               9     ^> 

OQ              "3  •§       .S     '                   >   °° 
*S  *""*                           *   |  -*          .« 

65               J'i        ^      '      "S    «8    ^0 

i   11  lil  1  1  i 

S                     r^^              ®   -fi"      J  ^  J    * 

1    ii  U  *1j? 

1    II  PlKi 

il    •  °    11  «f 

^2    g& 
11     :  s    ,-9-1      a 
!l    *!  Ill   .1 

JH     <D     fXi           -        0 
>PH^S§§S                     0 

.3                    i3^^       - 
*is               -       >  >*o 

,3           '-5  "2       ^ 

1      j|  §      s 
^      g§^     1 
-§      ^1     f 

^                  O    e3    §                w 

,2            o  S3  1           £ 

i  ill 

^       sse^s's  &i|| 

fia^Sg    -S      -J^ 

a      -J-J^'^s  «§    ^ 

2        s  ts  ®  -y*t    §3  .   2  *a 
5       •c-n-  S  g    frs  si 

o"                      -S      g 

.2                                .2       '43 
OQ                                         oa  -      08 

t=     '  vf  1   °° 

IS'" 

£          J" 

o            *r^ 

i 

0      ^A    f2^  5    60 

A*                                                           0*            '^ 

PH                                   PH       02 

1      £ 

« 

i   ii-i 

!i        1 

3   . 

1; 

1    igi 

?        ^I-S 

07 

£    '                     £ 

•8    • 

-4J 

C3 

i  : 

«*H          ' 

*o    -                           § 

g* 

C3 

O                             w>     °^     C? 

d    •                         -2 

S  S 

.2    ' 

1    III 

||            | 

M  ^O 

11 

•%         l?l 

fl 

O    c3 

pq"             M 

pq                     P? 

pq" 

PQ 

•fwusiuiwip  90  fivut,  9J,nsszj,d  pooiff                  'pdsm-ioui  90  from  zjmssud  poojfr 

SECTION  VIII. 

RESPIRATION. 

IT  has  been  seen  that  through  absorption  the  products  of  digestion 
enter  into  the  blood  and  are  carried  by  means  of  the  circulation  to  the 
various  organs  and  tissues  of  the  body.  Jn  spite,  however,  of  the  con- 
stant addition  of  these  substances  to  the  blood  its  general  composition 
remains  almost  uniform,  for  the  income  from  the  alimentary  tract  is 
balanced  by  the  outgo  through  the  different  tissues.  The  blood  in  its 
passage  through  the  capillaries  of  the  body  nevertheless  undergoes 
great  alterations  in  its  composition.  It  gives  up  to  the  tissues  the 
substances  brought  from  the  alimentary  tract  which  are  destined  to 
nourish  the  different  tissues  of  the  body.  Every  function  of  a  cell  is 
accompanied  by  chemical  change  in  its  composition,  the  resulting  prod- 
ucts in  the  majority  of  cases  being  no  longer  of  use  to  the  economy. 
The  blood  is  charged  to  remove  these  substances  from  the  tissues. 

Again,  it  has  been  found  that  the  vital  functions  of  every  cell 
necessitated  a  supply  of  oxygen.  It  is  the  function  of  the  blood  to  act 
as  carrier  of  this  gas  and  to  remove  as  well  the  gaseous  products  of  cell 
decomposition.  We  thus  find  that  the  blood  acts  not  only  as  an  organ 
of  nutrition,  but  as  an  organ  of  excretion  ;  in  fact,  as  a  common  carrier 
of  the  several  substances  essential  to  cell  life,  and  the  carrier  of  the 
deleterious  substances  resulting  from  the  breaking  down  of  cells,  and  it 
bears  them  to  different  parts  of  the  body  where  special  organs  are  set 
aside  for  their  removal.  The  removal  of  these  deleterious  substances 
constitutes  excretion,  the  mode  of  removal  depending  upon  the  nature 
of  the  substances  to  be  eliminated. 

One  of  the  most  striking  changes  which  occur  in  the  blood  in 
passing  through  active  organs  is  the  3rielding  up  of  oxygen  and  the 
overloading  of  the  blood  with  carbon  dioxide.  It  has  been  stated  that 
the  difference  between  the  arterial  and  venous  blood  is  that  the 
former  contains  an  excess  of  oxygen,  the  latter  an  excess  of  carbon 
dioxide,  the  oxygen  of  the  arterial  blood  being  derived  from  the  atmos- 
phere and  entering  into  composition  with  the  haemoglobin  as  the  blood 
passes  through  the  capillaries  of  the  lungs.  The  carbon  dioxide  is 
derived  from  the  breaking  down  of  the  cell-constituents,  and  is  likewise 
removed  from  the  blood  while  passing  through  the  pulmonary  capillaries. 
The  process  by  which  these  gases  enter  and  leave  the  blood  is  almost 

36  (561) 


562  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

purely  physical,  and  is  termed  respiration.  Respiration  may  therefore 
be  defined  as  that  function  by  means  of  which  oxygen  is  taken  into  the 
system  and  carbon  dioxide  eliminated.  Oxygen  passes  into  the  blood 
from  the  air,  mainly  by  a  process  of  gaseous  diffusion ;  the  same  process 
is  also  largely  concerned  in  the  giving  up  of  oxygen  by  the  blood  to  the 
different  tissues  and  the  absorption  of  carbon  dioxide  from  the  different 
tissues  by  the  blood,  and  the  yielding  of  this  gas  to  the  air  within  the 
lungs. 

1.  GENERAL  VIEW  OF  THE  ORGANS  OF  RESPIRATION. — The  function  of 
respiration  is  an  organic  function,  existing  in  the  vegetable  as  well  as  in 
the  animal,  the  products  of  respiration  being  the  same  in  both.  In  the 
vegetable  the  introduction  of  oxygen  and  elimination  of  carbon  dioxide 
takes  place  both  during  da}T  and  night,  but  during  the  day  the  function 
of  respiration  is  masked  by  the  processes  of  nutrition  in  which  the 
reverse  change  takes  place,  carbon  dioxide  being  appropriated  by  the 
plant  and  oxygen  set  free. 

In  examining  the  different  forms  of  respiratory  apparatus  peculiar 
to  different  kinds  of  organic  beings  it  is  readily  determined  that  in  all 
the  main  respiratory  tissue  is  that  part  of  the  respiratory  apparatus 
which  is  concerned  in  the  absorption  of  oxygen  and  in  the  elimination 
of  carbon  dioxide,  and,  like  the  digestive  tube,  is  simply  a  modification 
of  the  external  tegumentary  surface. 

In  the  simplest  forms  of  plant  life  the  external  tegumentary  covering 
constitutes  the  entire  respirator}7  apparatus,  and  it  is  through  this  that 
oxygen  is  absorbed  and  carbon  dioxide  eliminated.  But  in  the  more 
highly  organized  forms  of  plants  a  system  of  tubes,  known  as  the  spiral 
vessels,  are  found  ramifying  through  their  stems  and  leaves,  and  even  in 
their  most  perfect  form  seldom  contain  other  than  gaseous  matters. 
These  spiral  vessels  in  the  endogenous  plants  are  universally  distributed 
through  the  stem,  and  form  a  part  of  every  bundle  of  nbro-vascular 
tissue;  but  in  the  exogenous  plants  they  are  usually  confined  to  the 
medullary  sheath  immediately  surrounding  the  pith.  In  each  case,  how- 
ever, they  traverse  the  stems  in  such  a  manner  as  to  enter  the  leaves 
through  the  foot-stalks.  These  vessels  carry  air  from  the  exterior  to  the 
interior,  and  it  is  an  especial  fact  to  be  noted  that  the  atmospheric  air 
contained  in  them  possesses  a  larger  amount  of  oxygen  than  the  free 
atmosphere.  On  the  under  surfaces  of  leaves  are  also  to  be  found 
distinct  openings,  or  stomata,  which,  although  apparently  for  the  admis- 
sion of  materials  necessary  for  nutrition,  also  seem  to  have  the  power 
of  admitting  air  into  the  cavities  existing  in  the  leaves,  especially  beneath 
the  inferior  cuticle.  Thus,  it  is  the  external  surface  of  the  plant  through 
which  respiration  is  practical!}'  performed. 

So,   also,   in   animals,   respiration   always  takes  place  through  an 


BESPIKATION.  563 

external  membrane,  or  some  extension  of  such  membrane,  outward  pro- 
longations constituting  gills,  inward  prolongations  constituting  the  lungs ; 
so  that  all  animals  may  be  classed  as  air-breathers  or  water-breathers, 
the  latter  breathing  the  air  dissolved  in  water.  To  the  former  class 
belong  nryriapods,  spiders,  insects,  reptiles,  birds,  and  mammals,  while 
all  other  animals,  with  few  exceptions,  are  water-breathers ;  in  the  first 
class  the  organs  of  respiration  are  internal ;  in  the  latter  class  more  or 
less  external,  but  in  all  are  to  be  regarded  as  modifications  of  the  external 
integument  (Fig.  237). 

In  the  lowest  forms  of  animal  life,  all  of  which  are  inhabitants  of 
water,  there  are  no  prolongations  of  this  membranous  surface — aeration 
of  the  fluids  being  accomplished  by  their  exposure  to  the  surrounding 
medium  containing  oxygen  in  solution.  No  distinct  respiratory  organs 
are  present  in  these  forms  of  life,  unless  the  contractile  vesicles  described 
as  being  constantly  found  in  such  organisms  are  of  this  character.  In 
animals  belonging  to  the  group  of  protozoa  the  surface  of  the  body  is 


FIG.  237.— DIAGRAM  ILLUSTRATING  DIFFERENT  FORMS  OF  RESPIRATORY 
APPARATUS.     (Carpenter.) 

A,  simple  leaf-like  gill ;  B,  simple  respiratory  sac ;  C.  divided  gill ;  D,  divided  sac ;  E,  pulmonary 
branchia  of  spider. 

usually  more  or  less  provided  with  cilia,  which  serve  by  their  vibrations 
to  continually  change  the  stratum  of  water  immediatel}7  in  contact  with 
the  external  surface.  The  presence  of  a  fluid  containing  ox}*gen  in 
solution  in  contact  with  the  respiratory  surface  is  thus  alwa}Ts  insured. 

In  sponges,  as  in  infusoria  and  polyps,  we  find  that  the  respiratory 
surface  exists  in  the  form  of  tubulary  passages  through  the  body,  pro- 
vided at  certain  points  with  cilia,  the  air  being  absorbed  from  the  currents 
of  water  passing  through  them. 

In  the  ccelenterata,  which  are  all  aquatic,  no  circulatory  organs  are 
present,  and,  as  a  consequence,  no  respiratory  apparatus;  for  we  find 
that  while  organs  of  circulation  are  dependent  upon  the  complexity  of 
the  alimentary  apparatus,  so  the  presence  of  distinct  circulatory  organs 
governs  the  presence  of  organs  of  respiration. 

In  the  coelenterata  any  part  of  the  body  surface  appears  to  be  capable 
of  accomplishing  the  interchange  of  oxygen  and  carbon  dioxide.  In  some 
the  body  cavity  also,  doubtless,  fulfills  this  function.  This  would  seem  to 


564  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

indicate  a  step  higher  in  organization  and  a  beginning  of  a  specialization 
of  certain  tissues  for  carrying  on  the  functions  of  respiration.  This  is 
the  case  in  the  polyps  and  in  the  sea-anemone,  while  in  the  bryozoa 
there  is  a  marked  dilatation  of  the  pharynx,  which  seems  to  be  particu- 
larly intended  to  provide  for  the  aeration  of  fluids. 

In  certain  members  of  the  group  of  annuloida  a  still  higher  special- 
ization of  the  respiratory  apparatus  is  met  with.  Thus,  in  many  there 
exist  peculiar  ramified  contractile  vessels,  the  trunks  of  which  open 
upon  the  surface  of  the  body,  and  are  in  part  ciliated  in  their  interior. 
These  are  the  so-called  water-vessels,  and  are  supposed  to  be  subservient 
to  the  respiratory  process. 

In  various  of  the  echinoderms,  in  addition  to  numerous  gill-like 
fringes,  two  sets  of  canals  are  found,  the  one  carrying  the  nutritive  fluid, 

and  the  other  radiating  from  a  ring 
around  the  mouth,  and  distributing 
aerated  water. 

In  worms,  especially  in  the 
silk-worm,  a  system  of  spiral  vessels 
analogous  to  those  of  the  plant  and 
permeating  the  structure  in  every 
direction  is  often  to  be  detected. 
These  are  called  tracheae,  and  com- 
municate directly  with  the  atmos- 
phere by  open  breathing  orifices  on 
different  portions  of  the  body  of  the 

insect,  and  may  be  readily  noticed 
FIG.  238.— TRACHEAE  OF  INSECT,  SHOWING  J 

THE  SPIRAL  FIBRE.    (Jeffrey  Bell.)         in  the  caterpillar  as  dark  spots  upon 

the  sides.  In  fresh-water  worms, 

like  the  leech  and  earth-worm,  the  body  is  covered  externally  by  a  viscid 
fluid  which  has  the  power  of  absorbing  air;  so  such  animals  breathe  by 
the  skin,  beneath  which  lies  a  dense  net-work  of  blood-vessels.  In 
insects  one  of  these  spiracles,  as  they  are  also  named,  traverses  the 
body  on  either  side  along  its  whole  length,  sending  out  ramifications,  as 
referred  to  above.  The  tracheae  are  prevented  from  having  their  cavities 
obliterated  by  spiral  elastic  fibres  which  seem  an  analogue  of  the  carti- 
laginous rings  in  the  tracheae  and  bronchise  of  the  air-breathing  verte- 
brates (Fig.  238). 

Thus,  in  insects,  as  in  mammals,  the  air  is  carried  to  the  fluids  to  be 
aerated. 

In  marine  worms,  which  are  water-breathing  animals,  the  simplest 
form  of  gill  is  seen  ;  it  consists  of  delicate  veins  projecting  through 
the  skin  along  the  side  of  the  body  in  a  series  of  arborescent  tufts.  As 
these  float  in  the  water  the  blood  is  purified  (Figs.  239  and  240). 


RESPIKATION. 


565 


In  the  spider  the  respiratory  apparatus  consists  of  a  series  of  sacs, 
less  numerous  than  the  tracheas  of  the  silk-worm,  and  not  communicat- 
ing with  each  other ;  yet  additional  space  is  obtained  by  arranging  the 
lining  membrane  into  a  series  of  folds,  which  lie  in  close  relation  to  each 
other  like  the  leaves  of  a  book,  thus  forming  the  first  indication  of  a  lung. 
From  the  extensive  surface  thus  produced,  in  which  lies  a  net-work  of 
vessels,  the  blood  is  brought  into  immediate  relation 
with  the  air,  which  enters  through  the  breathing  parts 
referred  to.  The  exchange  of  air  in  the  sacs  is  accom- 
plished by  the  movements  of  the  body  of  the  insect, 
which  empty  the  sacs  by  compression  and  allow  them 
to  refill  by  the  elasticity  of  their  walls.  These  respira- 
tor}- cavities  are  called  pulmonary  branchiae  from  their 
resemblance  on  the  one  hand  to  the  lungs  of  the  higher 
animals,  and  on  the  other  hand  to  the  branchiae  or  gill- 
sacs  (Fig.  241). 

In  the  oyster  and  mollusk  we  have  an  approach  to 
the  respiratory  apparatus  of  the  fish.  On  opening  an 
oyster  a  delicate  membrane,  known  as  the  mantle,  is 
seen  lining  the  edge  of  the  cell.  The  gill  is  constituted 
by  a  double  fold  of  the  mantle  covered  with  cilia ;  upon 
the  gill  ramify  the  blood-vessels,  wrhich  are  bathed  by 
the  water  which  passes  over  them.  From  this  water 
the  blood  receives  oxygen  and  gives  carbon  oxide  to  it, 


FIG.  239.  —THE 
LOB-WORM  (Are- 
nicola).  (Carpen- 
ter.) 

The  arborescent  gills 
are  situated  on  certain 
segments  only. 


FIG.  240.— TRANSVERSE  SECTION  OF  ARENICOLA,  AFTER  GEGENBAUR. 
(Jeffrey  Bell.) 

D,  dorsal,  V,  ventral  sides :  N,  ganglionic  chain :  I,  intestine ;  BR,  gills :  v,  ventral  vessels ;  D, 
dorsal  vessel;  v',  visceral  vessel ;  P,  vessel  around  intestine;  A  B,  vessels  of  gills. 


— an  exchange  which  is  just  as  essential  to  the  oyster  as  for  breathing 
mammals  (Fig.  242). 

In  the  clam  the  gills  are  inclosed  in  the  mantle,  forming  a  tube,  the 
siphon,  through  which  the  water  is  forced  b}'  cilia. 

In  the  lowest  forms  of  crustaceans,  as  in  the  branchiopods,  the 
respiratory  appendages  are  nothing  more  than  thin  plates,  within  which 


566 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


the  blood  circulates,  and  outside  of  which  is  the  oxygenated  water  in 
which  they  are  bathed  (Fig.  243).  In  the  higher  orders,  as  exemplified 
by  the  crab,  we  find  external  gills  like  those  of  the  oyster,  and  attached 
to  movable  parts  of  the  body,  as  the  legs,  exemplifying  the  association 
of  locomotor  with  respiratory  activity.  They  are  kept  in  motion  to 
bring  the  respiratory  apparatus  in  contact  with  fresh  portions  of  water. 
In  the  crab  the  gills  are  inclosed  within  a  cavity  formed  by  a  doubling 
of  the  horny  integument,  and  the  stream  of  water  is  kept  up  through 


FIG.  241.— RKSPIRATORY  APPARATUS  OF  INSECT.    (Carpenter.) 

A,  first  pair  of  legs ;  B,  first  segment  of  thorax  ;  C,  origin  of  wing ;  D,  second  pair  of  legs  ;  E,  third 
pair  of  legs ;  F,  tracheae  ;  G,  stigmata ;  H,  air-sacs. 

these  by  means  of  a  valve  in  the  exit-pipe  worked  by  the  jaws.  The 
constant  movement  causes  a  regular  stream  of  water  to  issue  from  the 
gill-chamber. 

In  the  fish  the  respiratory  apparatus  in  all  essentials  corresponds 
with  that  of  the  mollusk,  the  branchial  element  onl^y  being  modified  and 
multiplied  in  accordance  with  the  higher  grade  of  life.  The  gills  are 
formed  of  folds  of  membrane,  between  which  are  distributed  the  blood- 
vessels, and  which  are  suspended  from  two  bony  or  cartilaginous  arches 


KESPIKATION. 


567 


(Fig.  244).  The  water  is  taken  in  by  a  process  of  swallowing,  the  mouth 
being  first  distended,  and,  as  the  muscles  contract,  the  water  is  expelled 
through  the  aperture  on  either  side  of  the  pharynx  into  a  cavity  called 
the  gill-cavit}T,  and,  as  it  passes  over  the  gills,  the  oxygen  of  the  atmos- 
phere held  in  solution  is  absorbed  by  the  blood. 

Fish  are  thus  admirably  fitted  for  aquatic  respiration,  but  die  on 
removal  from  the  water  from  the  fact  that,  as  the  gills  dry,  absorption 
of  oxygen  is  impaired,  and  the  gills  cling  together,  and  so  prevent  ex- 
posure of  their  greater  portion  to  the  air.  Under  such  circumstances 
fish  then  die  from  asphyxia.  In  some  cases  there  is  provided  in  addition 
an  air-bladder  or  swimming-bladder,  like  a  rudimentary  sac  of  the  air- 
breathing  apparatus  of  the  higher  animals.  In  its  simplest  condition 
it  is  entirely  closed,  and  can,  therefore,  serve  no  purpose  except  to 

C 


FIG.  242.— DIAGRAMMATIC  SECTION  OF  A  LAMEI/LTBRANCH  (FRESH-WATER 
MUSSEL,  Anodon)  THROUGH  THE  HEART.    (Huxley.) 

F,  ventricle  ;   G,  auricles ;  C,  rectum ;  P,  pericardium :  H,  inner  gill ;  I,  outer  gill ;  O  Q,  organ  of  Bojanus : 
B,  foot;  A  A,  mantle-lobes. 

regulate  the  specific  gravity  during  swimming.  In  others  this  bladder 
is  connected  with  the  alimentary  canal  by  a  short,  wide  tube,  called  the 
ductus  pneumaticus,  and  is  filled  by  the  process  of  swallowing. 

If  we  admit,  as  seems  perfectly  reasonable,  that  the  air-bladder  of  the 
fish  is  a  rudimentary  lung,  it  may  be  stated  that  all  vertebrates  in  the 
course  of  their  life  have  two  different  kinds  of  respiratory  apparatus. 
Every  form  of  vertebrate  breathes  through  gills  during  embryonic  life; 
in  the  fish  and  a  few  reptiles  the  gills  are  permanent,  but  in  others  they 
disappear,  and,  while  traces  of  a  lung  are  seen  in  all  vertebrates,  they 
acquire  full  development  only  in  reptiles,  birds,  and  mammals :  while, 
again,  certain  amphibians,  as  the  Proteus  and  Siren,  retain  both  gills  and 
lungs  to  adult  life,  and  thus  form  a  link  between  fishes  and  reptiles. 


568 


PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 


BR' 


FIG.  243.  —  TRANSVERSE  SEC- 
TION OF  A  BRANCHIOPOD, 
SHOWING  THE  LEAF-LIKE 
GILLS.  AFTER  GRUBE.  ( Jef- 
frey Bell.) 

C,  heart;  I,  intestine;  N,  ventral 
nerve-cord;  D,  fold  of  the  integument: 
BR  BR',  gills,  which  are  appendages  of 
the  body. 


Vertebrates  are  the  only  animals  that  breathe  through  the  nostrils  or 
mouth.    Fishes  inspire  only,  and  all  vertebrate  animals  in  whom  the  ribs 

are  absent  or  solidly  fastened  together 
swallow  air. 

In  reptiles  we  first  meet  with  a  complete 
adaptation  of  a  pulmonary  structure  for  the 
direct  aeration  of  the  blood  through  the 
influence  of  the  atmosphere.  In  them  there 
is  an  internal  prolongation  of  the  external 
integument,  constituting  the  lungs,  though 
they  exhibit  great  simplicity,  being,  for  the 
most  part,  capacious  sacs,  occupying  con- 
siderable bulk, .but  being  but  slightly  sub- 
divided, so  that  the  amount  of  surface 
exposed  is  really  very  small,  the  blood  being 
exposed  on  one  surface  only  to  aeration. 
The  greatest  diversity  is  met  with  in  these  animals  as  regards  the 
structure  and  mobility  of  the  thorax.  In  the  saurians,  the  thorax 
resembles  that  of  mammals,  with  movable  ribs;  in  the  chelonia,  the 

thoracic  walls  are  rigid  and  immovable ;  in  the 
ophidians,  the  ribs  are  very  numerous  and 
movable,  the  sternum  being  absent.  A  dia- 
phragm is  met  with  only  in  the  higher  sau- 
rians. In  reptiles  inspiration  is  not  accom- 
plished by  inhalation,  but  by  deglutition,  air 
being  drawn  into  the  pharynx  by  depression 
of  the  hyoid  apparatus,  and  the  nares  then 
being  closed,  the  air  is  forced  into  the  trachea. 
Expiration  is  accomplished  mainly  by  the 
elasticity  of  the  lungs,  aided  by  the  abdom- 
inal muscles,  and  in  saurians  and  ophidians 
by  the  intercostal  muscles  and  the  elasticity 
of  the  chest-walls.  In  snakes,  as  a  rule, 
there  is  a  single,  long,  c}rlindrical  lung, 
while  the  left  lung  is  rudimentary. 

In  birds,  though  the  diaphragm  is  still 
absent  or  rudimentary,  the  respiratory  appa- 
ratus is  more  complicated  than  any  yet 
considered,  so  that  the  energy  of  the  respira- 
tory process  is  much  increased,  and  yet 
the  general  plan  of  the  apparatus  is  much  more  closely  allied  to  that  of 
reptiles  than  of  mammals.  For  each  lung  may  be  considered  to  be  sub- 
divided into  lobules,  each  of  which  resembles  the  rudimentary  lung  of 


FIG.  244.— GILL  OF  THE  PERCH. 

(Jeffrey  Sell.) 

A,  branchial  artery ;  B,  branchial  arch 
(seen  in  cross-section)  ;  C,  branches  of  the 
branchial  vein,  V;  D,  branches  of  the 
branchial  artery. 


KESPIRATION.  569 

the  frog,  flattened  and  fixed  to  the  back  of  the  thorax.  In  addition  to 
the  elementary  lungs  numerous  large  air-sacs,  distributed  in  various 
parts  of  the  body,  as  the  abdomen,  the  muscular  interspaces,  interior 
of  the  bones,  etc.,  are  found  communicating  with  the  lungs.  And 
as  the  lining  membrane  of  the  bones,  as  well  as  of  all  these  cavities,  is 
extremely  vascular,  it  also,  in  these  localities,  serves  to  assist  in  the  aera- 
tion of  the  blood  by  exposure  to  the  air.  In  fact,  if  the  wind-pipe  be  tied 
and  an  opening  be  made  in  the  wing-bone,  respiration  may  still  go  on. 
This  large  increase  of  respiratory  surface  serves  as  well  as  store-room  for 
atmosphere  and  is  well  adapted  to  the  purposes  of  flight,  during  which 
the  respiratory  movements  are  less  free.  The  lungs  and  the  accessory 
apparatus  of  birds  is  filled  with  air  by  the  process  of  suction  through 
the  trachea,  in  consequence  of  the  permanent  distended  condition  of  the 
whole  cavity  of  the  trunk  from  the  nature  of  its  bony  encasement.  Such 
is  the  natural  condition  of  this  bony  frame-work  that  when  no  pressure 
is  made  upon  it  it  is  completely  distended  ;  as  a  consequence,  the  lung- 
tissue  permanently  attached  to  the  ribs  possesses  such  a  degree  of  elas- 
ticity as  to  enable  it  to  spontaneously  dilate.  Hence,  the  disposition  of 
the  air  to  fill  the  distended  cavities  until,  by  the  action  of  the  external 
muscles  upon  the  bony  frame-work,  a  portion  of  the  air  is  expelled  and  its 
place  again  immediately  taken  by  a  fresh  supply  of  air  on  relaxation  of 
these  muscles.  Inspiration,  therefore,  in  birds,  in  opposition  to  what 
we  shall  find  to  be  the  case  in  mammals,  is  passive,  while  expiration  is 
active  and  is  accomplished  by  drawing  the  sternum  toward  the  backbone 
by  muscular  contraction,  thus  compressing  the  lung  and  expelling  the  air. 

The  organs  of  respiration  in  man  and  mammals  generally  consist  of, 
first,  the  bony  frame-work  of  the  chest ;  second,  the  diaphragm  and  other 
muscles  ;  and,  third,  the  trachea,  bronchial  tubes,  and  air-vessels.  •  In 
mammals  alone  is  there  a  perfect  thorax,  i.e.,  a  closed  cavity  for  the 
heart  and  lungs,  with  movable  walls  and  a  muscular  partition,  the 
diaphragm,  separating  the  thoracic  from  the  abdominal  cavitj*. 

The  trachea  is  a  cylindrical  tube  consisting  of  a  varying  number  of 
cartilaginous  rings,  imperfect  posteriorly  in  man  and  most  animals. 
These  posterior  imperfect  spaces  are  occupied  by  the  muscles  which 
control  the  calibre  of  the  tube.  The  use  of  these  cartilaginous  rings  is 
to  keep  the  tube  patulous,  so  as  to  permit  the  entrance  and  free  egress 
of  air,  subserving  the  same  function  as  the  spiral  fibres  in  the  interior 
of  the  air-vessels  of  the  plant  and  insect  already  described.  Immediately 
within  the'  cartilaginous  rings,  which  are  bound  together  by  fibrous 
tissue,  is  found  a  fibrous  connecting  membrane ;  within  that  is  a  mucous 
membrane  continuous  with  that  of  the  mouth  and  the  pharynx,  supplied 
with  cylindrical,  ciliated,  epithelial  cells,  the  cilia  of  which  vibrate  toward 
the  pharynx  and  serve  the  purpose  of  facilitating  the  discharge  of  the 


570 


PHYSIOLOGY  OF   THE  DOMESTIC   ANIMALS. 


secretions  or  of  any  foreign  substance  which  may  lodge  upon  it.  When 
the  trachea  reaches  the  second  or  third  dorsal  vertebra  it  bifurcates  into 
two  principal  bronchi,  passing  one  to  each  lung,  and  subsequently  these 
again  divide  and  subdivide  in  various  directions  until  they  have  attained 
the  size  of  the  most  minute  bronchial  tubes. 

The  larynx,  which  is  placed  at  the  laryngeal  extremity  of  the 
trachea,  may  be  considered  as  corresponding  to  the  base  of  a  tree,  the 
trachea  to  its  trunk,  and  the  bronchi  to  its  different  branches  ;  while  the 
ultimate  bronchi  terminating  in  the  air-vesicles  of  the  lung  may  be 
regarded  as  representing  the  leaves  of  the  tree.  The  bronchi  have  the 
same  anatomical  constituents  as  the  trachea,  and  are  composed  of  carti- 
laginous rings,  musculo-fibrous  membrane, 
and  a  lining  mucous  membrane  (Fig.  245). 
The  cartilaginous  rings  are  also  imperfect, 
but  the  imperfect  spaces  are  irregularly  dis- 
tributed, sometimes  in  front  and  sometimes 
at  the  side.  The  object  of  the  rings  is,  of 
course,  the  same  as  those  of  the  trachea. 
The  tubes  are  thus  mere  gaseous  conduits 
kept  patulous  by  their  cartilaginous  constit- 
uents. In  the  bronchi  a  fibrous  basement 
membrane  is  found,  as  well  as  unstriped 
muscular  fibres,  and  in  the  bronchi  the 
muscular  fibres  do  not  merely  connect  the 
ends  of  the  rings,  but  completely  encircle  the 
tubes  in  the  form  of  annular  fibres.  These 
muscular  fibres  are  unstriped  and  involun- 
tary, and  therefore  possess  the  same  char- 
acteristics as  the  unstriped  muscular  fibre 
found  elsewhere,  and  serve  to  regulate  the 
calibre  of  the  tubes.  The  lining  mucous 
membrane  of  the  bronchi  is  also  a  ciliated  membrane  and  extends  down 
to  the  commencement  of  the  finest  bronchi.  In  the  mucous  membrane 
are  found  tubular  glands  forming  a  mucous  secretion.  In  the  minute 
bronchi  the  cartilaginous  rings  disappear  and  the  bronchioles  are  then 
constituted  of  a  la}rer  of  circular  muscular  fibres  with  an  inner  epithelial 
membrane,  the  cartilaginous  rings  disappearing  when  the  bronchi  have 
been  reduced  to  about  one-thirtieth  to  one-fiftieth  of  an  inch  in  diameter. 
The  bronchi  ultimately  terminate  in  a  dilated  portion,  termed  lobules  or  in- 
fundibula,  which  consist  simply  of  a  homogeneous  membrane  abundantly 
supplied  with  blood-vessels.  This  dilatation  is  formed  by  the  same 
material  as  constitutes  the  fibrous  wall  of  the  tube  thrown  up  into  folds, 
between  which  ramify  the  blood-vessels.  The  contained  blood  is,  there- 


FIG.  245.— BRANCHIAL  TREE  OF 
A  MAMMAL  (HORSE),  AFTER 
AEBY.  (Jeffrey  Bell.) 

A,  eparterial,  B,  hyparterial  ventral 
(V),  and,  D,  hyparterial  dorsal  bronchi ; 
PA,  pulmonary  artery;  PV~,  pulmonary 
vein. 


KESPIEATION.  571 

fore,  exposed  on  both  sides  to  the  atmosphere.  As  the  capillary  net- 
work is  spread  over  several  cells,  aeration  of  the  blood  is  thus 
thoroughly  secured,  and  in  this  locality  the  venous  blood  is  converted 
into  arterial.  The  calibre  of  these  capillaries  is  extremely  small,  being 
only  in  diameter  equal  to  the  thickness  of  a  red  blood-corpuscle.  It  has 
been  estimated,  nevertheless,  that  the  pulmonary  capillaries  in  man  are 
capable  of  containing  about  two  liters  of  blood,  and  it  has  been  further 
calculated  that  this  amount  is  renewed  ten  thousand  times  in  twenty-four 
hours.  And,  even  making  allowances  for  error  in  these  calculations,  it 
is  evident  how  large  is  the  surface  for  the  interchange  of  gases  between 
the  air  and  blood. 

The  diameter  of  the  air-vesicles  is  from  one  two-hundredth  to  one- 
seventieth  of  an  inch.  Their  number  is  almost  infinite.  It  has  been 
calculated  that  about  the  termination  of  each  bronchus  in  a  mammal  are 
collected  seventeen  thousand  seven  hundred  and  ninety  air-cells,  and 
their  total  number  has  been  computed  to  be  at  least  six  hundred  millions. 
It  has  been  further  calculated  by  Lieberkiihn  that  the  whole  extent  of 
respiratory  surface  of  both  lungs  in  man  is  fourteen  thousand  square 
feet,  or  two  hundred  square  meters,  and  this  surface  is  attained  through 
the  reduplications  of  the  membrane,  so  occupying  the  least  possible 
bulk.  The  air-vesicles  gradually  increase  in  number  from  infancy  to 
adult  life,  when  they  remain  stationary  for  a  time,  after  which  they 
decline,  so  that  there  is  less  respiratory  surface  in  infancy  and  old  age 
than  in  adult  life. 

The  walls  of  the  air-vesicles  are  highly  elastic,  from  the  presence  of 
elastic  fibres,  which  form  a  close  net-work  with  very  fine  meshes.  Through 
the  presence  of  this  elastic  tissue  the  air-vesicles,  therefore,  tend  contin- 
ually to  contract, — a  phenomenon  which,  as  will  be  later  demonstrated, 
is  of  the  greatest  importance  for  the  process  of  expiration.  All  the 
different  parts  of  the  lungs  are  held  together  by  delicate  elastic  tissue, 
and  outside  of  this  by  a  serous  membrane,  termed  the  pleura,  which 
covers  the  external  surface  of  the  lungs  and  is  reflected  on  to  the  internal 
surface  of  the  thorax.  The  pleural  membrane  thus  forms  a  shut  sac, 
and  the  lung  lies  on  the  outside  of  it. 

The  thorax  is  composed  of  a  closed  cavity  in  the  form  of  a  truncated 
cone,  of  which  the  sides,  back,  and  a  portion  of  the  interior  surfaces 
are  formed  by  the  ribs  and  costal  cartilages  with  their  intervening 
muscles.  Its  base  is  oblong,  more  or  less  flattened  laterally  in  quad- 
rupeds and  antero-posteriorly  in  man.  The  ribs  are  always  more  or  less 
curved,  with  their  concavity  directed  internally.  In  general,  the  first  rib 
is  the  shortest,  is  less  curved,  and  less  inclined  to  the  vertebral  column. 
As  a  rule,  it  may  be  stated  that  in  animals  in  whom  the  thorax  is  short 
the  ribs  are  more  curved  than  in  those  where  the  thorax  is  longer. 


572  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

The  backbone  forms  a  part  of  the  posterior  boundary  of  the  chest, 
the  sternum  the  anterior  boundary.  Below,  the  thorax  is  shut  off  from 
the  abdominal  cavity  in  mammals  by  the  diaphragm  ;  above,  it  is  closed 
by  the  muscles  of  the  neck.  The  lungs  are  suspended  in  a  semi-distended 
state  in  the  cavity  of  the  thorax,  and  with  Uie  heart  and  great  blood- 
vessels completely  fill  it.  Since  the  thorax  forms  an  air-tight  cavity 
there  is  through  the  elasticity  of  the  lungs  a  constant  tendency  to  the 
production  of  a  vacuum  between  the  pleural  surfaces.  This  tendency  to 
contraction,  due  to  the  elastic  fibres  of  the  lungs,  is  of  great  importance 
in  assisting  respiration.  If  an  opening  be  made  into  the  pleural  cavity 
the  atmosphere  at  once  enters,  and  the  lungs  then  through  their  elasticity 
collapse.  Atmospheric  pressure  being  the  same  within  and  without  the 
lungs,  the  resistance  of  the  walls  of  the  thorax  is  the  only  factor  which 
prevents  the  collapse  of  the  thorax  from  the  elasticity  of  the  lungs. 

This  tendency  to  retraction  of  the  thoracic  walls  is  readily  seen  in 
the  intercostal  spaces,  particularly  if  the  outer  muscular  Ia3-ers  be 
removed.  Distinct  depressions  may  then  be  recognized  between  each 
rib,  and  indicate  the  negative  pressure  produced  upon  the  walls  of  the 
thorax  by  the  constant  tendency  to  contraction  of  the  lungs.  This 
negative  pressure  is  likewise  exerted  on  the  upper  and  lower  extremities 
of  the  thorax.  There  is,  therefore,  a  constant  depression  of  the  soft 
tissues  of  the  neck  toward  the  thoracic  cavity,  until  the  increased 
tension  so  produced  results  in  equilibrium.  So,  also,  there  is  a  constant 
tendency  to  the  ascent  of  the  diaphragm  in  the  thoracic  cavity  by  the 
same  means.  In  the  passive  state  of  the  thorax  there  is,  therefore,  a 
constant  equilibrium  produced,  which  results  from  the  balance  between 
this  negative  pressure  exerted  by  the  lungs  and  the  resistance  of  the 
walls  of  the  thorax. 

The  walls  of  the  thorax,  in  so  far  as  they  are  constituted  by  the  ribs 
and  diaphragm,  are  not,  however,  rigid,  but  are  capable  of  undergoing 
change  in  position. 

The  ribs  are  acted  on  by  various  muscles  whose  contraction  results 
in  an  increase  in  the  lateral  and  antero-posterior  diameters  of  the  thorax. 
The  diaphragm  is  also  capable  of  changing  its  position,  but  when  it 
contracts  tends  to  depart  from  its  concave,  dome-like  position,  and 
become  more  horizontal.  The  contraction  of  the  diaphragm,  therefore, 
serves  to  increase  the  vertical  diameter  of  the  thorax. 

As  the  thorax  is  increased  in  its  dimensions  the  lungs  are  compelled 
to  follow  its  movements,  from  the  fkct  that  otherwise  there  would  be  a 
production  of  a  vacuum  in  the  pleural  cavity.  As,  however,  the  lungs 
likewise  become  increased  in  volume,  the  air  in  them  becomes  rarefied, 
and  since  the  air  within  the  lungs  is  in  direct  communication  with  the 
atmosphere  the  air  streams  in  from  without  to  the  interior  of  the  lungs, 


KESPIKATION. 


573 


until  equilibrium  is  produced  (Fig.  246).  On  the  other  hand,  if  the  forces 
which  produce  enlargement  of  the  thorax  cease  to  act,  the  elasticity  of 
the  lungs,  together  with  that  of  the  cartilages  of  the  ribs,  is  now  sufficient 
to  produce  a  return  of  the  thorax  to  its  original  volume.  The  lungs, 
therefore,  now  decrease  in  volume,  and  as  a  consequence  the  air  within 
them  tends  to  become  compressed,  and,  as  a  result,  a  portion  of  the  air 
is  expelled  through  the  air-passages  to  the  external  atmosphere.  The 
expansion  of  the  thorax  constitutes  inspiration ;  the  contraction  of  the 
thorax  constitutes  expiration. 

As  the  tension  of  air  in  the  lungs  becomes  decreased  through 
inspiration,  fresh  air  enters  the  lungs  which  is  less  charged  with  the 
carbon  dioxide  than  that  previously  present  in  the  lungs,  while  it  is  also 


FIG.  246.— DIAGRAMMATIC  REPRESENTATION  OF  THE  RELATIONS  BETWEEN 
THE  LUNGS  AND  THE  THORACIC  CAVITY,  AFTER  FUNKE.    (BeaUHlS.) 

The  bell-jar,  1,  represents  the  thorax ;  the  rubber  membrane,  4,  the  diaphragm  ;  the  membrane,  6,  the 
soft  parts  of  an  intercostal  space  ;  2,  the  trachea,  terminating  in  two  rubber  bulbs  representing  the  lungs ; 
3,  a  manometer  for  measuring  the  pressure  within  the  bell-jar. 

In  the  figure  to  the  left  the  atmospheric  pressure  within  the  bell-jar  is  the  same  as  on  the  outside,  and 
the  mercury  in  the  manometer  stands  at  the  same  level  in  both  arms.  If  the  rubber  membrane,  4,  ia 
drawn  downward  by  the  button,  5,  the  cavity  of  the  bell-jar  is  increased  and  the  atmospheric  pressure 
diminished,  as  shown  by  the  manometer  and  the  depressed  space,  6.  The  negative  pressure  thus  produced 
leads  to  the  entrance  of  air  through  the  tube,  2,  into  the  rubber  bulbs,  which  consequently  expand.  The 
action  of  the  diaphragm  in  producing  inspiration  is  precisely  similar. 

richer  in  oxygen.  By  diffusion,  from  the  inequality  of  these  gaseous 
tensions,  we  have  oxygen  brought  to  the  lowermost  strata  of  air  in  the 
lungs  and  carbon  dioxide  diffusing  from  them,  and  when  the  air  again 
leaves  the  lungs  in  expiration  it  has  been  the  means  of  introducing 
oxygen  into  the  lungs  and  removing  carbon  dioxide  from  them. 

The  amount  of  air  which  ordinarily  enters  the  lungs  in  inspiration 
and  is  dispelled  in  expiration  is  spoken  of  as  the  tidal  volume.  By 
forcible  muscular  contractions  the  capacity  of  the  thorax  may  be  both 
increased  and  decreased  beyond  the  dimensions  present  in  gentle  respi- 
ration. The  amount  of  air  so  drawn  in  by  a  forced  inspiration  is  spoken 
of  as  complemental  air;  that  expelled  from  the  lungs  in  violent  expiration 
is  spoken  of  as  supplemental  air;  while,  even  after  forced  expiration,  a 


574  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

considerable  amount  of  air  remains  in  the  lungs,  and  this  quantity  is 
spoken  of  as  the  residual  volume. 

2.  THE  MECHANICAL  PROCESSES  OF  RESPIRATION. —  The  Mechanism  of 
Inspiration. — Every  increase  in  the  diameters  of  the  thorax  produces,  as 
a  consequence,  for  the  reasons  already  referred  to,  an  expansion  of  the 
lungs ;  hence,  air  enters  the  lungs  from  the  difference  in  atmospheric 
pressures.  Such  a  movement  is  termed  an  inspiration.  It  is  clear  that 
in  the  production  of  inspiration  the  natural  elasticity  of  the  lungs  and 
the  thoracic  walls  must  be  overcome.  Inspiration  is,  therefore,  an  active 
movement  and  requires  the  exertion  of  muscular  force.  The  diameters 
of  the  thorax  may  be  increased  either  through  the  elevation  of  the  ribs 
or  through  the  descent  of  the  diaphragm.  It  is  through  the  latter  that 
in  quiet  respiration  inspiration  is  produced.  The  diaphragm  may,  there- 
fore, be  regarded  as  the  principal  muscle 
of  inspiration.  In  its  condition  of  relax- 
ation the  muscular  fibres  of  the  diaphragm 
together  form  a  curved  surface  whose  con- 
cavity extends  far  up  into  the  thorax. 
When  the  muscular  fibres  of  the  diaphragm 
shorten  they  tend  to  form  a  straight  line 
between  their  origins  and  insertions,  and, 
therefore,  the  diaphragm  in  its  condition 
of  extreme  contraction  tends  to  form  an 
almost  plane  surface  across  the  lower 
P01>tion  of  the  thorax.  The  origins  and 
THE  DIAPHRAGM.  (Xtciard.)  insertions  of  the  muscular  fibres  of  the 

If  A  represent  a  plane  extending  in  expi- 
ration from  the  sternum  to  the  vertebra,  and     diaphragm  may  be  regarded  as  compara- 

D  the  position  of  the  diaphragm,  in  inspiration  J 

^npdeLeendWto1rovet°tt'whilethediaphragm     tively    fixed.       The    central    tendon    is, 

moreover,  but  slightly  movable,  since  it  is 

firmly  connected  with  the  organs  occupying  the  mediastinum  above,  and 
below  is  more  or  less  supported  by  the  liver  and  stomach.  It  is,  there- 
fore, evident  that  the  diaphragm  in  inspiration  cannot  become  completely 
flattened,  since  its  curvature  corresponds  with  that  of  the  curvature  of 
the  abdominal  organs.  When  the  diaphragm,  then,  contracts,  the  curve 
is  slightly  flattened  out,  and  this  muscle  may,  therefore,  be  regarded  as 
acting  as  a  curved  piston  which  descends  in  the  cavity  of  the  thorax,  and 
so  increases  its  long  diameter ;  at  the  moment  in  which  the  diaphragm 
contracts,  the  ribs  in  which  it  is  inserted  anteriorly  are  actively  elevated. 
Thus,  while  the  diaphragm  in  descending  tends  to  lengthen  the  vertical 
diameter  of  the  chest,  the  elevation  of  the  inferior  ribs  would  appear  to 
diminish  this  diameter. 

The  ascent  of  the  lower  ribs  is,  nevertheless,  much  less  extensive 
than  the  descent  of  the  diaphragm.   It  is  further  to  be  noticed  that  every 


RESPIRATION.  575 

ascent  of  the  ribs  produces  an  increase  in  the  antero-posterior  diameter 
of  the  thorax ;  or,  in  other  words,  increases  the  distance  between  the 
sternum  and  vertebral  column.  Therefore,  this  ascent  of  the  ribs,  so 
far  from  diminishing  the  inspiratory  effect  of  the  diaphragm,  tends  even 
to  increase  it.  This  may  be  rendered  clear  by  the  diagram  (Fig.  247). 

At  the  same  time  the  diaphragm  contracts  the  abdominal  organs  are 
pressed  downward,  and  so  cause  a  projection  of  the  abdominal  walls. 

In  forced  inspiration  the  power  exerted  on  the  ribs  through  the  dia- 
phragm is  greater  than  that  which  tends  to  elevate  the  lower  ribs.  This 
is  especially  the  case  when  there  is  any  obstruction  to  the  entrance  of 
air  into  the  lungs.  In  such  cases  there  is  a  distinct  constriction  of  the 
thorax  at  the  points  of  insertion  of  the  fibres  of  the  diaphragm.  This 
reduction  in  the  circumference  of  the  chest  at  these  points  is,  however, 
of  but  slight  importance,  since  the  increase  of  the  thoracic  cavity  by  the 
greater  descent  of  the  diaphragm  more  than  compensates  for  the  decrease 
in  its  circumference.  It  is  probable  that  in  all  circumstances  this  de- 
pression of  the  lower  ribs  would  be  more  marked  in  strong  contraction 
of  the  diaphragm  were  it  not  for  the  fact  that  the  descent  of  the  ab- 
dominal organs  produces  an  increased  tension  in  the  abdominal  walls, 
and,  therefore,  offers  a  certain  resistance  to  the  production  of  this 
constriction. 

Colin  has  estimated  that  in  the  horse  the  diaphragm  in  inspiration 
descends  from  ten  to  twelve  centimeters  in  the  abdominal  cavity,  thus, 
to  this  extent,  increasing  the  long  diameter  of  the  thorax,  while  the 
transverse  diameter  at  the  same  time  increases  from  three  to  four  centi- 
meters. 

The  movements  of  the  ribs  in  producing  inspiration  are  much  more 
complicated.  Each  rib  articulates  by  two  facets  with  a  costal  cavity 
formed  by  the  junction  of  the  ribs  and  two  contiguous  dorsal  vertebrae. 
The  only  movement  possible  in  the  ribs,  therefore,  must  occur  around  a 
line  which  passes  between  these  two  points  of  articulation  ;  or,  in  other 
words,  nearly  coincides  with  the  axis  of  the  neck  of  the  rib.  If  the  ribs 
were  straight  they  would  be  only  able  to  turn  around  on  their  own  axes ; 
since,  however,  the  ribs  are  all  curved  in  different  degrees,  the  turning  of 
the  rib  around  the  axis  of  its  neck  causes  every  point  of  the  rib  to 
describe  an  arc  of  a  circle  (Fig.  248). 

Further,  the  point  of  articulation  of  each  rib  with  the  vertebral 
column  is  on  a  higher  plane  than  its  articulation  with  the  sternum  and 
costal  cartilages,  the  degree  of  inclination  being  greatest  in  the  first  rib, 
least  in  the  second,  and  then  gradually  increasing  until  the  last  rib  forms 
almost  the  same  angle  as  the  first.  From  this  arrangement  it  is  evident 
that  every  elevation  of  the  ribs  will  increase  the  distance  between  the 
sternum  and  the  vertebral  column,  while  the  rotation  of  the  ribs  will 


576 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


increase  the  lateral  diameters  of  the  thorax ;  for,  since  the  ribs  form 
arches,  each  increasing  in  its  radius  from  above  downward,  it  is  evident 
that  when  the  lower  rib  is  so  elevated  as  to  occupy  the  position  pre- 
viously held  by  an  upper  rib  the  lateral  diameter  of  the  thorax  at 
that  point  will  be  greater  than  before.  Still  further,  the  articulations  of 
the  ribs  with  the  sternum  are  more  or  less  fixed,  and  the  resistance, 
therefore,  which  these  articulations  offer  to  the  movement  of  the  ribs 


FIG.  248.— THE  ACTION  OF  THE  RIBS  OF  MAN  IN  INSPIRATION.    (Btclard.) 

The  shaded  parts  represent  the  positions  of  the  ribs  in  repose.  The  line  A  B  represents  a  horizontal 
plane  passing  through  the  sternal  extremity  of  the  seventh  rib  ;  the  line  C  D  represents  a  horizontal  plane 
touching  the  superior  extremity  of  the  sternum ;  the  line  H  G  indicates  the  linear  direction  of  the  sternum. 
When  the  ribs  are  elevated,  as  indicated  by  the  dotted  lines,  the  line  A  B  becomes  the  plane  a  b,  the  line  C  D 
the  line  c  d,  and  the  line  H  G  becomes  the  line  h  g,  the  projection  of  the  sternum  being  the  more  marked 
inferiorly.  The  distance  which  separates  the  line  M  N  from  the  line  m  n  measures  the  increase  in  the 
antero-posterior  diameter  of  the  thorax. 

will  in  the  elevation  of  the  ribs  tend  to  open  out  the  angles  between  the 
ribs  and  their  cartilages. 

By  the  elevation,  consequently,  of  the  ribs,  the  diameters  of  the 
thorax  are  increased  both  laterally  and  in  an  antero-posterior  direction. 
Hence,  everything  that  tends  to  elevate  the  ribs  will  produce  an  inspira- 
tory  movement;  everything  which  depresses  the  ribs  will  produce  an 
expiration.  All  muscles,  therefore,  which  in  any  way  may  produce 
elevations  of  the  ribs  are  inspiratory  muscles. 


EESPIKATION. 


577 


The  most  important  muscles  of  inspiration,  which  act  by  elevating 
the  ribs,  are  the  levatores  costarum.  These  are  small  muscles  which 
rise  from  the  upper  sides  of  the  cervical  and  dorsal  vertebrae,  and  are 
inserted  in  the  posterior  surfaces  of  the  ribs.  Although  these  are  small 
muscles,  they  are  inserted  near  to  the  axis  of  rotation  of  the  ribs,  and, 
consequently,  but  a  slight  degree  of  contraction,  the  lever  being  so  long, 
will  produce  considerable  elevation  of  the  anterior  extremity  of  the  ribs. 
At  the  anterior  extremity  of  the  upper  two  ribs  are  inserted  the  scalene 
muscles,  wrhich  rise  from  the  cervical  vertebra,  and  which  in  their  con- 

i 

_o k  f 


FIG.  249.— SCHEME  OF  ACTION  OF  THE  INTERCOSTAL  MUSCLES.    (Lantlois.) 

I.  When  the  rods  a  and  ft,  which  represent  the  ribs,  are  raised  the  intercostal  space  mnst  be  widened 
(«/><"0-    On  the  opposite  side,  when  the  rods  are  raised,  the  line  a  h  is  shortened  (/  A-<</  h,  the  direc- 
tion of  the  external  intercostals)  ;  I  m  is  lengthened  (lm<.on,  the  direction  of  the  internal  intercostals,'. 

II.  When  the  ribs  are  raised  the  intercartilaginei,  indicated  by  g  h,  and  the  external  intercostals,  in- 
dicated by  I  k,  are  shortened.   When  the  ribs  are  raised  the  position  of  the  muscular  fibres  is  indicated  by 
the  diagonals  of  the  rhombs  becoming  shorter. 

traction  serve  to  elevate  the  first  ribs,  and  so  also  tend  to  elevate  the 
entire  thoracic  wall. 

Between  the  ribs  are  found  the  intercostal  muscles,  which  form  two 
layers,  the  external  and  internal.  The  external  intercostal  muscles  are 
attached  to  the  adjacent  margins  of  each  pair  of  ribs,  and  extend  from 
the  tubercles  of  the  ribs,  behind,  to  the  commencement  of  the  cartilages 
of  the  ribs,  in  front,  where  they  terminate  into  a  thin,  membranous  aponeu- 
rosis,  which  is  continued  forward  to  the  sternum.  They  arise  from  the 
outer  lip  of  the  groove  on  the  lower  border  of  each  rib,  and  are  inserted 
into  the  upper  border  of  the  rib  below.  Their  fibres  are  directed  obliquely 

37 


578  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

downward  and  forward  (Fig.  249).  When  the  external  intercostal 
muscles,  therefore,  shorten,  they  tend,  of  course,  to  approximate  their 
origins  and  insertions,  and  so  bring  the  ribs  into  a  position  in  which 
the  distance  between  their  point  of  origin  and  insertion  will  be  the 
shortest  possible.  This  condition  is,  of  course,  fulfilled  when  the  ribs 
are  horizontal;  therefore,  the  contraction  of  the  external  intercostal 
muscles  serves  to  elevate  the  ribs,  and  these  muscles  are,  therefore,  to 
that  extent  inspiratory. 

In  quiet  inspiration  the  cavity  of  the  thorax  is  increased  by  the 
contractions  of  the  scalene  muscles,  the  levatores  costarnm,  and  external 
intercostal  muscles,  which  all  serve  to  elevate  the  ribs.  The  diaphragm 
also,  by  its  contraction,  is  perhaps  the  most  important  inspiratory 
muscle. 

If  the  head  be  fixed,  the  sterno-mastoid  muscle,  by  its  contraction, 
serves  to  elevate  the  sternum,  and,  as  a  consequence,  elevates  all  the 
ribs.  It,  therefore,  may  be  regarded  as  an  accessory  muscle  of  inspiration, 
which  is,  however,  only  employed  in  forced  inspiration.  If  the  scapula 
be  fixed,  the  pectoralis  minor  muscle,  which  rises  from  the  coracoid 
process  of  this  bone  to  be  inserted  into  the  anterior  extremities  of  the 
upper  ribs,  will  by  its  contraction  also  serve  to  elevate  the  ribs ;  so, 
also,  the  seratus  posticus  superior  muscle  may  also,  in  forced  inspiration, 
serve  to  elevate  the  ribs,  and  so  act  as  an  auxiliary  muscle  of  inspiration. 

The  Mechanism  of  Expiration. — In  the  production  of  the  enlarge- 
ment of  the  chest,  such  as  is  essential  to  the  accomplishment  of  inspira- 
tion, it  has  been  mentioned  that  the  elasticity  of  the  lungs  and  thoracic 
walls  has  to  be  overcome  by  exertion  of  muscular  force  ;  when  the 
inspiratory  muscles  relax,  the  elasticity  of  the  lungs  and  thorax  is  alone 
sufficient  to  cause  the  lungs  to  return  to  their  original  volume.  This 
contraction  of  the  lungs,  of  course,  occasions  the  expulsion  of  a  quantity 
of  air  from  their  interior,  and  expiration  is  therefore  produced.  It  is 
thus  seen  that  expiration  is  mainly  a  passive  movement,  due  to  the 
reaction  of  the  forces  which  have  to  be  overcome  in  the  production 
of  inspiration. 

It  has  been  stated  that  when  the  diaphragm  descends  in  inspiration, 
by  forcing  the  abdominal  contents  downward  the  abdominal  walls  are 
put  upon  the  stretch ;  when  the  diaphragm  relaxes  the  abdominal  walls 
tend  to  regain  their  original  position,  the  abdominal  organs  are  forced 
upward  into  the  thoracic  cavity,  and  the  borders  of  the  ribs,  which  had 
been  slightly  elevated,  are  now  depressed.  It  is  probable  that  the 
elasticity  of  these  different  organs  is  in  quiet  expiration  entirely 
sufficient  to  balance  the  displacement  produced  in  quiet  inspiration. 
The  thorax  may,  nevertheless,  be  also  reduced  in  volume  to  a  greater 
degree  than  is  possible  by  the  means  already  described.  The  muscles 


RESPIRATION. 


579 


which  by  their  contraction  lead  to  a  decrease  in  the  thoracic  capacity, 
and  which  thus  act  as  muscles  of  expiration,  are  mainly  the  muscles  of 
the  abdomen.  When  the  abdominal  muscles  contract,  they  not  only 
serve  to  still  further  force  the  abdominal  organs  up  into  the  thoracic 
cavity,  and  thus  lessen  its  vertical  diameter,  but  they  further  serve  to 
pull  down  the  sternum  and  the  middle  and  lower  ribs.  By  so  doing  they 
lessen  the  antero-posterior  and  transverse  diameters  of  the  thorax.  The 
internal  intercostal  muscles  also  probably  assist  in  producing  expiration 
by  depressing  the  ribs.  When  expiration  becomes  extremely  violent  all 
the  muscles  are  brought  into  play,  which,  through  their  contraction,  may 
either  depress  the  ribs,  press  on  the  abdominal  viscera,  or  offer  fixed 
support  to  muscles  having  those  actions. 

The  movements  of  the  thorax  in  respiration  are  accompanied  by 
movements  of  the  nostrils  and  glottis. 

In  inspiration  the  current  of  air  enters  through  the  nostrils,  and  not 
by  the  mouth,  and  by  exposure  to  the  vascular  mucous  membrane  of  the 


FIG.  250.— THE  HUMAN  GLOTTIS  IN  A 
GENTLE  INSPIRATION,  AFTER  MANDL. 
(Beaunis.) 

I,  tongue ;  e,  epiglottis  ;  pe,  pharyngc-epiglottic  fold ; 
o«,  aryteno-epiglottic  fold :  ph,  posterior  wall  of  the 
pharynx ;  c,  cartilage  of  Wnsberg ;  th,  superior  thyro- 
arytenoid  fold ;  ti,  inferior  fold ;  o,  glottis. 


FIG.  251.— THE  HUMAN  GLOTTIS  IN  A 
FORCED  INSPIRATION,  AFTER  MANDL. 
(Beaunis.) 

b,  tip  of  the  epiglottis ;  g,  pharyngo-laryngeal  pouch ; 
I,  tongue;  rap,  aryteno-epiglottie  fold;  or,  arytenoid 
cartilage;  c,  cuneiform  cartilage;  tr,  interarytenoid 
fold ;  rs,  false  vocal  cords ;  ri,  true  vocal  cords. 


nasal  passages  becomes  warmed  up  to  the  temperature  of  the  body.  At 
each  inspiration  the  external  nares  expand  by  the  contraction  of  their 
dilator  muscles ;  this  movement  is  especially  marked  in  labored  breathing. 
The  horse  is  incapable  of  breathing  through  the  mouth,  and  if  the  dila- 
tors of  the  nostrils  be  paralyzed,  as  by  section  of  the  facial  nerve, 
asphyxia  may  be  produced.  In  expiration,  the  elasticity  of  the  carti- 
lages of  the  nostrils  is  sufficient  to  cause  these  parts  to  return  to  their 
usual  position.  The  current  of  air  entering  through  the  nose  passes 
over  the  passive  soft  palate  to  enter  the  larynx,  after  passing  through 
the  pharynx.  At  each  inspiration  the  vocal  cords  are  separated  and  the 
glottis  is  thus  widely  opened  (Figs.  250  and  251).  At  each  expiration 
the  arytenoid  cartilages  approach  each  other,  so  approximating  the  vocal 
cords,  and  the  glottis  is  thus  narrowed. 

3.  THE  RHYTHM  OF  RESPIRATION. — The  movements  of  the  column  of 


580 


PHYSIOLOGY  OF   THE   DOMESTIC  ANIMALS. 


RESPIRATION. 


581 


air  in  respiration  in  the  smaller  mammals  may  be  recorded  by  connecting 
the  trachea  by  means  of  a  tube  with  Marey's  tambour: — 

This  instrument  consists  of  a  cylindrical  box,  the  upper  surface  of  which  is 
formed  by  a  sheet  of  rubber  membrane,  the  interior  being  connected  by  tubing 
with  the  trachea,  and  a  lever  so  adjusted  to  the  rubber  membrane  as  to  record. 
its  movements  (Fig.  252).  If  air  is  forced  into  this  box  it  will,  of  course,  produce 
bulging  of  the  rubber  membrane,  and  thus  cause  the  ascent  of  the  lever,  while, 
on  the  other  hand,  if  the  air  be  rarefied  in  the  interior  of  the  box  the  membrane 
will  be  depressed  and  the  lever  descend.  By  allowing  such  a  lever  to  record  its 
movements  on  some  revolving  surface,  as,  for  example,  on  the  smoked  paper 
of  a  kyinographion,  if  the  interior  of  the  box  be  connected  with  the  trachea  of  an 
animal,  namely,  in  the  dog  or  rabbit,  a  curve  somewhat  similar  to  the  following 
will  be  produced  (Fig.  253). 

The  descents  in  this  curve  represent  the  inspirations,  the  ascents  the 
expirations.  It  is  seen  that  the  curve  of  inspiration  begins  suddenly 
and  advances  rapidly,  and  is  then  succeeded  by  an  expiratory  movement, 
which  at  first  is  more  rapid  than  inspiration,  but  gradually  becomes 
slower.  No  pause  is  present  between  the  end  of  inspiration  and  the 
beginning  of  expiration,  but  a  short  pause  is  noted  at  the  end  of  expi- 


FIG.  253.— TRACING  OF  THORACIC  RESPIRATORY  MOVEMENTS.    (Foster.) 

(To  be  read  from  left  to  right.) 

A  whole  respiratory  phase  is  comprised  between  a  and  a,  inspiration  extending  from  a  to  b,  and  ex- 
piration from  b  to  a.    The  undulations  at  c  are  caused  by  the  heart's  beats. 

ration,  the  undulations  in  the  curve  at  this  point  being  caused  by  the 
heart's  beats. 

The  duration  of  inspiration  is,  as  a  rule,  shorter  than  expiration,  the 
proportion  being  from  ten  to  fourteen,  although  this  is  not  invariable. 
The  pause  which  is  noted  at  the  end  of  expiration  will  average  in  dura- 
tion about  one-fifth  to  one-third  the  time  occupied  by  the  entire  respira- 
tory movement. 

The  number  of  respirations  in  most  animals  may  be  placed,  as  a 
rule,  as  one  respiratory  movement  to  four  pulsations  of  the  heart.  Ex- 
ercise and  a  large  number  of  other  conditions  will  greatly  increase  the 
number  of  respiratory  movements  by  increasing  the  amount  of  tissue 
change,  and,  therefore,  increasing  the  amount  of  carbon  dioxide  in  the 
blood  which  has  to  be  eliminated  in  respiration. 

In  cattle  the  rate  of  respiration  is  higher  in  cows  than  in  bulls  or 
steers.  During  sleep  the  average  rate  in  the  cow  is  twenty-two  in  the 


582 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


minute  ;  during  rumination  it  varies  from  twenty-four  to  thirty -six,  the 
position  appearing  to  be  without  influence.  In  bulls  and  oxen  the  rate 
of  respiration  averages  twenty  in  the  minute.  The  frequent  eructation 
of  gas  and  pauses  caused  by  rumination  render  the  rhythm  of  respiration 
more  irregular  in  ruminant  than  in  other  mammals. 

In  the  horse  the  normal  respiratory  movements  ma}r  be  placed  at 
about  ten  in  a  minute ;  after  only  the  slight  exercise  of  walking  two 
hundred  yards,  respiration  in  the  horse  may  be  increased  to  twenty -eight 


FIG.  254.— GRAPHIC  REPRESENTATION  OF  THE  RESPIRATORY  MOVEMENTS  OF 
A  HORSE  WHILE  AT  REST  AND  AFTER  MOVEMENT.     (Thanhoffer.) 

1,  standing  at  rest ;  3,  after  a  few  minutes'  walk  :  7-8.  after  trotting ;  9,  after  a  short  rest :  11.  after 
several  minutes'  trotting  and  running ;  17,  after  a  short  rest  from  the  trot  and  run  ;  51,  curve  at  the  end  of 
the  experiment.  I  =  inspiration ;  E  =  expiration  ;  i  =  time  in  seconds. 

in  the  minute,  while  after  trotting  five  minutes  the  respirations  were 
found  by  Colin  to  be  fifty-two  to  the  minute,  falling  to  forty  in  the  fol- 
lowing three  minutes,  and  were  fifty-two,  likewise,  in  a  minute  after  five 
minutes'  gallop  (Fig.  254). 

In  all  animals  similar  facts  may  be  noticed.  Thus,  in  the  sheep  the 
normal  rate  of  respiration  is  fifteen  in  the  minute,  and  after  running  may 
be  raised  to  one  hundred  or  one  hundred  and  forty  in  the  minute ;  or 


RESPIRATION. 


583 


even  when  frightened  be  raised  from  fourteen  to  forty-five,  thus  showing 
the  effect  of  mental  impressions.    So,  also,  the  lion  has  a  normal  respira- 


FIG.  255.— GRAPHIC  REPRESENTATION  OP  THE  RATES  OF  RESPIRATION  IN  DIF- 
FERENT ANIMALS.    (Thanhoffer.) 

1,  fish;  2,  tortoise:- 3,  adder  (in  winterl :  4,  boa-constrictor  (in  summer);  5,  frog:  6,  alligator;  7, 
lizard;  8,  canary-bird  ;  9,  adult  dog;  10,  rabbit :  11,  man;  12,  dog;  13,  horse.  I  =  inspiration :  E  =  ex- 
piration; m/  =  deep,  n/=  superficial  respiration;  A  =  abscissse;  Coordinates. 

tory  rate  of  twelve  to  fourteen  movements  in  the  minute,  and  when 
excited  has  been  found  to  breathe  seventy  times  a  minute.     In  insects 


584 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


the  rate  of  respiration  is  very  much  more  rapid,  being  one  hundred  and 
sixty  in  the  beetle,  and  in  some  other  insects  as  high  as  two  hundred 
and  forty. 

The  following  table,  which  is  taken  from  that  compiled  by  Paul  Bert, 
represents  the  number  of  respiratory  movements  in  different  animals  : — 


Tiger, 

Lion, 

Cat, 

Dog, 

Ox, 

Rabbit, 


Rat, 


Rhinoceros,    . 
Hippopotamus, 

Horse,    . 
Condor, 
Pigeon, 
Canary, 


6  in  the  minute. 
10     " 
24     " 
15     " 
15-18     " 
55     " 
C  100  asleep. 
<  210  awake. 
(  320  excited. 

6  in  the  minute, 
f    1  in  the  water. 
(  10  out  of  water. 
10-12  in  the  minute. 
6     " 
30     " 
18     " 


The  rate  of  respiration  varies  also  according  to  the  age  of  different 
animals.     This  is  shown  in  the  following  tables  : — 


Newborn  infant, 

5  years, 

15  to  20, 

20  to  25, 

25  to  30, 

30  to  50, 

In  the  foal, 
Adult  horse. 
Young  ox,    . 
Adult  ox,     . 
Lamb, 
Sheep, 
Puppy, 
Dog,    . 


44  per  minute. 

26 

20 

18.7 

16 

18.1 


10  to  12 

9  to  20 

18  to  20 

15  to  18 

16  to  17 
13  to  16 
18  to  20 
15  to  18 


It  is  thus  seen  that  young  animals,  as  a  rule,  respire  more  frequently 
in  the  minute  than  adult  animals  ;  so,  also,  small  animals  breathe  faster 
than  large  animals.  Thus,  the  giraffe,  camel,  horse,  rhinoceros,  and 
hippopotamus  breathe  about  ten  times  in  the  minute;  the  llama  and 
deer,  sixteen  to  twenty  times  a  minute  ;  the  whale,  four  to  five  times  a 
minute ;  the  guinea-pig,  thirty-five  times  a  minute ;  the  larger  birds, 
twenty  to  thirty  times,  and  the  smaller  birds,  thirty  to  fifty  times  a 
minute. 

As  already  described,  the  respiratory  movements  may  vary  in 
intensity.  In  other  words,  inspiration  and  expiration  may  be  either 
shallow  or  deep.  It  is  self-evident  that  the  quantity  of  air  taken  in  in 
a  deep  inspiration  and  expelled  from  the  lungs  in  forced  expiration 


KESPIKATION.  585 

will  be  greater  than  the  volume  of  air  displaced  in  gentle  respiration ; 
and,  of  course,  the  deeper  the  inspiration  or  the  more  forced  the  expira- 
tion the  more  air  will  be  displaced.  There  is  a  limit  present  in  both 
cases  beyond  which  the  quantitj^  of  inspired  and  expired  air  cannot  be 
increased.  In  the  case  of  the  domestic  animals  it  has  not  as  yet  been 
established  what  is  the  average  quantity  of  air  displaced  in  respiration, 
but  that  it  depends  upon  the  size  of  the  animal  and  the  size  and  mode 
of  structure  of  the  thorax  is  self-evident.  From  the  few  experiments 
which  have  been  made  on  this  subject  it  may  be  assumed  that  in  a  quiet 
respiration  about  one-sixth  of  the  total  quantity  of  air  capable  of  being 
contained  within  the  lungs  is  displaced.  It  would  follow  from  this  that 
every  six  or  seven  respiratory  movements  would  serve  to  completely 
renew  the  air  within  the  lungs.  In  man,  the  volume  of  air  changed  in 
different  respiratory  movements  has  been  subjected  to  close  study.  It 
was  found  that  in  an  ordinary  respiratory  effort  about  thirty  cubic  inches 
of  air  enter  the  lungs.  With  this  accepted  as  a  fact,  and  placing  the 
average  number  of  respiratory  movements  at  twenty  in  a  minute,  the 
whole  amount  of  air  passing  through  the  lungs  in  a  minute  will  amount 
to  six  hundred  cubic  inches ;  in  an  hour,  to  thirty-six  thousand  cubic 
inches;  and  in  a  day,  to  eight  hundred  and  sixty-four  thousand  cubic 
inches,  or  five  hundred  cubic  feet.  Extending  these  periods,  one 
hundred  and  eight}^-two  thousand  five  hundred  cubic  feet  of  air  may  be 
estimated  to  pass  through  the  lungs  of  an  adult  man  in  a  year,  and  to 
produce  this  displacement  nine  million  respiratory  movements  are 
required.  This  quantity  of  air  is  employed  in  the  aeration  of  about 
three  thousand  five  hundred  tons  of  blood  sent  out  by  the  heart  to  the 
lungs  in  the  same  period.  With  these  facts  before  us,  we  may  obtain 
valuable  suggestions  upon  the  subject  of  ventilation.  Though  about 
five  hundred  cubic  feet  of  air  passes  through  the  lungs  in  twenty-four 
hours,  yet  this  amount  of  atmosphere  is  insufficient  to  sustain  life  for 
that  period,  for  after  the  introduction  of  carbon  dioxide  into  the  air 
the  liberation  of  gases  in  the  lungs  is  to  a  certain  degree  rendered  more 
difficult.  There  must  be  at  least  five  hundred  cubic  feet  of  pure  air  sup- 
plied, and  it  has  been  found  that  to  attain  this  at  least  eight  hundred 
cubic  feet  of  air  should  be  provided  for  each  individual. 

The  amount  of  air  taken  into  the  lungs  at  each  gentle  inspiration 
and  displaced  by  the  reverse  movement  constitutes  the  so-called  pressure 
or  tidal  volume,  and  has  been  placed  at  about  thirty  cubic  inches  in  man. 
At  the  end  of  every  gentle  inspiratory  effort  the  lungs  may  be  capable  of 
still  further  inflation,  and  the  additional  quantity  of  air  so  inspired 
amounts  to  about  one  hundred  and  ten  cubic  inches  (complemental 
volume).  At  the  end  of  every  gentle  expiratory  effort  the  lungs  may  be 
still  further  compressed ;  the  amount  of  air  so  displaced  by  this 


586 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


additional  effort  is  termed  the  reserve  volume,  and  also  amounts  to  about 
one  hundred  and  ten  cubic  inches.  After  a  forced  expiration  there  is 
still  a  certain  amount  of  air  which  cannot  possibly  be  forced  out  of  the 
lungs ;  this  constitutes  what  is  termed  the  residual  volume,  and  also 
equals  about  one  hundred  and  ten  cubic  inches. 

The  vital  capacity  volume  is  the  amount  of  air  which  man  is 
capable  of  expiring  by  the  greatest  expiratory  effort  after  the  greatest 
inspiratory  effort.  It  includes  the  complemental  volume,  the  breathing 
volume,  and  the  reserve  volume,  and  is,  therefore,  the  amount  of  air 
which  may  be  displaced  in  respiration.  It  has  been  shown  by  Dr. 
Hutchinson  that  this  volume  bears  a  relation  to  the  height  of  the 
individual,  which  is  especially  remarkable  when  we  recollect  that  the 
height  of  individuals  depends  upon  the  length  of  the  legs,  and  not  upon 
the  trunk,  the  same  persons  who  may  vary  greatly  in  height  while 
standing  exhibiting  but  slight  difference  in  height  when  sitting.  It  is 
curious,  also,  to  observe  that  the  vital  capacity  does  not  depend  upon 
the  capacity  of  the  chest  so  much  as  upon  the  degree  of  mobility.  Thus, 
a  man  of  greater  girth  may  have  less  amount  of  vital  capacity  than 
another  with  less  girth  but  greater  mobility  of  the  walls  of  the  chest. 
Mr.  Hutchinson  has  constructed  an  instrument  for  measuring  this  vital 
capacity  volume.  It  consists  of  a  bell-jar  so  mounted  as  to  be  readily 
displaced  by  the  power  which  is  exerted  by  the  air  in  passing  from  the 
mouth  and  air-passages.  With  the  interior  of  the  bell-jar  communicates 
a  tube  and  attached  mouth-piece.  The  person  to  be  experimented  upon 
takes  a  deep  inspiration,  and  then  breathes  out  by  the  tube  by  a  forced 
expiration,  which  causes  the  bell-jar  to  rise,  and  the  number  of  cubic 
inches  thrown  out  is  measured  by  a  graduated  scale,  suitably  placed  to 
indicate  the  rise  and  fall  of  the  bell-jar.  As  a  result  of  these  experi- 
ments it  was  found  that  every  inch  added  to  the  height  of  an  individual 
increases  about  eight  cubic  inches  the  vital  capacity.  This  appears  upon 
examination  of  the  following  table  : — 


Height.                                                           Vital  Capacity. 

5  feet  0  inches  to  5  feet  1  inch,   . 

174  cubic  inches. 

5 

1  inch 

5 

2  inches, 

182 

5 

2  inches 

5 

3 

190 

5 

3 

5 

4 

198 

5 

4 

5 

5 

206 

5 

5 

5 

6 

214 

5 

6 

5 

7 

222 

5 

7 

5 

8 

230 

5 

8 

5 

9 

238 

5 

9 

5 

10 

246 

5 

10 

5 

11 

254 

5 

11 

5 

12 

262 

The  age  has  a  marked  effect  upon  the  vital  capacity  volume ;  the 
volume  increases  from  15  to  30,  remains  about  stationary  from  40  to  45, 


KESPIEATION.  587 

and  above  this  age  diminishes.  In  females  it  is  about  half  that  of  males, 
although  it  may  amount  to  almost  as  much.  Weight  also  exerts  a  great 
influence.  It  has  been  shown  that  there  is  an  average  weight  to  every 
average  height.  If  the  weight  increase  above  this  amount  by  7  per 
cent.,  the  vital  capacity  decreases  one  cubic  inch  for  every  pound  for 
the  next  thirty-five  pounds  above  this  weight.  For  every  pound  thus 
gained,  an  inch  of  vital  capacity  volume  is  lost  for  the  next  thirty-five 
pounds. 

4.  THE  CHEMICAL  PHENOMENA  IN  RESPIRATION. — The  phenomena  in 
respiration  so  far  studied  have  been  purely  mechanical  in  nature,  and 
have  had  for  their  object  simply  the  introduction  of  air  into  the  lungs 
for  oxidizing  the  blood,  and  for  expelling  air  from  the  lungs  after  its 
object  has  been  served. 

We  have  now  to  study  the  chemical  changes  which  occur  in  respira- 
tion. We  find  that  these  are  of  two  kinds, — the  respiratory  changes 
occurring  in  the  air  in  the  lungs  and  the  respiratory  changes  occurring 
in  the  blood. 

The  atmosphere  consists  of  a  mechanical  mixture  of  oxygen  and 
nitrogen  in  the  proportion  of  about  twenty-one  of  the  former  to  seventy- 
nine  of  the  latter.  Watery  vapor  is  usually  present  in  small  but  variable 
amount,  while  carbon  dioxide  is  present  in  extremely  small  quantity, 
varying  from  about  0.03  to  0.05  per  cent.  During  inspiration  a  certain 
quantity  of  this  gaseous  mixture,  in  man  about  thirty  cubic  inches  in 
amount,  is  drawn  into  the  trachea  and  upper  air-passages.  These  air- 
passages,  as  well  as  the  more  deeply  located  portions  of  the  lungs,  are 
already  occupied  by  a  gaseous  mixture,  in  which  these  gases  are  present 
in  different  proportions.  It  has  been  found  that  expiration  immediately 
follows  inspiration  without  any  pause,  and  a  certain  amount  of  this 
inspired  air  is,  consequently,  at  once  again  expelled.  It  has  been  calcu- 
lated that  about  two-thirds  which  remain  after  expiration  at  once 
commences  to  mix  by  diffusion  with  the  air  already  in  the  lungs.  It  has 
been  found  that  when  gases  are  placed  in  contact  with  each  other  at  the 
same  temperature  and  pressure  they  mix  rapidly,  until  the  one  gas  is 
uniformly  diffused  throughout  the  other.  It  has  been  stated  in  a 
previous  section  that  this  diffusion  is  independent  of  gravity,  but  is 
inversely  as  the  square  root  of  the  densities  of  the  gases.  Mixtures  of 
gases  behave  precisely  like  single  gases,  and  diffusion  will  take  place 
from  one  gas  into  another,  precisely  as  if  into  a  vacuum. 

It  has  been  stated  that  the  object  of  respiration  was  to  supply 
oxygen  to  the  blood  and  to  remove  carbon  dioxide  from  it.  Without 
discussing,  at  present,  the  process  by  which  this  change  takes  place,  it  is 
evident  that  if  this  be  a  fact  the  air  in  the  deepest  portions  of  the  lungs 
will  have  lost  oxygen  to  the  blood  and  will  have  taken  up  carbon  dioxide- 


588  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

The  air  in  the  air  cells  will,  therefore,  be  richer  in  carbon  dioxide  and 
poorer  in  oxygen  than  fresh  air  taken  in  in  inspiration  ;  as  a  consequence^ 
we  have  the  phenomena  of  diffusion  at  once  taking  place,  the  oxygen  of 
the  inspired  air  diffusing  down  into  the  deepest  portions  of  the  lungs, 
while  the  carbon  dioxide  diffuses  up  from  the  air-cells  into  the  atmos- 
phere through  the  larger  bronchi  and  trachea.  As  the  air  penetrates, 
therefore,  by  diffusion  deeper  and  deeper  in  the  bronchial  tubes  it  loses 
oxygen  and  receives  more  and  more  carbon  dioxide,  but  the  rate  of 
diffusion  is  not  interfered  with :  for  in  the  deeper  portions  of  the  lungs 
the  descending  atmosphere  is  meeting  with  an  increasing  tension  of 
carbon  dioxide  and  a  decreasing  oxygen  tension,  so  that,  although  the 
atmosphere  now  is  poorer  in  oxygen  than  the  external  air,  it  is  yet  richer 
than  the  air  in  the  air-cells,  and  diffusion,  therefore,  continues.  This 
difference  in  tensions  remains  constant,  for  we  have  continually  fresh  air 
taken  in  in  inspiration,  and  just  as  continually  the  removal  of  the  oxygen 
from  the  air  in  the  lower  portions  of  the  lungs  and  the  addition  to  it  of 
carbon  dioxide. 

The  changes  which  the  air  undergoes  in  respiration  may  be  recog- 
nized by  a  comparison  of  the  composition  and  the  physical  character- 
istics of  the  expelled  air  as  contrasted  with  the  inspired  air. 

The  temperature  of  the  expelled  air  is,  as  a  rule,  higher  than  that  of 
the  inspired  air,  from  the  fact  that  the  temperature  of  the  body  is  almost 
invariably  higher  than  that  of  the  surrounding  medium.  The  expired 
air  is,  as  a  rule,  saturated  with  watery  vapor,  the  water  coming  directly 
from  the  blood  and  the  mucous  membrane,  the  quantity  being  estimated 
in  man  as  about  one  and  one-half  pounds.  The  watery  vapor  of  the 
expired  air  becomes  readily  perceptible  through  its  condensation  in  cold 
weather. 

Expired  air  contains,  further,  numerous  organic  substances  derived 
from  the  blood,  resulting  partly  from  the  decomposition  of  the  materials 
entering  into  the  composition  of  the  tissues,  and  partly  from  matters 
taken  into  the  blood  from  without  by  absorption.  Thus,  various  drugsy 
such  as  turpentine,  are  excreted  by  the  pulmonary  mucous  membrane, 
readily  revealing  this  in  the  odor  of  the  expired  air.  Ammonia,  also,  is 
contained  in  small  amount  in  the  air  leaving  the  lungs,  the  amount  given 
off  in  ordinary  respiration  in  twenty-four  hours  being  calculated  at  0.014 
per  cent.  The  presence  of  organic  matter  in  the  expired  air  may  be 
readily  proved  by  breathing  into  a  vessel,  stopping  it  tightly,  and  allowing 
it  to  stand  a  short  time  ;  the  odor  of  putrefaction  will  develop  itself,  and  it 
is,  without  doubt,  to  these  organic  substances  in  the  inspired  air  that  the 
odor  of  the  breath  is  due.  It  has  been  estimated  that  in  man  about  three 
and  one-half  grains  of  organic  matter  are  so  removed  in  the  twenty-four 
hours  in  expired  air.  Many  of  these  substances  which  are  organic  in 


RESPIRATION.  589 

nature,  and  find  their  way  into  the  expired  air,  are  probably  of  a  poisonous 
nature.  For  it  has  been  found  that  expired  air  is  much  more  poisonous 
to  animal  life  than  air  which  has  not  passed  through  the  lungs  of  an 
animal,  but  which  contains  the  same  amount  of  carbon  dioxide  and  the 
same  degree  of  decrease  of  oxygen.  It  is,  therefore,  probable  that  these 
organic  substances  which  are  removed  from  the  lungs  are  poisonous, 
rather  than  the  carbon  dioxide  which  accompanies  them. 

The  air  which  passes  through  the  lungs  actually  decreases  in  volume 
about  one-fortieth  or  one-fiftieth  of  the  amount  taken  in  in  inspiration, 
this  falling  off  being  probably  due  to  the  fact  that  all  the  oxygen  inspired 
does  not  reappear  as  carbon  dioxide,  but  enters  into  other  compositions 
in  the  body. 

The  most  striking  contrast  between  expired  and  inspired  air  is  in 
the  relative  proportions  of  oxygen  and  carbon  dioxide,  while  the  nitrogen 
undergoes  but  little  change.  The  following  represents  this  change: — 

Oxygen.    Nitrogen.  Carbon  Dioxide. 

Inspired  air  contains      .  .    20.81          79.15  .04 

Expired    "  .        .        .16.033        79.557          4.380 

The  expired  air,  therefore,  contains  from  4  to  5  per  cent,  less 
oxygen  and  4  to  5  per  cent,  more  carbon  dioxide  than  the  inspired 
air.  Taking  thirty  cubic  inches  as  the  amount  of  air  taken  in  in  each 
inspiration  in  man,  this  will  represent  about  one  and  one-half  cubic 
inches  of  oxygen.  Supposing  five  hundred  cubic  feet  to  be  taken  in  per 
diem,  the  oxygen  absorbed  would  amount  to  twenty-three  cubic  feet,  or 
one  and  one-third  pounds,  avoirdupois,  oxygen.  The  amount  of  oxygen 
varies  according  to  different  circumstances. 

The  following  conclusions  give  at  a  glance  some  principal  sources 
of  variations.  They  will  be  studied  more  in  detail  under  the  subject  of 
Nutrition : — 

A  man  in  repose  and  fasting,  with  an  external  temperature  of  90°  F., 
consumes  1465  cubic  inches  of  oxj^gen  per  hour. 

A  man  in  repose,  fasting,  with  an  external  temperature  of  59°  F., 
consumes  1627  cubic  inches  of  oxygen  per  hour. 

A  man  during  digestion  consumes  2300  cubic  inches  of  oxygen  per 
hour. 

A  man,  fasting,  while  he  accomplishes  the  labor  necessary  to  raise  in 
fifteen  minutes  a  weight  of  seven  thousand  three  hundred  and  forty-three 
kilos  to  the  height  of  six  hundred  and  fifty-six  feet,  consumes  3814 
cubic  inches  of  oxygen  per  hour. 

A  man,  during  digestion,  accomplishing  the  labor  necessary  to  raise 
in  fifteen  minutes  a  weight  of  seven  thousand  three  hundred  and  forty- 
three  kilos  to  the  height  of  seven  hundred  feet,  consumes  5568  cubic 
inches  of  oxygen  per  hour. 


590  PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 

As  already  mentioned,  the  quantity  of  oxygen  taken  in  at  each 
inspiration  does  not  all  appear  as  carbonic  acid ;  a  certain  quantity  of 
the  oxygen  disappears,  varying  with  the  nature  of  the  food 

If  a  dog  be  fed  upon  animal  food,  only  75  per  cent,  of  the  0x3^  gen 
of  inspiration  returns  in  the  form  of  carbon  dioxide.  If  it  be  fed  on 
vegetable  food,  90  to  95  per  cent,  returns  in  the  carbonic  acid. 

There  is  no  absolute  relation  between  the  amount  of  oxygen  inspired 
and  the  carbon  dioxide  expired,  but  a  certain  amount  of  oxygen  always 
remains  behind,  the  surplus  quantity  going  to  oxidize  certain  materials, 
such  as  sulphur,  phosphorus,  and,  perhaps,  certain  food-constituents. 

The  expired  air  also  contains  a  notable  quantity  of  carbon  dioxide, 
amounting  to  about  4  per  cent. 

If  we  take  thirty  cubic  inches  as  the  volume  of  each  expiration,  the 
average  of  carbon  dioxide  in  each  will  be  1.29,  or  about  twenty -three 
cubic  inches  per  minute,  about  one  thousand  three  hundred  and  ninety- 
three  per  hour,  or  twenty-seven  thousand  eight  hundred  and  sixty-four 
cubic  inches  per  day,  or  what  is  equivalent  to  about  seven  and  one-half 
ounces  of  solid  carbon. 

The  quantity  of  carbon  dioxide  thrown  off  by  the  lungs  is  notably 
diminished  by  the  presence  of  a  certain  amount  of  carbon  dioxide  in  the 
atmosphere  we  breathe. 

To  throw  off  the  full  amount,  the  surrounding  atmosphere  must  be 
devoid  of  this  gas.  If  we  breathe  the  same  air  over  and  over  again,  so 
as  to  permit  the  accumulation  of  carbon  dioxide,  the  difference  in  tension 
between  the  amount  of  carbon  dioxide  in  the  inspired  air  and  the  air  in 
the  lungs  will  be  decreased,  and  diffusion  interfered  with. 

It  has  been  found  that  if  5  per  cent,  of  carbon  dioxide  be  allowed  to 
remain  in  the  air  we  breathe  a  fatal  result  ensues  in  consequence  of  the 
difficulty  of  elimination  of  the  carbon  dioxide  from  the  blood.  Even  when 
carbon  dioxide  accumulates  in  the  air  below  2J  per  cent,  it  soon  begins 
to  produce  depressing  influences,  and  this,  together  with  the  accumula- 
tion of  other  deleterious  matters  which  are  normally  thrown  off  from  the 
lungs,  is  the  common  cause  of  the  languor  which  comes  on  in  crowded 
rooms.  When  gradually  subjected  to  these  influences  we  do  not  appre- 
ciate them  so  much  as  when  suddenly  subjected  to  them,  for  when  grad- 
ually brought  under  their  influence  the  vital  powers  become  depressed 
to  such  a  degree  that  they  do  not  require  the  same  amount  of  oxygen  as 
under  ordinary  circumstances.  A  person  passing  from  the  open  air  to  a 
room  which  has  been  occupied  for  some  time  by  a  large  number  of  per- 
sons at  once  experiences  a  depression,  but  after  remaining  there  a  little 
while  the  vital  powers  become  similarly  depressed  and  the  inconvenience 
resulting  from  the  presence  of  carbon  dioxide  in  the  atmosphere  is  no 
longer  appreciated. 


RESPIRATION.  591 

An  experiment  first  performed  by  Bernard,  showing  how  an  indi- 
vidual may  become  accustomed  to  bad  air,  fully  confirms  this  statement. 
He  placed  under  a  bell-jar  a  living  sparrow,  and,  having  allowed  it  to 
remain  there  for  a  certain  period,  he  removed  it  but  slightly  influenced 
by  the  accumulated  carbon  dioxide:  without  replenishing  the  air,  he 
placed  a  second  sparrow,  which  had  been  breathing  pure  air,  under  the 
bell-jar,  and  death  rapidly  ensued.  He  then  replaced  the  first  sparrow 
in  the  same  air,  and  it  also  died. 

The  influence  of  age  in  varying  the  quantity  of  carbon  dioxide  in  the 
expired  air  is  very  striking.  It  has  been  shown  that  there  is  a  notable 
increase  in  the  quantity  of  carbon  dioxide  exhaled  from  infancy  to 
puberty.  In  the  male  this  quantity-  continues  to  increase  after  puberty 
until  the  age  of  thirty  ;  from  thirty  to  forty,  it  remains  about  stationary  ; 
at  forty,  it  begins  to  decrease  and  continues  decreasing  until  the  age  of 
sixty,  when  but  little  more  carbon  dioxide  is  exhaled  than  by  a  child  of 
eight  years.  The  same  applies,  also,  to  the  female. 

Not  only  does  age,  but  time  of  day,  amount  of  exercise,  character 
of  food,  and  the  temperature  also  influence  the  quantity  of  carbon 
dioxide  exhaled.  More  carbon  dioxide  is  thrown  off  in  winter  than  in 
summer,  partly  because  more  food  is  consumed  in  winter,  and  partly, 
also,  because  a  cubic  foot  of  atmosphere  contains  a  larger  quantity  of 
oxygen  in  winter  than  in  summer,  when  it  has  a  lower  density.  During 
the  day  more  carbon  dioxide  is  thrown  off  than  at  night.  Alcohol  and 
other  articles  of  the  so-called  accessory  diet  diminish  the  quantity  of  this 
gas  removed  through  the  lungs,  probably  by  diminishing  the  waste  of  the 
tissues.  This  matter  will  be  again  referred  to  under  the  consideration 
of  nutrition. 

The  quantity  of  carbon  dioxide  eliminated  with  each  expiration  is 
diminished  after  rapidly  repeated  inspirations,  though  the  whole  quantity 
exhaled  is  increased. 

The  Respiratory  Changes  in  the  Blood. — As  has  been  already  indi- 
cated, the  main  points  of  contrast  between  the  arterial  and  venous  blood 
consists,  in  the  former  in  the  presence  of  an  excess  of  oxygen,  in  the 
latter  of  an  excess  of  carbon  dioxide,  while  as  the  venous  blood  circulates 
through  the  capillaries  of  the  lungs  it  larg'ely  gives  up  its  carbon  dioxide 
and  absorbs  oxygen.  We  have  now  to  consider  the  way  in  which  the 
gases  are  held  within  the  blood  and  the  manner  in  which  they  enter 
and  leave  the  blood  in  the  pulmonary  and  systemic  capillaries,  and  to 
trace  a  relationship  between  these  changes  in  the  blood  and  the  changes 
in  the  air  in  respiration. 

When  blood  is  exposed  to  a  vacuum  produced  by  a  mercurial  air- 
pump,  it  will  be  found  to  yield  about  sixty  volumes  of  gas  to  each  one 
hundred  volumes  of  blood,  the  temperature  being  zero  C.,  and  the 


592  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

height  of  the  barometer  seven  hundred  and  sixty  millimeters.  If  the 
gas  so  collected  be  analyzed  it  will  be  found  that  in  the  gaseous  mixture 
so  obtained  from  the  arterial  blood  there  will  be  more  oxygen  than  can 
be  obtained  from  the  venous  blood  ;  while,  on  the  other  hand,  the  gases 
so  abstracted  from  the  venous  blood  will  contain  more  carbon  dioxide 
than  those  obtained  from  the  arterial  blood.  Further,  it  may  be  repeated 
that  if  venous  blood  be  agitated  with  air  or  with  oxygen,  it  will  at  once 
assume  the  arterial  hue.  It  may,  therefore,  be  concluded  that  the  differ- 
ence in  the  relative  amounts  of  these  gases  present  in  the  blood  consti- 
tutes the  real  difference  between  arterial  and  venous  blood,  and  all  other 
differences,  such  as  difference  in  color,  are  dependent  upon  this  funda- 
mental fact.  The  amount  of  gas  which  may  be  abstracted  from  blood 
has  been  placed  at  sixty  volumes  for  each  one  hundred  volumes  of  blood. 
The  following  table  represents  the  proportions  of  these  gases  which 
may  be  obtained  from  one  hundred  volumes  of  arterial  and  venous 
blood : — 

Oxygen.  Carbon  Dioxide.  Nitrogen. 

Arterial  blood,      .     20  volumes.        36  volumes.  1  to  2  volumes. 

Venous  blood,      .     8  to  12  "  46        "  1  to  2 

All  measured  at  760  millimeters  and  0°  C. 

The  question  is  now  raised  as  to  the  manner  in  which  these  gases 
are  held  in  the  blood.  In  the  chapter  on  the  diffusion  of  gases  it  was 
pointed  out  that  every  liquid  possesses  the  power  of  absorbing  gases, 
and  that  the  co-efficient  of  absorption  varies  with  the  nature  of  the 
liquid,  the  nature  of  the  gas,  pressure  of  the  gas,  and  the  temperature 
to  which  it  was  subjected.  Blood,  therefore,  like  every  other  liquid, 
possesses  the  power  of  absorbing  gases.  When,  however,  we  measure 
the  quantity  of  oxygen  which  may  be  extracted  from  the  blood  loy 
exposing  it  to  a  vacuum,  we  are  struck  by  the  fact  that  the  amount  so 
removed  is  greatly  in  excess  of  that  which  may  be  held  in  solution  in 
the  blood,  regarding  it  merely  as  a  fluid,  by  exposure  to  a  gaseous 
medium  in  which  the  oxygen  is  in  no  higher  tension  than  it  is  in  the 
atmosphere. 

Again,  the  fact  is  worthy  of  notice  that  the  absorption  of  oxygen 
by  the  blood  and  its  release  from  the  blood  are  not  governed  by 
variations  of  pressure.  If  we  expose  blood  containing  little* oxygen  to 
a  successive  series  of  atmospheres  in  which  the  oxygen  tension  gradually 
increases,  we  shall  find  that  at  first  there  is  a  very  rapid  absorption  of 
oxygen,  and  that  this  suddenly  ceases;  while  if  we  submit  blood  highly 
charged  with  oxygen  to  an  atmosphere  containing  decreasing  amounts  of 
oxygen,  we  shall  find  that  at  first  but  little  oxygen  will  diffuse  out  from 
the  blood  until  the  pressure  has  been  reduced  almost  to  that  of  a  vacuum. 
Oxygen  then  suddenly  almost  totally  escapes  from  the  blood.  Again,  if 


RESPIRATION. 


593 


we  expose  blood-serum  to  an  atmosphere  of  oxygen  it  will  absorb  no 
more  oxygen  than  water  under  the  same  conditions  of  pressure,  and  the 
amount  so  absorbed  will  be  far  less  than  that  which  is  capable  of  being 


absorbed  by  the  blood.  The  absorption,  then,  of  oxygen  by  the  blood 
is  not  due  to  its  plasma.  If,  however,  a  solution  be  prepared  of  haemo- 
globin, or  the  coloring  matter  which  forms  90  per  cent,  of  the  dried  red 
corpuscles,  and  it  be  exposed  to  oxygen,  it  will  be  found  capable  of 


594  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

absorbing  nearly  the  total  amount  which  may.be  absorbed  by  the  blood. 
It,  therefore,  would  appear  that  oxygen  is  absorbed  by  the  blood  through 
the  mediation  of  the  red  coloring  matter.  The  general  characteristics  of 
haemoglobin  have  been  already  described  under  the  subject  of  the  blood. 
They,  however,  deserve  more  especial  attention  in  their  relationship  to 
the  respirator}7  functions  of  the  blood. 

When  a  tolerably  dilute  solution  of  haemoglobin,  which  possesses 
the  bright-red  color  of  arterial  blood,  is  placed  before  the  spectroscope, 
it  is  found  that  a  portion  of  the  red  end  of  the  spectrum  is  absorbed, 
together  with  a  portion  of  the  blue  end,  while  two  absorption  bands  are 
found  between  the  lines  D  and  E  ;  the  line  toward  the  red  side  of  the  spec- 
trum is  the  narrowest,  but  is  the  most  distinct,  and  with  very  dilute 
solutions  is  the  only  one  visible.  The  other  toward  the  blue  side  is  much 
broader,  but  less  distinct.  These  absorption  bands  are  characteristic  of 
solutions  of  haemoglobin.  When  stronger  solutions  of  haemoglobin  are 
used  the  bands  broaden  and  become  darker,  while  more  and  more  light  is 
shut  out  from  each  end  of  the  spectrum,  until  finally  the  two  bands 
become  fused  together,  and  only  the  green  and  red  rays  are  now  visible : 
with  still  stronger  solutions  the  red  rays  alone  pass,  and  finally  they 
also  may  disappear,  thus  indicating  the  cause  of  the  natural  color  of 
solutions  of  haemoglobin  in  transmitted  light  (Fig.  256). 

If  crystals  of  haemoglobin  are  subjected  to  a  vacuum,  oxygen  is 
given  up  and  the  crystals  become  darker  and  more  of  a  purple  color. 
The  quantity  of  oxygen  which  is  given  off  is  a  fixed  quantity,  each 
gramme  of  haemoglobin  giving  off  1.76  cubic  centimeters  of  oxygen, 
measured  at  a  pressure  of  seven  hundred  and  sixty  millimeters  and  at 
zero  temperature.  The  haemoglobin  is  then  spoken  of  as  reduced 
haemoglobin.  It  also  is  soluble  in  water  and  forms  a  purplish  solution. 
When  examined  under  the  spectroscope,  instead  of  the  two  absorption 
bands,  a  single,  less  distinct,  but  much  broader  band  is  found,  whose 
position  lies  about  midway  between  that  of  the  two  absorption  bands  of 
the  unreduced  haemoglobin. 

In  strong  solutions  of  reduced  haemoglobin  less  of  the  blue  than  of 
the  red  end  of  the  spectrum  is  absorbed,  and  with  concentrated  solutions 
the  blue  rays  may  still  pass,  thus  accounting  for  the  difference  in  color 
between  the  arterial  and  venous  blood,  the  former  allowing  the  red  and 
orange-yellow  rays  to  pass,  the  latter  the  red  and  bluish-green  rays ; 
hence  arterial  blood  appears  scarlet,  venous  blood  purple. 

The  oxygen  which  is  removed  from  venous  blood  or  from  oxyhaemo- 
globin  by  exposure  to  a  vacuum,  or  by  the  use  of  reducing  agents,  is  not 
the  oxygen  which  enters  into  the  molecular  constitution  of  haemoglobin, 
but  is  a  definite  volume  which  is  capable  of  entering  into  loose  chemical 
combination  with  it. 


KESPIKATION.  595 

If,  now,  such  a  solution  of  reduced  haemoglobin,  or  the  crystals  of 
reduced  haemoglobin,  be  exposed  to  the  atmosphere,  the}'  then  again 
absorb  oxygen  and  now  change  to  a  reddish  color,  the  amount  of  oxygen 
absorbed  being  again  precisely  similar  to  that  which  was  given  off  to  the 
vacuum. 

The  above  phenomena  serve  to  explain  what  occurs  in  the  process 
of  respiration.  As  the  venous  blood  leaves  the  right  ventricle,  its  haemo- 
globin has  already  largely  lost  its  oxygen  by  passing  through  the  83*8- 
temic  capillaries,  and  is  now  mainly  reduced  haemoglobin.  It  absorbs 
oxygen  from  the  atmosphere  through  the  walls  of  the  pulmonary  vesicles 
while  passing  through  the  pulmonary  capillaries,  and  now  becomes  oxy- 
haemoglobin  and  is  now  arterial  blood. 

As  the  arterial  blood  passes  through  the  S3*stemic  capillaries,  the 
oxj^gen  of  the  oxyhaemoglobin  is  largel}7  yielded  up  and  haemoglobin 
becomes  reduced. 

The  mode  in  which  the  carbon  dioxide  is  held  in  the  blood  does  not 
admit  of  as  ready  demonstration  as  is  the  case  with  the  oxygen.  It  is, 
however,  clear  that  almost  the  total  amount  of  carbon  dioxide  which  may 
be  extracted  by  the  vacuum  pump  from  the  blood  is  held,  in  some  way  or 
other,  in  the  blood-serum,  for  almost  quite  as  much  of  this  gas  may  be 
extracted  from  the  serum  as  from  the  blood  itself.  The  carbon  dioxide 
is  not,  however,  simply  dissolved,  for  here  also  the  degree  of  absorption 
of  this  gas  by  the  blood  is  not  governed  by  the  same  laws  as  would  apply 
to  its  absorption  by  water. 

When  blood-serum  is  exposed  to  a  vacuum,  about  25  volumes  per 
cent,  of  this  gas  is  extracted,  and  this  amount  is  spoken  of  ns  the  loose 
carbon  dioxide.  If,  now,  an  acid  be  added  to  the  serum,  about  5  volumes 
per  cent,  more  are  released,  and  it  may  therefore  be  concluded  that  this 
latter  amount  exists,  in  all  probability,  in  the  serum  in  the  form  of  car- 
bonates, and  probably  united  with  sodium. 

The  corpuscles  also  contain  about  5  volumes  per  cent,  of  carbon 
dioxide  ;  for,  if  the  corpuscles  separated  from  the  serum  be  exposed  to  a 
vacuum,  the}'  also  will  yield  this  amount  of  carbon  dioxide. 

If,  now,  corpuscles  and  serum,  from  both  of  which  gas  has  been 
separately  removed  by  pumping,  be  together  exposed  to  a  vacuum,  5  per 
cent,  again  of  carbon  dioxide  is  given  up,  from  which  it  would  appear 
that  the  corpuscles  in  this  experiment  play  the  r61e  of  an  acid ;  and  it 
may  be  assumed  that  perhaps  the  haemoglobin  in  its  decomposition 
liberates  aii  acid,  which  again  sets  free  the  combined  carbon  dioxide  from 
the  serum. 

It  is  not  by  any  means  established  as  to  in  what  manner  the  free 
carbon  dioxide  is  held  in  the  blood-serum.  A  certain  portion  of  it  is, 
without  doubt,  held  in  solution  under  the  simple  laws  of  absorption  0f 


596  PHYSIOLOGY  OF  THE   DOMESTIC  ANIMALS. 

gases  by  liquids,  and  increases  with  the  gaseous  tension;  while,  on  the 
other  hand,  a  larger  amount  must  be  held  in  some  form  of  chemical  com- 
bination, since  blood  is  capable  of  absorbing  under  equal  pressures  much 
more  carbon  dioxide  than  water. 

On  the  other  hand,  it  is  also  clear  that  this  chemical  combination 
must  be  a  very  loose  one,  since  it  is  broken  up  by  exposure  to  a  vacuum. 
It  is  probable  that  part  of  this  carbon  dioxide  is  present  in  the  serum  as 
a  bicarbonate  of  sodium, — a  combination  which,  by  reduced  pressure,  is 
readily  broken  up  into  sodium  carbonate  and  free  carbon  dioxide.  It  is 
further  possible  that  another  part  of  this  carbon  dioxide  may  be  loosely 
combined  with  a  sodium  biphosphate, — a  salt  which  is  likewise  present 
in  the  blood-serum,  and  which  has  been  shown  to  readily  combine  with 
carbon  dioxide.  It  is,  however,  to  be  noted  that  this  salt,  sodium  biphos- 
phate, is  solely  present  in  considerable  amounts  in  the  blood  of  carnivora 
and  omnivora,  while  only  traces  of  it  are  present  in  the  blood  of  her- 
bivora,  so  that  in  the  latter  this  combination  cannot  exist.  It,  in  any 
case,  seems  evident  that  the  red  blood-corpuscles  in  some  way  govern 
the  presence  of  this  gas  in  the  serum. 

The  nitrogen,  which  may  be  removed  from  the  blood  by  exposure  to 
a  vacuum  in  from  1  to  3  volumes  per  cent.,  is  without  doubt  simply 
held  in  solution  by  the  serum,  since  water  likewise  is  capable  of  absorb- 
ing this  gas  to  the  same  amount. 

The  exchange  which  takes  place  between  these  gases  in  the  blood 
and  the  atmospheric  air  in  the  lungs  is  governed  almost  purely  by  the 
simple  physical  laws  of  gaseous  diffusion.  As  already  mentioned,  the 
air  within  the  pulmonary  vesicles  is  separated  from  the  blood  in  the 
capillaries  only  by  the  delicate  epithelial  walls  of  the  vesicles  and  the 
structureless  walls  of  the  capillaries.  The  oxygen  of  the  blood?  as 
already  indicated,  is  loosely  combined  with  the  haemoglobin.  When  re- 
duced haemoglobin  is  exposed  to  an  atmosphere  of  oxygen  it  readily 
absorbs  that  gas,  provided  the  tension  of  the  oxygen  in  the  surrounding 
medium  be  greater  than  the  tension  of  the  oxygen  in  combination  with 
the  haemoglobin.  When,  therefore,  the  blood  from  the  pulmonary  arter- 
ies reaches  the  capillaries  of  the  lungs  a  large  part  of  the  haemoglobin 
there  present  exists  in  the  form  of  reduced  haemoglobin,  while  the  atmos- 
phere within  the  pulmonary  alveoli  contains  oxygen,  perhaps  in  a  lower 
tension  than  in  the  atmosphere,  but  at  any  rate  in  a  higher  tension  than 
is  present  in  the  haemoglobin.  As  a  consequence,  diffusion  phenomena 
set  in,  the  oxygen  passing  from  the  interior  of  the  alveoli  through  the 
moist  walls  of  the  alveoli  and  blood-capillaries  into  the  interior  of 
the  latter  vessels,  and  there  combining  with  the  haemoglobin.  It  may 
be  assumed  that  the  oxygen  tension  in  the  alveoli  of  the  lungs  amounts 
to  about  10  per  cent.  The  oxygen  tension  in  the  venous  blood  will, 


KESPIBATION.  597 

as  a  rule,  amount  to  about  3  per  cent.  This  difference  in  pressure  is, 
therefore,  sufficient  to  explain  the  entrance  of  oxygen  from  the  air  in 
the  pulmonary  alveoli  to  the  blood  in  the  pulmonary  capillaries.  The 
laws  of  absorption  of  oxygen  by  the  blood-corpuscles  are,  while  partially 
dependent  upon  the  differences  in  oxygen  tension  in  the  blood  and  in  the 
capillaries,  not  solely  dependent  upon  them  ;  otherwise  an  increase  in  the 
oxygen  tension  in  the  atmosphere  would  cause  a  proportionate  increase 
in  the  amount  of  oxygen  absorbed,  a  decrease  in  the  oxygen  tension  a 
diminution  of  the  amount  of  this  gas  which  enters  in  the  blood.  This  is 
not,  however,  the  fact,  for  it  has  been  determined,  as  already  stated,  that 
but  a  limited  quantity  of  oxygen  is  capable  of  combining  with  haemo- 
globin. If  the  oxygen  of  the  atmosphere  be  decreased  the  tension  of 
this  gas  in  the  lungs  will  also  be  decreased,  and,  therefore,  to  a  certain 
extent  the  blood  will  be  insufficiently  aerated  ;  this  will  perhaps  explain 
the  dyspnoea  which  is  so  often  noted  in  ascending  to  great  heights,  as  to 
the  tops  of  mountains,  and  in  balloons. 

As  regards  the  escape  of  carbon  dioxide  from  the  blood  in  the  capil- 
laries of  the  pulmonary  artery,  we  are  perhaps  warranted  in  assuming 
that  they  are  governed  purely  by  the  laws  of  gaseous  tensions ;  since 
we  may  assume  that  even  although  we  do  not  know  exactly  what  the 
tension  of  carbon  dioxide  in  the  pulmonary  alveoli  is,  and  although  it 
must  be  greater  than  that  in  the  expired  air,  it  is,  nevertheless,  less  than 
that  of  the  venous  blood. 

The  tension  of  carbon  dioxide  in  the  air  of  the  alveoli  has  been 
placed  at  twenty-seven  millimeters  of  mercury. 

The  tension  of  carbon  dioxide  in  the  blood  in  the  right  side  of  the 
heart  has  been  placed  at  forty-one  millimeters  of  mercury,  or,  in  other 
words,  fourteen  millimeters  higher  than  the  tension  in  the  alveoli.  This 
difference  will,  in  all  probability,  be  sufficient  to  inaugurate  phenomena 
of  diffusion. 

Thus,  in  passing  through  the  pulmonary  capillaries  the  venous  blood 
yields  up  carbon  dioxide  and  absorbs  oxygen,  and  becomes  converted 
fr-om  a  dark-red  venous  blood  into  the  bright  red  arterial  blood. 

The  characteristics  of  arterial  blood  are  preserved  throughout  the 
entire  arterial  system  until  the  capillaries  are  reached,  and  when  the 
capillaries  have  been  traversed  we  find  that  again  the  arterial  blood  loses 
its  characteristic  properties  and  now  becomes  venous.  In  other  words,  in 
the  capillaries  a  part  of  the  oxygen  disappears  and  is  replaced  by  carbon 
dioxide.  In  the  tissues,  therefore,  a  process  takes  place  which  is  exactly 
the  reverse  of  that  which  has  been  described  as  occurring  in  the  lungs. 
It  may  be  assumed  that  the  oxygen  leaves  the  blood  in  the  same  manner 
as  it  enters  in  the  pulmonary  capillaries ;  in  other  words,  in  the  tissues  it 
becomes  exposed  to  a  surrounding  medium  whose  gaseous  tension  in 


598  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

oxygen  is  less  than  that  of  the  arterial  blood.  As  a  consequence,  the 
oxyhaemoglobin  is  broken  up  and  yields  a  large  part  of  its  oxygen  to  the 
tissues,  passing  through  the  walls  of  the  capillaries  by  diffusion,  to  be 
used  up  in  the  tissues  in  the  processes  of  oxidation  which  are  there  con- 
tinually taking  place.  One  of  the  principal  results  of  such  oxidation 
processes  is  the  formation  of  carbon  dioxide,  and  here,  again,  we  have 
phenomena  of  diffusion  taking  place  between  the  tissues  and  capillaries. 
In  the  tissues  tthe  gaseous  tension  of  carbon  dioxide  is  higher  than  in  the 
capillaries,  and,  as  a  consequence,  by  diffusion  this  gas  leaves  the  tissues 
to  enter  the  blood-serum.  This  process  of  gaseous  interchange  in  the 
systemic  capillaries  may,  therefore,  be  spoken  of  as  internal  respiration, 
and  varies  in  intensity  in  different  conditions  of  the  system.  Thus  the 
interchange  is  more  rapid  and  extensive  in  muscles  during  contraction 
than  in  muscles  at  rest.  It  is  more  active  in  secreting  glands  than  in 
quiescent  glands. 

As  to  the  subsequent  fate  of  the  oxygen  after  leaving  the  blood- 
vessels, but  little  can  be  positively  said.  It  is  probable  that  processes  of 
oxidation  occur  in  the  tissues,  and  that  these  result  in  the  formation  of 
carbon  dioxide,  but  it  does  not  follow  that  the  oxygen  as  it  leaves  the 
blood  directly  unites  with  the  organic  tissue-constituents,  and  is  thus 
directly  returned  to  the  blood  as  carbon  dioxide;  for  we  know  that 
various  tissues  removed  from  the  body  and  placed  in  an  atmosphere 
entirely  devoid  of  oxygen  will  still  produce  carbon  dioxide.  It  is,  there- 
fore, possible  that  the  oxygen  that  leaves  the  blood-vessels  is  stored  up 
in  some  combination  or  other  in  the  tissues,  and  is  then  drawn  upon  as 
the  needs  of  the  tissues  demand,  finally  to  be  returned  to  the  blood  as 
carbon  dioxide. 

5.  THE  NERVOUS  MECHANISM  OF  RESPIRATION. — Although  the  muscles 
of  respiration  are  red,  striped,  voluntary  muscles,  and  although  through 
an  effort  of  will  the  rhythm,  number,  and  depth  of  the  respiratory  move- 
ments may  be  greatly  modified  and  changed,  the  act  of  respiration  is  to  be 
regarded  as  an  involuntarjr  action.  Although  the  breath  may  for  a  cer- 
tain time  be  held  and. the  movement  of  respiration  completely  interrupted, 
after  but  a  very  short  interval,  probably  not  more  than  between  two  and 
three  minutes,  in  spite  of  the  strongest  effort'of  the  will,  an  inspiration  must 
be  made.  The  fact  that  respiration  persists  in  the  absence  of  mental 
effort  points  further  to  the  fact  of  the  independence  of  respiration  of  the 
will.  Thus,  during  sleep  and  in  states  of  unconsciousness,  in  various 
diseases  and  as  an  effect  of  various  drugs,  respiration  may  be  perfectly 
performed.  So,  also,  in  the  lower  animals  the  brain  may  be  exposed  and 
may  be  gradually  removed  from  the  cerebrum  down  to  the  base  of  the 
brain,  and  still  respiration  be  unaffected,  provided  loss  of  blood  or  some 
other  accident  does  not  interfere  with  the  lower  portions  of  the  central 


KESPIKATION.  599 

nervous  system.  It  has  been  pointed  out  that  the  mechanical  operations 
of  respiration  require  the  associated  action  of  a  large  number  of  different 
muscles,  different  in  function  and  in  locality.  It  has  been  mentioned 
that  during  respiration  muscular  movements  occur  in  the  face,  neck, 
thorax,  and  abdomen,  and  it  is  found  that  the  character  of  the  contrac- 
tion of  these  muscles  is  the  same  in  each  group.  Thus,  in  gentle  inspi- 
ration we  notice  a  gentle  contraction  of  the  diaphragm,  of  the  scalene 
muscles,  the  external  intercostals,  and  the  elevators  of  the  ribs.  In 
gentle  expiration  we  notice  but  a  gentle  contraction  of  the  abdominal 
muscles.  The  degree  of  contraction  of  each  of  these  muscles  in  such  a 
respiratory  movement  is  identical.  When  any  one  muscle  or  group  of 
muscles  is  the  seat  of  an  especially  violent  contraction,  the  normal 
rhythm  of  respiration  is  departed  from.  Again,  in  forced  expiration  the 
same  state  of  affairs  holds;  the  degree  of  contraction  of  each  muscle  is 
proportionate  to  that  of  all  the  other  muscles  concerned  in  producing 
the  respiratory  movement.  These  facts  indicate,  as  in  the  case  of  other 
complex  associated  muscular  movements,  the  domination  of  some  part 
of  the  central  nervous  s3Tstem.  In  the  case  of  respiration  such  a  state 
of  affairs  will  also  be  noted.  In  other  words,  the  movements  of  respira- 
tion are  controlled  by  a  single  co-ordinating  centre,  located  in  the  me- 
dulla oblongata.  The  proof  of  this  statement  may  be  reached  in  quite  a 
number  of  ways. 

If  one  of  the  phrenic  nerves  is  divided,  the  corresponding  half  of  the 
diaphragm  is  paratyzed,  and,  although  motions  of  inspiration  still  are 
possible,  it  will  be  noticed  that  the  excursions  of  the  non-paralyzed  half 
of  the  diaphragm  will  be  greater  than  when  the  phrenic  nerve  has  not 
been  cut,  and  that  the  share  in  inspiration  borne  by  the  other  respiratory 
muscles  will  be  more  marked  than  is  normally  the  case. 

Section  of  both  phrenic  nerves  emphasizes  this  point  still  further ; 
the  diaphragm  is  then  completely  paralyzed,  but  inspiration  is  accom- 
plished solely  by  the  muscles  which  elevate  the  ribs. 

Again,  if  one  or  more  of  the  intercostal  nerves  be  divided  the  mus- 
cles supplied  by  those  nerves  will  be  paralyzed,  and  the  act  of  inspira- 
tion will  then  be  produced  by  calling  in  the  aid  of  an  increased  degree  of 
contraction  of  other  inspiratory  muscles. 

If  the  spinal  cord  be  divided  below  the  level  of  the  seventh  cervical 
nerve,  consequently  below  the  origin  of  the  phrenic  nerves,  all  thoracic 
and  abdominal  movement  will  cease,  but  respiration  will  still  be  possible, 
and  inspiration  will  be  accomplished  solely  by  the  contraction  of  the 
diaphragm,  while  expiration  will  be  dependent  entirel3r  upon  the  recoil 
of  the  elastic  tissue  of  the  lungs  and  thorax.  In  this  state  of  affairs  the 
transmission  of  impulses  to  the  muscles  of  respiration,  with  the  excep- 
tion of  the  diaphragm,  has  been  interrupted.  The  thorax  will  then  be 


600  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

quiescent,  but  that  the  respiratory  centre,  whose  location  we  have 
assumed  to  be  in  the  medulla,  is  still  sending  out  its  motor  impulses 
is  evidenced  by  the  increased  movements  of  the  nostrils  and  glottis.  If, 
now,  the  facial  and  laryngeal  nerves  be  cut  this  movement  will  also 
cease. 

These  facts  indicate  that  in  some  part  of  the  central  nervous  system 
arise  the  motor  impulses  which  are  conducted  to  the  muscles  of  respi- 
ration. As  one  after  the  other  of  the  paths  of  communication  between 
these  centres  and  the  muscles  are  interrupted,  we  find  that  one  after  the 
other  these  muscles  become  paralyzed. 

It  has  been  found,  as  already  mentioned,  that  the  brain  may  be 
removed  down  to  the  level  of  the  medulla  oblongata  and  still  respiration 
take  place,  thus  marking  the  upper  limit  of  this  centre.  On  the  other 
hand,  the  spinal  cord  may  be  divided  up  to  the  calamus  scriptorius,  and 
through  the  movements  of  the  face  the  evidence  of  the  activity  of  the 
respiratory  centre  may  still  be  made  out.  The  respiratory  centre,  there- 
fore, lies  some  place  between  these  two  points.  Its  exact  locality  has 
not  been  determined,  but  it  is  clear  that  it  lies  in  the  floor  of  the  fourth 
ventricle,  somewhat  lower  down  than  the  vaso-motor  centre,  and  nearer 
the  tip  of  the  calamus  scriptorius.  When  this  locality  is  injured,  as  by 
puncturing  with  a  sharp-pointed  instrument,  all  respiratory  movements 
at  once  cease.  The  motions  of  the  heart  are,  also,  at  once  arrested  from 
a  simultaneous  irritation  of  the  cardio-inhibitory  centre.  This  point, 
therefore,  when  injured  causes  instantaneous  death,  and  was,  conse- 
quently, termed  by  Flourens  the  vital  centre,  the  nceud  vital. 

The  action  of  this  centre  is  automatic  and  is  not  reflex,  though  it 
may  be  influenced  by  afferent  impulses  coming  through  various  sensory 
nerves.  Thus,  for  example,  a  dash  of  cold  water  on  the  skin  causes  a 
deep  inspiration  by  exalting  the  action  of  this  centre  through  the  con- 
duction of  impulses  to  it  from  the  external  integument. 

Again,  the  activity  of  the  respiratory  centre  may  be  influenced  by 
impressions  coming  from  above.  Thus,  the  various  emotions,  which  may 
be  regarded  as  impulses  originating  in  the  cerebrum,  also,  are  capable  of 
modifying  its  activity.  The  respiratory  centre,  while  not  dependent, 
however,  upon  impulses  coming  through  afferent  nerves,  is  especially 
modified  in  activity  by  impulses  traveling  through  the  pneumogastric 
nerves;  and  though  the  pneumogastric  nerves  ma}^  be  regarded  as  the 
principal  paths  of  conduction  of  afferent  impulses,  modifying  the  activitj^ 
of  the  respiratory  centres,  their  integrity  is  not  essential  for  the  mani- 
festation of  the  peculiar  action  of  this  ganglionic  centre.  This  fact  is 
demonstrated  by  the  modifications  produced  in  respiration  by  section  of 
these  nerves. 

If  one  pneumogastric  nerve  be  cut  respiration  becomes  slower  and 


KESPIKATION. 


601 


deeper,  while  the  pauses  between  the  respiratory  movements  are  more 
prolonged.  If  both  pneumogastric  nerves  are  divided  the  respirations 
are  still  further  slowed,  the  pauses  are  prolonged,  and  each  respiratory 
movement  is  deeper  than  normal.  If  the  quantity  of  air  displaced  in  any 
given  number  of  respiratory  movements  before  and  after  section  of  these 
nerves  be  estimated,  it  will  be  found  to  be  almost  unchanged;  in  other 
words,  the  increased  depth  of  the  respiratory  movements  after  section  of 
the  pneumogastric  compensates  for  their  decrease  in  frequency.  The 
amount  of  carbon  dioxide  exhaled  and  oxygen  absorbed  from  the  pul- 
monary surfaces,  therefore,  remains  unchanged. 

If  after  section  of  the  pneumogastrics  the  central  end  of  one  of  the 
divided  nerves  be  irritated,  the  rapidity  of  respiration 
will  be  increased.     By  carefully  graduating  the  strength 
of  stimulation  the  normal  rhythm  of  respiration  may  be 
again   almost  exactly  restored.      If  the   irritation    be 
gradually  increased,  the  movements  of  respiration  will 
increase  in  vigor  until,  finally,  they 
will  apparently  run  into  each  other, 
and  respiration  will  then  be  arrested 
with  the  diaphragm  in  a  condition  of 
tetanic    contraction.      Respiration   is 
thus  stopped  in  the  phase  of  extreme 
inspiration. 

If  the  central  end  of  the  superior 
larj-ngeal  nerve  be  stimulated  with  the 
faradic  current  the  respiratory  move- 
ments will  be  slowed,  and  with  a 
powerful  irritation  will  be  arrested, 
the  diaphragm  being  completely  re- 
laxed, and  the  thorax  and  lungs  being 
in  the  condition  seen  in  forced  expira- 
tion. It  would  therefore  appear  that  pXagi 

i  n       ,1  .         laryngeal;  CX.  pulmonary  fibres  of  vagus  that  excite 

the        trunks       Of      the       pneUmOgaStriC     inspiratory  centre;    CX/.  pulmonary  fibres  that  excite 

.  expiratory  centre;  CX",  fibres  of  superior  laryngeal 

nerves  are  the  pathS   OI     impulses  traV-     *hat  excite  expiratory  centre ;  IKK,  fibres  of  superior 

laryngeal  that  inhibit  the  inspiratory  centre. 

eling  from  the  lungs,  which,  reaching 

the  respiratory  centre,  tend  to  exalt  its  activity.  The  vagus  may, 
therefore,  be  regarded  as  a  stimulating  nerve  for  this  centre.  The  laryn- 
geal nerves,  on  the  other  hand,  may  be  regarded  as  inhibitory  nerves 
of  the  respiratory  centre,  and,  when  stimulated,  arrest  respiration,  the 
diaphragm  being  in  a  state  of  relaxation  and  the  thorax  contracted 
(Fig.  257). 

While  the  respiratory  centre  is  thus  capable  of  being  modified  by 
impulses  coming  from  these  nerves,  its  degree  of  activity  is,  above  all, 


FIG.  257.— SCHEME  OF  THE  CHIEF  RE- 
SPIRATORY NERVES,  AFTER  RUTHER- 
FORD. (Landois.) 

INS,  inspiratory,  and   EXP,  expiratory  centres— 


602  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

mainly  dependent  upon  the  character  of  blood  supplied  to  it.  Deficient 
oxygenation  of  the  blood  acts  as  a  stimulus  to  this  centre  and  causes 
the  respiratory  movements  to  become  quicker  as  well  as  deeper,  while 
expiration  becomes  especially  increased  in  power.  In  a  greater  degree  the 
deprivation  of  oxygen  from  the  blood  appears  to  cause  the  extension  of 
the  stimulus  from  the  respiratory  centre  to  other  adjoining  motor  centres, 
and  we  then  find  that  not  only  the  ordinary  muscles  of  respiration  are 
thrown  into  violent  action,  but  that  every  muscle  in  the  body  which  is 
connected  with  respiration  is  thrown  into  forced  contraction.  Such  a 
state  is  described  as  dyspnoea. 

On  the  other  hand,  the  blood  may  become  overcharged  with  oxygen, 
as  by  causing  an  animal  to  breathe  an  atmosphere  overcharged  with  this 
gas,  or  by  making  forced  artificial  respiration  in  one  of  the  lower  animals. 
The  blood  then  becomes  saturated  with  oxyhiemoglobin.  The  stimulus 
of  the  respiratory  centre  is  thus  removed,  and,  as  a  consequence,  we  find 
that  in  such  an  animal  the  motions  of  respiration  cease,  and  the  animal 
may  remain  perfectly  quiescent  without  breathing  for  a  number  of 
minutes  until  the  blood  has  •  freed  itself  from  the  excess  of  oxygen. 
These  facts  show  that  a  want  of  oxygen  in  the  blood  is  a  natural  stimu- 
'lus  to  the  respiratory  centre.  Blood  which  is  poor  in  oxygen  is  also 
to  be  regarded  as  rich  in  carbon  dioxide.  That  it  is  the  poverty  of  oxygen 
and  not  the  excess  of  carbon  dioxide  which  brings  this  centre  into 
activity  is  shown  by  the  fact  that  if  an  animal  be  caused  to  breathe  an 
atmosphere  deprived  of  oxygen,  or  one  which  will  not  interfere  with  the 
removal  of  carbon  dioxide,  the  phenomena  of  dyspnoea  will  still  appear. 
Thus,  an  animal  placed  in  an  atmosphere  of  hydrogen  will  not  be 
prevented  from  removing  carbon  dioxide  from  its  venous  blood,  but  will, 
of  course,  be  shut  off  from  all  supply  of  fresh  oxygen.  In  such  an 
animal  the  phenomena  of  dyspnoea  rapidly  appear.  This  action  on  the 
respiratory  centre  is  produced  directly,  and  not  through  the  mediation 
of  any  nerves,  for  even  when  the  spinal  cord  is  cut  and  the  supply  of 
oxygen  from  the  medulla  shut  off  the  phenomena  of  dyspnoea  are 
evidenced  in  the  spasmodic  contractions  of  the  nostrils  and  glottis,  even 
though  their  expression  through  the  muscles  of  respiration  is  rendered 
impossible.  So,also,ligating  the  vertebral  and  carotid  arteries  produces 
the  same  result  by  decreasing  the  Supply  of  oxygenated  blood  brought  to 
this  centre.  Again,  if  the  blood  distributed  to  the  respiratory  centre  be 
heated  above  normal,  dyspnoea  is  also  produced,  from  the  fact  that  the 
increased  temperature  of  the  blood  leads  to  an  increased  activity  of  the 
chemical  processes  in  the  body,  and  so  to  the  more  rapid  exhaustion  of 
oxygen.  Here,  also,  we  find  dyspnoea  produced  through  the  shutting  off 
of  the  supply  of  oxygen  from  this  centre. 

As  has  been  mentioned,  if  the  supply  of  oxygen  be  interfered  with, 


•  RESPIRATION.  603 

either  through  some  mechanical  obstruction  of  the  air-passages  or 
through  the  reduction  of  the  amount  of  oxygen  in  the  air,  as  by  breathing 
in  a  confined  space,  normal  respiration  gradually  is  replaced  by  dyspnoea, 
in  which  simply  all  the  accessory  muscles  of  respiration  are  brought  into 
play,  and  respiration  then,  instead  of  being  an  almost  imperceptible 
involuntary  movement,  now  becomes  convulsive.  If  this  interference 
with  the  normal  ox3^genation  of  the  blood  continues,  the  animal  then 
passes  into  a  state  of  asphyxia,  which  proves  rapidly  fatal. 

When  the  reduction  of  oxygen  in  the  blood  supplied  to  the  respira- 
tory centre  becomes  decreased,  the  overexcitation  of  the  respiratory 
centre  becomes  evident  in  the  increased  violence  of  the  respiratory 
movements;  expiration  becomes  gradually  convulsive,  until  often  every 
muscle  which  may  react  on  the  thorax  is  brought  into  play.  Very 
soon  almost  all  of  the  muscles  of  the  body  are  implicated  and  the  animal 
is  then  in  a  state  of  active  convulsions.  It  would  appear  that  these  con- 
vulsions are  due  simply  to  the  extension  of  the  activity  of  the  respira- 
tory centre  to  other  closely  associated  centres  in  the  medulla.  For  we 
notice  that  first  the  ordinary  respiratory  muscles  contract  with  greater 
vigor,  we  then  have  the  accessory  muscles  brought  into  play,  and  event- 
ually the  entire  muscular  sj^stem  of  the  body ;  and  although  a  con- 
vulsive centre  in  the  medulla  is  sometimes  spoken  of,  it  is  evident 
that  this  centre  must  be  closely  connected  with  the  respiratory  centre. 
After  a  variable  period  the  violent  muscular  contractions  suddenly 
disappear,  from  the  exhaustion  of  the  nervous  83- stem,  the  pupils  are 
then  found  to  be  dilated  to  their  utmost  and  are  unaffected  by  light, 
and  the  cornea  insensible  to  the  touch.  All  the  muscles  of  the  body 
are  now  in  a  condition  of  relaxation ;  and  although  the  respiratory 
movements  have  not  entirely  ceased,  they  are,  however,  far  between, 
are  gasping,  accompanied  by  twitching  of  other  muscles,  especially  of 
the  face,  and  the  intervals  between  them  become  gradually  increased  ;  the 
rhythm  of  the  respiratory  movements  becoming  irregular,  each  inspira- 
tion shallower  and  shallower,  again  implicating  the  other  muscles  of  the 
body,  with  the  head  thrown  back  and  the  mouth  open,  the  face  drawn 
and  the  nostrils  dilated,  the  last  breath  is  taken  in. 

It  is  thus  evident  that  the  phenomena  resulting  from  the  deprivation 
of  ox}Tgen  ma}'  be  divided  into  three  different  stages  : — 

First,  a  stage  of  dyspnoea,  characterized  by  an  extraordinary  mus- 
cular effort  in  the  muscles  of  respiration,  expiration  being  especially  con- 
vulsive. Second,  an  extension  of  the  convulsive  muscular  contractions 
to  all  the  other  muscles  of  the  body,  and  therefore  characterized  by 
general  convulsions,  while  the  final  stage  is  one  of  exhaustion,  in  which 
the  inspirations  become  slower  and  slower,  more  and  more  shallow, 
and  are  finalty  arrested. 


604  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

The  duration  of  asphyxia  varies  considerably  in  different  animals 
and  in  the  same  animal  under  different  circumstances.  As  a  rule,  young 
animals  will  bear  a  longer  deprivation  of  fresh  air  than  adults.  It  has 
thus  been  stated  that  while  a  full-grown  dog  will  rarely  recover  from  an 
immersion  in  water  over  one  and  one-half  minutes,  a  puppy  has  been 
known  to  recover  after  an  immersion  of  fifty  minutes.  This  is  evidently 
to  be  explained  by  the  fact  that  in  younger  animals  the  processes  of 
tissue  change  are  less  active  than  in  adults,  and,  as  a  consequence,  the 
demand  on.  the  oxygen  in  the  blood  is  less. 

During  asphyxia  the  circulation  is  the  seat  of  various  departures 
from  normal. 

In  the  stage  of  dyspnoea  and  convulsions  the  blood  pressure  is 
reduced,  while  in  the  final  stage  it  rapidly  falls  far  below  normal,  until 
at  the  period  of  death  the  blood  pressure  does  not  exceed  the  atmos- 
pheric pressure. 

The  heart  also  is  modified  in  ^its  activity.  At  first  it  beats  more 
rapidly  than  normal  and  then  is  slowed,  but  each  pulsation  is  greatly 
increased  in  force.  As  a  rule,  the  heart  continues  to  beat  for  some 
time  after  the  final  cessation  of  respiration.  During  the  first  and 
second  stages  of  asphyxia,  the  great  increase  in  blood  pressure  from  the 
contraction  of  the  arterioles  leads  to  great  increase  in  the  resistance 
met  with  by  the  heart  in  emptying  itself.  We  find,  therefore,  if  the 
chest  of  an  animal  is  opened  during  asphyxia,  that  the  right  side  of  the 
heart  especially  is  gorged  with  blood.  The  lungs  and  the  pulmonary  ves- 
sels are  overfilled  and  distended,  and,  as  a  consequence,  blood  collects 
in  the  venous  system,  so  accounting  for  the  cyanosed  appearance  seen 
on  all  external  surfaces,  and  so  characteristic  of  asphyxia. 

Modified  Respiratory  Movements. — In  addition  to  the  normal  respira- 
tory rhythm,  various  modifications  of  the  respiratory  movement  are  often 
noticed.  Many  are  involuntary,  and  yet  nearly  all  of  them  may  be  repro- 
duced by  a  direct  effort  of  the  will. 

Sighing  is  produced  by  a  long,  deep  inspiration,  air  being  inhaled 
through  the  nose  and  the  inspiration  followed  by  a  number  of  shorter 
expirations. 

Yawning  is  accomplished  by  a  deep  inspiration  through  the  mouth, 
and  is  accompanied  by  a  depression  of  the  lower  jaw  and  elevation  of 
the  shoulders. 

Hiccough  is  produced  by  a  sudden  contraction  of  the  diaphragm 
and  a  sudden  closure  of  the  glottis,  so  arresting  the  entrance  of  air  into 
the  lungs,  and,  by  the  striking  of  the  column  of  air  against  the  closed 
vocal  cords,  producing  the  sound  characteristic  of  this  phenomenon. 
Hiccough  is,  as  a  rule,  due  to  the  stimulation  of  the  gastric  branches  of 
the  pneumogastric,  especially  in  some  disturbance  of  digestion. 


KESPIKATION.  605 

Sobbing  is  produced  by  a  series  of  similar  convulsive  inspirations, 
in  which  the  glottis  is  closed  earlier  than  in  hiccoughing,  and  no  air,  con- 
sequently, enters  the  chest. 

The  foregoing  are  the  principal  modifications  of  the  inspiratory 
phase  of  the  respiratory  rhythm. 

The  following  owe  their  characteristics  mostly  to  some  modification 
of  expiration : — 

Coughing  is  produced  by  a  long,  deep  inspiration,  after  which  the 
glottis  becomes  firmly  closed.  A  forced  expiration  is  then  made  through 
the  violent  contraction  of  the  abdominal  muscles  and  serves  to  force 
open  the  glottis,  the  vibration  of  the  vocal  cords  producing  the  charac- 
teristic sound.  The  starting  point  of  the  act  of  coughing  may  be  found 
in  the  contact  of  any  foreign  body  with  the  mucous  membrane  of  the 
air-passages,  the  impression  being  conducted  through  the  superior  laryn- 
geal  nerve.  Other  parts  of  the  body  may,  however,  also  serve  as  the 
starting  point  to  the  act  of  coughing.  Thus,  stimulation  of  the  auricular 
branch  of  the  pneumogastric,  as  is  often  the  case  in  numerous  ear  dis- 
eases, may  produce  coughing,  as  may  the  stimulation  of  other  nerves. 

Sneezing  is  produced  by  a  mechanism  closely  similar  to  that  of 
coughing,  with  the  exception  that  the  expelled  column  of  air  passes 
through  the  nose  instead  of  the  mouth. 

The  point  of  origin  of  the  afferent  impulses  is  usually  found  in  the 
mucous  membrane  of  the  nose  and  is  conducted  through  the  fifth  pair  of 
nerves.  In  certain  individuals  the  optic  nerve  may  also  be  the  path  over 
which  the  afferent  impulses  travel  to  originate  the  act  of  sneezing. 

Laughing  consists  of  a  long  inspiration  followed  by  a  series  of  short 
expirations,  during  which  the  glottis  is  open  and  the  vocal  cords  thrown 
into  vibration  by  the  movement  of  the  column  of  air. 

Crying  is  produced  by  the  same  mechanism  as  laughing,  the  only 
difference  being  in  the  facial  expression.  As  a  consequence,  laughing 
frequently  verges  into  crying,  and  the  reverse,  and  the  two  are  frequently 
indistinguishable. 

6.  INFLUENCE  OF  THE  RESPIRATION  ON  THE  CIRCULATION. — In  the  exami- 
nation of  a  tracing  obtained  in  a  blood-pressure  experiment,  in  addition 
to  the  undulations  caused  by  the  variations  in  the  blood  pressure  due  to 
each  individual  heart  contraction,  a  larger  series  of  waves,  each  com- 
posed of  a  number  of  cardiac  pulsations,  may  be  noticed.  These  undula- 
tions have  already  been  referred  to  as  being  due  to  the  influence  of  the 
respiratory  movements  on  arterial  blood  pressure.  Their  mode  of  pro- 
duction is  now  to  be  considered.  Roughly  speaking,  it  may  be  stated 
that  during  every  inspiration  the  blood  pressure  falls,  and  during  every 
expiration  it  rises.  This  statement  is,  however,  not  absolutely  correct, 
but  requires  some  slight  modification. 


606  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

The  large  vessels  of  the  thoracic  cavity  vary  in  capacity  according 
to  the  degree  of  pressure  to  which  their  walls  are  subjected.  Naturally, 
the  veins,  possessing  thinner  and  less  rigid  walls,  are  more  influenced  by 
external  pressure  than  are  the  arteries.  When  the  thorax  becomes  ex- 
panded in  inspiration,  naturally  a  negative  pressure  is  likewise  exerted 
on  the  walls  of  the  veins,  and  tliey  consequently  tend  to  expand.  As  a 
consequence  the  flow  of  blood  toward  the  heart  is  accelerated,  and,  as 
has  been  already  indicated,  the  pressure  within  the  veins  in  the  neighbor- 
hood of  the  great  vessels  at  the  base  of  the  heart  becomes  negative  dur- 
ing inspiration.  If  an  opening  be  made  in  a  vein,  as,  for  example,  at  the 
root  of  the  neck,  at  each  inspiratory  movement  there  is  a  tendency  for 
air  to  enter  the  venous  trunks,  forming  one  of  the  serious  sources  of 
danger  in  wounds  of  the  large  veins.  As  a  consequence  of  the  greater 
increase  in  the  venous  blood-current  during  inspiration  a  larger  quantity 
of  blood  enters  the  right  auricle. 

Further,  if  an  opening  be  made  in  the  skull  of  an  animal,  a  distinct 
rate  of  pulsation,  which  is  synchronous  with  the  respiratory  movements, 
may  be  noticed,  in  addition  to  that  due  to  the  arterial  pulsation.  At 
each  inspiration  the  brain  sinks,  and  at  each  expiration  it  rises.  The 
production  of  this  phenomenon  is  evidently  due,  in  the  first  place,  to 
facilitation  of  the  flow  of  blood  from  the  brain  in  inspiration  and,  in  the 
second  place,  to  retardation  in  expiration,  since  it  disappears  on  ligature 
of  the  large  arteries  going  to  the  brain  or  when  a  free  opening  is  made 
in  the  venous  sinuses.  During  inspiration,  therefore,  a  larger  quantity 
of  blood  enters  the  right  side  of  the  heart,  and,  as  a  consequence,  a  larger 
quantity  escapes  from  the  left  ventricle,  more  blood  escapes  into  the 
aorta,  and  the  blood  pressure  is  increased. 

During  expiration  opposite  conditions  obtain.  The  pressure  on  the 
walls  of  the  great  veins  of  the  thorax  is  now  increased  by  the  reduction 
in  the  volume  of  the  thorax,  and  entrance  of  blood  into  the  thorax  is 
hindered,  less  blood  enters  the  heart,  less  is  thrown  out  by  the  left  ven- 
tricle, and,  as  a  consequence,  arterial  pressure  falls. 

This  state  of  affairs  is,  however,  not  quite  so  simple  as  this  would 
seem  to  indicate.  In  the  first  place,  the  effect  of  the  respiratory  move- 
ments on  the  arteries  must  be  different  from  that  on  the  veins,  for 
while  inspiration  tends  to  facilitate  the  flow  of  blood  in  the  veins  toward 
the  thorax,  it  likewise  tends  to  hinder  the  escape  of  blood  in  the  arteries 
from  the  thorax  ;  while  at  the  same  time  a  negative  pressure  is  exerted 
not  only  on  the  veins  but  on  the  arteries,  and,  therefore,  tends  to  produce 
expansion  of  the  arterial  trunks  in  the  same  way  as  expansion  of  the 
veins  is  produced.  Therefore,  the  effect  of  inspiration  on  the  great  arte- 
rial trunks  would  be  to  reduce  blood  pressure.  But  from  the  fact  that,  as 
already  indicated,  the  walls  of  the  arteries  are  less  yielding  than  those 


KESPIKATION.  607 

of  the  veins,  the  effect  of  inspiration  in  producing  expansion  of  the  blood- 
vessels is  less  marked  on  the  arteries  than  on  the  veins,  and,  as  a  conse- 
quence, the  reduction  of  blood  pressure  from  arterial  expansion  is  less 
marked  than  the  increase  of  blood  pressure  from  venous  expansion. 
During  expiration,  on  the  other  hand,  increase  of  pressure  without  the 
aortic  arch  acts,  of  course,  in  a  similar  manner  to  reduction  of  the  calibre 
of  the  aorta,  and  so  would  lead  to  an  increase  in  the  blood  pressure.  This 
reduction  is,  however,  likewise  less  than  the  compensating  reduction  in 
the  volume  of  the  veins ;  so  that  although  expiration  would  therefore  tend 
to  increase  arterial  pressure,  it  is  more  than  compensated  for  by  the 
reduced  amount  of  blood  brought  to  the  heart  through  the  veins. 

If,  however,  a  simultaneous  tracing  be  made  of  the  blood  pressure 
and  of  the  respiratory  movements,  it  will  be  seen  that  the  increase  of 
blood  pressure  does  not  exactly  coincide  with  the  commencement  of 
inspiration,  nor  is  the  fall  of  blood  pressure  synchronous  exactly  with 
expiration ;  but  it  will  be  found  that  at  the  commencement  of  inspira- 
tion blood  pressure  is  falling,  while  it  begins  to  rise  before  inspiration 
is  completed,  and  does  not  attain  its  maximum  until  after  expiration  has 
commenced.  Then,  before  expiration  is  completed,  the  fall  again  com- 
mences, and  continues  during  the  first  part  of  the  succeeding  inspiration. 
These  facts  show  that,  in  addition  to  the  mere  mechanical  changes  in  the 
blood  supply  produced  by  the  va^ing  pressure  in  inspiration  and  expira- 
tion, some  other  causes  are  at  work. 

The  respiratory  undulations  in  the  blood  pressure  are  due,  in  part, 
to  var}Ting  degrees  of  stimulation  of  the  vaso-motor  centre.  In  other 
words,  the  degree  of  tonicity  of  the  blood-vessel  walls  is  subject  to 
rhythmical  variations,  these  variations  depending  upon  coincident 
changes  in  the  degree  of  stimulation  of  the  vaso-motor  centre,  to  which 
are  added  the  changes  produced  in  a  purely  mechanical  way  by  altera- 
tions in  the  intra-thoracic  pressure. 

If  the  pulsations  be  counted  in  the  ascending  and  descending  phases 
of  the  blood  pressure,  it  will  be  noticed  that  the  pulse  beats  faster  dur- 
ing increase  of  pressure  than  where  it  is  decreasing.  This  variation  in 
the  pulse-rate  is  especially  marked  in  the  dog,  and  is  due  to  changes  in 
the  activity  of  the  cardio-inhibitory  centre  in  the  medulla  oblongata,  as 
is  proven  b}^  the  fact  that  section  of  both  vagi  causes  the  difference  in 
pulsation  to  disappear. 

It  is  therefore  evident  that  the  vaso-motor,  the  respiratory,  and  the 
cardio-inhibitory  centres  to  a  certain  extent  act  in  unison. 

The  state  of  affairs  is  different  in  cases  where  artificial  respiration  is 
carried  on,  as  in  curarized  dogs,  when  the  mechanical  causes  at  work 
must  necessarily  be  reversed.  If  a  dog  be  curarized  and  subjected  to 
artificial  respiration,  and  tracings  of  the  intra-thoracic  pressure  and  of 


608  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

the  blood  pressure  be  simultaneously  made,  the  respiratory  undulations, 
although  in  a  modified  form,  will  still  be  present.  In  this  case  the  con- 
ditions are  exactly  reversed,  for  in  inspiration  air  is  forced  into  the  lungs 
instead  of  being  aspirated,  so  that  the  pressure  in  the  thorax  is  increased 
during  inspiration  instead  of  being  decreased,  as  in  normal  inspiration. 
So  that  we  are  compelled  to  attribute  the  greatest  influence  in  the  pro- 
duction of  these  respiratory  undulations  to  varying  changes  in  the  vaso- 
motor  centres  rather  than  to  the  mechanical  causes  producing  changes  in 
the  intra-thoracic  pressure. 

Another  cause  which  may  be  concerned  in  the  production  of  these 
respiratory  undulations  is  also,  to  a  certain  extent,  mechanical,  and 
depends  upon  varying  pressures  within  the  abdomen.  As  the  diaphragm 
descends  in  inspiration,  the  abdominal  contents,  including  the  abdominal 
vessels,  are  pressed  upon,  and,  as  a  consequence,  the  blood  pressure  must 
be  increased.  The  reverse  naturally  obtains  during  expiration,  and  it  is 
found  that  section  of  both  phrenic  nerves  and  opening  of  the  abdominal 
cavity  causes  an  almost  entire  disappearance  of  the  respiratory  undu- 
lations ;  so  that,  therefore,  the  mechanical  changes  in  the  abdominal 
pressure  are  likewise,  to  a  certain  extent,  concerned  in  the  production  of 
the  respiratory  undulations. 


SECTION    IX. 

THE  MAMMARY  SECRETION. 

THE  milk  is  the  secretion  of  the  mammary  glands  of  the  females  of 
the  mammalian  group,  and  is  poured  out,  as  a  rule,  only  in  the  last 
stages  of  pregnancy  and  after  the  birth.  Sometimes,  especially  in 
goats,  the  secretion  of  milk  is  formed  by  the  rudimentary  glands  of  the 
male..  In  many  cases  the  mammary  glands  of  newly-born  infants  of  both 
sexes  also  pour  out  a  scanty  secretion,  which  is,  probably ,  closely  similar 
in  composition  to  milk,  although  it  has  been  but  slightly  investigated. 
This  secretion  commences  usually  three  or  four  days  after  the  birth, 
increases  np  to  the  eighth  day,  remains  a  few  days  stationary,  and  then 
commences  to  decrease,  and  by  the  end  of  the  first  month  has  usually 
entirely  disappeared. 

The  mammary  glands  of  various  animals  of  the  mammalian  type 
also  frequently  pour  out  a  secretion  immediately  after  birth.  These 
facts,  as  well  as  the  morphological  characters  of  the  mammary  gland, 
indicate  that  they  are  exceptionally  developed  sebaceous  glands ;  the 
close  similarity  in  composition  of  the  milk  and  the  secretion  of  the 
sebaceous  glands  of  the  skin  also  supports  this  view. 

The  following  table  represents  the  composition  of  this  secretion 
from  the  rudimentary  mammary  gland  : — 


Water, 
Solids, 

Casein, 
Albumen, 


Newly-Born  Five-weeks- 
infant,  old  FoaL 

95.705  93.10 

4.295  6.90 

0.557  0.50 

0.490  1.02 

1.456  (?) 


Fat, 

Milk-sugar, 0.956  3.67 

Inorganic  salts,  .        ,  "     .        .        .        .      0.826  0.44 

Before  and  shortly  after  delivery  pregnant  females  secrete  a  fluid 
from  their  mammary  glands  which  differs  considerably  from  that  of  the 
later  secretion.  It  is  termed  colostrum. 

Colostrum  is  an  opaque,  yellowish  fluid,  containing  a  large  amount 
of  the  so-called  colostrum  cells  (true  glandular  cells  in  different  stages 
of  fatty  degeneration),  few  milk-globules,  a  large  amount  of  albumen, 
little  or  no  casein,  and  but  little  fat,  milk-sugar,  and  salts.  On  account 
of  its  large  percentage  of  albumen,  it  coagulates  when  heated,  differing 
in  this  respect  from  milk ;  in  fact,  colostrum  when  first  secreted  closely 

39  (609) 


610 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


resembles  blood-serum,  with  the  addition  of  colostrum  corpuscles. 
Gradually,  however,  the  colostrum  secretion  passes  into  a  milk  secretion, 
albumen  and  colostrum  corpuscles  become  reduced  in  amount,  fat,  casein, 
sugar,  and  milk-globules  increase.  The  specific  gravity  of  colostrum 
varies  from  1040  to  1060,  being  higher  immediately  after  delivery  and 
falling  as  it  gives  place  to  a  true  milk  secretion.  Thus,  according  to 
Quevenne,  the  specific  gravity  of  colostrum  of  the  Cow  on  the  first  day 
after  calving  is  1060;  on  the  second,  1053;  on  the  third,  1035;  on  the 
fourth,  1040  ;  on  the  fifth,  102T.  The  reaction  of  colostrum  is  ordinarily 
alkaline  and  becomes  acid  on  standing.  Immediately  after  calving  the 
colostrum  of  the  cow  contains  8.5  per  cent,  albumen,  after  one  day  6.4 
per  cent.,  after  three  days  3.4  per  cent.,  after  seven  days  1.9  per  cent., 
and  after  twentj^-one  days  0.6  per  cent.  On  an  average,  colostrum  may 
be  said  to  have  the  following  composition : — 


Water, 

Casein, 

Albumen, 

Fats, 

Sugar, 

Salts, 


78.7  per  cent. 
7.3 
7.5 
4.0 
1.5 
1.0 


The  so-called  uterine  milk  is  a  white  or  rose-colored,  creamy,  alkaline 
fluid,  with  specific  gravity  of  1030  to  1040,  and  is  obtained  by  compres- 
sion of  the  placenta!  cotyledons  of  ruminant  animals.  It  rapidly 
becomes  acid  and  undergoes  spontaneous  coagulation.  It  contains  fatty 
particles,  free  nuclei,  and  epithelial  cells.  The  following  table  represents 
its  composition  in  the  cow  : — 

Water,     .        .        .    '    ,        ,,      »• '-.-   t        .  87.91  per  cent. 

Solids,      .        .        .        .••  ...'"'  . o"".        .  12.09 
Fats,         .        .        .        .  '      .        .        .       >      1  23 

Albumen  cells,        .        .        *.        .         .         .  10.40 

Albuminates, 0.16 

Ash, 0.37 

1.  THE  PHYSICAL  AND  CHEMICAL  PROPERTIES  OP  MILK. — Milk  is  an 
opaque  fluid,  with  a  sweetish  taste  and  an  opalescent  bluish  tint,  in  thin 
layers,  and  a  characteristic  odor  due  to  the  volatile  substances  derived 
from  the  secretions  of  the  cutaneous  glands. 

Milk  is  not  a  homogeneous  fluid,  but  is  an  emulsion,  which  consists 
of  the  so-called  milk-globules  suspended  in  milk-plasma,  the  latter  con- 
sisting of  a  solution  of  albumen,  sugar,  and  salts.  Examined  under  the 
microscope  the  milk-globules  appear  as  highly  refractive  drops  of  oil 
floating  in  the  clear  fluid  (Figs.  258  and  259). 

-The  size  of  these  globules  varies  from  0.01  to  0.03  millimeter. 

In  colostrum  the  corpuscles  are  much  larger  than  in  milk,  and  are 
capable  .of  amoeboid  movements.  The  milk-corpuscles  consist  almost 


MAMMARY   SECRETION. 


611 


entirely  of  fat,  and  are  composed  of  combinations  of  gtycerin  with 
oleic,  palmitic,  and  stearic  acids.  They  are  surrounded  by  a  thin  layer  of 
casein,  not  in  the  form  of  a  solid  deposition,  but  the  casein  probably 
exists  in  a  condition  of  high  imbibition  rather  than  in  a  state  of  solidity 
or  of  true  solution.  The  laj'er  of  casein  cannot  be  regarded  as  consti- 
tuting a  membrane,  although  it,  to  a  certain  extent,  fulfills  the  same 
function.  If  acetic  acid  is  added  to  a  preparation  of  milk,  under  the 
microscope  it  will  be  seen  that  the  caseous  envelope  is  dissolved  and  the 
oil-globules  run  together  and  form  irregular  masses  of  oil. 

When  cows'  milk  is  shaken  up  with  caustic  potash  and  then 
agitated  with  ether  the  oil  passes  into  solution  in  the  ether.  The 
previous  subjection  to  the  action  of  caustic  potash  is,  however,  essential, 
since  ether  will  not  dissolve  the  oil  from  cows'  milk  unless  the  casein 
envelopes  be  previously  dissolved  by  acetic  acid  or  potash. 


FIG.  258.— MICROSCOPIC  APPEARANCE  OP  MILK  AND  COL,OSTRTTM.    (Landois.) 

The  upper  half  of  the  figure  represents  milk ;  the  lower  half  colostrum. 

If  milk  be  allowed  to  stand  for  some  time  the  oil-globules,  which  in 
freshly  secreted  milk  are  uniformly  distributed  through  the  milk,  now 
rise  to  the  surface  and  form  a  layer  largely  composed  of  fat,  or  the 
so-called  cream. 

The  reaction  of  freshly  secreted  milk  is  alkaline  in  the  herbivora  and 
in  the  human  female,  while  that  of  the  carnivora  is  acid. 

The  milk  of  herbivora  frequently  will  exhibit  both  an  alkaline  and 
an  acid  reaction,  due  to  the  presence  of  an  acid  sodium  phosphate 
(H2NAP04)  and  of  an  alkaline  disodic  phosphate  (NAaHP04).  Such 
a  reaction  is  spoken  of  as  amphioter. 

When  milk  is  allowed  to  stand,  the  alkaline  reaction,  when  present, 
gives  place  to  an  acid  reaction,  which  is  due  to  the  fermentation  of  the 
milk-sugar  and  its  conversion  into  lactic  acid.  When  the  cream  is 


612 


PHYSIOLOGY  OF  THE   DOMESTIC  ANIMALS. 


removed  from  milk  the  skimmed  milk  is  less  opaque  and  white,  while 
the  edges  in  contact  with  the  vessel  have  a  distinct  bluish  tint. 

The  specific  gravity  of  milk  varies  from  1018  to  1040.  Cows'  milk, 
when  pure,  may  vary  between  sp.  gr.  1028  and  1034,  usually  increasing 
from  the  first  to  the  eighth  month  of  lactation  from  1031  to  1039. 

In  composition  milk  consists  of  solids  partly  dissolved  and  partly 
suspended  in  a  fluid  plasma,  the  amount  varying  from  12  to  13  per  cent. 
Of  these  solids,  3  to  6  per  cent,  is  represented  by  the  fats,  9.25  per  cent, 
by  the  other  solids. 

In  composition,  milk  is  composed  of  85  to  90  per  cent,  water, 
casein,  albumen,  fat,  milk-sugar,  lecithin,  and  salts,  with  carbon  dioxide, 


FIG.  259.— MICROSCOPIC  APPEARANCES  OF  MILK,  I;  CREAM,  II;  BUTTER,  HI;  COLOS- 
TRUM OF  MARE,  IV;  AND  COLOSTRUM  OF  Cow,  V.    (Thanhoffer.) 

oxygen  arfd  nitrogen  gases,  urea,  and  various  accidental  constituents, 
such  as  lactic  acid  after  milk  fermentation,  haematin,  bile  coloring- 
matters,  and  mucin.  It  often  serves  to  eliminate  various  substances  such 
as  drugs,  among  which  may  be  mentioned  potassium  iodide,  iodine,  salts 
of  various  metals,  the  oil  of  garlic,  and  various  other  bodies.  When 
filtered  through  animal  membrane  or  porous-clay  filters,  the  milk-plasma 
is  obtained  as  a  clear,  slightly  opalescent  fluid,  which  contains  casein, 
serum-albumen,  peptone,  milk-sugar,  salts — in  fact,  all  the  constituents 
of  milk,  with  the  exception  of  the  oil-globules  and  a  considerable  portion 
of  the  casein,  the  amount  of  the  latter  which  is  kept  back  being  greatly 
•-  increased  when  a  fresh  animal  membrane  is  used  as  a  filter. 


MAMMARY    SECRETION. 


613 


The  following  tables   represent  various  analyses   of  this  secretion 
in  different  animals  : — 

I.     COMPOSITION   OP   THE   MILK   OF   DIFFERENT  ANIMALS.     (AFTER  GORUP- 
BESANEZ,  LIEBERMANN,  GAUTIER,  ETC.) 


Woman. 

CONSTITUENTS. 

Ass. 

Cow. 

Goat, 

Sheep. 

Mare. 

Colos- 

truin. 

Water,   

86  27 

8891 

8777 

84.08 

90  70 

8656 

86.76 

83.30 

8284 

Solids,    

13.72 

11.09 

12.23 

15.92 

19.30 

13.44 

13.24 

16.69 

17.16 

Casein,       > 
Albumen,  $ 

2.95 

3.92 

2.34 

3.23 

1.70 

C    3.50 
{    0.58 

2.92? 
1.31$ 

5.73 

1.64 

Butter,  .... 

5.37 

2.67 

3.68 

5.78 

1.55 

4.03 

4.48 

6.05 

6.87 

Milk-sugar,  .    . 
Inorganic  salts, 

5.13 
0.22 

4.36 
0.14 

5.55 
0.23 

6.51 
0.35 

5.80 
0.50 

4.60 
0.73 

3.91 
0.62 

3.96  > 
0.68  $ 

8.65 

II. 


In  100  Parts. 

Cow. 

Goat. 

Sheep. 

Ass. 

Mare. 

Sow. 

"Woman. 

Water 

85  7 

864 

840 

91  0 

828 

824 

888 

Solids,      

14.3 

13^6 

16.0 

9.0 

17.2 

17.6 

11.2 

Casein,      
Albumen,. 

4.8 
06 

3.3) 
12S 

5.3 

2.0 

1.6 

6.1 

3.5 

Fats,    

4.3 

4.4 

5.4 

1.3 

6.9 

6.4 

3.5 

Sugar,  
Salts  

4.0 

0.6 

4.0 
0.7 

4.1) 

0.7$ 

5.7 

8.7 

$    4.0 

I    1.1 

4.0 
0.2 

Asses'  milk  is  nearest  in  composition  to  women's  milk ;  cows'  milk 
has  one-half  more  fat  and  almost  one-half  more  albuminoids. 


III.     THE  ASH  OF  MILK  IN  100  PARTS. 


WOMEN'S  MILK. 

Cows' 

MILK. 

(Wildenstein.) 

(Weber.) 

(Haidlen.) 

Sodium,  

4.21 

6.38 

8.27 

Potassium 

3159 

2471 

15.42 

Chlorine      . 

1906 

1439 

16.96 

Calcium 

18  78 

17.311 

Magnesium,     .... 

0.87 

1.90  I 

56.52 

Phosphoric  acid,  

19.00 
2.64 

29.13  J 
1.15 

Ferric  oxide         ...               . 

0.10 

0.33 

0.62 

Silica,     

trace 

0.09 

614  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

IV.     THE  RELATIVE  VALUE  OF  DIFFERENT  KINDS  OF  MILK. 


Water. 

Casein  and 
Albumen. 

Butter. 

Sugar  and 
Walts. 

Mares'  milk,  .     .               . 

91.15 

1.03 

1.27 

6.12 

Asses'      "      .     . 

89.01 

3.57 

1.85 

5.57 

Women's  milk,  . 

87.24 

2.88 

3.68 

5.78 

Goats' 

86.85 

3.79 

4.34 

3.78 

Cows'           "       . 

84.28 

4.35 

6.47 

4.34 

Sheep's        "                     . 

83.30 

5.73 

6.05 

O  G£J 

o.t/O 

V.     SOLIDS  IN  A  PINT  OF  MILK. 

Nitrogenous  constituents, 23.9  grammes. 

Fatty  22.7 

Saccharine              "                 .        .        .        .        .80.3        " 
Salts, 4.0 

2.  CASEIN  AND  MILK  COAGULATION. — Casein  is  a  proteid  body  of  an 
acid  reaction  which  is  scarcely  soluble  in  water  but  soluble  in  dilute  acids 
and  alkalies.  In  milk  its  solution  is  rendered  possible  by  its  combina- 
tion with  soluble  alkali  albuminates  and  through  the  presence  of  calcium 
phosphate.  In  amount  it  varies  from  3  to  5  per  cent.,  the  relative  pro- 
portions of  casein  and  albumen  being  from  1.87  per  cent,  to  4.68  per 
cent,  of  the  former  and  from  0.60  per  cent,  to  1.77  per  cent,  of  the  latter. 

Casein,  although  closely  similar  in  composition  to  alkali  albumen,  is 
not  identical  with  it,  but  is  probabty  to  be  regarded  as  a  combination  of 
alkali  albuminate  and  nuclein.  Casein  may  be  obtained  from  milk  by 
dilution  with  four  times  its  volume  of  water,  the  addition  of  dilute  acetic 
acid  (0.1  per  cent.)  until  a  precipitate  begins  to  appear,  th.en  passing  a 
current  of  carbonic  acid  gas,  filtering,  and  washing  the  precipitate  with 
water,  alcohol,  and  ether. 

Casein  may  also  be  obtained  from  milk  by  the  addition  of  magnesium 
sulphate  to  saturation. 

When  freed  by  ether  from  fats  after  its  preparation  by  the  latter 
process  and  dissolved  in  water,  casein  is  a  snow-white  powder  and  in 
solution  rotates  yellow  light  eighty  degrees  to  the  left;  in  dilute  alkaline 
solution,  seventy-six  degrees  to  the  left;  in  strong  alkaline  solution, 
ninety-one  degrees  to  the  left ;  and  in  dilute  hydrochloric  acid,  eighty- 
seven  degrees  to  the  left.  It  leaves  no  ash  on  incineration. 

When  milk  is  boiled  the  serum-albumen  of  milk  becomes  coagulated, 
while  the  skim  formed  is  due  to  the  deposition  of  a  thin  pellicle  of  casein 
due  to  evaporation,  and  which  is  renewed  as  fast  as  it  is  removed. 

The  coagulation  of  milk  depends  upon  the  precipitation  of  casein. 
Everything,  therefore,  which  causes  casein  to  become  insoluble  causes 
coagulation  of  milk.  Such  agents  are  acids,  rennet,  tannin,  alcohol,  and 
mineral  salts. 


MAMMARY   SECRETION.  615 

Milk  is  coagulated  by  all  acids.  Several,  especially  acetic  acid  in 
excess,  again  dissolve  the  precipitate  of  casein.  Casein  is  precipitated 
by  acids  only  when  a  certain  degree  of  acidity  is  reached,  since  alkaline 
phosphates  must  be  first  neutralized ;  if  the  alkaline  phosphates  are 
removed,  even  carbon  dioxide  is  then  capable  of  precipitating  casein. 
The  spontaneous  coagulation  of  milk  is  produced  by  the  development  of 
lactic  acid,  which  is  formed  from  milk-sugar  in  the  milk  by  the  action 
of  bacteria  introduced  from  without  or  by  the  action  of  the  lactic  acid 
ferment  which  appears  to  be  present  in  milk.  In  this  process  the  neutral 
alkaline  phosphate  is  converted  into  acid  phosphate.  The  casein  is  sepa- 
rated from  its  combination  with  calcium  phosphate  and  is  precipitated, 
the  sugar  being  decomposed  into  lactic  acid  and  carbon  dioxide.'  When 
milk  coagulates  spontaneously,  or,  in  other  words,  curdles,  it  separates 
into  a  tough,  jelly-like  substance  or  curd,  which  consists  of  the  insoluble 
casein  and  fat,  floating  in  an  opalescent  acid  fluid,  or  whey.  The  whey 
contains  the  greater  part  of  the  salts  of  the  milk,  the  lactic  acid,  the 
undecomposed  milk-sugar,  and  certain  amounts  of  fat  and  the  albumi- 
noids. That  the  spontaneous  curdling  of  milk  is  due  to  the  action  of  the 
ferment  contained  itself  in  milk  (which  decomposes  the  milk-sugar  into 
lactic  acid)-  is  proved  by  the  fact  that  boiling  greatly  retards  the  spon- 
taneous coagulation,  evidently  through  the  destruction  of  this  ferment. 
This  lactic  acid  ferment  may  be  precipitated  from  milk  by  the  addition  of 
an  excess  of  alcohol.  If  the  ferment  is  then  dissolved  in  water  and  added 
to  solutions  of  milk-sugar  it  will  produce  rapid  fermentation.  The  action 
of  the  milk-curdling  ferment,  as  pointed  out  in  the  chapters  on  Digestion, 
is  very  different.  Here,  the  casein  is  rendered  insoluble  by  the  action  of 
the  rennet  ferment,  even  in  alkaline  fluids  and  without  at  all  calling  in 
the  aid  of  lactic  acid.  The  salts  in  milk,  especially  the  calcic  phosphate, 
are  essential  to  the  action  of  milk-curdling  ferment ;  for,  when  milk  is 
subjected  to  dialysis,  rennet  is  then  rendered  incapable  of  producing 
coagulation. 

Spontaneous  coagulation  of  milk  may  be  prevented  by  the  addition 
of  sodic  carbonate,  boracic  or  salicylic  acids.  So,  also,  the  addition  of 
one  drop  of  the  ethereal  oil  of  mustard  to  twenty  cubic  centimeters  of 
milk  will  likewise  preserve  its  fluid  condition. 

Colostrum,  sows'  milk,  and  the  milk  of  carnivora  coagulate  when 
heated.  Boiled  milk  coagulates  spontaneously  only  with  difficulty,  and 
is  also  more  difficult  to  coagulate  with  rennet,  but  when  acidulated  the 
casein  coagulates  even  more  readily  than  in  fresh  milk. 

A  high  temperature  facilitates  both  forms  of  coagulation.  Milk 
which  has  become  acid,  but  which  is  still  fluid,  will  coagulate  when 
heated.  ' 

In  addition  to  casein,  milk  contains  other  albuminoids,  one  of  which 


616  PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 

in  all  of  its  characteristics  closely  resembles  serum-albumen.  It  is 
present  in  about  0.5  per  cent.,  though  in  colostrum  it  is  in  much  larger 
percentage.  It  is  there  present  in  about  15  per  cent.,  but  rapidly  de- 
creases  for  about  four  weeks,  when  it  reaches  its  average  percentage  of 
0.5  per  cent. 

When  the  plasma  of  milk  is  slightly  acidulated  and  boiled  it  coagu- 
lates between  10°  and  80°  C.  Peptone  is  also  present  in  small  amounts 
as  a  trans  udat  ion  from  the  blood. 

3.  MILK-SUGAR.  —  Milk-sugar  is  an  animal  carbohydrate  found  only 
in  milk  ;  its  average  percentage  is  4.5  per  cent.,  varying  from  3  to  7  per 
cent.  Of  all  the  constituents  of  the  milk  the  milk-sugar  is  least  influ- 
enced by  external  conditions.  It  is  found  dissolved  in  milk-serum  and  in 
whey,  whether  after  the  spontaneous  coagulation  of  the  milk  (acid  whey) 
or  after  the  action  of  rennet  (sweet  whey).  It  may  be  obtained  by  coag- 
ulating milk  and  evaporating  the  whey  until  Crystals  form.  It  occurs 
with  one  molecule  of  water  in  rhombic  prisms  soluble  in  from  five  to  six 
parts  of  cold  water  and  in  three-  parts  of  boiling  water.  It  is,  therefore, 
very  insoluble  in  comparison  with  the  other  forms  of  sugar.  It  is  only 
slightly  soluble  in  alcohol  and  water,  and  is  not  readily  crystallizable. 

Its  formula  may  be  placed  at  C6H12O6.  Heated  up  to  100°  C.  it 
loses  some  of  its  water,  and  may  thus  be  represented  by  the  formula 
C12H220U. 

The  specific  rotation  of  milk-sugar  containing  water  of  crystalliza- 
tion is  -f-  52.53°  at  20°  C.  ;  anhydrous  milk-sugar  =  -\-  81.3°.  When 
warmed  with  alkalies  it  becomes  brown,  like  dextrose  (Moore's  test),  and 
likewise  reduces  Fehling's  solution. 

The  milk-sugar  of  the  human  female,  the  cow,  and  the  goat  agree  in 
their  chemical  characteristics,  their  form  of  crystallization,  and  their 
action  on  polarized  light. 

The  spontaneous  coagulation  of  milk  is  due  to  the  formation  of 
lactic  acid  from  milk-sugar,  one  molecule  of  milk-sugar  forming  foui* 
molecules  of  lactic  acid.  The  formula  may  be  represented  as  follows  :  — 


When  lactic  acid  forms,  it  unites  with  the  alkaline  phosphates  to 
form  lactates  of  the  alkalies  and  acid  salts,  and  coagulation  only  occurs 
when  all  the  alkaline  phosphates  have  been  converted  into  acid  salts.  A 
slight  further  development  of  lactic  acid  is  then  sufficient  to  cause  coag- 
ulation. 

If  two  glasses,  one  containing  milk  and  the  other  a  pure  solution  of 
milk-sugar,  are  subjected  to  the  same  conditions,  after  a  fewtla}^  the 
former  will  contain  so  much  lactic  acid  that  the  milk  will  be  coagulated; 
while  not  the  slightest  trace  of  acidity  will  be  found  in  the  milk-sugar 


MAMMAKY  SECRETION.  617 

solution.  This  proves  that  the  milk  contains  a  ferment  which  is  capable 
of  splitting  up  milk-sugar  into  lactic  acid.  Such  a  ferment  is  widely 
distributed  in  the  animal  body.  It  may  be  often  extracted  from  the 
gastric  mucous  membrane,  and  is  entirely  distinct  from  pepsin  or  the 
milk-curdling  ferment,  since  it  preserves  its  action  even  after  the  other 
ferments  are  destroyed  by  dilute  caustic  soda.  The  ferment  may  be 
obtained  from  milk  after  dialysis  by  precipitation  with  alcohol,  and, 
after  drying,  dissolving  the  precipitate  in  water.  Such  a  precipitate  will 
coagulate  milk  and  will  cause  the  development  of  lactic  acid  in  solu- 
tions of  milk-sugar. 

This  ferment  has  a  neutral  reaction  and  is  soluble  in  glycerin.  It  is 
destroyed  by  boiling,  and  appears  to  regain  its  activity  when  treated 
with  oxygen.  This  would  indicate  that  it  is  a  ferment  generator  and 
not  a  true  ferment,  and  explains  why  boiled  milk  may  be  kept  longer 
than  unboiled ;  while  the  fact  that  even  boiled  milk  will  ultimately  coag- 
ulate is  to  be  attributed  to  the  subsequent  development  of  the  ferment 
through  the  action  of  the  air. 

Increase  of  temperature  increases  the  activity  of  the  ferment.  Milk- 
sugar  is  not  directly  fermentable;  that  is,  it  cannot  be  directly  converted 
into  alcohol,  though  by  the  action  of  dilute  sulphuric  or  hydrochloric 
acids  it  ma}^  be  partly  transformed  into  a  fermentable  lactic  acid.  This 
process  is  concerned  in  the  manufacture  of  koumiss  from  mares'  milk, 
which  contains  a  large  amount  of  sugar.  A  similar  fermented  liquid 
may  be  obtained  from  cows'  milk  through  the  action  of  the  yeast-plant. 

4.  FAT  AND  CREAM. — Fat  is  present  in  milk  in  the  form  of  minute 
globules,  the  average  percentage  being  3  to  3|  per  cent.,  although  it 
may  vary  from  2^  to  5J  per  cent. 

The  following  fatty  acids  have  been  found  in  milk  :  But}'ric,  caproic, 
caprylic,  caprinic,  myristic,  palmitic,  stearic,  and  oleic.  The  percentages 
of  palmitic,  oleic,  and  stearic  acids  vary.  So  the  melting  point  of  butter 
also  varies,  as  does,  also,  its  specific  gravity.  Normally,  the  melting  point 
varies  from  32°  to  37.5°  C. 

Cows'  butter  contains  about  68  per  cent,  palmitin,  30  per  cent, 
olein,  and  2  per  cent,  other  fats,  the  solid  fats  apparently  being  more 
abundant  in  winter  than  in  summer.  The  butter  may  be  separated  from 
milk  by  mechanical  agitation  (churning),  the  enveloping  layers  of  casein 
being  thus  ruptured.  It  was  formerly  supposed  that  the  fatty  globule 
of  milk  had  a  solid  envelope,  because  the  fat  does  not  pass  into  solution 
in  ether  unless  caustic  potash  had  been  previously  added.  At  most, 
however,  we  may  assume  that  the  fat  is  surrounded  by  an  envelope  of 
fluid  casein,  rendered  more  consistent  here  than  elsewhere  by  the  mo- 
lecular attraction  exerted  by  the  fat-globules.  Casein  is  not  present  in 
the  milk  in  the  form  of  a  true  solution,  but  rather  in  a  high  degree  of 


618  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

imbibition ;  so  the  effect  of  caustic  potash  is  to  enable  the  casein  to  pass 
into  solution,  and  so  render  the  oil  accessible  to  ether.  The  absence  of 
any  solid  envelope  of  the  oil-globule  is  proved  by  the  absence  of  any 
such  formation  after  mechanically  breaking  up  the  oil-globules,  while  the 
proof  of  the  fact  of  non-solution  of  casein  in  the  milk  is  found  in  the 
fact  that  when  milk  is  filtered  through  porous  earthenware  scarcely  any 
casein  passes  through,  while  the  other  albuminoids  which  are  really  in 
solution  do  so  pass.  Casein,  therefore,  in  milk  acts  like  the  gum  around 
the  oil-globules  in  an  artificial  mucilage  emulsion. 

On  account  of  the  lighter  specific  gravity,  when  milk  stands  the  oil- 
globules  rise  to  the  top  and,  accompanied  by  varying  amounts  of  the 
other  constituents  of  the  milk,  constitute  the  cream ;  the  largest  rise 
first,  while  the  smaller  ones  remain  suspended  in  the  body  of  the  milk. 
The  ascent  of  the  cream  is  the  more  rapid  the  smaller  the  distance  the 
fat-globules  have  to  traverse.  Hence,  cream  is  formed  more  rapidly  in 
broad,  shallow  vessels  than  in  tall,  narrow  ones.  Unless  the  temperature 
of  the  milk  is  constant,  currents  are  set  up  in  the  milk  from  the  differ- 
ences of  temperature,  and  the  formation  of  cream  is  delayed  until  the 
entire  volume  of  milk  and  the  external  medium  are  of  the  same  tempera- 
ture. Hence,  shallow  metal  pans,  by  leading  to  a  rapid  equalization  of 
temperatures,  are  usually  employed  for  the  separation  of  the  cream.  As 
the  milk  has  a  greater  volume  when  warm  than  when  cold,  the  cream  will 
contain  less  serum  when  the  molecules  of  the  fluid  are  further  separated 
from  each  other.  So  cream  formed  from  warm  milk  has  a  higher  per- 
centage of  fat  in  a  small  volume  than  cream  formed  from  cold  milk,  and 
the  higher  the  temperature  at  which  the  formation  of  cream  takes  place 
the  smaller  the  amount  of  fat  left  in  the  skimmed  milk. 

If  the  cream  has  been  removed  from  milk  by  means  of  the  centri- 
fugal machine  the  separation  is  much  more  complete  (often  only  O.L 
per  cent,  of  fat  remaining  in  the  milk),  while  the  milk  remains  sweet 
instead  of  becoming  sour,  as  ordinarily  occurs  in  the  usual  method  of 
separating  the  cream.  Skimmed  milk  so  obtained  is,  therefore,  a  more 
valuable  food,  since  it  still  contains  all  the  sugar  and  is  less  apt  to  pro- 
duce disturbances  of  digestion. 

The  addition  of  a  small  amount  of  water  facilitates,  the  addition  of 
salt  interferes  with,  the  separation  of  the  cream. 

The  following  table  represents  the  composition  of  cream  : — 

Water,  .        .        .        .        .        •*,.,%        .  61.67 

Fat,  .        .        .        .        .        ....        .        .  33.43 

Casein,  . "  .        .        .  2.62 

Sugar, ...  1  56 

Salts, .  0.72 

By  the  process  of  churning,  which  is  only  effective  after  the  milk 
has  become  slightly  acid,  only  about  two  thirds  of  the  fat  are  removed ; 


MAMMARY  SECRETION.  619 

the  other  third  remains  in  suspension  in  the  buttermilk.  Churning  is 
best  accomplished  at  about  14°  C.,  with  thirty  to  forty  strokes  of  the 
churn  per  minute. 

The  average  composition  of  buttermilk  may  be  placed  as  follows : 
Fat,  0.50  to  0.75  per  cent. ;  casein,  3.60  per  cent. ;  albumen,  3.7  per  cent. ; 
sugar,  0.52  per  cent. ;  ash,  0.52  per  cent. ;  water,  91.7  per  cent. 

The  amount  of  cream  which  may  be  obtained  from  milk  varies  very 
considerably  in  different  animals  and  under  different  conditions,  and  will 
be  subsequently  referred  to. 

Usually  about  80  per  cent,  of  the  entire  amount  of  fat  contained  in  the 
milk  passes  into  the  cream,  and  if  the  average  percentage  of  fat  in  milk 
be  placed  at  3.5  per  cent.,  the  fat  in  cream  would  amount  to  2.7  per  cent. 

When  butter  becomes  rancid  the  volatile  fatty  acids  are  set  free  and 
acrolein  and  formic  acid  are  formed  from  the  glycerin. 

Skimmed  milk  has  a  higher  specific  gravity  than  unskimmed  milk, 
from  the  fact  that  the  lighter  constituents,  that  is,  the  oils,  have  been 
largely  removed.  The  specific  gravity  of  skimmed  milk  may  rise  to 
1037,  or  even  higher.  Its  composition  may  be  placed  as  follows  : — 

Water, 89.65 

Fat, 0.79 

Casein 3.01 

Sugar, 5.72 

Salts, .  0.83 

5.  THE  INORGANIC  CONSTITUENTS  OF  MILK. — In  addition  to  the  albu- 
minoids, fats,  and  carbohydrates  contained  in  milk,  the  mineral  constitu- 
ents necessary  for  the  support  of  the  animal  body  are   also   present, 
their  average  amount  being  about  as  follows : — 

Phosphoric  acid,     .        . 28.31 

Chlorine, 16.34 

Calcium  oxide, 27.00 

Potassium,       .         .        .        .        .        .        .        .        .17.34 

Sodium, 10.00 

Magnesium, 4.07 

Ferric  oxide, 0.62 

Oxygen,  nitrogen,  and  carbon  dioxide  are  also  present;  and  since 
these  gases  may  be  entirely  removed  by  pumping,  they  are,  therefore,  in  a 
condition  of  solution  in  the  milk. 

Nitrogen  is  present  in  0.7  volumes  per  cent. ;  oxygen,  0.1  per  cent. ; 
carbon  dioxide,  7.7  per  cent. 

6.  VARIATIONS  IN  THE  QUANTITY  AND  COMPOSITION  OF  MILK. — The 
variations  which  occur  in  the  quantity  and  composition  of  milk  are 
largety  dependent  on  the  quantity  and   composition  of  the  food;    in- 
sufficient food  leads  to  a  reduction  in  both  the  absolute  quantity  and 
solid  constituents  of  the  milk.     In  addition  to  these  conditions,  to  be 


620 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


studied  in  detail  directly,  the  amount  and  character  of  the  milk  depends 
largely  upon  the  period  of  pregnancy  and  suckling,  as  there  is  a  close 
sympathy  between  the  secretion  of  the  mammary  glands  and  the  genital 
organs.  The  period  of  activity  of  the  mammary  gland  is  inaugurated 
shortly  before  the  first  birth,  and  shortly  thereafter  yields  the  largest 
amount  of  secretion,  which  in  the  best  Dutch  cattle  may  be  as  large  as 
30-35  liters  each  day.  This  maximum  persists  for  several  weeks,  and 
then  commences  gradually  to  decline,  there  being  a  continual  and  gradual 
relative  increase  in  the  albuminoids  and  a  decrease  in  the  fats  and  sugar, 
and  at  the  end  of  the  tenth  month  only  one-quarter  or  one-sixth  as  much 
milk  is  secreted  as  at  first.  During  the  first  ten  months  of  lactation  in 
the  best  cows  more  than  6000  liters  may  be  secreted  ;  fairly  good  cows 
will  form  3000  liters,  and  poor  cows  not  more  than  1000  liters  of  milk  in 
the  same  time 

Quite  frequently  good  cows  will  yield  as  much  milk,  nearly,  after  ten 
months  as  in  the  first  week  after  birth. 

Colostrum  is  far  richer  in  solids  than  the  later  secretions  of  milk. 


Immediately  aftei 
1st  day  after  cal 
2d    " 
3d     "       " 
4th  " 
5th   "       " 
6th  "       " 
14th  " 
28th  "       " 

r  calving, 
ving,     . 

9 

Solids. 
.     38.4 
.     30.1 
.     23.1 
.     15.3 
.     14.9 
.     13.7 
12  9 

Water. 
61.6 
69.9 
76.9 

84.7 
85.1 
86.3 

87.1 
87.4 
87.6 

.     ::•' 

.     12.6 
.     12.4 

The  solids  contain  the  following  constituents  : — 


Immediately  after  calving, 

1st  day  after  calving, 

2d 

3d 

4th 

5th 

6th 
14th 
28th  " 


Fat. 

8.4 

5.9 

6.2 

4.0 

4.5 

3.7 

3.0 

25 

2.6 


Sugar.     Albuminoids. 


0.0 
0.2 
0.9 
2.5 
3.6 
3.9 
4.3 
4.3 
4.4 


15.5 

13.7 

10.9 

8.6 

5.1 

3.4 

2.0 

1.6 

0.7 


Colostrum  contains  3.3  per  cent,  salts,  and  it  therefore  follows  that 
the  percentage  of  casein  must  be  11.2  per  cent. 

The  quantity  of  milk  depends  upon  the  breed  of  cow.  Some  races 
are  good  milkers,  while  others  are  better  as  meat  producers  and  beasts  of 
burden.  Nevertheless,  the  quantity  of  milk  is  directly  proportionate  to 
the  degree  of  development  of  the  mammary  gland.  Even  in  two  cows 
of  the  same  breed,  and  on  precisely  the  same  food,  the  amount  of  milk 
secretion  will  depend  upon  the  degree  of  development  of  the  glandular 
tissue. 


MAMMARY   SECEETION. 


621 


The  following  table  gives  the  average  milk  grven  by  different  breeds 
of  Irish  and  English  cattle  (Schmidt-Mulheim): — 


English  Cattle. 


Breed. 


f'SSSffin.     Total  Milk. 


1.  Shorthorns  (Wiltshire),      . 

2.  "  ... 

3.  "  ... 

4.  Cross-bred  (Cheshire), 

5.  Yorkshire,  ...... 

6.  Half-bred  and  Shorthorns  (Cheshire), 

7.  North-bred  and  South  Devon,   Jer- 

seys and  Shorthorns  (Devon), 

8.  Yorkshire  (Hunts),     .... 

9.  Half-bred  Yorkshire  (Hunts),    . 

10.  Hereford, 

11.  Yorkshire  (Surrey),    .... 

12.  Shorthorns  (Yorkshire),     . 

Average, 

Irish  Cattle. 
Breed. 

1.  Cross-bred,    Durham,    and  Ayrshire 

(Kerry) 

2.  Cross-bred,    Irish,     and    Shorthorns 

(Limerick),      .        .        .        .        .270 

3.  Half-bred,  Shorthorns  (Cork),  .        .     270 

4.  Cross-bred  (Cork),      .        .        .        .270 

Average, 274 


270  days.  2160  quarts. 

240 

2520 

• 

255 

3060 

t 

240 

2880 

t 

270 

3465 

« 

240 

2640 

' 

320 

3840 

< 

240 

1440 

< 

180 

2520 

( 

240 

1920 

< 

270 

3240 

' 

235 

2142 

t 

250 


2652 


Duration  Tntal  \fi11r 

of  Lactation.      «*»«•* 


285  days.     1995  quarts. 


2430 
2700 
2970 

2524 


As  the  milk-glands  in  the  cow  weigh  only  about  five  kilos,  with  24  per 
cent.,  or  1.2  kilos,  solids,  it  is  evident  that  each  gland  produces  two  and 
a  half  times  its  own  weight  in  solids. 

Goats  give  one-half  to  one  liter  of  milk  daity. 

Women  produce  one  to  one  and  one-third  liters  of  milk  daily. 

The  milk  of  different  breeds  of  cattle  varies  not  only  in  quantit3T, 
but  also  in  quality.  As  a  rule,  the  milk  of  the  Dutch  cattle  contains  the 
largest  percentage  of  fat  and  albumen ;  then  come  the  Swiss  and  Tyro- 
lean cows  and  Normandy  cows  with  greatest  percentage  of  solids. 

The  composition  of  milk  also  varies  according  to  the  stage  of  lacta- 
tion, casein  and  fat  increasing  in  women  up  to  the  second  month,  while 
sugar  decreases  even  in  the  first  month. 

In  five  to  seven  months  fat  decreases.  Casein  decreases  after  the 
ninth  to  tenth  month.  Salts  increase  in  first  five  months  and  then 
decrease. 

In  goats  casein  first  sinks,  then  remains  constant,  and  then  increases. 
Fat  gradually  decreases. 

So,  in  dogs,  albuminous  diet  increases  the  fat  in  milk.  This  influ- 
ence is  less  marked  in  cows.  Fat  in  food  appears  to  decrease  the  fat  in 


622  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

milk  if  there  is  an  insufficient  amount  of  albumen  given  at  the  same 
time. 

Carbohydrates  in  food  of  carnivora  appear  to  be  without  influence 
on  amount  of  milk-sugar.  Also,  in  herbivora,  milk-sugar  depends  for  its 
origin  principally  on  the  albumen  of  the  food. 

The  mode  of  living  is  of  the  greatest  influence  on  the  milk  secretion. 
When  a  large  quantity  of  milk  is  desired,  the  animals  must  remain  per- 
fectly at  rest,  as  every  excitement  or  movement,  even  of  the  animals' 
body  muscles,  decreases  the  milk  secretion.  When  the  animals  are  per- 
fectly motionless  the,  greater  part  of  the  blood-stream  passes  through 
the  glands,  and  vice  versa.  So  a  much  smaller  quantity  of  milk  is  pro- 
duced by  grazing  than  by  stall-fed  animals,  and  it  has  been  found  that 
even  leading  cows  out  to  drink  decreases  the  amount  of  milk. 

The  feeding  has  also  a  certain  influence  on  the  composition  of  the 
milk ;  to  produce  a  large  quantity  of  good  milk,  the  animal,  naturally, 
must  receive  enough  food  to  maintain  a  good  condition.  If  a  poor  food 
is  given  the  milk  will  not  be  very  seriously  influenced,  nor  will  a  rich 
food  increase  the  quantity  of  milk  to  any  great  extent.  The  milk  secre- 
tion is  far  more  closely  dependent  on  the  breed  of  cattle  than  on  the 
feeding ;  a  certain  maximum  which  is  peculiar  to  each  individual  cannot 
by  any  artificial  means  be  increased: 

Water,  of  all  foods,  seems  -to  have  the  greatest  influence  on  the 
composition  of  milk.  When  large  quantities  of  water  have  been  drunk, 
the  milk  contains  a  higher  percentage  of  water.  The  amount  of 
albuminoid  constituents  of  the  food  exerts  great  influence  on  both 
the  composition  and  quantity  of  the  milk.  An  increase  in  the  pro- 
teids  in  the  food  increases  the  total  quantity  and  solids  of  the  milk, 
the  fats  being  relatively  more  increased  than  the  albuminoids.  As  an 
illustration  of  these  facts,  Weiske  has  found  that  a  goat  which  on  a 
diet  of  one  thousand  five  hundred  grammes  potatoes  and  three  hundred 
and  sevent}T-five  grammes  chopped  straw  secreted  seven  hundred  and 
thirty-nine  grammes  milk,  secreted  one  thousand  and  fifty-four  grammes 
milk  when  two  hundred  and  fi/ty  grammes  of  meat  residue  was  added 
to  the  ration,  the  fat  in  the  milk  increasing  from  2.71  per  cent,  to  3.14 
per  cent.  In  carnivora,  also,  a  rich  proteid  diet  leads  to  the  production 
of  a  copious  secretion,  which  may  be  almost  completely  arrested  by 
confinement  to  a  carbohydrate  diet.  In  the  human  female,  a  rich 
albuminous  diet  leads  not  only  to  an  increase  in  the  amount  of  milk, 
but  also  of  its  solid  constituents,  as  is  seen  in  the  following  table : — 

Water.       Solids.      Fats.       Casein. 

On  scanty  diet,  .        .        .     914.0        86.0        8.0         35.5          39.5 
One  week  later,  after  abun- 
dant meat  diet,       .        .     880.6      119.4      34.0         37.5          45.4 


MAMMAKY  SECRETION.  623 

In  herbivora,  carnivora,  and  omnivora,  therefore,  the  same  general 
rule  holds,  that  an  increase  in  the  albuminous  constituents  of  the  food 
increases  both  the  total  amount  of  milk  and  its  percentage  in  fats.  In 
cows,  however,  it  is  to  be  noted  that  the  relative  percentages  of  casein 
and  fat  are  not  dependent  so  much  on  the  amount  of  albumen  of  the 
food  as  on  the  breed  and  individual  characteristics.  The  influence  of  the 
fatty  constituents  of  the  food  on  the  composition  of  the  milk  is  less 
marked. 

It  will  be  shown,  under  the  subject  of  Nutrition,  that  the  addition 
of  fat  to  the  food  serves  to  reduce  the  waste  of  tissue-albumen,  and 
therefore  permits  the  deposition  of  nitrogenous  tissue-constituents.  To 
this  extent,  by  yielding  a  greater  supply  of  albuminous  bodies  to  the 
glandular  epithelium,  a  fatty  diet  may  help  the  milk  secretion,  but  not, 
as  will  be  shown  directly,  by  an  immediate  transfer  of  the  fat  of  the  food 
to  the  milk.  In  fact,  the  addition  of  fat  to  the  food  even  seems  to  reduce 
the  amount  of  butter  in  the  milk  if  the  amounts  of  albuminoids  in  the 
food  are  not  amply  sufficient  for  the  nutritive  needs  of  the  economy. 
When,  however,  the  albuminoids  and  other  constituents  of  the  food  are 
ample  for  preserving  nutritive  equilibrium,  the  further  addition  of  fat 
will  increase  the  percentage  of  butter  in  the  milk. 

The  milk  secreted  at  different  hours  of  the  day  shows  certain  con- 
stant, though  small,  variations  in  composition. 

Morning  milk  has  the  largest  percentage  of  water;  midday  milk  the 
smallest. 

In  100  Parts.        -  Morning.  Noon.  Evening. 


Water, 

88.46 

88.16 

88  30 

Solids, 
Butter, 

11.54 
2.69 

11.84 
2  94 

11.70 
2  82 

Milk-sugar, 

4.87 

4.90 

4  87 

Casein, 

3.15 

3.27 

3  21 

Salts, 

0.828 

0.725 

0.802 

So/also,  the  first- and  last-drawn  portions  of  milk  have  different  com- 
positions. The  last  portions  have  more  solids,  and  especially  more  fat, 
than  the  earlier  portions.  A  difference  of  four  hours  in  time  of  milking 
makes  this  most  apparent.  It  has  been  attempted  to  attribute  this  differ- 
ence to  the  rising  of  the  cream  in  the  udder  of  the  cow,  just  as  occurs  in 
milk  standing  in  a  vessel  outside  the  body.  The  same  differences  may, 
however,  be  made  out  in  human  milk,  where  this  mechanical  explanation 
can  have  but  little  force.  It  must  not  be  forgotten  that  in  milking  not 
only  ready-formed  milk  is  withdrawn,  but  during  the  act  new  milk  is 
secreted,  and  it  is  quite  warrantable  to  suppose  the  cell  processes  which 
result  in  the  production  of  the  solids  of  the  milk  are  less  active  in  the 
pauses  than  during  the  act  of  milking  or  suckling,  when  the  process  is 
stimulated  from  the  irritation  of  the  nipples. 


624 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 
QUANTITATIVE  COMPOSITION  OP  MILK. 


•d 

4 

^ 

S3 

d 

a 

3 

g 

^ 

fl    • 

J 

a 

In  1000  Parts. 

i 

c3 

s 

8 

1 

£ 

tc'Sc 

| 

5 

1 

's 
S 

'5 

£* 

'o 

§ 

o 

•tJ 

"35 

^ 

d 

"3 

I 

GC 

H 

> 

OQ 

ft 

w 

W  < 

Q 

P 

W 

Water,   . 

851.98 

817.40 

849.90 

853.15 

871.80 

837.48 

803.20 

845.62 

839.72 

857.70 

841.80 

Solids,    . 

148.02 

182.60 

1.50.10 

146.85 

128.20 

162.52 

196.80 

154.38 

160.28 

142.30 

158.20 

Casein, 

22.56 

41.98 

37.64 

22.63 

42.18 

46.50 

45.62 

32.46 

34.87 

31.50 

28.52 

Albumen 

3.08 

7.60 

8.00 

8.82 

5.15 

7.24 

7.90 

11.14 

7.32 

9.10 

10.20 

Butter, 

70.88 

79.60 

51.40 

62.80 

32.40 

57.04 

98.80 

64.10 

68.46 

62.20 

63.40 

Sugar. 

45.90 

48.42 

46.26 

46.20 

42.12 

45.54 

37.26 

39.70 

43.50 

32.92 

49.68 

Salts,  . 

5.60 

5.00 

6.80 

6.40 

6.00 

6.20 

7.22 

6.82 

6.14 

6.78 

6.40 

7.  THE  SECRETION  OF  MILK. — The  mammary  glands  belong  to  the 
t}Tpe  of  compound  acinous  glands,  and  are  constructed  on  a  similar  plan 
to  the  salivary  glands.  The  alveoli  are  lateral  expansions  at  the  termi- 
nations of  the  excretory  ducts  and  are  formed  of  a  closed  membrane 
covered,  as  is  also  the  case  with  the  ducts,  with  a  single  layer  of  cells, 
whose  appearances  vary  according  to  the  stage  of  activity  of  the  glands. 
The  secretory  cells  are  composed  of  polyhedral  cellular  structures 
containing  a  round  nucleus  and  usually  a  varying  number  of  oily 
globules.  During  the  stage  of  greatest  activity  the  secretory  cells 
increase  in  size,  the  nucleus  often  is  apparently  reduplicated,  and  the 
number  of  oil-globules  greatly  increased.  In  active  secretion,  during 
which  the  oil-globules  and  cell-contents  appear  to  be  extruded,  the 
remaining  cells  are  much  smaller  and  only  contain  a  single  nucleus.  The 
excretory  ducts,  which  are  short,  are  likewise  supplied  with  flat  epithelial 
cells  and  terminate  in  a  canal  which  in  each  part  of  the  gland  becomes 
enlarged,  especially  at  the  base  of  the  nipple,  where  it  becomes  dilated 
to  form  the  so-called  milk-cistern,  which  is  connected  at  the  exterior  by 
several  canals  which  open  at  the  end  of  the  nipple  (Fig.  260).  This 
cistern  is  lined  with  a  mucous  membrane  composed  of  cylindrical  epi- 
thelial cells  (Fig.  261).  In  the  canals  and  in  the  nipple  the  epithelial 
coat  becomes  converted  into  pavement  epithelium.  The  excretory 
canals  are  abundantly  supplied  with  unstriped  muscular  fibres,  which  at 
the  opening  into  the  nipple  become  developed  into  strong  circular  layers. 

It  is  evident  from  the  composition  of  milk  that  its  most  important 
constituents  must  result  from  a  special  cell  activity,  since  neither  casein 
nor  milk-sugar  are  found  in  the  blood,  and,  although  fat  is  a  constant 
constituent  of  the  blood,  the  amount  in  comparison  with  that  found  in 
the  milk  is  almost  infinitesimal.  It  follows,  therefore,  that  the  milk,  like 
the  other  secretions,  cannot  be  regarded  as  a  transudation,  but  is  a  result 
of  the  protoplasmic  activity  of  the  epithelial  cells  of  the  mammary  glands. 
But,  further,  good  cows  may  yield  as  much  as  twenty-five  kilos  of  milk 
daily,  containing  as  much  as  2.5  kilos  of  albuminoids,  fats,  and  sugar. 


MAMMAEY   SECEETION. 


625 


The  weight  of  the  milk-gland  is  not  more  than  4.8  kilos,  with  24.2  per 
cent,  solids,  including  all  the  glandular  tissue  (vessels,  capsule,  connective 
tissue,  etc.),  or  1.16  kilos  solids.  Consequently,  the  gland  must  renew 
itself  2.09  times  dail}*  to  furnish  this  amount  of  organic  matter  if  derived 


M 


•ms 


FIG.  260.— SECTION  OP  THE  UDDER  AND  NIPPLE  OF  THE  Cow.    (ThanTicffer.) 

Ma,  gland-substance :   B,  nipple;   ms,  acini  of  gland;    tj,  milk-ducts ;   C,  milk-cistern  ;   r,  folds  in  wide 
milk-ducts ;  z,  section  of  sphincter  muscle ;  kb,  external  skin ;  ki,  narrow  milk-duct  in  the  nipple. 

solety  from  the  secreting  cells.  This  would,  however,  require  an  incred- 
ibly rapid  cell  growth,  and  we  are  compelled  to  assume  that  although  the 
growth  and  disappearance  of  the  secreting  cells  is  of  the  greatest  im- 
portance in  furnishing  the  organic  constituents  of  the  milk,  these  sub- 
stances are  not  derived  solely  from  the  breaking  down  of  the  cells,  but 

40 


626 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


that  in  their  functional  activity  they,  to  a  certain  extent,  simply  modify 
certain  substances  already  existing  in  the  blood  and  lymph. 

As  regards  the  production  of  the  fat  of  milk,  oil-globules  may  be 
seen  to  collect  in  the  epithelial  cells  and  escape  into  the  excretory  ducts, 
either  by  a  breaking  up  of  the  epithelial  cells  or  by  a  process  of  contrac- 
tion similar  to  that  observed  in  the  amoeba  in  the  process  of  ejecting 
the  residue  from  digestion.  The  origin  of  the  fat  is,  without  doubt,  in  a 
process  of  fatty  degeneration  of  the  protoplasmic  cell-contents,  for  the 


cw 


cw 


cw      cw 


FIG.  261.— DIAGRAM  OF  THE  FORMATION  OF  THE  NIPPLE,  AFTER  KLAATSH. 

(Ellenberger.) 

I,  cat ;  II,  mare ;  III,  woman ;  IV,  cow.    DR,  milk-cistern ;  CW,  cutaneous  surface. 


amount  of  fat  contained  in  milk,  so  far  from  being  increased,  is  actually 
diminished  by  an  increase  of  fat  in  the  food ;  while,  further,  the  fats  in 
milk  do  not  necessarily  coincide  in  nature  with  the  fats  of  the  food.  On 
the  other  hand,  an  increase  in  proteid  diet  increases  the  amount  of  fat  in 
the  milk.  In  microscopic  examination  of  the  epithelial  cells  of  the 
mammary  glands,  oil-globules  may  be  actually  seen  to  increase  in  size 
and  number  until  often  the  protoplasmic  contents  become  almost  entirely 


MAMMAKY  SECKETION.  627 

replaced  by  oil-globules,  which  entirely  agree  in  their  characteristics  with 
the  oil-globules  found  in  milk.  So,  also,  in  feeding  animals  on  highly 
albuminous  diet  they  may  even  be  seen  to  increase  in  weight,  while  at 
the  same  time  more  fat  is  removed  in  the  milk  than  could  be  taken  in  the 
food,  while  the  increase  in  weight  indicates  that  the  origin  of  fat  is  not 
from  the  adipose  tissue  of  the  bod}^.  On  the  other  hand,  it  is  impossible 
that  in  the  herbivora  the  fat  of  the  milk  should  be  derived  from  the  break- 
ing up  of  albuminoids  in  the  gland,  for  the  total  amount  of  albuminoids 
breaking  up  in  the  body  is  insufficient  to  furnish  the  fat  removed  in  the 
mammary  secretion.  Part  must,  therefore,  be  derived  from  the  blood. 

As  regards  the  casein,  this  substance  is,  without  doubt,  developed 
at  the  expense  of  the  albuminous  cell-contents,  since  it  is  absent  from  the 
blood,  the  alkali  albuminate  being  directly  derived  from  the  breaking 
down  of  the  protoplasm,  while  the  nuclein,  which  is  to  be  regarded  as  a 
constant  component  part  of  the  casein,  is,  without  doubt,  derived  from 
the  nucleus  which  disappears  in  the  process  of  secretion.  This  con- 
version of  the  albuminous  contents  into  casein  is  still  further  evidenced 
by  the  fact  that  the  proportion  of  casein  in  the  milk  depends  upon  the 
degree  of  perfection  of  cell  activity.  Thus,  in  the  earlier  stages  of 
lactation,  in  the  formation  of  colostrum,  the  amount  of  albuminoid 
matter  contained  in  the  milk  is  greatly  in  excess  of  the  amount  contained 
in  milk  after  lactation  has  become  thoroughly  established,  while  coinci- 
dently  with  the  decrease  in  albumen  there  is  a  proportionate  increase 
in  the  percentage  of  casein.  A  ferment  has  even  been  extracted  from 
the  mammary  gland  which  possesses  the  power  of  converting  albumen 
into  casein. 

The  origin  of  milk-sugar  is  less  clearly  established,  although  it  also 
seems,  without  doubt,  to  originate  in  changes  occurring  in  the  proto- 
plasmic contents  of  the  epithelial  cells  of  the  mammary  gland.  For  the 
amount  of  sugar  in  the  milk  is  entirely  independent  of  the  amount  of 
carbohydrate  constituents  of  the  food,  and  remains  unchanged  even 
when  animals  are  fed  on  a  purely  meat  diet.  It  would,  therefore,  appear 
that  the  milk-sugar,  casein,  and  fats  are  all  formed  by  the  direct  activitv 
of  the  epithelial  cells  as  a  result  of  the  decomposition  of  their  proto- 
plasmic contents  or  their  action  on  the  food-constituents  in  the  blood. 

The  other  constituents  of  the  milk,  the  water  and  salts,  evidently 
result  from  a  direct  process  of  transudation  from  the  blood,  with  the 
exception  that,  without  doubt,  a  certain  percentage  of  the  potassium 
salts  and  phosphates,  like  the  specific  milk-constituents,  originate  in  the 
metamorphosis  of  the  protoplasm  of  the  secretory  cells. 

The  process  of  secretion  of  milk  may,  therefore,  be  regarded  as  a 
process  of  molting  of  the  epithelial  cells,  which  undergo  decomposition 
and  discharge  the  resulting  products  into  the  excretory  ducts. 


628 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


According  to  the  results  of  Heidenhain,  the  histological  appearance 
of  the  cells  of  the  mammary  glands  differs  according  as  they  are  examined 
at  the  commencement  or  termination  of  secretion  or  while  the  secretion 
is  at  its  height. 

In  the  first  stage  of  secretion  the  cells  are  flattened  and  lie  against 
the  walls  of  the  alveoli,  of  which  they  may  be  regarded  as  forming  a 
protoplasmic  boundary.  Their  nuclei  are  at  this  period  spindle-formed, 
lying  close  to  the  contours  of  the  cells,  scarcely  detectable  on  examina- 


FIG.  262.— MAMMARY  GLAND  OP  THE  DOG  IN  FIRST  STAGE  OF  SECRETION. 

(Heidenhain.) 

a,  b,  section  through  the  centre  of  two  alveoli  of  the  mammary  gland  of  the  dog,  the  epithelial  cells  seen 
in  profile ;  c,  surface  view  of  the  epithelial  cells. 

tion  in  transverse  section.  Seen  from  above,  however,  the  epithelial 
cells  are  found  to  be  polygonal,  and  each  containing  a  round  nucleus. 
In  the  terminal  period  of  secretion  the  cells  may  be  found  to  have  greatly 
increased  in  size,  possess  one  to  three  nuclei,  and  contain  in  the  portions 
directed  toward  the  alveoli  large  numbers  of  fat-globules.  Often  the 
cells  may  be  seen  to  undergo  subdivision,  a  part  falling  free  into  the 
alveolus  (Figs.  262,  263,  and  264).  Between  these  two  extreme  periods 


FIG.  203.— MAMMARY  GLAND  OF  THE  DOG  IN  SECOND 
STAGE  OF  SECRETION.    (Heidenhain.) 


FIG.  264.— MAMMARY  GLAND  OF 
THE  DOG  IN  MIDDLE  STAGE 
OF  SECRETION.  (Heidenhain.) 


various  intermediary  stages  may  be  recognized.  From  these  histological 
changes  Heidenhain  concludes  that  in  the  formation  of  colostrum  the 
epithelial  cells  are  not  dissolved,  and  that,  therefore,  the  colostrum 
corpuscles  are  not  fatty,  degenerated  epithelial  cells,  but  that  only  the 
free  end  of  the  epithelial  cells  with  their  contained  oil-globules  is  liber- 
ated ;  that  the  broken-down  protoplasm  becomes  dissolved  in  the  milk, 
and  the  fat-globules  are  thus  set  free. 


MAMMARY  SECEETION.  629 

As  regards  the  influence  on  the  mammary  secretion  of  the  nervous 
system,  while  certain  data  have  been  clearly  established  (thus,  the 
influence  of  the  emotions  on  the  mammary  secretion  is  well  known),  the 
process  is  by  no  means  so  thoroughly  understood  as  is  the  case  as  regards 
the  salivary  secretion. 

It  is  well  known  that  the  maintenance  of  the  milk  secretion  is  closely 
dependent  upon  periodic  emptying,  whether  by  suckling  or  milking,  of 
the  milk-gland,  and  the  question  arises,  What  connection  is  there  between 
this  emptying  of  the  gland  and  the  act  of  secretion?  Does  the  reduced 
internal  pressure  which  follows  emptying  the  gland  start  the  secretion 
anew,  or  does  the  act  of  suckling  or  milking  stimulate  the  secretion 
reflexly  ?  It  is  clear  that  when  the  milk-ducts  and  cistern  are  filled  with 
fluid  the  activity  of  secretion  must  be  reduced,  and  when  the  gland  is 
emptied  by  milking  it  again  fills  itself,  at  first  rapidly,  and  then  more 
and  more  slowly ;  but  that  this  augmented  secretion  is  not  due  solely  to 
decreased  internal  pressure  is  evident  from  the  following  facts :  The 
cavities  of  the  milk-gland  of  the  cow  are  capable  of  containing  about 
three  thousand  cubic  centimeters  of  fluid, — a  quantity  very  much  less 
than  may  be  withdrawn  from  the  milk-gland  in  a  single  milking,  so  that 
evidentty  during  milking  renewed  secretion  is  excited  even  before  the 
gland  is  emptied,  and,  as  is  well  known,  frequent  milking  increases  the 
total  milk  secreted.  It  would,  therefore,  appear  that  this  renewed 
secretion  is  produced  reflexly  from  stimulation  of  the  nipple  in  a  manner 
to  be  described  directly. 

The  first  stimulus  to  the  activity  of  the  mammary  glands  is  found 
usually  coincident  with  the  birth  of  young,  although  the  gland  even  for 
several  days  before  birth  is  the  seat  of  a  more  or  less  active  secretion. 
In  this  way  the  connection  between  the  generative  organs  and  the 
mammary  glands  is  clearly  indicated. 

The  influence  of  the  nervous  system  on  the  secretion  of  milk  has 
been  especially  studied  by  Rohrig. 

The  mammary  gland  is  innervated  in  quadrupeds  (in  addition  to 
the  ileo-inguinal  nerve  distributed  to  the  skin)  by  the  external  spermatic 
nerve.  This  nerve  originates  from  the  lumbar  portion  of  the  spinal  cord 
and  passes  out  between  the  greater  and  lesser  psoas  muscles,  dividing 
in  the  pelvis  into  three  branches,  of  which  one  is  distributed  to  the 
abdominal  muscles,  while  the  other  two  leave  the  abdominal  cavity 
through  the  femoral  ring  accompanying  the  crural  artery,  and  then, 
following  the  course  of  the  external  pudic  artery,  are  distributed  to  the 
mammary  gland.  These  nerves  may  be  spoken  of  as  the  middle  and 
inferior  branches  of  the  external  spermatic  nerve.  The  middle  branch 
divides  at  the  base  of  the  gland  into  three  twigs:  first,  a  small  filament 
which  follows  the  course  of  the  pudic  artery  and  is  lost  in  its  walls ; 


630  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

second,  a  much  larger  branch,  termed  the  papillary  branch,  which  is 
distributed  to  the  nipple;  third,  one,  or  occasionally  two,  glandular 
branches,  which  are  supplied  to  the  walls  of  the  milk-ducts  and  the 
cistern. 

According  to  Rohrig,  section  of  the  papillary  branch  produces  no 
change  in  the  milk  secretion,  but  simply  causes  relaxation  of  the  nipple. 
Irritation  of  the  peripheral  end  of  this  nerve  causes  erection  of  the 
nipple  without  change  of  glandular  secretion,  while  irritation  of  the  cen- 
tral end  of  this  nerve  produces  considerable  increase  in  the  secretion. 

Section  of  the  glandular  branch,  on  the  other  hand,  produces  slow- 
ing of  the  amount  of  secretion  by  causing  relaxation  of  the  walls  of  the 
duct,  while  stimulation  of  this  nerve  may  increase  twenty-fold  the  secre- 
tion of  milk  by  causing  contraction  of  the  milk-ducts  and  consequent 
discharge  of  their  contents. 

Section  of  the  inferior  branch  produces  great  increase  in  the  amount 
of  milk  secreted,  while  the  stimulation  of  the  peripheral  end  of  this 
nerve  produces  arrest  of  secretion. 

The  explanation  of  these  two  classes  of  phenomena  are  understood 
through  a  study  of  the  character  of  this  nerve.  The  median  branch  is 
a  compound  nerve  composed  of  both  sensory  and  motor  fibres,  the  latter 
being  especially  found  in  the  papillary  branch  distributed  to  the  nipple, 
while  the  glandular  branch  is  almost  solely  motor.  When  the  papillary 
branch  is  stimulated  it  produces,  by  a  reflex  action,  the  contraction  of 
the  muscular  fibres  of  the  excretory  ducts,  and  so  causes  discharge  of 
their  contents,  while  it  also,  in  all  probability,  acts  through  the  inferior 
branch,  and  by  it  also  increases  the  amount  of  milk  formed  in  a  manner 
to  be  referred  to  directly. 

When  the  glandular  branch  is  stimulated  the  muscular  fibres  of  the 
ducts  contract,  and,  although  no  more  milk  may  be  actually  formed, 
there  is,  nevertheless,  an  increase  in  the  amount  poured  out  through 
the  contraction  of  the  walls  of  the  milk-ducts. 

On  the  other  hand,  the  inferior  branch  is  a  vaso-motor  nerve.  When 
its  peripheral  termination  is  stimulated,  the  milk  secretion  is  arrested 
through  the  constriction  of  the  blood-vessels  supplied  to  this  gland. 

On  the  other  hand,  when  it  is  divided,  the  blood-vessels  become 
greatly  relaxed,  more  blood  passes  through  the  organ,  and  its  activity  is 
largely  increased. 

Whether  any  of  these  processes  are  associated  with  the  action  of 
true  secretoiy  nerves  is  not  known,  but  from  analogy,  from  what  we  have 
seen  in  the  case  of  the  salivary  gland,  it  may  be  assumed  that  such  is  the 
case. 

The  explanation  of  the  connection  long  known  between  the  mechan- 
ical irritation  of  the  nipple,  as  in  suckling  and  milking,  and  the  increased 


MAMMAKY  SECEETION.  631 

secretion  of  the  gland  is  thus  evidently  to  be  found  in  reflex  action,  the 
afferent  impulses  passing  through  the  sensory  nerves  of  the  nipple,  the 
secretory  impulses  passing  through  the  inferior  branch  and  the  glandular 
branch  of  this  nerve. 

It  is  thus  seen  that,  as  far  as  we  know,  the  mammary  secretion  is 
dependent  upon  the  amount  of  blood  passing  through  the  glands. 
Changes  in  the  general  blood  pressure,  by  modifying  the  blood  supply 
of  the  mammary  gland,  also  influence  the  amount  of  milk  secreted. 

Thus,  various  substances  which  act  as  stimuli  to  the  vaso-motor 
centre,  and  so  produce  increase  of  blood  pressure,  produce  likewise  an 
increase  in  the  amount  of  milk  secreted.  Strychnine  in  small  amount, 
digitalis,  caffeine,  and  pilocarpine  are  all  galactagogues  and  probably  act 
in  this  way,  while  through  reduction  of  blood  pressure,  as  by  means  of 
chloral,  the  milk  secretion  may  be  considerably  reduced. 

8.  MILK  INSPECTION  AND  ANALYSIS. — Good  cows'  milk  is  white,  with  a  faint 
yellowish  tint,  and  only  bluish  when  diluted.  If  a  drop  of  good  milk  is  placed  on 
the  thumb-nail  it  retains  its  shape  instead  of  spreading  gut,  as  occurs  when  diluted 
or  unhealthy.  Milk  is  most  apt  to  be  adulterated  with  water,  which  within  cer- 
tain limits  may  be  detected  by  determination  of  the  specific  gravity.  Unskimmed 
milk  possesses  a  higher  specific  gravity  than  that  of  the  skimmed  milk  from  the 
effect  of  the  removal  of  the  fats,  so  that  a  milk  from  which  all  the  cream  has  been 
removed  might,  if  dependence  be  placed  upon  the  specific  gravity  alone,  be  con- 
sidered as  a  better  specimen  than  the  pure  milk.  The  average  specific  gravity  of 
normal  cows'  milk  may  be  placed  at  about  1030  at  60°  F. ;  if  diluted  with  half  its 
volume  of  water  the  specific  gravity  will  fall  to  about  1014  or  1016.  As  a  conse- 
quence, by  the  determination  of  specific  gravity  a  general  idea  may  be  obtained 
as  to  how  much  water  has  been  added  to  diluted  milk.  The  following  table  may 
serve  to  assist  in  this  determination  : — 

With  With 

Skimtned  Milk.    Unskimmed  Milk. 
A  specific  gravity  of  1087  to  1033  or  1033  to  1029  indicates  a  pure  milk. 

1033  to  1029  or  1029  to  1026       "  milk  with  10  per  cent,  water. 

"               "           1029  to  1026  or  1026  to  1023        "  "        "    20        "               " 

"               "           1026  to  1023  or  1023  to  1020        "  "        "    30        "               " 

"          1023  to  1020  or  1020  to  1017       "  "       "    40       "              " 

The  instrument  by  which  the  specific  gravity  of  milk  is  determined  is  usually 
termed  the  lactometer,  and  simply  consists  of  a  hydrometer  with  a  scale  running 
from  1000,  which  is  the  specific  gravity  of  distilled  water  and  is  marked  zero  on 
the  scale,  to  1034,  marked  120,  which  is  the  specific  gravity  of  a  rich  sample  of 
milk.  In  using  the  lactometer  special  attention  must  be  paid  to  the  physical 
characteristics  of  the  milk,  since  a  little  attention  would  readily  detect  skimmed 
inilk  from  unskimmed,  although  their  specific  gravity  might  be  the  same.  In 
milk  rich  in  cream  where  the  specific  gravity  might  be  abnormally  low,  its 
physical  appearance  and  the  fact  that  it  clings  to  the  instrument  would  enable  it 
to  be  recognized,  while  watered  or  skimmed  milk  is  bluish  and  does  not  cling  to 
the  lactometer ;  so,  if  a  sample  of  milk  should  read  above  110  on  the  lactometer 
without  manifestly  being  full-bodied,  it  would  be  only  fair  to  presume  that  a 
portion  of  the  cream  had  been  removed.  Milk  diluted  with  spring-water  may  be 
recognized  by  the  detection  of  nitrates  in  the  milk.  Sulphuric  acid  is  added  to 
the  milk,  the  precipitate  filtered  off,  the  filtrate  distilled,  and  nitric  acid  looked  for 
in  the  distillate.  This  may  be  readily  accomplished  by  converting,  through  milk- 
sugar,  the  nitric  into  nitrous  acid.  A  few  drops  of  pure  H2SO4,  potassium  iodide 
solution,  and  boiled  starch  solution  are  then  added  to  the  distillate;  if  nitrous  acid 
is  present  iodine  is  liberated  from  the  potassium  iodide  solution  and  the  starch  is 
colored  blue. 


632 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


The  cream  maybe  roughly  determined  in  milk  by  placing  it  in  a  tall  cylindrical 
glass,  graduated  into  one  hundred  parts  The  milk  should  be  allowed  to  stand  in 
this  creamometer  for  twenty -four  hours  and  the  volume  of  cream  separated  on  the 
surface  may  then  be  determined,  one  gramme  of  cream  equaling  about  0.2 
grammes  of  fat.  Good  cows'  milk  should  separate  from  ten  to  fifteen  volumes  of 
cream.  This  method  is,  however,  not  thorouhgly  reliable,  since  different  speci- 
mens of  milk  will  throw  up  their  cream  with  different  degrees  of  readiness.  The 
second  method,  and  a  much  more  reliable  one,  of  determining  the  amount  of  fat 
or  cream  present  is  by  means  of  the  lactoscope.  This  instrument  consists  of  a 
little  cup  with  two  of  its  sides  formed  of  two  parallel  plates  of  glass,  distant  from 
each  other  half  a  centimeter.  For  applying  this  test,  in  addition  to  such  a  glass, 
a  jar  graduated  to  one  hundred  cubic  centimeters  and  a  pipette  of  three  cubic 
centimeters  are  needed.  Three  cubic  centimeters  of  milk  are  taken  and  shaken 
up  well  with  one  hundred  cubic  centimeters  water,  and  the  mixture  then  placed 
in  the  glass  cup  with  the  parallel  sides  and  a  lighted  stearin  candle  placed  one  meter 
from  it  in  a  dark  room.  If  at  the  first  experiment  the  contour  of  the  flame  can  be 
seen,  the  milk  is  poured  back  into  the  large  measure  and  a  further  measured  quantity 
of  undiluted  milk  added  until  the  contour  of  the  candle-flame  is  entirely  obscured. 
The  percentage  of  fat  is  then  determined  by  the  following  formula  :  If  x  equal 
the  percentage  of  fat  and  n  the  number  of  cubic  centimeters  of  milk  required,  then 

»).»    o 

x  equals  _  "^   -f-  0.23.     Thus,  if  three  cubic  centimeters  of  milk  were  required  to 


obscure  the  light,  the  formula  would  read  :  x  = 


23.2 


1.23,  or  x  =  1. 96,  the  per 


cent,  of  fat  in  the  milk.  Six  cubic  centimeters  of  pure  cows'  milk  with  one  hun- 
dred cubic  centimeters  water  should  form  a  mixture  which  will  obscure  the  candle- 
flame  ;  if  more  milk  is  required,  then  the  milk  has  been  diluted.  Thus,  twelve 
cubic  centimeters  indicate  50  per  cent,  water,  and  eight  cubic  centimeters  about 
30  per  cent,  water.  The  following  table  gives  the  percentages  of  fat  in  the  milk 
when  the  candle-flame  is  obscured  by  different  amounts  of  milk  in  Vogel's  galacto- 
scope : — 

3    cubic  centimeters  of  milk  indicate  7.96  per  cent,  of  fat. 


3.5 
4.0 
4.5 
5.0 
5.5 
6.0 
6.5 
7.0 
7.5 
8.0 
8.5 
9.0 
9.5 
10.0 
11.0 
12.0 
13.0 
14.0 


6.03 

5.38       " 

4.87 

4.-15 

4.09 

S.fcO 

3.54 

3.32 

3.13 

296 

2.80 

2.77 

2.55 

2.43 

2.16 

2.01 

1.86 


Another  ready  method  of  estimating  the  fat  in  milk  is  by  means  of  Marchand's 
lactobutyrometer.  As  improved  by  Caldwell  and  Parr  (Amer.  Chem.  Journ.,  Nov. 
1885),  this  method  is  performed  as  follows  : — 

The  instrument  employed  consists  of  a  thick  glass  tube,  open  at  each  end, 
with  a  stem  six  cubic  centimeters  in  diameter  and  twenty-three  centimeters  long, 
graduated  in  ^  cubic  centimeter,  and  a  bulb  about  eight  centimeters  in  length, 
and  of  such  a  capacity  that  in  passing  from  the  lowest  graduation  on  the  stem 
to  the  inner  end  of  the  stopper  in  the  lower  mouth  one  passes  from  five  to  thirty- 
three  cubic  centimeters.  Then  the  ether-fat  solution  will  always  come  within  the 
range  of  the  graduation  on  the  stem.  Closing  the  lower  mouth  with  a  good  cork, 
ten  cubic  centimeters  of  the  well-mixed  sample  of  milk  are  delivered  into  the 
well-dried  tube  from  a  pipette,  then  eight  cubic  centimeters  of  ether  (Squibb's 
stronger)  and  two  cubic  centimeters  of  80  per  cent,  alcohol.  Close  the  smaller 
mouth  of  the  tube  with  a  cork  and  mix  the  liquids  by  thorough  shaking  (not 
violently  nor  prolonged).  Both  corks  should  be  held  in  place  by  the  fingers 
during  this  operation,  and  the  upper  one  should  be  once  or  twice  carefully 


MAMMARY  SECRETION.  633 

removed  to  relieve  the  pressure  within,  otherwise  it  is  apt  to  be  forced  out,  with 
consequent  loss  of  material.  Lay  the  tube  on  its  side  for  a  few  minutes  and  then 
shake  it  again  ;  add  one  cubic  centimeter  of  ordinary  ammonia  diluted  with  about 
its  volume  of  water,  and  mix  as  before  by  shaking  ;  then  add  ten  cubic  centimeters 
of  80  per  cent,  alcohol  and  mix  again  thoroughly  by  moderate  shaking,  holding 
the  tube  from  time  to  time  in  an  inverted  position. 

Now,  put  the  tube  in  water  kept  at  40°  to  45°  until  the  ether-fat  solution  sepa- 
rates ;  this  separation  may  be  hastened  by  transferring  the  tube  to  cold  water 
after  it  has  stood  in  the  warm  water  for  a  few  minutes,  and  then  returning  it  to 
the  warm  water.  Finally,  transfer  the  tube  to  water  at  20°  C.,  and  as  the  level  of 
the  liquid  falls  in  the  stem  by  contraction  of  the  main  body  of  it  in  the  bulb, 
gently  tap  the  side  of  the  tube  below  the  ether-fat  solution  to  dislodge  any  flakes 
of  solid  matter  that  may  adhere  to  the  side.  The  readings  are  to  be  taken  from 
the  lowest  part  of  the  surface  meniscus  to  the  line  of  separation  between  the  ether- 
fat  solution  and  the  liquid  below  it. 

The  following  table  gives  the  percentages  of  fat  corresponding  to  each  tenth 
of  a  cubic  centimeter  of  ether-fat  solution  down  to  one  cubic  centimeter,  and  for 
each  twentieth  of  a  cubic  centimeter  thereafter  : — 

Reading.          Per  Cent,  of  Fat.  Reading.          Per  Cent,  of  Fat. 

3.0 1.  13.5 3.51 

4.0 1.23  14.0 3.63 

50 .  1.47  14.5 3.75 

6.0.        ...                .  1.71  15.0.                        .        .        .  3.87 

7.0 1.95  15.5 4.00 

8.0 2.19  16.0 4.13 

9.0 2.43  16.5 4.26 

10.0 2.67  17.0.        .        .        .        .        .4.39 

10.5 2.79  17.5.                        .        .        .  4.52 

11.0 2.91  18.0 4.65 

11.5 3.03  18.5 .  4.78 

12.0 3.15  19.0.                                        .  5.01 

125 3.27  19.5 5.14 

13.0 3.39  20.0 5.27 

This  method  has  been  applied  with  fairly  satisfactory  results  to  the  milk  of  a 
herd  of  cows  receiving  bran  and  cotton-seed  meal  in  their  rations,  the  objection 
to  the  unreliability  of  this  method  under  these  circumstances  being  overcome  by 
the  use  of  the  ammonia.  Various  other  forms  of  lactoscope  are  used,  depending 
on  the  property  that  the  opacity  of  milk  varies  with  and  is  proportional  to  the 
amounts  of  fats  present.  Skimmed  milk  contains  smaller  fat-globules  than  intact 
milk,  and  this  causes  a  greater  cloudiness  in  proportion  to  the  amount  of  fat  pres- 
ent than  the  large  ones,  and,  hence,  the  application  of  this  test  to  skimmed  milk 
would  give  a  higher  percentage  of  fat  than  is  actually  present. 

For  the  quantitative  estimation  of  the  different  milk-constituents  the  following 
methods,  taken  from  Charles's  "Physiological  and  Pathological  Chemistry,"  are 
the  simplest  and  require  the  least  apparatus  : — 

1.  The  Solids. — (j.)  To  ten  grammes  dry  sand  or  powdered  gypsum  add  five 
cubic  centimeters  milk,  then  dry  the  mixture  for  a  long  time  at  100°  until  the 
weight  is  constant.     The  increase  in  weight  is  equal  to  the  solids  in  five  cubic 
centimeters  milk.      Suppose  this  to  be  =05  gramme,  then  one  hundred  cubic 
centimeters  rnilk  contain  ten  grammes,  or  10  per  cent,  solids  (Baumhauer). 

Instead  of  five  cubic  centimeters,  ten  grammes  of  milk  and  twenty  grammes 
of  dry  sea-sand  may  be  weighed  in  a  tared  capsule  of  about  fifty  cubic  centimeters, 
and  evaporated  at  100°  until  the  weight  is  constant.  When  quite  cold,  the  cap- 
sule, with  its  contents,  is  weighed  in  a  desiccator  over  sulphuric  acid. 

(ij.)  Place  a  little  milk  in  a  platinum  capsule,  and,  having  weighed  it,  add  a 
few  drops  of  alcohol  or  acetic  acid  ;  evaporate  over  a  water-bath,  dividing  the 
coagulum  against  the  sides  of  the  dish,  and  dry  it  at  100°  to  110°  until  the  weight 
is  constant.  It  is  generally  completed  in  six  hours  (Gerber).  Cover  carefully 
before  weighing,  as  the  residue  is  very  hygroscopic. 

The  total  solids  should  not,  as  a  rule,  be  much  less  than  11.5  per  cent.;  cows' 
milk,  for  example,  varies  between  10.5  and  15  per  cent.;  less  than  this  indicates 
dilution. 

2.  The  Butter.— (j.)  Shake  the  milk  well,  and  to  twenty  cubic  centimeters  of 
it  add  twenty  cubic  centimeters  of  a  10  per  cent,  caustic  potash  solution  and 
then  some  ether  (sixty  to  one  hundred  cubic  centimeters),  and  agitate  vigorously 


634:  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

for  some  time  ;  on  standing,  the  ethereal  solution  of  the  liberated  fat  rises  to  the 
surface  and  is  to  be  carefully  decanted  into  a  weighed  porcelain  dish.  Some  more 
ether  is  to  be  added  to  the  alkaline  milk,  and  after  vigorous  agitation  it  also  is  to 
be  transferred,  as  before,  to  the  capsule.  The  same  process  may  be  repeated 
several  times  if  necessary.  The  ethereal  extract  is  now  evaporated  over  a  water- 
bath,  and  after  having  been  dried  in  an  air-bath  at  110°  the  weight  of  the  residue 
is  to  be  ascertained  ;  this  multiplied  by  5  gives  the  percentage.  With  cows'  milk 
it  varies  between  2  and  5  per  cent.,  but  the  normal  minimum  for  fats  is  about  2.75 
(Cameron). 

3.  The  Casein  and  Albumen. — (j.)     (a)  Dilute  twenty  cubic  centimeters  milk 
with  four  hundred  cubic  centimeters  water,  and  treat  the  mixture  with  very  dilute 
acetic  acid,  added  drop  by  drop,  until  a  flocculent  precipitate  begins  to  appear. 
Now  pass  a  current  of  carbonic  acid  gas  through  the  fluid  for  fifteen  to  thirty 
minutes  and  lay  aside  for  one  or  two  days.     Collect  the  precipitated  casein  on  a 
weighed  filter,  wash  it  with  spirit,  and  then  with  ether  until  a  drop  of  the  wash- 
ings leaves  no  fatty  stain  on  paper  ;  dry  at  100°  and  weigh.     Subtract  the  weight 
of  the  filter,  and  the  difference  multiplied  by  5  gives  the  percentage  of  casein.     In 
human  milk,  precipitate  the  casein  by  saturating  with  magnesic  sulphate. 

(6)  The  filtrate  from  the  casein  precipitate  is  to  be  concentrated  to  a  small 
bulk  over  a  water-bath  and  an  acetic  acid  tannin  solution  added  so  long  as  any 
precipitate  occurs  ;  after  the  precipitate  has  settled,  collect  it  on  a  weighed  filter, 
where  it  is  to  be  washed  with  dilute  spirit  until  the  filtrate  gives  no  blue  coloration 
with  ferric  chloride  (indicating  absence  of  tannin)  ;  dry  now  at  100°  and  weigh. 
The  weight  multiplied  by  5  gives  the  percentage  of  albumen. 

In  cows'  milk  the  casein  varies  between  3.3  and  6  per  cent.,  and  the  other 
albumens  from  0.3  to  0.4  per  cent.  In  diseased  milk  the  casein  may  be  as  low  as 
0.2  per  cent.,  and  the  other  albumens  as  high  as  10  per  cent. 

(ij.)  (#)  Ten  cubic  centimeters  milk  are  diluted  with  one  hundred  cubic  cen- 
timeters distilled  water  and  well  mixed ;  a  copper  solution,  made  by  dissolving 
sixty-three  and  five-tenths  grammes  of  cupric  sulphate  in  one  liter  of  water,  is 
then  added  slowly  with  stirring  until  the  coagulum  begins  to  settle  quickly.  The 
whole  mixture,  together  with  half  the  cupric  sulphate  solution  already  employed, 
is  then  added  to  some  potash  solution  (fifty  grammes  of  potash  to  the  liter),  and 
after  a  short  interval  the  clear  fluid  is  filtered  off  through  a  filter  dried  at  110°  C.; 
the  precipitate  is  washed  until  the  washings  amount  to  two  hundred  and  fifty 
cubic  centimeters,  and  the  sugar  is  to  be  estimated  in  this  subsequently. 

(&)  The  coagulum  on  the  filter  is  next  treated  with  absolute  alcohol,  slowly 
dried,  and  extracted  with  ether;  the  ethereal  and  alcoholic  extracts  are  then  to  be 
distilled,  and  the  fatty  residue  dried  and  weighed.  The  coagulum,  after  having 
been  dried  at  125°,  is  weighed,  then  ignited,  the  ash  deducted,  and  the  difference 
taken  as  pure  albuminoid  (Ritthausen). 

4.  The  Sugar. — (j)  Take  twenty-five  grammes  of  milk,  acidify  with  hydro- 
chloric acid,  boil,  and  filter,  washing  the  coagulum  with  water;   to  convert  the 
milk-sugar  into  glucose,  boil  the  filtrate  and  washings  for  an  hour  or  so  in  a  flask, 
to  the  mouth  of  which  a  long  tube  has  been  attached.     When  the  liquid  cools, 
make  its  volume  up  to  two  hundred  cubic  centimeters  and  determine  the  sugar 
by  Fehling's  method,  measuring  twenty  cubic  centimeters  Fehling's  solution  into 
a  flask,  diluting  with  eighty  cubic  centimeters  water,  and  to  the  boiling  mixture 
add  the  diluted  filtrate  from  a  Mohr's  burette  until  the  copper  is  entirely  reduced. 

(ij.)  This  sugar  determination  may  be  readily  effected  by  the  polariscope. 
Measure  forty  cubic  centimeters  milk  into  a  flask  of  one  hundred  cubic  centimeters 
capacity,  add  some  carbonate  of  sodium  if  the  milk  is  not  alkaline,  and  then 
twenty  cubic  centimeters  moderately  concentrated  solution  of  neutral  acetate  of 
lead,  and  shake  well ;  having  next  fitted  the  neck  of  the  flask  to  a  long  glass  tube 
or  to  the  condenser  of  a  Liebig's  still,  boil  it  over  a  small  flame  ;  then  filter,  and 
test  the  filtrate  with  the  polariscope.  With  a  one-decimeter  tube  the  percentage 
of  sugar  is  obtained  by  multiplying  the  rotation  by  1.44. 

*For  other  ready  methods  of  milk  analysis  and  for  the  detection  of  foreign  substances 


f.    J.  ft-tCf  /«-tM /V«//f'U/C,    -IOCXJ,    i  i  i    j  wj  M  U..  U,   c».  -ntr   ,      I    .   ^   *  .   K7UW1  i<.   -*i  »fir,  i  .   \^  ri/orr*tisic<(,  ,/  i  rrr  i  /&.,   .rVMl  11.   1OOI5    U.   J.W  , 

Morse  APigott,  Jft.,  April,  1887,  p.  108 ;  F.  A.  Woll,  /&.,  February,  1887.  p.  60 ;  Morse  and  Burton, 
J6.,  June,  1887,  p.  222 ;  A,  July,  1888,  p.  322. 


SECTION   X. 

THE   RENAL  SECRETION. 

THE  blood  not  only  bears  to  the  different  tissues  the  substances 
required  for  their  nutrition,  but  also  removes  from  the  tissues  the 
different  waste  products  which  result  from  their  Ararious  metabolic 
processes.  In  the  lungs,  part  of  these  oxidation  products,  especially  of 
the  carbon  compounds,  are  removed,  while  the  results  of  nitrogenous 
waste  largely  pass  through  the  lungs  to  be  carried  through  the  aorta 
from  the  left  ventricle  to  the  kidneys,  whose  function  is  to  remove  these 
nitrogenous  excrementitious  substances,  together  with  the  carbon  com- 
pounds  which  have  passed  the  lungs,  with  various  salts  and  water.  The 
product  of  this  functional  activity  of  the  kidneys  is  the  urine,  which  is 
a  pure  excretion,  since  all  its  constituents  are  waste  products  which 
must  be  removed  from  the  organism. 

1.  THE  PHYSICAL  AND  CHEMICAL  PROPERTIES  OF  URINE. — Urine  is 
in  general  a  thin,  yellowish  colored,  transparent  fluid  (the  depth  of  color 
depending  on  the  concentration)  of  a  salty  taste  and  peculiar  aromatic 
odor,  due  to  the  presence  of  various  volatile  acids.  Its  reaction  may 
be  faintly  acid,  neutral,  or  alkaline :  it  rotates  the  plane  of  polarized 
light  to  the  left.  The  reaction  in  the  carnivora  and  in  fasting  or 
suckling  herbivora  is  acid ;  in  the  herbivora  and  omnivora,  when  on 
vegetable  diet,  it  is  alkaline.  The  explanation  of  the  production  of  an 
acid  renal  secretion  from  the  alkaline  blood  is  to  be  attributed  to  a 
specific  property  of  the  renal  epithelium  similar  to  that  possessed  by  the 
gastric  mucous  membrane.  The  more  alkaline  the  blood,  the  less  acid 
the  urine ;  hence  the  great  alkalinity  of  the  blood  of  herbivora  causes 
the  urine  to  have  an  alkaline  reaction.  For  although  sulphuric  acid  is 
formed  from  the  decomposition  of  vegetable  just  as  it  is  from  animal 
albumen,  vegetable  foods  contain  large  amounts  of  organic  salts  which 
break  up  into  alkaline  carbonates,  and  so  neutralize  the  sulphuric  acid. 
These  salts  are  absent  from  the  food  of  carnivora,  hence  the  acids  are 
less  perfectly  neutralized.  It  is,  therefore,  the  form  of  diet  which,  by 
modifying  the  alkalinity  of  the  blood,  determines  the  reaction  of 
the  urine.  The  specific  gravity  of  urine  varies  between  1005  and  1050. 
When  exposed  to  the  air,  the  urea  undergoes  decomposition  and  is 
transformed  into  ammonium  carbonate ;  a  part  of  the  ammonia  then 
combines  with  magnesium  phosphate,  and  ammonium-magnesium  phos- 

(635) 


636 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


phates,  together  with  calcium  phosphate,  are  deposited  as  a  crystalline 
precipitate.  This  process  is  known  as  ammoniacal  fermentation,  and  is 
due  to  the  action  of  ferments  derived  from  the  atmosphere.  In  some 
animals  the  urine  always  deposits  mucus  derived  from  the  membranes 
over  which  it  passes.  Its  quantity  is  subject  to  great  variations. 

The  most  important  constituents  of  the  urine  are  water,  salts,  gases, 
and  certain  specific  constituents.  Among  the  salts,  potassium  com- 
pounds are  more  abundant  than  sodium.  Lime  and  magnesium  are  in 
varying  amounts.  Of  the  acids  H2SO4  and  P206  are  most  abundant. 
C02  in  combination  is  found  in  the  urine  of  the  herbivora.  When 
NaCi  forms  part  of  the  diet,  this  salt  is  also  a  large  constituent  of 
urine. 

The  following  are  the  specific  constituents  of  urine  : — 

1.  The   decomposition   products   of  the  albuminoids,  as  urea,  uric 
acid,  hippuric   acid,  kreatin   and   kreatinin,  and   the   combinations  of 
H2S04  with  indol  and  phenol. 

2.  Coloring  matters,  of  which  urobilin  is  the  best  known. 

3.  Aromatic  bodies  which  give  the  urine  its  peculiar  odor. 
The  gases  C02,  N,  and  O  are  found  free  in  the  urine. 

As  regards  quantitative  composition  there  is  great  inconstancy. 


Water,    . 
Organic  matter, 
Inorganic  matter,  . 


Horse. 
90. 
5.5 
4.5 


Ox. 
91. 

5. 

4. 


Sheep. 

89. 

8. 

3. 


Hog. 

98. 
0.5 
1.5 


COMPOSITION  OF  THE  URINE  (BOUSSINGAULT). 


Urea,         . 

Horse  (1). 
.     31  0 

Cow  (2). 
18  5 

Pig  (3). 
4  9 

Potass,  hippurate, 
Alkaline  lactates, 
Potass,  bicarb., 
Mag.  carb., 

.      4.7 
.     20.1 
.     15.5 
.      4.2 

16.5 
17.2 
16.1 
4.7 

0.0 

10.7 
09 

Calcium  carb., 
Potass,  sul  ph., 
Sodium  chloride, 
Silica,        . 
Phosphates, 
Water  and  undetermined 
stances,  . 

.     10.8 
.       1.2 
.      0.7 
.      1.0 
.      0.0 
sub- 
.  910.0 

0.6 
3.6 
1.5 
traces 
0.0 

921.3 

traces 
2.0 
1.3 

0.1 
1.0 

979.1 

1000.0  1000.0 

(1)  Diet  of  oats  and  clover-grass. 

(2)  Diet  of  hay  and  potatoes. 

(3)  Diet  of  cooked  potatoes. 


1000.0 


The  water,  K,  Na,  Ca,  and  Mg  compounds  are  derived  directly 
from  the  blood,  and  in  greater  part  directly  from  the  food  and  drink,  and 
in  fasting  animals  from  waste  of  tissues.  H2SO4  originates  in  oxidation 
of  the  sulphur  compounds  in  food ;  the  phosphates  from  the  oxidation 
of  albuminoids  of  food  and  tissues  ;  carbonates,  partly  directly  from 


KENAL  SECRETION.  637 

food  and  drink,  partly  from  modifications  of  the  vegetable  acid  com- 
pounds in  vegetable  foods. 

The  urea  and  uric  acid  are  the  nitrogenous  end  products  of  the 
decomposition  of  the  albuminoids  of  food  and  of  the  tissues. 

Kreatin  and  kreatinin  are  closely  dependent  on  the  animal  matter 
taken  as  food,  since,  even  in  muscle,  kreat in  is  formed  as  a  modification 
of  its  own  albuminoid  constituents. 

Hippuric  acid  is  a  combination  of  glycochol  with  benzoic  acid,  and 
originates,  to  a  great  extent,  in  the  constituents  of  vegetable  foods,  the 
cuticular  substance  of  which  develops  the  benzoic  acid. 

Phenol  is  derived  from  the  decomposition  of  albuminoids  in  the 
intestine,  and  in  the  excretory  ducts  of  the  kidney  unites  with  H3S04. 

Indican  originates  in  indol. 

Many  other  substances  are  accidentally  present  in  urine,  such  as 
aromatic  constituents  of  food,  alkaloids,  metals,  bile  coloring-matter,  etc. 

The  quantity  of  the  urine  is  dependent  on  the  amount  of  water 
taken  in  food  and  drink,  on  the  diminution  of  excretion  of  water  by 
other  organs,  especially  the  skin,  on  the  amount  of  excretory  products, 
especially  urea,  and  on  the  amount  of  substances  taken  in  food,  e.g., 
salts,  which  must  be  excreted. 

It  is  to  be  noted  that  all  the  water  taken  as  food  is  not  excreted 
through  the  kidneys,  but  that  part  is  removed  by  the  lungs,  skin,  and 
intestinal  canal.  The  proportion  of  water  removed  through  these 
different  organs  varies  in  different  species : — 

In  the  Urine.  Through  the  Lungs. 
In  herbivora,  20  per  cent,  of  water  is  removed;  80  per  cent. 

In  omnivora,  60        "  "  "  40       " 

In  carnivora,  85        "  "  "  15       " 

Various  conditions  maj^,  however,  modify  these  proportions. 

In  fasting  and  suckling  animals  of  both  the  herbivora  and  carnivora 
the  urine  has  the  same  characters,  since  in  them  the  tissues  alone  are 
undergoing  waste. 

There  is  the  greatest  difference  between  the  urine  of  carnivora  and 
herbivora. 

In  carnivora  the  urine  is  smaller  in  amount, is  acid,  clear,  and  richer 
in  solids,  especially  urea,  uric  acid,  and  kreatin;  sodium  salts,  sulphates, 
and  phosphates  are  in  excess,  and  the  urine  has  a  higher  specific  gravit}'. 
Phenol  and  sulphuric  acid  only  are  present  in  small  amount  and  hippuric 
acid  absent  when  on  a  purely  flesh  diet. 

In  herbivora  it  is  larger  in  amount,  is  turbidr  contains  few  solids, 
hippuric  acid  replaces  uric  acid,  and  the  reaction  is  alkaline;  urea  is 
present  only  in  small  amount.  Potassium  salts  are  in  excess  unless 
sodium  chloride  is  given  with  the  food.  Lime  and  magnesium,  united 
with  C0a,  are  in  abundance,  phosphates  often  absent ,  sulphates  abundant. 


638 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


That  this  difference  is  dependent  only  on  differences  in  diet  is  proved 
by  the  fact  that  during  fasting  the  urine  of  the  herbivora  agrees  in  all 
its  characteristics  with  the  urine  of  the  carnivora.  Under  such  circum- 
stances the  herbivora  are  not  consuming  vegetable  matters,  but  living  at 
the  expense  of  their  own  tissues,  are  then  practically  carnivorous,  and 
their  urine  becomes  acid,  clear,  and  rich  in  urea  and  phosphatic  salts. 

The  Urine  of  the  Horse  is  cloudy  and  has  an  alkaline  reaction.  Its 
specific  gravity  varies  from  1016  to  1060,  1050  being  about  the  average. 
It  contains  a  large  percentage  of  mucin,  and  is  therefore  viscid  and  may 
be  drawn  into  threads.  It  becomes  brown  on  exposure  to  the  air,  deposits 
CaC02,  and  a  pellicle  forms  on  it,  showing  iridescent  colors. 

The  characteristics  of  normal  horses'  urine  depend  largely  on  the 
mode  of  feeding.  When  fed  exclusively  on  hay  and  straw  the  urine  is 
always  alkaline,  while  when  oats  constitute  the  principal  food  it  is 
secreted  in  small  quantity,  is  turbid,  and  of  acid  reaction,  and  more 
viscid  than  alkaline.  The  influence  of  the  diet  on  the  amount  of  solids 
in  the  urine  is  shown  in  the  following  table  : — 


SOLIDS  IN  URINE. 

In  100  C.  C. 

Total. 

Hay. 

Oats. 

Wheat- 
Straw. 

Kilos. 

Kilos. 

Grammes. 

Grammes. 

8  kilos. 

2  kilos. 

22.31 

5.04 

11.2 

566.6 

7 

2 

1  kilo. 

26.33 

4.72 

11.2 

529.4 

6 

4 

21.36 

4.99 

10.3 

511.8 

4 

4 

2  kilos. 

27.55 

4.66 

10.2 

477.0 

4 

6 

. 

23.73 

4.53 

10.4 

460.7 

1 

6 

2.6" 

24.60 

6.03 

5.7 

346.1 

A  high  percentage  of  calcium  salts  is  characteristic  of  horses'  urine. 
Of  the  amount  contained  in  the  food,  from  one-third  to  one-half  passes 
into  the  urine,  while  in  the  ruminant,  especially  in  the  sheep,  not  more 
than  5  per  cent,  passes.  In  the  case  of  potassium  the  conditions  are 
just  reversed.  In  the  sheep  95  per  cent,  of  the  potassium  in  the  food 
passes  into  the  urine,  while  in  the  horse  at  most  66  per  cent,  appears. 
The  following  table  gives  the  percentage  of  inorganic  constituents  in 
one  hundred  parts  of  the  ash  of  horses'  urine : — 

Potassium,      «.       ,        «        .        .        .        .36.85  per  cent. 

Sodium, 3.71 

Calcium, 21.92 

Magnesium,     . 4.41 

Phosphoric  acid,     .        .        .        .        .        .... 

Sulphuric  acid,        .        .        .        .        .        .17.16 

Chlorine 15.36 

Silicic  acid, 0.32 


KENAL  SECKETION.  639 

Horses'  urine  contains  urea  and  hippuric  acid  in  inverse  proportions. 
When  one  increases  the  other  decreases,  the  amount  of  the  latter  depend- 
ing on  the  amount  of  green  forage  or  hay  or  straw,  the  former  on  the 
amount  of  oats,  grains,  roots,  etc.  The  percentage  of  urea  in  ordinary 
feeding  varies  from  2.5  to  4.0  per  cent. 

Very  large  amounts  of  aromatic  sulphur  compounds  are  present, 
especially  of  phenol  and  indican.  The  former,  with  hippuric  acid,  causes 
the  peculiar  odor ;  the  latter,  the  colors  seen  in  the  film  which  forms 
when  exposed  to  the  atmosphere.  Brenzcatechin  is  also  present  and  is 
the  cause  of  the  brown  color  which  forms  on  standing. 

CaC03  is  the  principal  salt,  and  is  rapidly  deposited  as  a  sediment. 
Sulphur  compounds  are  found  in  varying  amounts.  Phosphates,  except 
in  abundant  feeding  with  grains,  are  only  present  in  traces.  The  amount 
of  urine  is  only  about  five  to  six  liters  daily,  evacuated  in  three  to  four 
portions,  since  a  large  amount  of  water  is  lost  through  the  skin  in 
perspiration. 

The  Urine  of  the  Ox. — The  amount  of  urine  depends  not  only  upon 
the  amount  of  water  taken,  but  especially  on  the  amount  of  nitrogenous 
food.  Thus,  when  the  diet  has  been  poor  in  nitrogen,  the  amount  of 
urine  passed  daily  will  vary  from  9.7  to  12.6  kilos,  and  when  a  richer 
nitrogenous  diet  is  given  the  amount  will  be  increased  to  from  16.3  to 
16.8  kilos.  This  is,  without  doubt,  partly  to  be  attributed  to  the  larger 
amount  of  water  required  in  a  rich,  nitrogenous  diet.  The  evacuation 
of  the  urine  occurs  from  eight  to  ten  times  daily,  averaging  about  one 
kilo  each  time.  The  character  of  the  food  exerts  the  greatest  influence 
on  the  reaction  of  the  urine.  Fodder  rich  in  alkaline  carbonates  or  com- 
pounds of  the  organic  vegetable  acids  occasions  an  alkaline  reaction  of 
the  urine.  The  amount  of  carbonates  in  the  solids  of  the  urine  is 
directly  in  proportion  to  its  alkalinity.  Carbon  dioxide  is  especially 
abundant  when  fed  on  beets,  clover,  hay,  or  bean-straw,  when  it  may 
amount  to  10  or  12  per  cent.  When  fed  with  oat-straw  or  barle3T-straw, 
the  carbon  dioxide  sinks  to  from  3  to  6  per  cent.  Exclusive  feeding  with 
wheat-straw  is  said  to  cause  an  acid  reaction  of  the  urine  on  account  of 
the  poverty  of  carbonates  and  vegetable  acids.  The  total  amount  of 
solids  in  the  urine  averages  about  6.8  per  cent.,  composed  of — 

C,  .  .  .        ...  .  .  27.8  to  53.1  per  cent. 

H, .  .  •„•*•.        .  .  .      3.5  to    6.9 

N, .  .  .        .        .        .  .  .      8.9  to  33.6 

O,  .  .  .    <   .        .        .  .  .  15.6  to  50.2       " 

The  quantity  and  quality  of  the  organic  matter  in  the  urine  varies 
greatly  according  to  the  food,  varying  between  4.2  to  11.3  per  cent.,  and 
is  especially  dependent  upon  the  digestible,  nitrogenous  food-stuffs.  The 
non-nitrogenous  food-stuffs  are  without  influence  on  the  organic  urine 


640  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

constituents.  Uric  and  hippuric  acids  are  the  representatives  of  the 
nitrogenous  organic  constituents.  Uric  acid  and  hippuric  acid  are  found 
in  proportions  which  are  governed  by  the  character  of  the  diet  in  the 
same  way  as  in  the  case  of  the  horse.  The  mineral  constituents  are  like- 
wise dependent  on  the  food,  potassium  and  lime  combinations  being 
especially  abundant.  The  urine  of  the  ox  is  clear,  yellowish,  or  greenish, 
and  possesses  a  peculiar,  musky  odor.  Its  specific  gravity  varies  from 
1020  to  1030,  depending  on  the  amount  of  water  in  the  food.  It  is 
always  poorer  in  solids  than  the  urine  of  the  horse.  It  also  contains  less 
sulphuric  acid  compounds,  especially  of  the  aromatic  group,  than  horses' 
urine.  The  phosphates  are  entirely  absent,  or  present  only  in  traces. 

The  Urine  of  the  Sheep  and  Goat  is  similar  to  that  of  the  ox,  but 
shows  great  variation  in  the  salts  derived  from  the  food.  Its  specific 
gravity  varies  from  1006  to  1015  ;  the  amount  from  five  hundred  to  eight 
hundred  and  fifty  cubic  centimeters  daily.  Urea  and  hippuric  acid  are 
present  in  the  proportion  of  about  two  to  three,  the  hippuric,  contrary 
to  what  is  the  case  in  the  horse,  being  more  abundant  when  on  a  diet  of 
young  hay  rich  in  proteids. 

The  Urine  of  the  Pig  is  clear,  yellowish,  with  a  faint  alkaline  reac- 
tion;  specific  gravity,  1010  to  1015.  It  contains  urea,  but  rarely  uric  or 
hippuric  acids.  The  salts  depend  on  the  character  of  food.  In  general, 
the  urine  resembles  that  of  carnivora. 

The  Urine  of  the  Dog  is  deep  yellow  in  color,  acid  reaction  ;  specific 
gravity,  1050  when  fed  on  meat.  It  is  rich  in  urea,  but  contains  but  little 
uric  acid.  Kreatin  and  indican  are  present,  but  no  phenol.  Mg  salts  are 
in  larger  amount  than  Ca  salts,  while  the  chlorides  are  scanty  ;  sulphates 
and  phosphates  abundant.  It  readily  undergoes  ammoniacal  fermenta- 
tions (from  urea)  and  deposits  phosphates.  Its  composition  and  character 
likewise  vaiy  greatly  with  the  nature  of  the  food.* 

2.  THE  MECHANISM  OF  RENAL  SECRETION. — The  substances  which 
exist  in  the  urine  in  a  state  of  solution  also  exist  in  the  blood,  and  the 
process  of  secretion  of  the  urine  is,  therefore,  largely  a  process  of 
mere  infiltration.  Nevertheless,  certain  constituents  of  the  urine  are 
evidently  manufactured  in  the  kidney,  since  their  presence  has  not  yet 
been  detected  in  the  blood.  Renal  secretion  is  thus  possessed  of  two 
factors, — a  phjTsical  process  of  filtration  and  a  process  of  true  secretion 
dependent  upon  the  activity  of  the  renal  epithelium. 

The  mechanism  of  the  renal  secretion  is,  to  a  certain  extent,  capable 
of  explanation  by  the  study  of  the  structure  of  the  kidney.  The  kidney 
is  composed  of  a  series  of  fine  tubules,  which,  starting  from  the  hilum 

*For  further  detail s  as  to  the  composition  of  the  urine  of  the  domestic  animals  under 
different  forms  of  diet  the  reader  is  referred  to  the  "  Encyclopaedic  der  Gesammten  Thier- 
heilkunde,"  Bd.  iv,  p.  202. 


EEXAL   SECRETION. 


641 


in  the  medullary  portion  of  the  kidney,  form,  by  frequent  subdivisions, 
a  series  of  straight,  branching  canals,  the  so-called  urinary  tubules. 
After  frequent  subdivision  each  branch  terminates  in  a  looped  tubule, 
which,  after  undergoing  various  convolutions  in  the  cortical  portion  of 
the  kidney,  terminates  in  a  bladder-like  expansion.  In  each  of  these 
expansions  enters  a  small  branch  of  the  renal  artery,  the  vas  afferens, 
which  undergoes  division  into  a  bunch  of  capillaries  which  is  so  placed 
as  to  be  surrounded  by  a  double  layer  of  the  bladder-like  expansion  of 


FIG.  265.— NAKED-EYE   APPEARANCES  OP    THE    KIDNEY  OF    MAN,   AFTER 
TYSON  AND  HENLE.     (Landois.) 

1,  cortex;  If,  medullary  rays;  1",  labyrinth;  2,  medulla;  2f,  papillary  portion  of  the  medulla;  2'f, 
boundary  layer  of  the  medulla;  3,  transverse  section  of  tubules  in  boundary  layer;  4,  fat  of  renal  sinus; 
5,  artery  :  *,  transversely  coursing  medullary  rays ;  A,  branch  of  renal  artery ;  C,  renal  calyx ;  U,  ureter. 

the  tubules.  The  relation  between  this  bunch  of  vessels  and  the  expan- 
sion of  the  tubules  is  similar  to  what  would  be  expected  if  a  tip  of  the 
finger  of  a  glove  was  inverted  from  the  outside.  The  collection  of  capil- 
laries is,  therefore,  in  contact  with  the  external  layer  of  the  tubule,  and 
is  surrounded  by  a  space  which  is  in  direct  communication  with  the  in- 
terior of  these  tubes.  After  having  undergone  subdivision  into  capilla- 
ries in  this  expansion  of  the  tubules,  the  efferent  vessel,  which  collects 

41 


642 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


the  blood  which  has  passed  through  this  series  of  capillaries,  again  un- 
dergoes subdivision  into  a  second  net-work  of  capillaries  distributed 
around  the  urinary  tubules.  In  the  glomerulus  is  represented  the  filtra- 
tion apparatus,  in  which,  through  the  influence  of  blood  pressure,  the 
substances  held  in  solution  in  the  blood-serum  may  be  removed  from  the 
blood  and  forced  into  the  interior  of  the  commencement  of  the  urinary 
tubules.  The  conditions  are,  therefore,  evidently  different  here,  where 
transudations  directly  enter  into  the  excretory  ducts,  from  what  holds  in 
the  case  of  other  glands,  where  the  transudations  simply  pass  into  lymph 
and  require  some  other  force  for  their  transference  to  the  secretion. 


Cortex. 


Boundary  or 
marginal  zone. 


Papillary  zone. 


FIG.  266.— LONGITUDINAL  SECTION  ov  A  MAI/PIGHIAN  PYRAMID.    (Landois.) 

PF,  pyramids  of  Ferrein  ;    RA,  branch  of  renal  artery ;    RV,  lumen  of  a  renal  vein  receiving  an  inter- 
lobular  vein ;  VR,  vasa  recta;  PA,  apex  of  a  renal  papilla;  b  b  embrace  the  bases  of  the  renal  lobules. 

That  this  separation  of  the  constituents  of  the  blood  through  the  glom- 
eruli  of  the  kidney  is  actually  dependent  upon  the  blood  pressure  is 
shown  by  the  fact  that  if  the  blood  pressure  be  reduced  below  fifty  milli- 
meters of  mercury  secretion  ceases,  while  if  it  be  increased  the  secretion 
is  correspondingly  augmented.  The  contrast  between  this  fact  and  the 
secretion  of  saliva  is,  therefore,  very  striking. 

If,  however,  pressure  is  increased  by  venous  obstruction,  then,  in- 
stead of  an  increased  secretion,  the  reverse  takes  place.  That  this  does 
not  contradict  the  filtration  hypothesis  is  explainable  by  the  fact  that  ob- 
struction of  the  veins  increases  the  pressure  in  the  capillaries,  and  these 


RENAL   SECRETION. 


643 


so  expand  in  the  unyielding  capsule  of  the  kidney  that  the  urinary 
tubules  are  completely  compressed,  and  nitration  is,  of  course,  at  once 
arrested. 

Various  conditions  may  modify  the  blood  pressure  in  the  kidneys. 
Thus,  for  example,  the  local  blood  pressure  may  be  increased  by-  general 


Sub-capsul  ar  layer 
without  Malpi- 
ghian  corpuscles. 


12.  First  part  of  col- 
lecting tube. 

11.  Distal  convoluted 
tubule. 

A.  CORTEX. 

10.  Irregular  tubule. 


4.  Spiral  tube 


13.  Straight  part  of 
collecting  tube. 

9.  Wavy  part  of  as- 
cending limb  of 
Henle's  loop. 

Inner  stratum  of  cor- 
tex without  Mal- 
pighian  corpuscles 


7  and  8.  Ascending 
limb  of  Henle's 
loop  tube. 


3.  Proximal      convo- 
luted tubule. 

9.  Wavy  part  of  as- 
cending limb. 

2.  Constriction  or 
neck. 

4.  Spiral  tubule. 

1.  Malpighian  tuft 
surrounded  by 
Bowman's  capsule. 


8.  Spiral  part  of  as- 
cending limb  of 
Henle's  loop. 


B.  BOUNDARY  ZONE. 
5.  Descending     limb 
of     Henle's     loop 
tube. 

I 


6.  Henle's  loop. 


C.  PAPILLARY  ZONE. 


FIG.  267.— DIAGRAM  OF  THE  COURSE  OF  Two  URINIFEROUS  TUBULES, 
AFTER  KLEIN  AND  NOBLE-SMITH.    (Landois.) 


increase  of  blood  pressure  or  by  a  relaxation  of  the  renal  arter}7,  accom- 
panied by  the  constriction  of  other  vascular  areas,  which,  while  dimin- 
ishing the  pressure  in  the  renal  artery  itself,  increases  the  pressure  in  its 
capillaries.  Of  course,  pressure  w&y  be  reduced  in  the  kidney  by  the 
reverse  causes. 


644 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


The  principal  constituent  of  the  urine  which  is  removed  by  a  process 
of  filtration  is,  of  course,  water.     Therefore,  in  the  quantity  of  urine, 


FIG.   268.— BLOOD-VESSELS  AND    URINIFEROUS  TUBULES  OF  THE  KIDNEY 

(SEMI-DIAGRAMMATIC).      (LandOtS.) 

A,  capillaries  of  the  cortex ;  B,  of  the  medulla ;  a,  interlobular  artery ;  1,  vas  afferens ;  2,  vas 
efferens ;  r  e,  vasa  recta ;  c,  venae  rectae ;  v  v,  interlobular  vein  ;  S,  origin  of  a  vena  stellata ;  i  i,  Bow- 
man's capsule  and  glomerulus;  X  X,  convoluted  tubules;  1 1,  Henle's  loop;  n  n,  junctional  piece;  o  o, 
collecting  tubes ;  O,  excretory  tube. 

which,  of  course,  means  quantity  of  water,  the  variations  in  the  activity 
of  the  process  of  filtration  may  be  mainly  made  out.     Wherever  the 


KENAL   SECKETION. 


645 


renal  secretion  is  diminished,  it  may  almost  invariably  be  concluded  that 
the  process  of  filtration  has  been  interfered  with  by  some  means  or 
other ;  and,  conversely  and  as  a  consequence,  the  so-called  diuretics  are, 
as  a  rule,  substances  which  directly  increase  blood  pressure  and  thus 
facilitate  transudation.  So,  anything  which  reduces  blood  pressure  in 
the  kidneys  will  reduce  the  secretion.  Section  of  the  spinal  cord  acts  in 
this  way.  By  the  universal  vascular  relaxation  produced,  the  blood 
pressure  is  reduced  in  the  kidney,  as  elsewhere,  and  filtration  rendered 
almost  impossible. 

Stimulation  of  the  spinal  cord  acts  in  the  opposite  direction  by  con- 
stricting the  general  vascular  areas,  together  with  the  renal  artery,  and 
yet  produces  the  same  result ;  for  the  increase  of  general  pressure  does 
not  compensate  for  the  increased  resistance  in  the  renal  artery.  As  a 


v 


FIG.  269.— THE  SECRETING  PORTIONS  OF  THE  KIDNEY.    (Landois.) 

II,  Bowman's  capsule  and  glomerulus:  a,  vas  afferens  ;  «,  vas  efferens;  c,  capillary  network  of  the 
cortex;  k,  endothelium  of  the  capsule;  h,  origin  of  a  convoluted  tubule.  Ill,  "rodde'd"  cells  from  a 
convoluted  tubule  ;  2.  seen  from  the  side,  with  g,  inner  granular  zone ;  1,  from  the  surface.  IV,  cells 
lining  Henle's  loop.  V,  cells  of  a  collecting  tube.  VI,  section  of  an  excretory  tube. 

consequence,  the  flow  of  blood  in  the  latter  is  reduced  and  filtration  pre- 
vented. 

If  the  local  pressure  in  the  kidney  be  increased,  as  by  section  of  the 
renal  nerves  or  by  section  of  the  splanchnics,  both  of  which  lead  to  the 
dilatation  of  the  renal  arteries,  and  hence  an  increased  pressure  in  the 
glomeruli,  an  increased  secretion  is  produced.  Conversely,  stimulation 
of  the  splanchnic  or  renal  nerves  arrests  filtration  by  reducing  the  blood 
supply  to  the  kidney. 

The  correlation  between  the  action  of  the  kidneys  and  skin  is 
explainable  on  these  data :  It  is  known  that  in  cold  weather  the  kidneys 
are  more  active  than  in  warm  weather,  while  the  reverse  holds  with  the 
skin.  In  cold  weather  the  capillaries  of  the  external  integument  are  con- 
stricted and  the  blood  pressure  in  the  internal  organs  is,  therefore, 


646  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

increased  and  nitration  through  the  kidneys  facilitated.  As  a  conse- 
quence, the  urine  in  cold  weather  is  of  low  specific  gravity  from  the  large 
amount  of  water  forced  through  the  glomeruli.  In  warm  weather,  on  the 
other  hand,  the  capillaries  of  the  skin  are  relaxed,  general  blood  pressure 
is,  therefore,  reduced  and  filtration  to  that  extent  interfered  with,  and 
the  urine  is  now  scanty  and  of  a  higher  specific  gravity  from  the  decrease 
in  its  percentage  of  water. 

Filtration  is  not,  however,  the  only  process  concerned  in  the  forma- 
tion of  urine.  This  is  evident  from  the  examination  of  the  composition 
of  urine ;  for  if  it  were  merely  a  filtrate  from  the  blood  it  could  con- 
tain no  soluble  constituent  in  greater  proportion  than  it  exists  in  the 
blood ;  for  a  solution  cannot  by  filtration  through  a  moist  animal  mem- 
brane become  more  concentrated.  Yet  the  urine  contains  many  sub- 
stances, especially  urea,  in  much  larger  amount  than  in  the  blood,  and  it 
must,  therefore,  be  assumed  that  the  fluid  which  is  removed  from  the 
blood  by  filtration  through  the  glomeruli  differs  in  important  respects 
from  the  urine.  It  must  be  almost  identical  with  transudations  from 
the  blood  in  other  localities.  It  is,  however,  probable  that  it  is  free  from 
albumen.  For  the  fluids  which  leave  the  blood  must  traverse  not  only 
the  walls  of  the  capillaries  of  the  glomeruli,  but  also  the  walls  of  the 
capsule,  and  it  is  well  known  that  such  relatively  thick  membranes  offer 
difficulty  to  the  filtration  of  albumen. 

It  is  well  known  that  normal  urine  is  free  from  albumen,  and  this  is  to 
be  explained  either  by  the  statement  above  mentioned,  or  by  the  assump- 
tion that  albumen  does  pass  through  the  glomeruli  into  the  interior  of 
the  urinary  tubules,  but  is  again  absorbed  by  the  epithelial  cells  lining  the 
looped  portion  of  the  tubules.  This,  however,  is  perhaps  supported  by  the 
fact  that  in  kidney  diseases,  where  the  epithelium  of  the  tubules  is 
diseased  or  absent,  and  absorption,  presumably,  thus  interfered  with, 
albumen  is  then  constant^  found  in  the  urine. 

It  is  readily  conceivable  that  various  constituents  may  be  added  to 
the  urine  in  its  passage  through  the  different  portions  of  the  uriniferous 
tubules.  That  such  is  the  case  is  rendered  probable  by  the  histological 
structure  of  the  kidney.  The  fluid  removed  by  the  glomeruli  from  the 
blood  passes  through  a  series  of  convoluted  tubules  lined  with  epithelial 
cells  similar  to  those  found  in  other  secreting  organs  and  surrounded  by 
a  second  net-work  of  capillaries.  The  epithelial  cells  lining  the  tubules 
may  be  regarded  as  specific  secretory  cells  which  are  concerned  in 
removing  the  specific  constituents  of  the  urine  from  the  blood.  That 
they  are  capable  of  removing  substances  from  the  blood  circulating  in 
the  capillaries  may  be  demonstrated  by  the  injection  into  the  blood-cur- 
rent of  indigo  carmine,  after  previous  section  of  the  spinal  cord,  thus 
preventing  the  formation  of  the  urinary  secretion  by  filtration.  If  ani- 


KENAL  SECRETION.  647 

mals  are  killed  at  various  periods  after  such  an  injection,  indigo  carmine 
may  be  traced  from  the  blood  into  the  interior  of  the  epithelial  cells  and 
from  there  into  the  interior  of  the  uriniferous  tubules.  No  trace  of  this 
pigment  passes  through  the  glonaeruli. 

This  experiment  demonstrates  that  even  when  the  blood  pressure  is 
greatly  reduced  the  epithelial  cells  of  the  kidney  do  not  lose  their 
activity,  but  are  still  able  to  remove  substances  from  the  blood  and 
transfer  them  into  the  interior  of  the  tubules. 

Certain  substances  which  belong  to  the  group  of  diuretics  produce 
a  flow  of  urine  without  at  all  increasing  the  blood  pressure ;  such  sub- 
stances are  urea,  urates,  etc.  It  follows  that  if  the  blood  pressure  has 
not  been  increased,  or,  in  fact,  may  even  have  been  decreased,  and  yet 
the  flow  of  urine  not  be  interfered  with,  some  other  portion  of  the 
kidney  besides  the  glomeruli  is  concerned  in  the  separation  of  the  water 
together  with  the  other  constituents  of  the  urine. 

It  is  capable  of  demonstration  that  urea  passes  from  the. blood  into 
the  renal  secretion  through  the  activity  of  the  renal  cells. 

In  amphibious  animals  the  kidney  receives  a  suppty  of  blood  from 
the  renal  artery  and  also  from  the  renal  portal  system,  which  is  formed 
by  a  branch  of  the  femoral  vein  which  joins  its  fellow  from  the  opposite 
side  to  form  the  anterior  abdominal  vein. 

The  renal  artery  alone  supplies  the  glomerulus ;  the  renal  portal 
vein  alone  supplies  the  uriniferous  tubules.  If  the  renal  artery  be  tied, 
the  blood  is,  of  course,  shut  off  from  the  glomeruli,  and  all  filtration  is 
thus  prevented.  Urea,  nevertheless,  is  still  a  constituent  of  the  secre- 
tion formed  by  such  a  kidney,  and  when  urea  is  injected  into  the  blood 
it  likewise  causes  a  secretion  of  urine. 

On  the  other  hand,  substances  which  are  presumably  removed  from 
the  blood  by  a  process  solely  of  filtration,  viz.,  sugar,  peptones,  and  vari- 
ous salts,  do  not  appear  in  the  urine  after  the  renal  artery  has  been  tied. 

It  is  thus  evident  that  the  secretion  of  urine  is  a  double  process, 
partty  a  process  of  filtration,  in  which  water  and  crystalline  substances 
are  removed  from  the  blood  by  a  process  of  transudation  occurring  in 
the  glomeruli.  Everything,  therefore,  which  increases  blood  pressure  in 
the  renal  arteries  will  lead  to  transudation  and  to  an  increase  in  the 
watery  constituents  of  the  urine. 

The  renal  secretion  is  also  an  active  secretory  process  in  which  the 
epithelial  cells  lining  the  convoluted  portions  of  the  uriniferous  tubules 
are  concerned  in  removing  the  specific  constituents  of  the  urine  from  the 
blood,  while  perhaps  completing  the  process  of  transformation  of  some  of 
the  antecedents  of  urea  into  that  substance.  This  subject  will  again  be 
referred  to  from  this  point  of  view  when  we  consider  the  problems  of 
nutrition  which  occur  in  the  animal  body. 


648  PHYSIOLOGY  OF  THE   DOMESTIC  ANIMALS. 

3.  THE  MECHANISM  OF  MICTURITION. — The  secretion  of  urine,  like 
the  bile,  is  constant,  and  if  the  ureters  be  divided  it  will  be  found  that 
there  will  be  a  steady  flow  of  urine,  drop  by  drop.  The  urine  has  been 
described  as  a  pure  excretion — that  is,  it  is  composed  solely  of  sub- 
stances which  no  longer  have  any  office  to  fulfill  in  the  economy,  and 
which  are  deleterious  and  must  be  removed.  Arrest  of  the  renal  secre- 
tion, or  so-called  suppression  of  urine,  by  preventing  the  elimination  of 
these  substances  invariably  leads  to  a  fatal  result. 

The  urinary  constituents  eliminated  from  the  blood  through  the 
action  of  the  glomeruli  and  epithelial  cells  of  the  uriniferous  tubules  pass 
drop  by  drop  through  the  straight  canals  into  the  pelvis  of  the  kidney, 
and  from  there  through  the  peristaltic  contractions  of  the  muscular  walls 
of  the  ureters  into  the  bladder. 

The  bladder  is  a  muscular  organ  composed  of  an  internal  mucous 
coat  and  double  muscular  coat.  The  fibres,  which  are  of  the  unstriped 
variety,  are  arranged  in  oblique  and  circular  layers,  the  latter  being  es- 
pecially developed  at  the  neck  of  the  bladder.  Externally  situated  is  a 
fibrous  membrane,  while  the  upper  portion  of  the  bladder  is  covered  by 
the  peritoneum.  The  ureters  pierce  the  vesical  walls  obliquely,  and  at  the 
orifice  of  entrance  of  the  ureters  into  the  bladder  is  located  a  valvular 
fold  of  mucous  membrane.  As  the  bladder  fills  the  increased  pressure 
on  its  walls  tends  to  obliterate  the  orifice  of  entrance  of  the  ureters, 
and  so  prevent  regurgitation  through  the  ureters  back  to  the  kidneys. 
Sometimes,  as  a  consequence  of  obstruction  to  the  flow  of  urine  from  the 
bladder,  it  will  be  found  that  the  ureters  are  then  the  seat  of  considera- 
ble distention.  Such  distention  is  not,  however,  caused  by  a  reflux  from 
the  bladder,  but  is  only  produced  when,  the  bladder  becoming  distended 
to  its  full  capacity,  the  constant  secretion  of  urine  still  continues  to 
collect  in  the  ureters  behind  the  bladder.  As  the  urine  accumulates  in 
the  bladder  it  rises  from  the  c&vity  of  the  pelvis  to  occupy  the  lower 
portion  of  the  abdominal  region,  where  in  man,  when  fully  distended,  it 
may  be  recognized  by  percussion,  and  extends  from  eight  to  ten  centi- 
meters above  the  symphysis  of  the  pubes. 

The  urine  is  retained  in  the  bladder  by  the  normal  tonic  contraction 
of  the  circular  sphincter  of  the  bladder,  aided  by  the  tonic  contraction 
of  the  sphincter  urethras  and  the  elastic  fibres  surrounding  the  urethrse. 
As  the  bladder  becomes  distended  the  sphincter  becomes  relaxed,  and 
the  contact  of  the  escaping  urine  with  the  upper  part  of  the  membranous 
portion  of  the  urethra  causes  the  desire  to  urinate.  Escape  of  urine  may 
at  this  time  be  prevented  by  the  contraction  of  the  sphincter  urethra 
muscle,  which  is  a  red,  striped,  voluntary  muscle. 

In  animals  and  infants  this  contact  of  the  urine  with  the  mucous 
membrane  of  the  urethrse  starts  the  process  of  micturition,  which,  in 


BENAL   SECKETION.  649 

such  circumstances,  is  a  purely  reflex  action,  and  may  be  carried  on 
without  the  assistance  of  the  will. 

The  state  of  contraction  of  the  vesical  muscular  fibres,  as  was 
found  to  be  the  case  as  regards  the  rectum,  is  governed  by  a  spinal  centre 
located  in  the  lumbar  portion  of  the  spinal  cord.  When  the  spinal  cord 
is  divided  in  the  dorsal  region  in  a  dog,  after  the  shock  of  the  operation 
has  passed  off  the  bladder  may  fill  with  urine,  and,  when  distended, 
empties  itself  in  a  perfectly  normal  manner. 

The  distention  of  the  bladder  starts  sensory  impulses,  which  are 
conducted  to  the  spinal  cord  through  the  posterior  roots  of  the  third, 
fourth,  and  fifth  sacral  nerves.  The  centre  of  micturition,  which  in  dogs 
is  situated  opposite  the  fifth  and  in  rabbits  opposite  the  seventh  lumbar 

c 


FIG.  270.— DIAGRAM  OF  THE  NERVOUS  MECHANISM  OF  MICTURITION.    ( Yeo.) 

B,  bladder ;  M,  abdominal  muscles ;  C,  cerebral  centres  ;  R  represents  impulses  which  pass  from  the 
bladder  to  the  centre  in  the  spinal  cord,  whence  tonic  impulses  are  reflected  and  pass  along  T  to  the 
sphincter  which  retains  the  urine.  When  the  bladder  is  distended,  impulses  pass  to  the  brain  by  1,  and 
when  we  will,  the  tonus  of  the  spinal  centre  stimulating  the  sphincter  is  checked,  and  the  abdominal 
muscles  are  made  by  2  to  force  some  urine  into  the  neck  of  the  bladder,  whence  impulses  pass  by  3  to 
inhibit  the  sphincter  centre  and  excite  the  detrusor  through  4. 

vertebra,  is  then  called  into  play,  and  the  muscular  fibres  of  the  sphinc- 
ter of  the  bladder  relax,  while  contractions  of  the  longitudinal  fibres,  or 
the  so-called  detrusor  urinae  muscle,  are  called  forth. 

The  contraction  of  this  muscle  serves  to  contract  the  capacity  of 
the  bladder  in  all  directions,  its  contents  are  thus  forced  out  through 
the  relaxed  sphincter  muscle  through  the  urethras,  and  urination  is  ter- 
minated by  the  rhythmical  contraction  of  the  bulbo  cavernosus,  or 
ejaculator  nrinae  muscle. 

Ordinarily  the  emptying  of  the  bladder  is  assisted  by  the  co- 
operation of  the  abdominal  muscles  in  the  same  way  as  their  contraction 
aids  in  defsecation.  A  deep  inspiration  is  made  as  the  bladder  becomes 


650  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

almost  totally  emptied,  the  glottis  closes,  and  the  abdominal  muscles, 
contracting,  serve  to  force  down  the  abdominal  contents  into  the  pelvis, 
and  so  by  pressure  from  above  aid  the  emptying  of  the  bladder.  Section 
of  the  spinal  cord  above  the  level  of  this  centre  first  causes  retention  of 
urine  by  increasing  the  reflex  activitjr  of  the  urethral  sphincter  and  by 
interfering  with  the  conduction  of  inhibitory  impulses  from  the  brain. 
As  soon  as  the  bladder  becomes  distended  the  sphincter  becomes  mechan- 
ically dilated,  and  the  urine  trickles  away  in  drops,  but  less  rapidly  than 
it  enters  from  the  kidney  ;  so  the  bladder  becomes  enormously  dilated 
and  the  retained  urine  is  apt  to  undergo  ammoniacal  fermentation. 
Goltz,  however,  has  seen  dogs  micturate  in  a  perfectly  normal  manner 
after  complete  division  of  the  spinal  cord  above  the  lumbar  region. 

While  urination  is  thus  originally  a  purely  reflex  action,  it  is  pos- 
sible by  education  to  bring  it,  to  a  very  considerable  extent,  under  the 
control  of  the  will.  The  contact  of  the  first  few  drops  of  urine  with  the 
mucous  membrane  of  the  urethrse,  instead  of  inaugurating  the  act  of 
micturition,  may  by  an  exertion  of  the  will  lead  to  an  increase  of 
the  tonic  contraction  of  the  sphincter  of  the  bladder  instead  of  to  its 
inhibition.  The  act  of  micturition  is  thus  voluntarily  postponed 
(Fig.  270). 

In  addition  to  this  voluntary  control  of  the  act  of  micturition,  this 
process  is  also  largely  governed  by  the  emotions,  and  the  starting  point 
of  the  act  may  originate  not  only  in  the  distention  of  the  bladder,  but 
in  various  forms  of  irritation  of  the  genital  apparatus.  Such  a  cause 
will  frequently  be  found  to  explain  the  urinary  incontinence  of  children. 


SECTION     XL 
THE  CUTANEOUS  FUNCTIONS. 

ANOTHER  source  of  loss  to  the  blood  occurs  in  its  passage  through 
the  capillaries  of  the  external  integument  by  means  of  the  sweat  and 
the  sebaceous  glands.  As  already  indicated,  the  waste  products  of  the 
animal  economy  are  mainly  urea  and  its  antecedents,  carbon  dioxide, 
salts,  and  water.  In  the  study  of  respiration  we  found  that  the  pul- 
monary mucous  membrane  constituted  the  organ  whose  function  as  an 
excretory  organ  was  mainly  concerned  in  the  removal  of  carbon  dioxide, 
water,  and  certain  organic  products  from  the  blood.  The  kidney  we 
found  to  be  especially  active  in  removing  urea,  various  salts,  and  water. 
These  two  organs  constitute  the  main  paths  of  elimination  of  substances 
no  longer  of  use  to  the  economy,  and,  as  a  consequence,  constitute  the 
most  important  excretory  organs  of  the  body. 

The  skin  may  be  regarded  as  an  organ  supplemental  in  its  action 
to  the  lungs  and  kidneys,  since  the  skin  by  its  secretion  is  capable  of 
removing  a  considerable  quantity  of  water  from  the  blood,  small  amounts 
of  carbon  dioxide,  and  small  amounts  of  salts,  and  in  certain  instances 
during  suppression  of  renal  secretion  a  small  amount  of  urea. 

The  skin  is  thus  an  excretory  organ,  serving  to  remove  gaseous, 
liquid,  and  solid  waste  products.  The  skin  is  also  the  chief  organ  for  the 
regulation  of  animal  heat,  by,  on  the  one  hand,  through  conduction, 
radiation,  and  evaporation  of  water,  permitting  of  loss  of  heat,  while  it 
also,  through  mechanisms  to  be  considered  directly,  is  able  to  regulate 
the  amount  of  heat  lost.  Since  the  skin  is  more  permeable  to  gases 
than  a  dry  membrane,  a  certain  amount  of  gaseous  interchange  takes 
place  through  the  skin.  The  skin  further,  through  the  various  forms 
which  the  epidermal  organs  may  take  on,  whether  hoofs,  horns,  claws, 
fur,  or  feathers,  furnishes  means  of  protection  and  offensive  organs. 
Thus,  the  hairs  (fur  or  feathers)  furnish  protection  against  extreme  and 
sudden  variations  of  temperature  by  the  fact  that  they  are  poor  con- 
ductors of  heat,  and  inclose  between  them  a  still  layer  of  air,  itself  a 
poor  conductor  of  heat.  The  hairs  are  also  furnished  with  an  apparatus 
by  which  the  loss  of  heat  may  be  regulated  ;  thus,  in  cold  weather,  through 
the  contraction  of  the  unstriped  muscular  fibres  of  the  skin  (the  erectores 
pili},  the  hairs  become  erect  and  the  external  coat  thus  becomes  thicker. 
Further,  cold  acts  as  a  stimulus  to  the  growth  of  hair,  and  we  find,  as  a 

(651)  ' 


652  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

consequence,  a  thicker  coat  in  winter  than  in  summer.  This  is  not  only 
seen  in  the  thicker  fur  in  animals  which  inhabit  a  cold  climate,  as  con- 
trasted with  the  same  species  in  warmer  latitudes,  but  also  in  the  periodic 
growth  and  shedding  of  hair  seen  in  the  horse  and  ox  in  the  change  of 
the  seasons.  The  hairs  also  furnish  protection  against  wet,  from  the  fact 
that  they  are  always  more  or  less  oily,  from  the  secretions  of  the  sebaceous 
glands,  and  thus  shed  water.  The  hairs,  through  their  elasticity,  furnish 
mechanical  protection,  and  through  the  thickness  of  the  coat,  to  a  certain 
degree,  resist  the  attacks  of  insects  ;  thus  the  external  auditory  meati, 
the  external  nares,  and  the  eyes  are  protected  by  hairs.  Finally,  the  hairs 
assist  the  sense  of  touch. 

1.  THE  SWEAT  SECRETION. — The  sweat-glands,  which  are  found  only 
in  mammals,  occur  in  their  simplest  form  in  the  domestic  animals  in  the 
ox,  where  they  are  simply  oval  sacs,  which  in  man  and  the  horse  and  in 
the  feet  of  the  dog  and  cat  and  snout  of  the  hog  become  developed  into 
long,  convoluted  tubes,  passing  through  the  entire  thickness  of  the  skin. 

In  the  horse  the  sweat-glands  are  comparatively  highly  developed, 
especially  in  the  inguinal  region,  where  they  are  also  abundant  in  the 
sheep.  In  the  ox  the  sweat-glands,  as  alread}r  mentioned,  are  rudimentary, 
and,  as  a  consequence,  this  animal  sweats  but  very  little.  Cats,  rabbits, 
and  rats  do  not  sweat  at  all,  the  carnivora  generally  sweating  only  in  the 
soles  of  their  feet. 

The  sweat  is  a  transparent,  colorless  liquid  with  a  characteristic 
odor,  varying  as  to  its  source  from  different  parts  of  the  skin,  with  a 
salty  taste.  Its  specific  gravity  is  about  1004.  Its  reaction  may  be 
said  to  be  normally  alkaline  or  neutral.  The  frequent  acid  reaction  is  to 
be  attributed  to  the  development  of  fatty  acids  in  the  decomposition  of 
fatty  matters  formed  by  the  sebaceous  glands,  and  which  are  ordinarily 
mixed  with  the  perspiration.  Its  quantity  is  very  variable,  governed  by 
conditions  to  be  referred  to  directly.  It  may  be  stated  in  a  general  way 
that,  as  a  rule,  twice  as  much  water  is  given  off*  by  the  skin  as  by  the 
lungs,  while,  as  a  rule,  in  man  eleven  grains  of  solids  are  eliminated  by 
the  skin  in  twenty-four  hours,  in  contrast  to  seven  grains  removed  by 
the  lungs.  The  sweat  contains  no  structural  elements  with  the  exception 
of  epithelial  scales,  which  may  be  accidentally  removed  from  the 
epidermis. 

The  sweat  in  its  composition  contains  about  1.8  per  cent,  of  solids, 
of  which  two-thirds  are  inorganic  and  mainly  constituted  by  alkaline 
chlorides.  The  nitrogenous  constituents  of  the  sweat  consist  almost 
solely  of  urea,  which  by  its  decomposition  may  give  rise  to  ammonia. 
The  non-nitrogenous  constituents  of  the  sweat  are  composed  of  volatile 
fatty  acids,  such  as  formic,  acetic,  butyric,  proprionic,  and  caproic,  which 
give  to  the  sweat  its  characteristic  odor.  Cholesterin  and  neutral  fats 


CUTANEOUS   FUNCTIONS.  653 

coming  from  the  sebaceous  glands  are  also  frequently  found  in  it.  The 
mineral  matters  are  composed  mainly  of  sodium  chloride,  potassium 
chloride,  phosphates,  and  alkaline  sulphates,  phosphatic  earths,  and 
traces  of  iron.  The  sweat,  in  addition,  contains  traces  of  free  carbon 
dioxide  and  small  amounts  of  nitrogen. 

The  following  table  represents  the  different  anatyses  of  the  sweat: — 


In  1000  Parts. 

Favre. 

Schottin. 

Funke. 

Water 

995.573 

977.40 

988.40 

4.427 

22.60 

11.60 

4.427 

4.20 

2.49 

Fats,   . 

0.013 

4.20 

2.49 

Lactates,     . 

0.317 

4.20 

2.49 

Chlorine  sudorates, 

1.562 

4.20 

2.49 

Extractive  matters, 

0.005 

11.30 

2.49 

Urea,  . 

0.044 

11.30 

1.55 

Sodium  chloride, 

2.230 

3.60 

1.55 

Potassium  chloride, 

0.024 

3.60 

1.55 

Sodium  phosphate, 

traces 

3.60 

1.55 

Alkaline  phosphates 
Phosphatic  earths, 

0.011 
traces 

1.31 
0.39 

1.55 
1.55 

Other  salts,. 

traces 

7.00 

4.36 

The  quantity  of  sweat  is  very  variable.  In  man  its  amount  has  been 
placed  at  five  hundred  to  nine  hundred  grammes  daily,  although  under 
different  conditions  it  may  be  increased  to  fifteen  hundred  or  two  thou- 
sand grammes,  or  even  more.  Under  all  conditions  in  which  the  activity 
of  the  skin  is  not  absolutely  prevented  a  considerable  quantity  of  perspi- 
ration is  formed  by  the  skin,  the  water  of  which  evaporates  as  rapidly  as 
it  is  poured  out.  The  secretion  of  sweat  is  then  spoken  of  as  insen- 
sible perspiration.  Under  other  circumstances  fluid  may  be  noticed 
to  collect  on  the  surface  of  the  skin,  and  is  then  spoken  of  as  sensible 
perspiration.  The  proportion  of  the  sensible  to  the  insensible  perspi- 
ration will  depend  upon  a  number  of  external  conditions.  Thus,  sup- 
posing the  rate  of  secretion  to  remain  constant,  the  drj-er  and  hotter  the 
air  and  the  more  rapid  the  circulation  of  air  in  contact  with  the  body,  the 
greater  will  be  the  amount  of  sensible  perspiration  which  undergoes 
evaporation  and  is  thus  converted  into  insensible  perspiration.  On  the 
other  hand,  when  the  air  is  cool,  and  especially  when  saturated  with 
moisture,  evaporation  from  the  surface  of  the  body  is  prevented,  and, 
even  although  the  rate  of  secretion  by  the  skin  be  no  greater  than  in  the 
previous  condition,  the  amount  of  sweat  which  remains  on  the  surface  of 
the  body  as  sensible  perspiration  will  be  greatly  increased. 

The  total  amount  of  secretion  poured  out  by  the  skin  is  not  only 
modified  by  the  condition  of  the  atmosphere,  but  also  by  the  character 
and  quantit}*-  of  the  food  and  by  the  amount  of  exercise,  and  especially 
by  the  amount  of  fluid  drunk.  It  is  also  influenced  by  the  mental  con- 
ditions, by  medicines,  poisons,  and,  as  pointed  out  under  the  heading  of 


654  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

Renal  Secretion,  the  activity  of  the  skin  as  a  secreting  organ  is,  as  a  rule, 
inverse  to  that  of  the  kidnej^.  As  a  consequence,  in  warm  weather  the 
cutaneous  blood-vessels  relax,  more  blood  circulates  through  the  skin, 
and  the  perspiration  is,  therefore,  increased,  while  the  amount  of  water 
eliminated  by  the  kidnej's  is  decreased.  Hence,  in  warm  weather  the 
urine  is  scanty  and  of  high  specific  gravity.  On  the  other  hand,  in  cold 
weather  the  cutaneous  capillaries  are  contracted,  the  activity  of  the  sweat- 
glands  diminished,  while  from  the  increased  blood  pressure  in  the  internal 
organs  the  activity  of  the  kidney,  especially  of  the  glomeruli,  is  increased, 
and  the  urine  is  now  more  abundant  in  quantity  and  of  lower  specific 
gravity. 

The  formation  of  sweat  is  a  true  secretion  and  is  dependent  upon 
the  secretory  activity  of  the  epithelial  cells  of  the  sweat-glands.  The 
relation  between  the  activity  of  the  sweat-glands  and  of  the  blood  supply 
has  been  very  clearty  made  out.  Nearly  all  conditions  which  increase 
the  blood  supply  to  a  part  will  lead  to  an  increased  secretion  of  sweat. 
This,  as  already  mentioned,  will  probably  explain  the  increased  secretion 
when  the  skin  is  subjected  to  a  high  temperature. 

Bernard  also  succeeded  in  producing  secretion  by  the  skin  by 
division  of  the  vaso-motor  nerves  supplying  the  part.  Thus,  division  of 
the  cervical  sympathetic  in  the  horse  will  cause  an  abundant  secretion  of 
sweat  on  the  corresponding  side  of  the  face. 

The  sweat-glands  are  further  governed  by  special  secretory  nerves. 
This  statement  is  supported  not  only  by  the  production  of  sweat  in 
various  pathological  conditions  and  in  the  evident  influence  of  the 
emotions  on  the  sweat  secretion,  even  in  the  absence  of  increased  circu- 
lation, but  also  has  been  demonstrated  by  direct  experiment. 

If  in  a  dog  or  cat  the  peripheral  end  of  the  sciatic  nerve  be  stimu- 
lated with  an  interrupted  current,  a  profuse  secretion  of  perspiration  is 
produced  on  the  balls  of  the  toes.  Such  a  secretion  is  evidently  not 
produced  by  modifications  of  the  blood  supply ;  for  stimulation  of  the 
sciatic  nerve,  as  a  rule,  may  be  said  to  lead  to  the  constriction  of  the 
blood-vessels  in  this  part,  and  the  secretion  may  even  be  produced  after 
ligation  of  the  blood-vessels  of  the  limb  or  even  after  its  amputation. 
Moreover,  the  vaso-motor  effects  may  be  produced,  as  in  the  case  of  the 
secretion  of  the  saliva,  and  the  secretory  effects  prevented  by  the  injection 
of  atropine.  The  analogy,  therefore,  between  the  secretion  of  sweat  and 
that  of  saliva  is  clearly  established,  and  we  are  warranted  in  stating  that 
the  sciatic  nerve,  like  the  chorda  tympani,  contains  special  secretory 
fibres  whose  stimulation  leads  to  an  increased  activity  of  the  secretory 
epithelium. 

Moreover,  experiment  enables  us  to  determine  that  the  sweating 
produced  by  exposure  to  high  temperature  is  not  solely  due  to  the 


CUTANEOUS  FUNCTIONS.  655 

increased  blood  supply  of  the  part,  but  to  direct  action  on  the  nervous 
system.  For  if  the  sciatic  nerve  be  divided  in  a  cat,  on  exposure  to 
high  temperature  the  part  removed  from  the  central  nervous  system  will 
form  no  secretion,  while  the  other  surfaces  of  the  body  will  form  an 
abundant  secretion  of  sweat,  thus  clearly  showing  that  heat  acts  mainly 
as  a  stimulant  to  the  secretion  of  sweat  by  calling  into  play  the  activity 
of  the  central  nervous  S3^stem. 

Sweat  may  also  be  produced  by  stimulating  the  central  end  of  the 
divided  sciatic  nerve,  where,  of  course,  its  production  is  clearly  of  a 
reflex  nature,  and  is  attributed  to  the  stimulation  of  the  so-called  sweat 
centres  located  in  the  spinal  cord.  The  sweat  secretion  may  also  be 
called  forth  by  various  drugs,  especialty  by  pilocarpine,  the  alkaloid  of 
jaborandi,  which  appears  to  act  as  a  local  stimulant  to  the  sweat-glands, 
although  it  may  also  have  some  stimulating  action  on  the  sweat  centres. 
As  in  the  case  of  the  secretion  of  saliva,  it  may  be  antagonized  by  atro- 
pine.  The  function  of  the  sweat-glands  in  the  formation  of  sweat  is 
mainly  that  of  an  excretoty  organ,  while,  added  to  this,  by  the  evapora- 
tion of  the  perspiration  from  the  external  surfaces  of  the  bod}7  it  exerts 
a  considerable  influence  as  a  regulator  of  the  temperature  of  the  body. 
As  a  consequence,  therefore,  when,  as  in  warm  weather,  the  secretion  of 
the  skin  is  increased,  the  corresponding  increase  in  evaporation  tends  to 
prevent  the  overheating  of  the  body. 

2.  THE  SEBACEOUS  SECRETION  OF  THE  SKIN. — In  the  derm  are  found 
a  large  number  of  racemose  glands  whose  excretory  ducts,  as  a  rule, 
open  into  the  hair-follicles.  The  excretory  ducts  are  lined  with  pave- 
ment epithelium,  which  in  the  deeper  portions  gives  place  to  true  secretory 
cells  in  which  a  nucleus  is  present,  although  only  capable  of  being 
detected  with  difficulty,  its  presence  being  usually  obscured  by  the  large 
number  of  fatty  globules  surrounding  it.  Such  sebaceous  glands  are 
not  uniformly  distributed  over  the  animal  body,  but  are  especially 
developed  in  points  most  abundantly  supplied  with  hair.  During  foetal 
life  the  external  body  surface  is  covered  with  a  thick  layer  of  sebaceous 
matter,  the  so-called  vernix  caseosa,  which  protects  it  from  maceration 
in  the  amniotic  fluid.  The  secretion  formed  by  these  glands  is  a  soft, 
crumbling,  fatty  mass,  suspended  in  a  tolerably  small  amount  of  water, 
and  contains  a  small  amount  of  albuminous  matter  and  considerable 
amounts  of  potassium  salts  and  of  cholesterin.  The  secretion  is  formed 
by  the  activity  of  the  protoplasmic  secretory  cells,  which  remove  certain 
substances  from  the  transudations  from  the  blood-vessels,  and  whose 
protoplasm  itself  undergoes  fatty  degeneration.  The  secretion,  there- 
fore, consists  mainly  of  the  breaking  down  of  the  cell-contents.  It  is 
composed  of  about  31  per  cent,  water,  61  per  cent,  of  albuminous  matter 
and  epithelium,  5  per  cent,  of  neutral  fat  and  soaps,  and  1  per  cent,  of 


656  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

inorganic  salts.  Olein  and  palmatin  are  the  principal  representative 
fatty  bodies,  phosphatic  earths  and  chlorides,  and  salts.  The  wool  of 
the  sheep  contains  a  fatty  potassium  salt  which  is  soluble  in  water,  and 
which  constitutes  at  least  one-third  in  weight  of  raw  merino  wool. 

The  function  of  the  sebaceous  secretion  is  to  act  as  a  lubricant  to 
the  skin  and  epidermal  appendages. 

3.  CUTANEOUS  ABSORPTION. — When  the  body  is  plunged  in  a  liquid 
medium,  as  into  a  bath,  a  considerable  amount  of  water  is  absorbed  by 
imbibition  through  the  epithelium.     From  there  it  is  able  to  pass  by 
absorption  into  the  vessels  which  circulate  through  the  superficial  layers 
of  the  derm,  and  from  there  into  the  general  blood-current.     This  state- 
ment may  be  demonstrated  b^y  the  increase  in  weight  which,  as  a  general 
rule,  follows  immersion  in  fluid.     The  result  of  such  an  immersion  will, 
however,  vary  according  to  the  temperature  of  the  fluid.     When  the 
temperature  of  the  bath  is  above  that  of  the  body,  the  increased  secretion 
from  the  skin  will  more  than  counterbalance  the  gain  in  absorption,  and, 
as  a  consequence,  the  weight  of  the  body  may  be  decreased.     If,  on  the 
other  hand,  the  temperature  of  the  bath  is  lower  than  that  of  the  body, 
the  body  may  gain  in  weight  through  the  absorption  of  water.     The 
epidermis  is,  nevertheless,  not  equally  permeable  by  substances  brought 
into   contact   with   it.     And  this  interference  with  absorption  is  also 
increased  by  the  sebaceous  secretion  of  the  skin.     Substances  held  in 
solution  in  water  are  accordingly  absorbed  but  to  an  extremely  slight 
extent,  unless  this  immersion  be  so  prolonged  as  to  permit  of  softening 
of  the  epidermis. 

Absorption  through  friction  of  the  skin  surface  with  different  sub- 
stances, especially  when  suspended  in  a  fatty  excipient,  is  to  be  explained 
by  the  mechanical  forcing  of  such  substances  into  the  sebaceous  glands, 
and.  it  may  be,  even  into  the  interstices  of  the  epidermal  cells.  Thus, 
friction  with  tartar  emetic  suspended  in  oils  may  produce  vomiting, 
with  mercury  may  produce  salivation,  and  with  belladonna  dilatation 
of  the  pupil. 

Abrasion  of  the  skin  leads  to  a  marked  increase  in  its  facility  for 
absorption. 

4.  CUTANEOUS  RESPIRATION. — The  skin  of  man  and  animals  in  whom 
the  skin  is  bare  offers  a  certain  analogy  to  the  lungs  in  that  it  is  abun- 
dantly supplied  with  blood-vessels  which  are  nearty  in  contact  with  the 
external  atmosphere.     It  is,  therefore,  conceivable  that  through  the  skin 
there  may  be  an  interchange  between  the  gases  of  the  atmosphere  and 
blood.     Experiments  show  this  to  be  a  fact.     If  the  body  be  inclosed  in 
an  air-tight  chamber  extending  to  the  neck,  and  after  a  time  the  air 
within   this   chamber  be  analyzed,  it  will  be  found  that   it  will  have 
decreased  in  the  amount  of  oxygen  and  gained  in  carbonic  acid.     The 


CUTANEOUS  FUNCTIONS. 


657 


skin  is,  however,  of  considerable  density,  and  from  its  structure,  as 
compared  with  that  of  the  pulmonary  mucous  membrane,  must  offer 
great  resistance  to  the  diffusion  of  gases.  As  a  consequence,  the 
amount  of  such  interchange  which  occurs  through  the  skin  must  be 
slight.  In  animals,  however,  in  which  the  skin  is  not  only  bare,  but 
thin  and  moist,  gaseous  interchange  through  the  skin  may  be  of  much 
greater  importance ;  thus,  for  example,  it  has  been  found  that  if  the 
entrance  of  air  ?nto  the  lungs  of  the  frog  be  entirely  prevented  by  sur- 
rounding the  head  with  a  rubber  membrane,  life  may  be  preserved  in 
contact  with  the  air  for  several  da3~s,  and  b}~  examining  the  composition 
of  the  atmosphere,  if  the  frog  be  placed  in  a  confined  space,  it  will  be 
found  that  the  frog  has  absorbed  oxygen  and  set  free  carbonic  acid.  In 
other  words,  the  frog  is  able  to  breathe  without  lungs,  the  respiration 
carried  on  through  its  skin  being  sufficient  for  its  needs. 

In  cold-blooded  animals  this  degree  of  cutaneous  respiration  is  much 
more  extensive  than  in  warm-blooded  animals,  while  the  function  is 
least  developed  in  warm-blooded  animals  whose  skin  is  covered  with  fur, 
hair,  or  feathers.  In  fact,  it  is  probable  that  whatever  gaseous  inter- 
change does  occur  takes  place  from  the  capillary  net-work  surrounding 
the  sweat-glands.  The  exhalation  of  carbon  dioxide  may  be  readily 
demonstrated  by  placing  the  arm  in  a  vessel  containing  distilled  water 
and  which  is  closed  from  the  external  atmosphere ;  after  an  hour's  im- 
mersion only  in  the  water  the  addition  of  lime-water,  by  the  character- 
istic precipitate  of  carbonate  of  lime,  will  demonstrate  its  transudation 
through  the  skin. 

The  amount  of  carbon  dioxide  eliminated  by  the  skin  may  be  readily 
determined  by  collecting  the  total  amount  of  carbon  dioxide  liberated 
both  by  the  skin  and  lungs  and  then  deducting  the  latter  amount  from 
the  total.  Or  it  may  be  directly  measured  by  closing  the  bod}7"  in  an  air- 
tight chamber  and  preventing  entrance  of  the  expelled  air  by  breathing 
through  a  tube.  It  has  been  found  in  this  way  that  the  amount  elimi- 
nated by  the  lungs  is,  in  man,  about  one  hundred  and  thirty  times  as 
much  as  passes  through  the  skin.  The  following  experiments  by  Reg- 
nault  and  Reiset  indicate  this  amount  in  the  rabbit  and  dog: — 


ANIMAL. 

Body   Weight 
in  Grammes. 

Duration  of  Experiment  in 
Hours. 

CO2  Exhaled  in  Grammes. 

Through  the 
Skin  in  One 
Hour. 

Through  the 
L  unks  in 
One  Hour. 

Rabbit,  .     . 
Dog,.     .     . 

2425 
4159 

(  8  hours  25  minutes 
(  7  hours  25  minutes 
f  7  hours  33  minutes 
(  8  hours  50  minutes 

0.358 
0.197 
0.136 
0.176 

20.63 
19.38 
39.15 
42.50 

658  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

It  was  long  ago  noticed  that  if  the  skin  be  covered  with  a  thick 
varnish  death  will  be  rapidly  produced.  The  most  probable  explanation 
is  that  in  addition  to  the  rapid  cooling  of  the  body  by  the  dilatation  of 
the  cutaneous  capillaries  the  suppression  of  perspiration  causes  the 
retention  in  the  economy  of  some  poisonous  principle,  for  the  general 
symptoms  closely  resemble  those  of  poisoning — the  respiration  becomes 
slow  and  disturbed,  the  pulsation  of  the  heart  reduced  in  frequency, 
and  convulsions  frequently  accompany  the  final  stages. 

5.  THE  LACHRYMAL  SECRETION. — The  lachrymal  glands  belong  to 
the  group  of  compound  racemose  glands,  and  secrete  a  fluid  which  is 
tolerably  rich  in  albuminous  constituents.  The  tears  are  a  colorless 
liquid  of  salty  taste  and  alkaline  reaction.  They  contain  about  1  per 
cent,  of  solids,  which  consist  of  a  small  amount  of  mucus  and  albumen, 
coagulable  by  heat,  and  traces  of  fat  and  mineral  salts.  Of  the  latter 
sodium  chloride  is  the  principal  representative,  with  a  small  quantity  of 
alkaline  and  earthy  salts. 

The  following  table  represents  their  analyses  : — 

Water, 982.00 

Albumen  and  traces  of  mucus,     .....  5.00 

Sodium  chloride, 13.00 

Other  inorganic  salts, 0.2 

The  lachrymal  secretion  is  continuous  and  is  produced  by  the  direct 
protoplasmic  activity  of  the  secretory  cells  of  this  gland  :  the  blood 
pressure  is  of  special  influence,  and  it  is  probable  that  the  lachrymation 
which  accompanies  laughing,  coughing,  vomiting,  etc.,  is  produced  by 
local  increase  of  pressure  through  the  arrest  of  the  venous  circulation. 

The  lachrymal  secretion,  like  that  formed  by  the  other  glands,  is 
under  the  control  of  the  nervous  system.  Normally  the  lachrymal  secre- 
tion is  of  reflex  origin,  the  afferent  impulse  being  conducted  either  from 
the  conjunctiva  or  nasal  fossae,  over  the  first  and  second  branches  of  the 
trigeminal  nerve,  from  a  retinal  stimulation,  as  by  intense  light,  or  through 
some  mental  impression.  As  a  rule,  such  stimuli  lead  to  an  increased 
secretion  of  the  glands  on  both  sides,  with  the  exception  of  stimuli 
originating  in  the  nasal  fossae  or  conjunctiva,  in  which  case  the  secretion 
is  unilateral.  The  secretory  nerve  is  the  lachrymal  nerve.  Its  stimula- 
tion is  followed  by  an  abundant  secretion  of  tears,  while  its  section  is 
followed  after  a  time  by  a  continuous  secretion  corresponding  to  the 
paralytic  secretion  which  follows  section  of  the  chorda  tympani. 

Normally  the  tears,  after  passing  over  the  anterior  surface  of  the 
eyeball,  partially  evaporate  and  partially  are  conducted  through  the 
lachrymal  passages  to  the  nose,  only  when  in  excess  overflowing  the 
lower  eyelid  and  running  over  the  cheeks.  The  function  of  the  tears  is 
to  protect  the  eye  by  keeping  its  surface  moist  and  to  wash  away  foreign 
bodies. 


SECTION  XII. 

NUTRITION. 

IT  has  been  found  that  the  blood  is  constantly  losing  portions 
of  its  constituents  in  the  formation  of  the  different  secretions  and 
excretions  of  the  body  and  in  supplying  nutritive  substances  to  the 
different  tissues.  The  excretions  and  the  substances  removed  from  the 
blood  in  supplying  the  tissues  with  nutriment  are  to  be  regarded  as 
permanent  losses  to  the  blood,  since  in  the  former  case  the  substances 
so  separated  are  conducted  directly  without  the  body,  while  in  the  latter 
case  they  undergo  modifications  in  the  tissues  which  deprive  them  of  all 
nutritive  value.  In  the  case  of  secretions,  on  the  other  hand,  it  has 
been  found  that  the  losses  which  the  blood  undergoes  in  their  formation 
are  temporary,  the  matters  removed  from  the  blood  in  these  processes 
being  again  returned  to  it  after  the  secretions  have  fulfilled  their  function. 
The  milk  alone  is  an  exception  to  this  statement. 

On  the  other  hand,  we  have  seen  that  in  absorption  from  the 
alimentary  canal  the  blood  is  constantly  receiving  additions.  The 
balance  between  this  income  and  outgo  of  the  blood  constitutes  nutrition. 
If  the  income  exceed  the  outgo  the  body  increases  in  weight ;  if  the 
latter  predominates,  the  body  loses  weight. 

Two  methods  are  open  to  us  for  studying  the  processes  which  are 
concerned  in  the  maintenance  of  nutritive  equilibrium.  We  have  found 
that  the  income  of  the  body  or  the  substances  which  enter  the  blood  and 
lymph  in  the  form  of  peptone,  sugar,  albumen,  salts,  and  fats  are  con- 
stituted of  the  elements  of  carbon,  hydrogen,  oxygen,  and  nitrogen  in 
various  proportions.  It  has  been  seen  that  the  waste  products  of  the 
animal  body  are  urea,  carbon  dioxide,  water,  and  salts. 

We  know  that  nearly  all  the  carbon  taken  in  the  food  is  removed  by 
the  lungs  and  skin  in  the  form  of  carbon  dioxide;  we  know  that  nearly 
all  the  nitrogen  taken  in  with  the  food  is  excreted  in  the  form  of  urea. 
Alt  the  h\'drogen  is  excreted  in  the  form  of  water,  while  the  oxj-gen 
leaves  the  animal  economy  in  combination  with  carbon  as  carbon  dioxide, 
or  with  hydrogen  as  H20. 

The  attempt  to  trace  the  intermediary  stages  through  which  the 
constituents  of  the  food  pass  before  reaching  these  final  excretory 
products  is  accompanied  by  the  greatest  difficulty.  But  little  is  known 
as  to  the  way  in  which  these  substances  are  transformed  one  into  the 

(659) 


660  PHYSIOLOGY   OF   THE   DOMESTIC  ANIMALS. 

other,  or  as  to  the  manner  in  which  energy  is  set  free  and  made  use  of. 
Certain  of  these  processes  of  conversion  nuiy,  however,  be  followed,  and 
the  fact  that  these  processes  may  in  certain  instances  be  located  in 
special  tissues,  in  the  continuation  of  the  plan  of  specialization  of 
function,  we  are,  perhaps,  warranted  in  speaking  of  certain  tissues  as 
set  aside  to  elaborate  the  raw  materials  which  result  from  the  absorption 
of  digestive  products  and  to  so  modify  the  waste  products  as  to  permit 
of  their  ready  removal  from  the  body.  Such  tissues  are  spoken  of  as 
metabolic  tissues,  and  the  study  of  the  chemical  changes  which  occur  in 
these  tissues  furnishes  us  with  one  method  of  tracing  the  conversion  of 
the  substances  absorbed  into  the  matters  excreted. 

The  other  method  of  stud3Ting  the  nutritive  phenomena  of  the 
animal  body  is  what  is  knowrn  as  the  statistical  method. 

We  may,  by  chemically  examining  the  composition  of  the  food- 
stuffs, ascertain  the  total  quantity  of  each  constituent.  By  chemical 
analysis  we  may  also  determine  the  total  amount  of  these  different  con- 
stituents removed  from  the  body  in  the  excretions.  By  the  comparison 
of  the  results  obtained  in  these  two  examinations  valuable  conclusions 
may  be  drawn  as  to  the  changes  which  occur  in  the  body  in  the  con- 
version of  the  income  into  the  outgo.  These  methods  will  be  referred 
to  in  turn. 

I.  THE  FATE  OF  THE  ALBUMINOUS  FOOD-CONSTITUENTS. 

It  has  been  seen  that  the  albuminous  food-constituents  in  digestion, 
through  a  process  of  hydration  by  the  action  of  ferments,  are  converted 
into  peptone,  which  enters  through  absorption  into  the  radicals  of  the  por- 
tal vein,  but  an  insignificant  portion  being  absorbed  by  means  of  the  lac- 
teals.  When  once  within  the  blood-current,  possibly  in  the  process  of 
absorption  itself,  the  peptone  must  apparently  be  reconverted  to  the  form 
of  albumen,  for  the  amount  of  peptone  capable  of  detection  in  the  portal 
vein,  even  after  an  abundant  albuminous  diet, is  too  insignificant  to  repre- 
sent the  amount  of  albuminous  matters  absorbed.  We  may, therefore,  state 
that  almost  immediately  on  entering  the  blood-current  the  albuminous 
food-constituents  are  converted  mainly  into  serum-albumen.  It  has 
further  been  stated  that  urea  represents  the  end  product  in  the  series  of 
decompositions  which  the  albuminous  bodies  of  the  tissues  undergo. 
The  attempt  to  trace  the  changes,  commencing  with  albumen  and  termi- 
nating in  the  production  of  urea,  is,  however,  shrouded  with  the  greatest 
obscurit}r.  It  is  known  that  the  amount  of  urea  removed  gives  an  index 
of  the  amount  of  albuminous  destruction  occurring  in  the  animal  body. 
Numerous  experiments  have  proved  that  with  the  withdrawal  of  all  food 
the  excretion  of  urea  decreases,  and  that  a  small  amount  continues  to  be 
removed  through  the  urine  until  the  occurrence  of  death  through  starva- 


FATE   OF  THE   ALBUMINOUS   FOOD-CONSTITUENTS.  661 

tion,  this  evidently  being  formed  at  the  expense  of  the  albuminous  con- 
stituents of  the  tissues.  It  is  further  clear  that  tshe  excretion  of  urea  may 
be  increased  by  an  albuminous  food,  and  that  the  amount  of  urea  elimi- 
nated increases  proportionately  to  the  increase  in  the  albumen  given  in 
the  food.  Urea  is  not,  however,  a  simple  product  of  oxidation  of  albu- 
minous bodies,  but  is  a  product  of  complicated  decompositions  which 
are  peculiar  to  the  animal  body,  and  which  are  accompanied  by  the  pro- 
duction of  such  bodies  as  kreatin,  allantoin,  guanin,  xanthin,  and  uric 
acid.  It  is  not  improbable  that  the  albumen,  like  many  of  these  inter- 
mediary products,  retains  the  nitrogen  in  the  form  of  a  cyanogen  radical, 
and  that  it  is  only  in  its  conversion  into  urea  that  by  the  re-arrangement 
of  the  nitrogen  it  becomes  converted  into  a  member  of  the  amide  group. 

In  the  sketch  which  we  have  given  of  the  chemical  processes  occurring 
in  the  animal  body  it  was  mentioned  that  uric  acid  might  be  regarded  as 
an  antecedent  of  urea,  since  the  administration  of  uric  acid  to  animals 
is  followed  by  an  increase  in  the  amount  of  urea  removed  by  the  kidne3Ts. 
This,  however,  applies  only  to  the  case  of  mammals,  for  the  reverse  is 
noticed  in  birds,  where  the  administration  of  urea  increases  the  uric  acid 
of  the  urine,  indicating  in  the  latter  case  a  process  of  synthesis  rather 
than  of  destruction.  It  cannot  be  assumed,  however,  that  urea  is  invari- 
ably preceded  by  the  production  of  uric  acid,  or,  in  other  words,  that  it 
results  from  a  further  oxidation  of  the  latter. 

From  an  examination  of  the  constituents  of  the  different  tissues, 
such  as  the  muscles,  the  liver,  the  spleen,  and  all  organs  in  which  it  is 
known  that  the  destruction  of  albuminoids  takes  place,  the  detection  of 
nitrogenous  crystalline  bodies,  such  as  kreatin,  xanthin,  hypo-xanthin, 
etc.,  would  indicate  that  they  are  also  products  of  the  destruction  of 
albumen  and  perhaps  antecedents  of  urea.  In  the  case  of  kreatin  it 
has  been  found  that  muscular  tissue,  under  nearly  all  circumstances,  will 
contain  from  two-tenths  to  four-tenths  of  1  per  cent,  of  this  body ;  and 
since  kreatin  is  a  diffusible,  crystalline  body,  it  must  further  be  assumed 
that  large  quantities  of  it  are  continually  entering  the  blood-current  from 
the  muscular  tissue.  An  examination  of  the  urine  again  shows  that 
kreatin  and  kreatinin,  into  which  the  former  is  readily  converted,  are 
constant  constituents,  and  the  supposition  might  at  first  appear  warrant- 
able that  the  kreatin  formed  in  the  activity  of  muscular  tissue  after 
entering  the  blood  is  at  once  removed  without  change  by  the  kidneys. 
This  hypothesis  is,  however,  negatived  by  the  fact  that  increased 
muscular  activity,  which  leads  to  the  increase  in  the  formation  of  kreatin, 
does  not  lead  to  increase  in  the  kreatin  eliminated  by  the  kidneys.  On 
the  other  hand,  during  starvation  the  kreatin  entirely  disappears  from 
the  urine;  so  that  it  would,  therefore,  appear  that  the  kreatin  eliminated 
through  the  kidneys  does  not  represent  tissue  waste,  but  a  product  of 


662  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

the  breaking  down  of  the  albuminous  food-constituents  which  has  com- 
menced in  the  intestinal  canal,  perhaps  through  the  formation  of  leucin 
and  tyrosin.  Again,  it  seems  clearly  established  that  increase  in  mus- 
cular exercise  leads  to  an  increase  in  the  elimination  of  urea.  Since,  as 
has  been  stated,  the  amount  of  kreatin  formed  by  the  muscles  increases 
with  exercise,  and  the  amount  of  urea  eliminated  by  the  kidneys 
increases  under  the  same  circumstances,  it  would  appear  warrantable  to 
assume  that  the  kreatin  resulting  from  the  breaking  down  of  the  albu- 
minous tissue-constituents  of  muscles  and  nerves  represents  the  main 
source  of  urea.  As  to  where  this  conversion — which,  it  should  be  stated, 
can  only  be  acknowledged  to  have  a  certain  degree  of  probability — takes 
place,  but  little  positive  information  can  be  given. 

It  does  not  occur  solely  in  the  kidney,  for  the  suppression  of  urine 
is  followed  by  an  accumulation  in  the  system  of  a  large  amount  of  urea. 
Again,  the  urea,  under  all  circumstances,  is  a  constant  constituent  of  the 
blood,  indicating  that  even  if  a  part  of  the  urea  be  formed  in  the 
kidneys  the  renal  epithelium  is  not  the  sole  source  of  the  manufacture  of 
this  body.  As  to  where  kreatin  becomes  converted  into  urea  no  data 
can  be  given. 

Another  possible  source  of  urea  may  be  found  in  the  products  of 
the  decomposition  of  albuminous  matter  in  the  intestine.  It  has  been 
seen  that  the  introduction  of  a  large  amount  of  proteid  in  the  alimentary 
canal  is  followed  by  a  corresponding  increase  in  the  amount  of  urea 
eliminated.  It  is  further  known  that  the  excess  of  proteid  over  and 
above  that  needed  for  nutrition  in  the  alimentary  canal  breaks  down 
under  the  influence  of  pancreatic  digestion  into  leucin  and  t3Trosin.  If  . 
leucin  be  itself  introduced  into  the  intestinal  tube  the  amount  of  urea 
eliminated  will  be  proportionately  increased.  Leucin,  therefore,  may 
represent  a  step  in  the  processes  of  conversion  of  albumen  into  urea.  In 
the  latter  case  we  can  probably  locate  the  conversion  of  leucin  into  urea 
in  the  liver,  for  the  liver,  unlike  other  glands,  normally  contains  large 
quantities  of  urea;  and  if  we  again  assume,  as  perhaps  seems  warranted, 
that  the  leucin  is  absorbed  by  the  portal  vein,  the  formation  of  urea  out 
of  leucin  would  be  a  natural  conclusion. 

Uric  acid  has  also  been  found  to  be  a  constant  constituent  of  the 
urine  of  carnivora  and  of  suckling  herbivora.  It  is  never  met  with  in 
the  free  condition,  but  in  the  form  of  uric  acid  salts.  In  the  urine  of 
birds  and  reptiles  it  replaces  urea.  It  also  evidently  results  from  the 
decomposition  of  proteids,  and,  perhaps,  under  certain  circumstances,  is 
an  antecedent  of  urea,  since  by  oxidation  one  molecule  of  uric  acid  may 
be  split  up  into  two  molecules  of  urea  and  one  molecule  of  mesoxalic 
acid.  This  is  not,  however,  to  be  regarded  as  invariably  taking  place, 
but  the  majority  of  evidence  would,  perhaps,  point  to  the  formation  of 


FATE   OF   THE  ALBUMINOUS   FOOD-CONSTITUENTS.  663 

uric  acid  by  a  process  of  decomposition  of  albuminous  matters,  differing 
slightly  from  that  which  results  in  the  production  of  urea.  Sarkin  and 
xanthin,  by  progressive  oxidation,  might  perhaps  be  converted  into  uric 
acid,  and,  since  they  are  usually  found  accompanying  each  other,  will, 
perhaps,  indicate  one  source  of  uric  acid. 

Sarkin,  xanthin,  and  uric  acid  differ  from  each  other  only  in  one 
atom  of  oxygen,  thus  :  — 

Sarkin      =  C5H4N4O. 

Xanthin  =  C5H4N4O2. 

Uric  acid  =C5H4N403. 

As  to  where  this  conversion  takes  place  we  have  no  data  to  fall  back 
on,  except  that  it  does  not  occur  in  the  kidneys,  for  the  excision  of  the 
kidneys  or  the  ligation  of  the  renal  vessels  leads  to  an  accumulation  of 
uric  acid  in  the  economy.  Of  the  different  localities  where  uric  acid 
is  especially  met  with  the  spleen  occupies  the  first  position.  In  the 
spleen  uric  acid  is  constantly  found  in  large  quantities,  even  in  the  her- 
bivora,  whose  urine  is  free  from  uric  acid  ;  and  conditions  which  lead  to 
an  increased  blood  supply  to  the  spleen,  as  in  its  enlargement  in  malarial 
diseases,  lead  also  to  an  increased  excretion  of  uric  acid.  The  spleen 
may  therefore  be  looked  upon  both  as  the  place  of  origin  of  uric  acid  in 
the  carnivora  and  of  its  destruction  in  the  herbivora. 

In  the  herbivora  uric  acid  is  represented  by  hippuric  acid,  which 
differs  from  uric  acid  in  containing  three  atoms  less  of  nitrogen,  one 
atom  more  of  carbon,  and  five  atoms  more  of  hydrogen. 

Its  formula  is,  therefore,  C6H9N08. 

In  the  herbivora  the  hippuric  acid  of  the  urine  represents  a  peculiar 
decomposition  occurring  in  their  food.  Hippuric  acid  is  a  compound  of 
benzoic  acid  and  glycochol,  and  the  administration  of  benzoic  acid  to 
any  animal,  whether  carnivorous  or  herbivorous,  will  result  in  the  elimi- 
nation of  hippuric  acid  through  the  kidneys. 

This  process  of  synthesis  may  be  represented  as  follows  :  — 


Hippuric  acid  has,  therefore,  its  origin  in  the  food.  As  long  as  the 
herbivora  are  being  suckled,  or  when  fasting,  it  is  absent  from  the  urine, 
but  appears  whenever  vegetable  matter  is  added  in  sufficient  quantity  to 
the  food.  Certain  forms  of  vegetable  food  are  not,  however,  followed  by 
the  elimination  of  hippuric  acid.  Hippuric  acid  is  absent  from  the  urine 
of  animals  fed  on  peas,  wheat,  oats,  or  potatoes,  but  nearly  all  grasses 
are,  however,  followed  by  its  appearance  in  the  urine. 

When  benzoic  acid  is  given  to  animals,  hippuric  acid  is  invariably 
found  in  the  urine,  and  an  examination  of  the  vegetable  matters  whose  use 
as  food  is  followed  by  the  formation  of  hippuric  acid  will  nearly  always 
indicate  the  presence  in  such  foods  of  benzoic  acid  or  some  allied  body. 


664  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

Glycochol,  through  whose  union  with  benzoic  acid  hippuric  acid  is 
formed,  is  manufactured  in  the  liver,  the  formation  of  hippuric  acid 
occurring  probably  both  in  the  liver  and  kidneys. 

II.  THE  FATE  OF  THE  FATTY  CONSTITUENTS  OF  FOOD. 

It  has  been  found  that  the  fats  contained  in  the  food  are  largely 
absorbed  unchanged  in  the  form  of  an  emulsion,  a  small  fraction  only 
being  converted  into  fatty  soaps.  Such  absorption  was,  moreover,  found 
to  occur  mainly  b}'  means  of  the  chyle-ducts  and  only  partially  through 
the  blood-vessels.  It  may,  therefore,  be  stated  that  fats  are  absorbed 
unchanged  in  the  forms  in  which  they  enter  the  alimentary  canal.  The 
attempt  to  trace  the  progress  of  the  fats  through  the  animal  body  will 
be  aided  by  the  study  of  the  changes  which  occur  in  the  adipose  tissue. 
This,  of  all  the  tissues  of  the  body,  varies  most  rapidly  and  in  widest 
extremes.  Within  a  short  space  of  time,  as  in  starvation,  the  adipose 
tissue  of  the  body  may  almost  totally  disappear  ;  while,  on  the  other  hand, 
it  may,  under  exceptional  circumstances,  accumulate  with  the  greatest 
rapidity.  In  describing  the  histology  of  adipose  tissue  it  was  stated  that 
the  oil-globules  appeared  in  the  centre  of  the  connective-tissue  corpuscles 
and  at  their  expense,  and  the  process  was  likened  to  the  nutritive  pre- 
hension of  food  in  a  small  mass  of  undifferentiated  protoplasm,  such  as 
the  amoeba. 

The  fat,  we  have  seen,  enters  the  blood  in  all  important  respects 
unchanged,  and  the  simplest  explanation  of  the  development  of  the  adi- 
pose tissue  would  be  to  suppose  that  the  connective-tissue  corpuscles, 
by  a  process,  of  vital  appropriation,  pick  out  the  oil-globules  from  the 
fluid  in  which  they  are  bathed.  Several  difficulties,  however,  oppose 
this  simple  theory.  In  the  first  place,  it  is  well  known  that  but  a  small 
amount  of  fat  deposited  in  adipose  tissue  can  come  directly  from  the  fat 
of  the  food  :  for,  as  is  well  known,  the  butter  in  cream  is  far  in  excess  of 
the  fat  contained  in  the  food,  and  it  has  been  shown  that  in  a  fattening 
hog  for  every  one  hundred  parts  of  fat  in  the  food  four  hundred  and 
seventy-two  parts  are  stored  up  as  adipose  tissue.  Again,  if  animals  are 
fed  on  a  meat  diet  and  soaps  the}7  accumulate  adipose  tissue — a  process 
which  is  scarcely  capable  of  being  explained  by  the  re-transformation  of 
the  fats  by  taking  up  glycerin  and  giving  up  alkali. 

On  the  other  hand,  the  fats  of  different  animals  differ  in  composition, 
and  if  two  animals  of  different  species  are  fed  with  the  same  fat  the 
chemical  composition  of  their  adipose  tissue  will  vary.  Thus,  for  ex- 
ample, if  a  dog  be  fed  with  meat,  palmitin,  stearin,  and  soap,  the  fat 
of  its  adipose  tissue  will  be  found  to  contain  olein  fat  as  well  as  palmitin 
and  stearin.  So  it  is,  therefore,  clear  that  the  latter  neutral  fat  must  have 
been  manufactured  by  the  organism. 


FATE  OF  THE  FATTY  CONSTITUENTS  OF  FOOD.      665 

If  a  lean  dog  be  fed  on  a  diet  of  meat  and  spermaceti,  a  large  amount 
of  adipose  tissue  may  be  accumulated,  in  which,  however,  but  a  trace  of 
spermaceti  may  be  found.  Again,  fat  alone,  as  we  know,  is  incapable,  as 
a  food,  of  sustaining  life,  although  it,  to  a  certain  extent,  saves  the  wast- 
ing of  tissue ;  so,  as  a  consequence,  when  fat  alone  is  given  as  a  food, 
the  amount  of  urea  excreted  by  the  kidneys  is  less  than  would  be 
excreted  by  a  starving  animal.  This,  evidently,  is  to  be  explained  by  the 
fact  that  fat,  being  readily  oxidized,  is  rapidly  converted  into  carbon 
dioxide,  which  is,  of  course,  eliminated  in  the  expired  air  and  serves  to 
a  certain  extent  to  spare  the  elimination  of  the  proteids  in  oxidation. 

It  is,  then,  clear  that  in  the  animal  body  fats  are  made  from  some- 
thing which  is  not  fat.  Two  possible  sources  of  fat  suggest  themselves. 
It  is  known  that  the  nitrogen  of  urea  represents  the  total  amount  of 
nitrogen  passing  through  the  body,  and  that  a  certain  quantity  of  urea 
(one  hundred  grammes)  represents  a  certain  quantity  of  proteids  (three 
hundred  grammes).  If,  however,  we  estimate  the  quantity  of  carbon  in 
one  hundred  grammes  of  urea,  we  will  find  that  a  large  amount  of  carbon 
remains  unaccounted  for.  Part  of  this  evidently  goes  off  as  carbon 
dioxide.  It  is  probable  that  the  remainder  is  fixed  in  the  body  as  fat. 
It  may,  therefore,  be  assumed  that  proteids  split  up  into  non-nitrogenous 
and  nitrogenous  compounds,  the  former,  when  not  completely  oxidized 
into  carbon  dioxide  and  water,  being  deposited  as  fat,  the  latter  leaving 
the  body  oxidized  as  urea.  Other  illustrations  as  to  the  development  of 
fats  from  proteids  may  be  readily  given.  Thus,  in  the  pancreatic  diges- 
tion of  proteids  fatt}r  acids  may  be  developed.  The  fatty  degeneration 
of  muscle  is  evidently  due  to  the  decomposition  of  proteids,  while 
animals  fed  on  a  pure  diet  of  lean  meat  with  a  small  amount  of  fat  will 
deposit  in  their  tissues  more  fat  than  is  contained  in  the  food. 

Still  other  lines  of  study  point  to  the  development  of  ftit  from 
proteids.  It  is  known  that  in  poisoning  with  phosphorus  various  organs 
rich  in  proteids  undergo  fatty  degeneration,  and  that  the  fat  so  formed 
is  produced  at  the  expense  of  the  tissue-albumen,  the  fat  being  formed 
from  the  non-nitrogenous  residue  of  the  proteids  after  the  formation  of 
urea.  The  following  experiment  proves  this  : — 

A  large  dog  was  allowed  to  fast  for  twelve  days,  so  freeing 
its  tissues  almost  entirely  from  fat,  and  was  then  slowly  poisoned 
with  phosphorus.  Death  occurred  on  the  twentieth  day  of  fasting. 
Before  poisoning,  from  the  fifth  to  the  twelfth  day  of  fasting,  the 
elimination  of  urea  in  the  urine  was  about  constant,  and  amounted 
to  7.8  grammes  daily;  as  a  consequence  of  the  phosphorus  poisoning 
the  elimination  of  urea  was  greatly  increased,  amounting  at  last  to  23.9 
grammes  daity,  or  more  than  three  times  the  normal  amount  removed 
during  fasting.  The  post-mortem  examination  showed  extensive  fatty 


666  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

degeneration  of  various  organs,  the  increase  in  urea  elimination  proving 
that  the  fat  was  derived  from  the  albumen. 

As  regards  the  carbohydrates,  which  may  also  be  regarded  as  a 
possible  source  of  fat,  considerable  doubt  exists  as  to  the  manner  in 
which  they  act.  As  is  well  known,  carbohydrates  are  always  an 
important  constituent  of  fattening  foods,  and  it  may  be  assumed  either 
that  the  carbohydrates,  being  themselves  readily  oxidized,  save  the 
non-nitrogenous  bodies  derived  from  the  proteids,  and  so  enable  them  to 
be  converted  into  fat,  or  that  they  may  be  directly  concerned  in  the 
formation  of  fats.  It  is  clear  that  carbohydrates  may  undergo  the 
butyric  acid  fermentation,  and  other  ferment  actions  might  likewise 
serve  to  manufacture  other  fats.  Thus,  Pasteur  claims  that  glycerin, 
which  is  the  basis  of  neutral  fats,  may  be  formed  from  pure  carbo- 
hydrates. It  is  probable,  therefore,  that  in  both  of  these  ways  the 
carbohydrates  serve  to  increase  the  adipose  tissue  of  the  body  both 
directly  and  by  enabling  the  non-nitrogenous  matters  derived  from  the 
proteids  to  be  converted  into  fat  and  stored  up  as  such. 

The  following  experiments  recently  made  in  Vienna  with  a  hog 
thirteen  months  old  and  weighing  one  hundred  and  forty  kilos  are  of 
special  interest  in  this  connection  :  Two  kilos  of  soft-boiled  rice  were 
given  daily  as  fodder,  and  a  comparison  of  the  income  and  outgo 
demonstrated  the  daily  deposit  in  the  tissues  of  thirty-eight  grammes  of 
albumen  and  351.8  grammes  of  fat.  For  the  development  of  the  latter 
at  most  only  65.4  grammes  of  proteid  in  the  food,  corresponding  to  33.6 
grammes  fat  and  7.9  grammes  fodder  fat  can  be  reckoned  on.  The 
excess  (351.8  —  41.5  =  310.3  grammes),  or  88.2  per  cent,  of  the  entire 
amount  of  fat  deposited  in  the  body,  can  only  have  been  derived  from 
the  carbohydrates  of  the  food. 

So,  also,  in  the  case  of  geese  and  bees,  the  development  of  fat  from 
carbohydrates  admits  of  proof.  The  dog,  however,  like  other  carnivora, 
seems  incapable  of  developing  fat  from  carbohydrates. 

III.    THE   FATE   OF  THE  CARBOHYDRATE   FOOD-CONSTITUENTS. 

The  metamorphosis  of  the  carbohydrate  food-constituents  may  be 
somewhat  more  readity  followed.  It  has  been  seen  that  under  the  influence 
of  the  salivary,  pancreatic,  and  intestinal  ferments,  starch  and  dextrin 
are  turned  into  maltose  and  cane-sugar  into  invert-sugar,  the  sugar  as 
such  entering  the  blood  by  absorption ;  or,  in  a  rich  amylaceous  diet, 
splitting  up  in  the  intestine  into  lactic  and  but}7ric  acids.  In  the  blood, 
the  sugar  is  either  reconverted  to  a  member  of  the  starch  group 
(glycogen)  in  a  process  to  be  considered  directly,  or  is  rapidly  oxidized 
into  C02  and  H20,  the  intermediary  products  being,  however,  unknown. 
That  sugar  is  directly  oxidized  would  seem  probable  from  the  fact  that 


FATE   OF   THE   CAKBOHYDKATE   FOOD-CONSTITUENTS.          667 

when  on  an  amylaceous  diet  a  larger  proportion  of  the  inspired  oxygen 
is  returned  to  the  atmosphere  as  CO2  than  when  on  animal  diet.  It 
would  appear,  however,  from  the  fattening  which  occurs  on  excessive 
carbohydrate  diet,  that  this  oxidation  is  not  complete,  but  that  part  of 
the  carbohyd rates  remain  in  the  body.  It  has  been  already  mentioned  that 
albuminoids  may  split  up  into  fat,  and  it  will  be  shown  under  the 
statistical  consideration  of  nutrition  that  the  addition  of  carbohydrates 
to  a  rich  albuminous  diet  spares  a  certain  amount  of  albumen  from 
destructive  oxidation,  and  in  this  way  carbohydrates  may  lead  to  the 
deposit  of  fat.  On  the  other  hand,  the  connection  between  the  carbo- 
hydrates and  fat  must  be  closer  than  this,  for  bees  on  a  pure  diet  of  sugar 
are  able  to  manufacture  wax, — a  substance  closely  allied  to  the  fats. 
Besides,  it  has  been  shown  that  in  the  putrefaction  of  car  bo  hyd  rates,  in 
addition  to  lactic,  butyric,  and  caproic  acids,  fixed  fatty  acids  are  also 
developed;  and,  since  a  similar  fermentation  occurs  in  the  alimentary 
canal,  it  is  possible  that  these  fatty  acids  are  in  the  body  converted  into 
neutral  fats. 

The  seat  of  the  oxidation  of  the  carbohydrates  is  to  be  found 
mainly  in  the  muscles,  as  evidenced  by  the  shortness  of  breath  produced 
by  excessive  muscular  exertion,  for  it  is  only  natural  to  suppose  that  the 
more  rapid  breathing  is  to  enable  the  body  to  get  rid  of  the  decom- 
position products  normally  removed  through  the  lungs,  i.e.,  C0a,  and  to 
introduce  larger  amounts  of  oxygen.  The  fact  may,  however,  be  proved 
directl}'  by  estimating  the  C02  in  the  venous  blood  coming  from  a  con- 
tracting and  resting  muscle.  That  the  CO2  thus  formed  in  muscular 
action  is  from  oxidation  of  the  carbohydrate,  and  not  albuminoid 
muscle  constituents,  is  proved  by  the  following  facts :  An  animal 
in  a  given  time  accomplishes  a  certain  amount  of  muscular  work,  and  by 
the  estimation  of  the  urinary  constituents  it  may  be  determined  how 
much  albumen  has  undergone  oxidation.  The  comparison  of  the  amount 
of  work  represented  by  the  combustion  of  this  amount  of  albumen  and 
the  amount  actually  accomplished  shows  that  the  latter  must  have  been 
at  the  expense  of  the  combustion  of  some  other  substance  than  albumen. 
This  substance,  in  all  probability,  consists  of  carbohydrate  material. 

In  addition  to  the  changes  already  sketched,  the  carbohydrates  are 
closety  concerned  in  the  function  of  glycogenesis,  or  the  formation  of 
glycogen  in  the  liver, — one  of  the  processes  of  metabolic  change  which 
has  been  most  clearly  localized.  When  comparative  estimates  are  made 
as  to  the  amount  of  sugar  contained  in  the  hepatic  and  portal  veins, 
contrary  to  what  would  be  expected,  it  will  be  found  that  in  the  hepatic 
vein  sugar  is  constantly  found,  even  though  none  may  be  present  in  the 
blood  of  the  portal  vein.  So  far,  therefore,  from  destroying  sugar,  as  was 
formerly  supposed,  the  liver  is  evidently  concerned  in  the  manufacture 


668  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

of  sugar.  Even  after  death,  if  the  blood  be  removed  from  the  liver  by 
injecting  water  through  the  portal  vein,  it  will  be  found  that  after  every 
trace  of  sugar  has  disappeared,  if  the  liver  be  allowed  to  stand  for  a 
time  in  a  warm  place,  the  repetition  of  these  injections  will  again  remove 
sugar  from  the  liver. 

If  the  liver  be  removed  from  an  animal  immediately  after  death  and 
divided  into  two  portions,  if  one  of  these  is  thrown  immediately,  after 
rapid  mincing,  into  a  large  quantity  of  previously  prepared  boiling  water, 
an  opalescent  decoction  will  be  obtained  which  will  contain  barely  a 
trace  of  sugar.  If  a  decoction  be  made  of  the  other  portion  of  the 
liver,  after  allowing  it  to  remain  for  several  hours  in  a  warm  place,  the 
decoction  will  be  clear,  and  not  opalescent,  and  will  contain  large  quan- 
tities of  reducing  sugar. 

On  the  other  hand,  if  to  a  small  quantity  of  the  opalescent  decoction 
which  was  free  from  sugar  be  added  a  few  drops  of  saliva,  or  of  the 
diastatic  ferments  of  the  pancreatic  juice,  sugar  will  be  abundantly 
formed. 

It  is  evident,  therefore,  that  the  liver  contains  something  which  is 
capable  of  being  converted  into  sugar  through  the  influence  of  some 
ferment  contained  either  in  the  liver-cells  or  in  the  blood. 

If  the  opalescent  infusion  be  tested  with  iodine,  a  mahogany-red 
color  will  be  formed  ;  it  is  evident,  therefore,  that  this  substance  is  some- 
what of  the  nature  of  dextrin  or  starch,  and  Bernard,  its  discoverer, 
gave  to  it  the  name  of  glycogen. 

Glycogen  may  be  obtained  from  such  a  decoction,  after  rapidly  cooling  by 
surrounding  it  by  a  freezing  mixture  of  snow  and  salt,  by  the  alternate  addition 
of  hydrochloric  acid  and  the  potasso-mercuric  iodide  solution*  until  no  further 
precipitate  occurs.  By  this  means  the  albuminous  constituents  are  removed. 
This  precipitate  should  be  filtered  off,  and  glycogen  may  be  precipitated  from  the 
filtrate  by  the  addition  of  alcohol  until  about  60  per  cent,  of  absolute  alcohol  is 
present  in  the  mixture.  The  glycogen  is  then  to  be  collected  on  a  filter  and 
washed  with  60  per  cent,  alcohol  until  the  washings  give  no  cloudiness  with  a 
mixture  of  dilute  caustic  potash,  ammonia,  and  ammonium  chloride.  It  is  then 
to  be  washed  with  alcohol  and  ether.  The  glycogen  remaining  should  then  be 
dried  on  a  piece  of  porous  earthenware  at  a  moderate  temperature.  It  may  be 
further  purified,  if  necessary,  by  dissolving  in  hot  water  and  precipitating  with 
alcohol  containing  a  little  ammonia,  redissolving  as  before,  and  precipitating  with 
spirit  containing  a  little  acetic  acid. 

This  last  precipitate  should  then  be  washed  with  alcohol  and  ether,  and  then 
dried. 

As  obtained  by  this  method,  glycogen  is  a  white,  amorphous,  non- 
nitrogenous  substance,  which,  with  water,  forms  an  opalescent  solution 
and  rotates  the  plane  of  polarized  light  strongly  to  the  right  to  about 

*The  potasso-mercuric  iodide  solution  is  prepared  by  precipitating  a  saturated 
solution  of  potassic  iodide  with  a  saturated  solution  of  mercuric  chloride,  and,  after 
washing  the  precipitate,  making  a  saturated  solution  of  it  in  a  hot  solution  of  potassic 
iodide. 


FATE   OF   THE   CAEBOHYDEATE   FOOD-CONSTITUENTS.          669 

three  times  the  degree  possessed  by  grape-sugar ;  it  is  inodarless  and 
insoluble  in  alcohol  or  ether.  Under  the  action  of  the  salivary  or  pan- 
creatic ferments,  namely,  diastase,  or  the  action  of  dilute  mineral  acids, 
it  is  converted,  like  other  carbohydrates,  into  a  mixture  of  maltose  and 
dextrin.  Its  formula  may  be  given  as  a  multiple  of  C6H1006. 

Glycogen  is  not  confined  to  the  liver-cells,  although  its  presence  may 
be  recognized  there  by  treating  a  section  of  hepatic  tissue  with  iodine, 
when  it  may  be  recognized  by  the  characteristic  red  staining  with  iodine 
in  the  neighborhood  of  the  cell-nucleus.  It  is  present,  also,  in  the  pla- 
centa, in  muscular  tissue,  white  blood-cells,  the  brain,  and  in  various 
embryonic  tissues.  From  the  fact  that  it  is  found  in  largest  amount 
in  growing  tissue  it  would  appear  to  be  especially  concerned  in  the 
phenomena  of  development. 

The  amount  of  glycogen  which  may  be  present  in  the  liver  varies  in 
very  wide  amount,  from  a  maximum  to  an  absolute  absence,  the  amount 
being  dependent  upon  the  state  of  the  nutrition  of  the  animal.  If  a 
rabbit  is  allowed  to  starve  to  death,  and  its  liver  be  treated  as  described 
above,  it  will  be  found  that  the  decoction  of  the  liver  will  be  absolutely 
free  from  glycogen.  In  other  words,  it  would  appear  that  the  glycogen 
is  derived  from  the  food-stuffs  which  are  absorbed  by  the  walls  of  the 
alimentary  tract  and  are  carried  by  the  portal  vein  to  the  liver.  If  it 
be  determined  by  experiment  how  long  starvation  must  be  continued  to 
remove  all  traces  of  glycogen  from  the  liver,  and  after  the  lapse  of  such 
an  interval  the  animal  be  abundantly  supplied  with  carbohydrate  food 
and  then  killed,  it  will  be  found  now  that  the  liver  has  regained  its 
store  of  glycogen,  and  that  the  decoction  now  made  will  show  the  maxi- 
mum quantity  of  glycogen  present.  If  after  starving  for  the  same  length 
of  time  the  animal  be  fed  with  a  meat  diet,  a  certain  amount  of  gtycogen 
will  also  be  detected  in  the  liver,  but  in  much  less  amount  than  after  the 
carbolmlrate  diet. 

The  question  arises  at  this  point  as  to  whether  the  glycogen  so 
developed  originates  from  the  albuminous  constituents  of  the  meat  diet, 
as  it  is  known  that  meat,  especially  the  meat  of  the  horse,  which  is  em- 
ployed in  such  experiments,  contains  representatives  of  the  carbohydrate 
group.  This  question  may  be  settled  by  substituting  a  pure  albuminous 
substance  as  diet,  and  it  will  then  be  found  that  although  the  amount  of 
glycogen  obtainable  from  the  liver  is  larger  than  that  obtained  from  a 
starving  animal,  it  still  falls  below  the  amount  obtained  after  feeding 
with  meat.  It  would,  therefore,  appear  that  the  development  of  glycogen 
on  the  meat  diet  is  only  partially  due  to  the  conversion  of  the  albuminous 
constituents  of  the  food  into  gtycogen,  but  mainly  to  the  carbolrydrate 
constituents. 

If  a  starving  animal  be  fed  on  a  fat  diet,  even  though  abundant,  no 


670  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

more  glycogen  will  be  found  in  the  liver  than  would  be  obtainable  from 
this  organ  in  a  starving  animal.  It  would,  therefore,  appear  that  while 
the  amount  of  glycogen  in  the  liver  is  dependent  upon  the  food,  it  is 
especially  the  carbohydrates  which  are  the  sources  of  this  substance. 

As  already  stated,  the  digestible  carbolrydrates  in  the  alimentary 
canal  are  converted  into  some  form  of  sugar,  are  absorbed  by  the 
intestinal  walls,  and  enter  the  blood  of  the  portal  vein,  and  are  thus  carried 
to  the  liver.  As  is  well  known,  the  food  of  herbivora  is  constituted 
largely  of  carbohydrates,  and  these  substances  can  only  be  absorbed  after 
being  converted  into  sugar.  On  the  other  hand,  it  is  well  known  that  the 
presence  of  sugar  in  the  blood  above  a  very  small  percentage  at  once 
leads  to  its  elimination  through  the  kidneys,  constituting  gtycosuria. 
Admitting,  therefore,  that  large  quantities  of  sugar  in  these  animals 
enter  the  blood  through  the  walls  of  the  alimentary  canal,  two  possibil- 
ities arise — either  it  is  eliminated  as  rapidly  as  absorbed,  or  it  at  once, 
through  combustion,  serves  in  the  development  of  heat. 

Neither  of  these  possibilities  are,  however,  actual^  the  case,  since 
even  after  the  richest  carbohydrate  diet  but  traces  of  sugar  are  to 
be  found  in  the  urine,  and  it  is  not  conceivable  that  the  large  amount  of 
sugar  which  may  be  absorbed  in  the  food  at  once  is  converted  into 
carbon  dioxide  and  water. 

The  onl}7  remaining  conclusion  is  that  the  sugar  at  once,  after  its 
absorption,  is  carried  by  the  portal  vein  to  the  liver,  and  is  there  con- 
verted into  some  less  diffusible  form  by  which  its  immediate  excretion  by 
the  kidne3rs  is  avoided.  Such  a  substance  is  evident!}7  found  in  glycogen, 
and  the  liver  may,  therefore,  be  regarded  as  a  storehouse  for  one  of  the 
most  important  food-stuffs,  which  is  again  reconverted  into  sugar,  as  the 
needs  of  the  economy  demand. 

Bernard  believed  that  there  is  a  continual  conversion  of  glycogen 
into  sugar  going  on  in  the  liver,  and  that  the  sugar  so  formed  is  carried 
by  the  hepatic  vein  to  the  general  circulation  to  be  oxidized  in  the  lungs 
and  muscles. 

It  is  evident  that  this  hypothesis  necessitates  the  presence  of  a 
larger  amount  of  sugar  in  the  hepatic  than  in  the  portal  vein,  and  such 
a  state  of  affairs  is  claimed  by  Bernard  to  be  a  fact,  although  his  state- 
ments have  met  with  a  certain  amount  of  contradiction.  It  may,  however, 
be  concluded  that  even  if  the  estimates  made  by  Bernard  as  to  the 
comparative  amount  of  sugar  in  the  hepatic  and  portal  veins  are  not 
absolutely  conclusive,  the  statements  of  his  opponents  are  no  more 
trustworthy. 

As  to  the  ultimate  end  of  the  sugar  derived  from  the  conversion  of 
the  glycogen,  but  little  can  be  accurately  stated.  It  is  known  that 
normal  blood  contains  always  a  definite  amount  of  sugar.  If  this 


FATE   OF   THE   CAEBOHYDKATE   FOOD-CONSTITUENTS.          671 

amount  be  increased,  sugar  appears  in  the  urine,  and  it  appears  that  the 
sugar  in  the  blood  is  largely  made  use  of  in  the  chemical  processes 
occurring  in  contracting  muscles.  It  would  seem,  therefore,  that  the 
object  of  the  ghrcogenic  function  of  the  liver  is  to  store  up  in  a  non- 
diffusible  form  the  excess  of  carbohydrate  matter  taken  into  the  blood 
during  a  meal  rich  in  carbohydrates,  and  then  to  distribute  it,  little  by 
little,  to  the  economy  as  occasion  may  demand. 

The  liver  converts  glycogen  into  sugar  through  the  action  of  its 
own  peculiar  diastatic  ferment. 

If  a  fragment  of  liver  be  washed  with  water  and  then  with  spirit  to 
remove  the  blood,  and  then  cut  up  into  small  pieces  and  immersed  in 
absolute  alcohol  for  twenty -four  hours,  if  the  alcohol  be  removed  and  a 
gtycerin  extract  made  of  the  residue,  a  solution  will  be  obtained  which 
will  be  capable  of  rapidly  converting  glycogen  infusion  into  sugar. 

In  the  process  of  making  the  decoction  of  gtycogen  this  hepatic  fer- 
ment is  destro^yed  by  heat,  while  in  the  experiment  above  alluded  to,  in 
which  the  liver  was  exposed  to  a  warm  temperature  after  removal  from 
the  body  before  making  an  infusion,  the  absence  of  gtycogen  from  such 
infusion  and  the  presence  of  sugar  indicate  the  conversion  by  this 
hepatic  ferment  of  the  glycogen  into  sugar.  Such  a  conversion  also 
undoubtedly  takes  place  during  life.  As  to  why,  during  life,  all  the  gly- 
cogen of  the  liver  is  not  rapidly  converted  into  sugar,  it  being  admitted 
that  such  a  ferment  is  present,  it  can  only  be  stated  that  this  problem 
belongs  to  the  same  group  of  phenomena  as  to  why  the  blood  does  not 
coagulate  in  the  living  blood-vessels,  why  the  active  and  living  pancreas 
and  stomach  do  not  digest  themselves,  and  wh}-  the  living  muscle  does 
not  become  rigid.  That  this  process  of  conversion  is,  however,  capable 
of  occurring  in  the  living  liver,  and  that  this  ferment  is  not,  as  has  been 
claimed,  simply  a  post-mortem  development,  is  proven  by  the  various 
conditions  which  lead  to  the  abnormal  conversion  of  gtycogen  into  sugar 
in  greater  amounts  than  the  system  can  use,  and  the  consequent  elimina- 
tion of  the  excess  of  sugar  from  the  blood  b}-  the  kidneys,  constituting 
the  disease  glycosuria,  or  diabetes  mellitus. 

Bernard  discovered  that  if  the  medulla  oblongata  be  punctured  in 
the  neighborhood  of  the  vaso-motor  centre  in  a  rabbit,  after  abundant 
feeding  with  carbohydrates,  in  an  hour  or  less  a  considerable  quantity 
of  sugar  may  be  detected  in  the  urine,  which,  after  a  day  or  two,  will 
disappear. 

If  a  similar  operation  be  performed  on  a  rabbit  which  has  been 
deprived  of  food  for  several  days,  no  such  glycosuria  will  result,  and  it 
therefore  seems  clear  that  this  diabetic  puncture  produced  the  gtycosuria 
through  the  rapid  conversion  of  the  glycogen  of  the  liver  into  sugar. 
It  therefore  appears  that  the  glycogenic  function  of  the  liver  is  under 


672  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

the  control  of  the  nervous  system,  and  the  path  of  this  influence,  which 
originates  in  the  neighborhood  of  the  vaso-motor  centre,  may  be  traced 
along  the  spinal  cord,  and  then,  by  means  of  the  vagi,  to  the  third  and 
fourth  dorsal  ganglia,  from  this  to  the  thoracic  ganglia,  and  from  there 
to  the  liver  by  some  path  not  yet  absolutely  determined. 

The  production  of  diabetes  by  such  an  operation  is  probably  to  be 
regarded  as  of  a  vaso-motor  nature.  It  seems  clear  that  through  this 
operation  the  small  branches  of  the  hepatic  artery  are  largely  dilated,  and 
the  liver,  consequently,  receives  a  larger  amount  of  arterial  blood,  and 
that  simple  division  of  any  part  of  this  nervous  path,  such,  for  example, 
as  removal  of  the  first  thoracic  ganglion,  will  likewise  produce  diabetes. 

If  the  splanchnic  nerves  be  divided  previous  to  this  operation  g\y- 
cosuria  will  not  result,  evidently  by  withdrawing  a  large  quantity  of 
blood  into  the  abdominal  organs  and  so  preventing  relatively  any  dilata- 
tion of  the  hepatic  artery. 

IV.      THE  STATISTICS  OF  NUTBITION. 

The  preceding  sketch  as  to  the  fate  of  the  different  organic  food- 
constituents  gives  but  an  imperfect  idea  as  to  the  metabolic  processes 
occurring  within  the  animal  body.  By  a  close  comparison  of  the  income 
and  outgo  of  the  economy  statistics  of  nutrition  may  be  formed  which 
are  of  great  value  for  obtaining  an  idea  of  the  nutritive  processes  of  the 
economy  under  different  forms  of  diet,  and  thus  assist  in  the  formation 
of  scientific  methods  of  feeding. 

When  we  compare  the  income  with  the  outgo,  the  ingesta  with  the 
excreta,  we  learn  not  only  what  part  of  the  ingesta  is  retained  in  the 
body,  but  by  the  detection  of  substances  in  the  excreta  not  present  in 
the  food  we  may  extend  our  idea  of  the  changes  which  the  body  has 
undergone  under  the  influence  of  the  food. 

In  determining  the  true  income  of  the  body  the  constituents  of  the 
faeces  must  be  subtracted,  for,  as  already  noted,  the  faeces  consist  almost 
solely  of  food-stuffs  which  have  escaped  digestion  and  absorption,  the 
amount  of  excretory  matter  in  the  fasces  being  so  small  as  to  be  dis- 
regarded. From  the  study  of  the  composition  of  the  food  we  know 
that  in  certain  amounts  of  proteids,  fats,  carbohyd rates,  salts,  water,  and 
inspired  air,  the  animal  body  takes  in  definite  quantities  of  nitrogen, 
oxygen,  carbon,  hydrogen,  sulphur,  phosphorus,  salts,  and  water. 

The  determination  of  statistics  of  nutrition  is  based  upon  the 
following  facts : — 

1.  With  the  exception  of  wool-  and  milk-producing  animals,  all  the 
nitrogen  is  excreted  in   the  urine ;    that  found  in  the  faeces  may  be 
regarded  as  derived  almost  solely  from  undigested  food. 

2.  From  the  difference  between  the  amounts  of  nitrogen  in  the  food 


STATISTICS   OF   NUTEITION.  673 

and  in  the  urine  and  faeces  it  may  be  determined  whether  there  is  an 
increase  or  a  waste  of  the  nitrogenous  matter  (albuminoids)  of  the 
economy. 

3.  The  nitrogen  in  the  urine  is  a  measure  of  the  decomposition  of 
albuminoids  in  the  body,  while  from  the  sum  of  the  amounts  of  nitrogen 
in  urine  and  faeces  may  be  deduced  the  amount  of  albuminoids  which 
become  fixed  in  the  body. 

4.  The  difference  in  amount  of  carbon  in  income  and  outgo  (including 
that  which  is  given  off  by  lungs  and  skin),  taking  into  account  the 
carbon  derived  from  decomposition  of  albuminoids,  gives  us  a  means  of 
estimating  the  changes  in  the  fat  of  the  animal  body,  since  with  the 
exception  of  fat  there  is  not,  in  any  important  amount,  tiny  other  carbon 
compound  in  the  body. 

5.  Differences  in  the  amount  of  water  in  the  economy  are  readily 
calculated.     It  is  only  necessary  to  compare  the  increase  or  decrease  of 
body  weight  with  the  data  determined  as  to  the  decomposition  of  albumen 
and  fat.  • 

For  making  the  above  estimates  the  composition  of  albumen  is 
placed  as  follows : — 

C.  H.  N.  O.  8. 

53.6  per  cent.    7.0  per  cent.     16.0  per  cent.     23.0  per  cent.     1.0  per  cent. 

Albumen  thus  consisting  of  16  per  cent,  of  nitrogen,  if  the  amount 
of  nitrogen  in  the  urine  is  multiplied  by  6.25  (=  Iffi)  we  are  able  to 
determine  the  amount  of  albumen  represented  by  the  nitrogen  in  the 
urine. 

As  regards  the  fats,  all  the  animal  fats  are  remarkably  constant  in. 
their  composition ;  they  possess  in  mean  76.50  per  cent,  carbon. 

From  the  difference  in  carbon  in  income  and  outgo  the  amount  of 
carbon  of  the  decomposed  albumen  is  first  deducted  (53.6  per  cent.), 
and  from  the  remainder  by  multiplication  by  the  factor  1.307  (—  j£j$)  the 
amount  of  fat  may  be  calculated. 

The  behavior  of  the  mineral  constituents  is  calculated  from  the 
mineral  constituents  of  the  food  and  that  of  the  urine  and  faeces.  So, 
also,  for  water  in  a  like  manner. 

The  following  example  (quoted  by  Schmidt-Mulheim,  who  has  been 
largely  followed  in  this  chapter)  makes  clear  the  method  by  which  such 
statistics  of  nutrition  are  reached  : — 

Henneberg  fed  a  full-grown  ox,  weight  712.5  kilos,  for  twent}^-eight 
clays  with  5  kilos  clover-ha}-,  6  kilos  oat-straw,  3.7  kilos  crushed  beans, 
0.06  kilo  salt,  and  56.1  kilos  water.  During  the  experiment  the  animal 
increased  daily  1.035  kilos  in  weight. 

From  the  analysis  of  the  food,  faeces,  and  nvrine,  and  from  the  esti- 

43 


674 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


mate  of  the  excretion  of  C02  by  means  of  Pettenkofer.'s  apparatus  and 
car b u retted  hydrogen  of  the  intestinal  canal,  the  following  data  were 
obtained : — 

A.  Daily  Income. 


70.975  kilos  food, 


Water. 
58.200 


Mineral 
Matter. 

0.890 


c. 

5.825 


H. 

7.500 


N. 
0.310 


o. 

4.900 


B 

.  Daily  ( 

)utgo. 

Water." 

Mineral 
Matter. 

C. 

H. 

N. 

O. 

40.65  kilos  faeces, 

.     35.075 

0.575 

2.585 

0.310 

0.105 

2.00 

13.9  kilos  urine, 

.     13.075 

0.305 

0.22 

0.025 

0.170 

0.105 

9.795  kilos  CO2, 

.       ... 

2.67 

0.03  kilo  CH2, 

002 

0.01 

Total, 


48.150        0.880        5.495        0.345        0.275        0.230 


In  addition  to  the  above,  9.5025  kilos  water  in  the  form  of  aqueous 
vapor  were  removed  through  the  lungs  and  skin. 

The  total  of  amounts  daily  appropriated  and  kept  in  the  body,  con- 
sequently, were  : — 


Water. 
0.525 


Mineral 
Matter. 

0.010 


C. 
0.330 


H. 

0.050 


N. 
0.035 


O. 
0.850 


These  figures  corresponded  to  a  daily  increase  of — 


Albumen, 0.220  kilo. 

Fat, 0.280     " 

Salts,       ..-.-. 0.010    «' 

Water, 0.525     " 

The  calculation  of  the  statistics  of  nitrogen  in  milk-  and  wool-pro- 
ducing animals  is  somewhat  more  complicated  than  the  above,  as  the 
amount  of  the  above  productions  have  also  to  be  taken  into  account. 

1.  TISSUE  CHANGES  IN  STARVATION. — Before  attempting  to  study  in 
detail  the  influence  of  food  on  tissue  change,  the  changes  which  occur  in 
the  animal  body  when  all  food  is  withheld  must  first  be  studied.  And 
here  it  should,  in  the  first  place,  be  recollected  that  the  skeletal  muscles 
form  nearly  one-half  the  body,  and  about  one-quarter  of  all  the  blood  in 
the  body  is  contained  within  them,  while  another  fourth  of  the  blood  is 
contained  in  the  liver.  These  two  facts  are  sufficient  to  indicate  that  $ 
large  part  of  the  metabolism  of  the  body  is  carried  on  in  the  muscles 
and  liver. 

In  fasting  animals  there  is  a  steady  waste  of  the  various  tissues  and 
an  excretion  of  those  waste  products  ;  and  since  this  waste  is  not  sup- 
plied by  new  matter,  there  is  a  progressive  loss  of  body  weight. 


STATISTICS   OF   NUTKITION. 


675 


Thus,  in  a  dog  weighing  one  thousand  and  twelve  grammes  and  fast- 
ing for  fourteen  days  there  was  a  daily  loss  of  body  weight  as  follows-:— ^ 


1st  day  of  fasting, 

2cl 

3d 

4th 

5th 

6th 

7th 

8th 

9th 
10th 
llth 
12th 
13th 
14th 


82  grammes. 
44 


40 
32 
27 
31 
25 
26 
26 
22 
23 
21 
19 


From  this  table  it  is  seen  that  the  loss  is  far  greater  on  the  first  day 
of  starvation  than  on  any  other,  and  that  after  the  first  day  the  loss 
gradually  becomes  less  and  less  marked. 

It  has  also  been  found  that  age  is  of  marked  influence  on  the  degree 
of  loss  of  body  weight  in  starvation.  The  younger  the  animal,  the 
greater  the  loss. 

It  is  also  noticed  that  birds  can  stand  a  greater  relative  loss  of  body- 
weight  from  starvation  before  death  occurs  than  mammals  and  other 
warm-blooded  animals ;  in  the  latter  death  only  occurs  when  40  per  cent, 
of  the  bod}'"  weight  has  been  lost. 

It  has  been  found  that  if  water  is  freely  given,  a  horse  may  stand  a 
complete  fast  for  from  eight  to  fifteen  days  without  any  serious  conse- 
quences. If  this  time  is,  however,  passed,  even  feeding  will  then  be 
unable  to  prevent  death. 

Herbivora  stand  starvation  worse  than  carnivora,  even  although  they 
lose  only  one-half  as  much  tissue-albumen  ;  it  is  stated  that  death  from 
starvation  in  the  horse  does  not  occur  until  the  twentieth  to  the  thirtieth 
day,  while  a  dog  may  live  from  forty  to  sixty  days  without  food  before 
death  takes  place. 

If  the  body  of  an  animal  dead  of  starvation  is  examined  there  will 
be  found  the  greatest  difference  in  the  loss  which  the  different  tissues 
have  undergone.  Adipose  tissue  suffers  most,  muscles  and  viscera  less, 
and  nervous  system  least  of  all,  and  this  latter  fact  is  worthy  of  especial 
notice,  since  fat  forms  a  large  constituent  of  the  nervous  system.  The 
body  is  greatly  emaciated  ;  all  subcutaneous  and  perivisceral  fat  has 
disappeared  ;  the  muscles  and  other  organs  are  atrophied  ;  and  with  the 
exception  of  the  alimentary  canal,  in  which  fluid  is  generally  found,  all 
the  tissues  are  markedly  'dry  and  free  from  water.  In  the  stomach  the 
fluid  has  an  acid  reaction  ;  in  the  intestine  there  is  a  slim}'  fluid  matter 
which  is  evidently  decomposed  bile. 


676 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


Since  fat  and  muscle  have  disappeared  in  largest  amount,  it  is  evi- 
dent the  starving  animal  feeds  on  its  own  flesh,  and,  under  such  circum- 
stances, the  urine  of  the  herbivora  and  carnivora  are  identical. 

Of  the  diiferent  organs  the  percentage  of  loss  of  original  weight  is 
as  follows  : — 


Bones 

Muscles, 

Liver, . 

Kidneys, 

Spleen, 

Pancreas,    . 

Testicle, 

Lungs, 

Heart, 

Intestine,    . 

Brain  and  Cord, 

Skin,    . 

Fat,     . 

Blood, 

Other  organs, 


13.4  per  cent,  or   5.4  per  cent,  of  total  loss. 


30.5 
537 
25.9 
66.7 
17.0 
40.0 
17.7 

2.6 
18.0 

3.2 
20.6 
97.0 
27.0 


42.2 
4.8 
0.6 
0.6 
0.1 
0.1 
0.3 
0.02 
2.0 
0.1 
8.8 

26.2 
3.7 
5.0 


Since  in  fasting  all  the  nitrogen  leaves  the  body  in  the  form  of 
urea,  the  amount  of  urea  in  the  urine  gives  a  means  of  measuring  the 
waste  of  the  albuminoid  constituents  of  the  body.  Even  up  to  the  time 
of  death  the  body  continues  to  eliminate  urea  without,  of  course,  any 
new  albuminoid  matter  entering  the  economy,  thus  showing  that  there  is 
a  gradual  and  constant  waste  of  proteids  in  the  body.  The  amount  of 
urea  eliminated  progressively  decreases,  as,  of  course,  there  is  no  repair 
of  the  stock  of  proteids  from  which  it  is  drawn.  Thus,  a  dog,  which 
during  feeding  eliminates  daily  63.96  grammes  of  urea,  during  the  first 
day  of  starvation  removes  only  14.91  grammes,  and  there  is  then  a 
gradual  diminution  in  the  amount  up  to  the  time  of  death.  Thus,  on  the 
fifty-ninth  day  of  starvation  the  dog  alluded  to  above  only  eliminated 
3.50  grammes  of  urea. 

Of  course,  the  richer  the  tissues  are  in  proteids,  the  greater  will  be 
the  difference  between  the  amount  of  urea  eliminated  in  the  first  and  sub- 
sequent days  of  starvation.  If  before  the  commencement  of  the  starva- 
tion experiment  the  animal  has  been  on  a  spare  diet,  less  urea  will  be 
eliminated  in  the  first  daj-s  of  fasting,  and  then  the  decrease  in  amount 
will  be  more  gradual  than  if  it  had  been  well  fed. 

The  destruction  of  albumen  in  starvation  is,  however,  by  no  means 
parallel  to  the  amount  of  proteids  in  the  entire  body  ;  or,  in  other  words, 
an  animal  which  on  the  first  day  of  starvation  destroys  five  times  as 
much  albumen  as  on  the  tenth  does  not  have  on  the  first  day  five  times 
as  much  proteid  in  the  body  as  on  the  tenth. 

Yoit  has  found  that  the  excretion  of  urea  on  the  first  day  after  full 
feeding  is  so  much  greater  than  under  other  circumstances  that  he  con- 
cluded that  the  amount  of  proteids  in  the  body  is  of  less  importance 


STATISTICS   OF   XUTEITION.  677 

than  the  amount  of  albumen  in  the  preceding  diet  in  determining  the 
degree  of  albumen  destruction  in  the  first  days  of  starvation,  and  that 
the  albumen  destruction  from  starvation  is  dependent  upon  two 
causes  : — 

1.  A  very  variable  one,  which  only  acts  in  the  first  days  and  which 
is  dependent  on  the  preceding  diet  and  the  general  condition  of  the 
body. 

2.  A  constant  cause,  which  alone  remains  in  force  after  the  cessa- 
tion of  action  of  the  first. 

The  following  table  shows  how  the  amount  of  urea  excreted 
increases  with  the  amount  of  nitrogenous  matter  in  the  preceding 
meals : — 


Food  given  Before                                         Ui 
Starvation. 

2500  grammes  meat,        . 

:ea  in  Last  Day    Urea  in  First  Day 
of  Feeding.              of  Fasting. 

180.8                          601 
142.9                       33.6 
110.8                       29.7 
51.8                      19.8 

26.2          .           16.9 
16.1                       15.4 

2000        ••            "             .        ..'.'. 

1500         "            "             .... 
800        "            "  and  200  grammes  fat, 
Decreasing  amount  of  meat  on  last  clay 
176  grammes,        ..... 
Abundance  of  fat  after  starvation, 

Yoit  concludes  that  animals  possess,  first,  a  considerable  available 
"  store  "  of  albumen,  which  is  capable  of  being  increased  by  a  previous 
meal  rich  in  albuminoids  and  which  is  again  rapidly  removed  in  any 
drain  on  the  economy ;  and,  second,  a  much  larger  amount  of  proteid 
matter,  which  represents  all  the  proteids  of  the  animal  body  and 
which  he  terms  "  tissue-albumen."  Of  this  latter  but  a  small  portion 
comes  under  the  conditions  of  decomposition.  The  rapid  fall  in  elimi- 
nation of  urea  in  starvation  depends  upon  the  using  up  of  the  "  stored  r' 
albumen;  when,  however,  this  is  all  consumed,  then  the  tissue-albumen 
in  its  turn  undergoes  destruction.  Of  course,  the  stored-up  albumen  is 
also  located  in  the  various  tissues. 

Herbivora  contain  in  their  tissues  a  lesser  amount  of  this  stored- 
up  or  reserve  albumen  than  do  the  carnivora ;  even  the  tissue-albumen 
is  present  in  relatively  smaller  amount.  Thus,  it  has  been  found  that  a 
full-grown  ox  during  starvation  will  only  use  up  1.27  kilos  of  proteids, 
while,  measured  by  the  albuminoid  waste  in  carnivora,  at  least  double  the 
amount  of  nitrogenous  excretion  products  might  be  expected. 

In  addition  to  the  influence  of  these  amounts  of  albumen  on  the 
proteid  waste  of  fasting  animals,  the  amount  of  fat  in  the  animal  body 
is  also  of  moment;  the  greater  the  amount  of  fat,  the  less  the  nitrogenous 
waste,  and  this  holds  whether  the  fat  is  already  stored  up  in  the  economy 
or  is  given  to  thin  animals  in  the  food. 

Voit,  by  giving  one  thousand  five  hundred  grammes  of  meat  daily 
to  a  dog,  brought  it  to  a  nutritive  condition  in  which  the  excretion  of 


678 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


Last  da 
1st  day 
2d 
3d 
4th 
5th 
6th 
7th 
8th 
9th 

y  of  fee 
of  fasti 

ding, 
ng, 

i 

A. 

Urea  in 

Grrammes. 

110.8 
26.5 
18.6 
15.7 
14.9 
14.8 
12.8 
12.9 
12.1 

11.9 

urea  remained  constant.  He  was  then  allowed  to  fast  for  ten  daj'S  and 
the  urea  estimated  (A).  He  was  then  fed  with  the  same  food,  and  then 
for  ten  days  received  nothing  but  one  hundred  grammes  of  fat  (B). 
The  following  results  were  obtained  : — 

B. 

Urea  in 
Grammes. 

111.8 
27.2 
16.3 
14.1 
12.9 
12.4 
10.8 
10.5 
10.7 
10.2 

Through  the  administration  of  the  fat  14.1  grammes  of  albumen 
escaped  destruction,  or,  as  Yoit  expresses  it,  was  "  saved." 

Water  also  exerts  a  considerable  influence  on  the  destructive 
processes  in  starvation,  a  large  consumption  of  water  always  increasing 
the  excretion  of  urea.  This  evidently  points  to  an  increased  decom- 
position of  proteids,  and  not  a  mere  increase  in  the  amount  of  urea 
washed  out,  since  it  has  been  proved  that  when  water  is  withheld  there 
is  no  accumulation  of  urea  in  the  economy. 

On  the  other  hand,  the  most  violent  muscular  movements  during 
starvation  produce  but  little  appreciable  increase  in  the  amount  of  urea 
eliminated,  thus  showing  that  the  combustion  of  albuminoids  is  not  the 
source  of  muscular  force. 

In  earlier  times,  with  the  exception  of  the  lime  salts  in  the  bones, 
the  inorganic  substances  found  in  the  animal  body  were  regarded  as 
secondary  in  importance  and,  in  fact,  almost  as  accidental  constituents. 
Liebig  and  his  scholars  first  recognized  the  importance  of  these  bodies; 
especially  Na,  Cl,  Ca,  K,  Mg,  Fe,  and  P2O6  are  absolutely  essential  for 
the  health  of  the  animal  body.  If  these  bodies  are  removed  from  the 
food,  or  even  reduced  in  amount,  the  animals  rapidly  perish,  even  though 
supplied  with  an  abundance  of  organic  food. 

This  disturbance  of  nutrition  is  not,  as  was  first  supposed,  because 
the  removal  of  salts  interferes  .with  the  activity  of  the  digestive  secre- 
tions, since  digestion  and  absorption,  even  under  such  circumstances,  is 
perfectly  carried  out,  but  because  salts  are  removed  constantly  from  the 
body,  and  if  they  are  not  supplied  in  food  the  animal  rapidly  perishes,  as 
these  salts  are  essential  to  the  various  functions  of  the  economy. 

Forster  fed  a  dog  with  food  which  was  as  much  as  possible  freed 
from  salts;  as  proteids,  he  used  the  residue  from  the  manufacture  of 
beef  extracts,  butter  freed  from  salts,  potato-starch  washed  with  HC1, 
and  distilled  water. 


STATISTICS   OF  NUTRITION.  679 

A  dog  weighing  thirt}'-two  kilos,  which  experience  showed  could 
be  kept  in  constant  weight  by  receiving  six  hundred  to  seven  hundred 
grammes  meat  and  one  hundred  and  fifty  grammes  fat,  was  allowed  to 
eat  as  much  as  he  would  take  of  the  above  foods,  and  3ret  he  rapidly 
commenced  to  fail,  and  in  fourteen  days  was  unable  to  stand  from  his 
great  weakness.  After  three  weeks  disturbance  of  digestion  appeared — 
indigestion,  diarrhoea,  and  finally  vomiting. 

The  comparison  of  the  inorganic  income  and  outgo  showed  that,  as 
regards  phosphoric  acid,  21.9  grammes  were  taken  in  while  51. 7  grammes 
were  excreted;  consequently,  the  dog  had  lost  29.8  grammes  of  phos- 
phoric acid,  or  ten  times  the  amount  which  is  normally  contained  in  the 
blood  ;  7.24  grammes  of  NaCl  were  lost. 

These  results  show  that  the  body  cannot  be  sustained  by  organic 
substances  alone,  but  must  also  receive  a  certain  amount  of  inorganic 
salts.  If  the  amount  of  salts  in  the  food  sinks  below  a  certain  figure 
or  is  entirely  suspended,  salts  are  excreted  by  the  economy,  and  the 
body  passes  into  such  a  state  of  malnutrition  that  death  speedily  results. 

As  regards  the  amount  of  inorganic  salts  required  by  different 
animals  in  order  to  preserve  perfect  nutrition,  it  appears  that  the 
amount  of  NaCl  in  meat,  which  amounts  to  0.11  per  cent.,  is  sufficient 
for  the  needs  of  the  carnivorous  animal.  As  a  consequence,  these  ani- 
mals prefer  unsalted  to  artificially  salted  foods. 

It  is  quite  different  with  the  herbivora,  for,  although  these  animals, 
as  a  rule,  receive  proportionately  quite  as  much  salt  in  their  food  as  the 
carnivora,  they  will,  nevertheless,  always  greedily  devour  salt. 

As  regards  the  relative  proportion  of  these  salts  required  by  different 
animals,  it  appears  that  all  animals  require  relatively  similar  propor- 
tions of  chlorine  and  sodium,  but  that  herbivora  take  in  their  daily 
food  at  least  double  as  much  potassium  as  carnivora. 

Thus:  One  kilogramme  cat,  fed  with  mice,  takes  daily  0.1434 
gramme  K,  0.0743  Na,  0.0652  Cl!  One  kilo  ox,  fed  solely  with  clover- 
hay,  0.3575  gramme  K,  0.0266  Na,  0.0433  Cl ;  when  fed  with  beet-roots 
and  oat-straw,  0.2923  gramme  K,  0.0674  Na,  and  0.0603  Cl. 

The  following  table  gives  the  amounts  of  K,  Na,  and  Cl  in  various 
foods : — 


Oat  -straw,  . 

K. 

.     1040 

Na. 
1.36 

Cl. 
2.97 

Clover, 

.     21.96 

1.39 

2.66 

Sweet  grasses,    . 
Prairie-grass, 
Acid  grasses, 
Vetches, 

.     20.80 
.     15.28 
.     20.60 
.     33  93 

2.57 
2.65 
5.74 

6  77 

3.67 
4.35 
4.52 
3.65 

Beet  (roots), 
Beet  (tops), 
Carrot  (roots),    . 
Sugar-beet  (tops), 

.     34.79 
.     46.68 
.     19.65 
.     50.07 

10.24 
30.80 
12.32 
25.76 

5.40 
22.56 
2.90 
20.16 

680 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


Bunge  has  stated  that  it  is  this  large  amount  of  K  in  the  food  of 
the  herbivora  that  causes  them  to  require  so  much  NaCl.  For  when 
potassium  salts,  the  electro-negative  constituent  of  which  is  other  than 
chlorine,  such  as  carbonate,  phosphate,  or  sulphate  of  potassium,  come 
into  watery  solution  with  NaCl  at  the  body  temperature  they  are  partly 
decomposed,  both  salts  give  up  their  acids,  and,  in  addition  to  potassium 
chloride,  the  carbonate,  phosphate,  and  sulphate  of  sodium  result  through 
double  decomposition.  If  these  K  salts  enter  the  alimentary  canal  they 
are  rapidly  absorbed  and  meet  with  NaCl  in  the  blood.  As  the  above 
interchange  then  takes  place,  the  blood  in  attempting  to  preserve  its 
normal  composition  allows  the  new  substances  rapidly  to  diffuse  away 
through  the  kidneys.  Consequently,  through  the  taking  in  of  potassium 
sulphate,  carbonate,  or  phosphate,  the  blood  loses  both  Na  and  01,  and 
this  loss  must  be  replaced  by  the  ingestion  of  extra  amounts  of  NaCl. 
Consequently,  herbivora,  whose  diet  is  rich  in  K  salts,  require  more 
XaCl  than  the  carnivora. 

It  is  thus  seen  that  the  character  and  extent  of  the  tissue  changes 
in  starvation  will  be  largely  governed  by  the  previous  nutritive  condition 
of  the  animal.  The  following  table,  after  Lawes  &  Gilbert,  shows  the 
percentage  of  albumen,  fat,  salts,  and  water  in  the  tissue  of  animals  in 
different  conditions : — 


IN  100  PARTS. 

THE  SOLJDS  CONTAIN. 

Solids. 

Water. 

Inorganic 
Matter. 

Fat. 

Albumen. 

1.  Fattened  oxen,     . 

51.4 

48.6 

4.1 

31.9 

15.0 

2.  Half-fattened  oxen, 

43.9 

56.1 

5.1 

20.7 

18.0 

3.  Fattened  sheep,    . 

53.8 

46.2 

2.9 

37.9 

13.1 

4.  Thin  sheep, 

39.0 

61.0 

3.4 

19.9 

15.9 

5.  Fattened  hogs,     .      '  'M 

57.1 

42.9 

1.7 

44.0 

11.9 

6.  Thin  hogs,   .        .      . 

41.8 

58.2 

2.8 

24.6 

14.1 

2.  THE  NUTRITIVE  PROCESSES  IN  FEEDING. — (a)  Feeding  with  Meat. — 
When  animals  are  fed  exclusively  with  fats  or  carbohydrates  there  is  but 
little  difference  in  the  metamorphosis  of  proteids  other  than  is  seen  in  star- 
vation. So,  also,  exercise,  water,  and  various  other  conditions  are  of  little 
influence.  When,  however,  proteids  are  given  with  the  food  there  is  an 
immediate  increase  in  the  amount  of  urea  eliminated,  for  the  albumen  of 
the  food  after  being  absorbed  almost  at  once  undergoes  decomposition. 

Bischoff  and  Yoit  found  that  a  fasting  dog  which  eliminated  daily 
twelve  grammes  of  urea,  when  fed  with  twent3^-five  hundred  grammes  of 
meat  eliminated  one  hundred  and  eighty-four  grammes  of  urea  daily ; 
the  destruction  of  albumen,  therefore,  increased  more  than  fifteen  fold. 

It  would  at  first  appear  that  if  the  same  amount  of  albumen  is 


STATISTICS   OF   NUTKITION.  681 

given  to  an  animal  as  is  lost  during  starvation,  the  destruction  of  the 
proteids  of  the  tissues  would  cease.  But  since  the  administration  of 
albumen  increases  the  tissue  waste  this  is  not  the  case,  and  at  least 
two  and  a  half  times  as  much  albumen  must  be  given  as  the  body  loses 
in  starvation  in  order  to  preserve  the  balance.  If  enough  of  albumen  is 
given  to  an  animal  to  prevent  its  drawing  on  the  albuminoids  of  its  tis- 
sues, then  the  amount  of  nitrogen  eliminated  will  just  equal  the  amount 
contained  in  the  food,  and  a  nitrogenous  balance  is  thus  preserved. 

If,  now,  to  such  an  animal  a  larger  amount  of  meat  is  given,  the 
eliminated  nitrogen  does  not  at  first  increase,  and  a  certain  amount  of 
the  nitrogen  remains  in  the  body  to  increase  the  albuminoids  of  the 
tissues.  Soon,  however,  the  nitrogen  eliminated  increases  until  finally  a 
nitrogenous  balance  is  again  regained.  Every  increase  in  the  albumen 
of  the  food  has  the  same  result — first,  an  increase  in  the  store  of  pro- 
teids of  the  body,  and  then  an  increase  of  urea,  until  the  nitrogen  of  the 
latter  equals  the  nitrogen  of  the  food.  A  maximum  is  soon,  however, 
reached  in  which  the  limit  of  albumen  which  can  be  digested  and  ab- 
sorbed is  attained. 

A  similar  state  of  affairs  holds  in  animals  in  a  condition  of  nitro- 
genous balance  when  the  albumen  of  the  food  is  diminished.  At  first 
there  is  no  decrease  in  the  amount  of  urea  eliminated,  so  the  albuminoids 
of  the  tissues  must  have  been  drawn  upon  to  make  up  the  excess  of 
nitrogen  in  the  urine  over  that  of  the  food.  Then  in  a  few  days  the 
elimination  of  nitrogen  becomes  reduced,  until  again  a  nitrogenous  bal- 
ance is  regained.  Every  further  decrease  in  the  ration  of  albumen  has 
the  same  effect — first,  decrease  of  the  store  of  tissue-albumen,  and  then 
nitrogenous  balance.  The  minimum  limit  is  then  reached.  When  too 
small  an  amount  of  albumen  is  given  in  food  to  balance  the  tissue  waste 
inanition  then  commences. 

These  facts  show  that  the  requisite  amount  of  albumen  in  the  food 
to  prevent  excess  of  tissue  waste  is  dependent  on  the  store  of  albumen 
in  the  body,  and  that  the  better  the  body  is  nourished  by  previous  feed- 
ing the  more  food  must  be  given  to  preserve  a  nutritive  balance.  Con- 
sequently, well-nourished  animals  require  more  food,  badly-nourished 
animals  less  food,  to  preserve  an  equilibrium. 

The  amount  of  albumen  in  the  food  has,  also,  an  influence  on  the 
body  fat.  If  a  small  amount  of  albumen  undergoes  destruction,  fat 
must  be  given  up  by  the  body  in  order  to  supply  the  amount  of  carbon 
necessary  to  form  C0a.  If  the  body  is  rich  in  fat,  and  in  consequence  of 
abundant  albuminous  food  a  large  amount  of  albumen  undergoes  de- 
struction, the  fat  decreases ;  but  if  only  a  little  fat  is  stored  up  and  still 
a  large  amount  of  albumen  is  given  in  food,  and  there  is,  consequently, 
a  large  destruction  of  albumen,  all  the  nitrogen  is  eliminated  in  the  urine, 


682  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

while  a  part  of  the  carbon  remains  behind  to  be  stored  up  as  fat.  Con- 
sequently, the  body  may  be  kept  stationary  as  regards  its  store  of  albumen 
and  fat  through  the  administration  of  meat  alone,  but  then  a  large 
quantity  is  required.  An  increase  in  tissue-fat  and  albumen  may  also, 
to  a  slight  degree,  take  place  from  the  administration  of  albumen  alone, 
but  only  in  illy-nourished  individuals. 

If  peptone  is  given  as  food  it  is  entirely  destro3Ted,  and  the  destruc- 
tion of  the  tissue-albumen  is  completely  prevented ;  but  there  is  no 
increase  in  the  body  albumen,  thus  showing  that  peptone  is  earlier 
destroyed  than  albumen  and  can  only  partially  replace  the  albumen  of 
the  food. 

If  gelatin  and  gelatinous  tissue  (bones,  tendons,  etc.)  are  given 
exclusively  the  destruction  of  albumen  does  not  cease,  thus  showing 
that  gelatin  cannot  replace  albumen.  But  if  gelatin  and  albumen  are 
given  together  the  destruction  of  albumen  is  greatly  reduced. 

(b)  Feeding  with  Fat. — The  influence  of  fat  on  the  destruction  of 
albumen  is  seen  in  the  fact  that  in  fasting  animals  the  destruction  of 
albumen  is  less  in  fat  than  in  thin  animals ;  this  action  is  also  seen  in  the 
administration  of  proteid  foods  alone,  where  the  destruction  of  albumen 
is  less  in  fat  than  in  thin  animals.  Indeed,  we  have  seen  that  in  an 
abundant  albuminous  diet,  whereby  the  excretion  of  urea  is  increased,  in 
fat  animals  there  may  even  be  an  increase  in  the  body  fat. 

If  fat  is  given  alone  as  food  to  a  carnivorous  animal  the  destruction 
of  albumen  is  reduced  but  not  prevented  ;•  when  large  amounts  of  fat  are 
given  the  fat  of  the  body  may  even  increase  and  yet  the  animals  pass 
into  a  state  of  starvation,  for  the  tissue-albumen  is  gradually  being 
reduced. 

If  enough  albumen  is  given  to  cause  a  nitrogenous  balance  and  then 
fat  is  added  to  the  food,  the  nitrogenous  elimination  is  reduced  and  all 
the  carbon  of  the  fat  does  not  appear  in  the  C02;  carbon  is,  therefore, 
kept  back  in  the  body  and  stored  up  in  the  form  of  fat,  while  a  certain 
amount  of  nitrogen  also  being  retained  indicates,  an  increase  of  the 
body  albumen.  So,  the  addition  of  fat  to  the  food  leads  to  both  an 
increase  of  tissue-fat  and  albumen,  though  this  only  occurs  when  a  large 
amount  of  fat  is  added  to  a  moderately  small  amount  of  albumen. 

If  the  amount  of  albumen  is  increased  the  elimination  of  urea  also 
increases,  and,  as  a  consequence  of  the  great  destruction  of  albumen,  a 
certain  amount  of  the  fat  is  spared  and  is  stored  up  in  the  body.  But 
if  the  amount  of  albumen  is  reduced  more  fat  is  used  up,  and  fat  may 
even  be  taken  awa}r  from  the  body. 

The  amount  of  fat  in  the  body  in  feeding  with  albumen  and  fat  is 
also  of  influence  on  the  metabolism  of  the  body ;  a  body  poor  in  fat, 
which  needs  and  destroys  more  albumen,  more  readil}-  stores  up  fat; 


STATISTICS  OF  NUTRITION.  683 

while  a  body  rich  in  fat,  since, it  needs  and  destroys  less  albumen,  must 
draw  on  its  store  of  fat.  Young  animals,  since  they  are  thin,  therefore 
need  more  albumen  and  fat  than  older  ones,  while  young  animals,  to 
fatten,  require  more  food  than  older  ones.  It  is  also  easier  to  fatten  thin 
animals  than  to  make  tolerably  fat  animals  still  fatter. 

(c)  Feeding  with  Carbohydrates. — The  action  of  the  carb.ol^drates 
in  nutrition  is  especially  seen  in  the  herbivora,  which  are  incapable  of 
being  supported  with  albumen  alone  or  with  albumen  and  fat.  Experi- 
ment has  shown  that  in  so  far  as  they  are  digestible  all  carbohydrates 
have  the  same  influence  on  the  metabolism  of  the  body.  This  applies  to 
starch,  cane-,  grape-,  and  milk-sugar,  dextrin,  and,  to  a  certain  extent,  to 
cellulose. 

It  is  generally  assumed  that  all  the  carbohydrates  which  enter  the 
animal  body  unite  with  the  oxygen  obtained  in  inspiration  to  form  C02 
and  H20,  so  that  an  increase  in  carbohydrate  diet  means  an  increase  in  the 
CO3  of  the  expired  air.  This  is  not,  however,  universally  true,  since 
under  many  circumstances  the  carbohydrates  may  be  retained  in  the 
body  as  fat;  on  the  other  hand,  it  cannot  be  positively  stated  whether 
the  carbohydrates  which  are  converted  into  sugar  in  digestion  are 
directly  oxidized  as  sugar,  or  are  all  first  converted  into  glycogen. 

Feeding  dogs  exclusively  with  carbohydrates  has  proven  that  the 
destruction  of  tissue-albumen  and  fat  is  under  such  circumstances  less 
than  when  the  animal  is  deprived  of  all  food,  but  that  the  destruction 
of  albumen  is  constant,  and  that  such  animals  finally  perish  from 
inanition.  If  albumen  is  given  together  with  the  carbohydrates  in 
increasing  quantities,  the  excretion  of  nitrogen  increases  correspond- 
ingly, but  in  a  much  less  degree  than  when  albumen  alone  or  albumen 
and  fat  constitute  the  diet ;  therefore  the  carbohydrates  in  food  serve  to 
spare  the  tissue  change  in  proteids  to  a  greater  extent  even  than  fat. 
Hence,  to  keep  the  body  in  a  state  of  nutritive  balance  a  moderately 
small  amount  of  albumen  is  required  with  a  large  amount  of  carbo- 
hydrates, and,  as  a  consequence,  the  herbivora  are  kept  in  good  nutrition 
with  the  small  amount  of  albumen  found  in  their  food.  If  the  smallest 
amount  of  albumen  is  given  with  the  corresponding  amount  of  carbo- 
hydrates under  which  the  body  weight  may  be  maintained  without  losing 
albumen  or  fat,  and  then  the  albumen  of  the  food  is  increased,  the 
elimination  of  nitrogen  is  also  increased,  but  to  a  less  degree  than  if 
albumen  was  given  alone ;  there  is,  therefore,  now  an  increase  in  the 
albumen  and  fat  of  the  bod}'.  If,  now,  the  amount  of  carbohydrates 
is  increased  without  diminishing  the  quantity  of  albumen  in  the  food, 
fat  then  accumulates  in  the  body;  and  if  the  albumen  is  also  increased 
both  albumen  and  fat  accumulate. 

It  is  not  yet  quite  clear  whether  this  fat  is  formed  from  the  carbon 


684  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

of  the  albumen,  as  is  generally  acknowledged  to  be  the  case  in  the  car- 
nivora,  or  whether  fat  may  not  also  be  formed  from  the  carbohydrates 
directly.  It  thus  seems  clear  that  the  addition  of  carbohydrates  to  the 
diet  spares  the  waste  of  tissue-albumen  and  body  fat,  and  the  attempt 
has  been  made  to  determine  the  amount  of  carbohydrates  which  in  their 
nutritive  value  are  equivalent  to  a  given  amount  of  fat.  This  has  been 
fixed  by  Yoit  at  the  ratio  of  one  hundred  and  seventy-five  to  one  hun- 
dred ;  in  other  words,  one  hundred  and  seventy-five  grammes  of  starch 
are  equivalent  to  one  hundred  grammes  of  fat. 

V.   THE  FOOD  KEQUIKED  BY  THE  HERBIVORA   UNDER  DIFFERENT 

CONDITIONS. 

The  nutritive  processes  in  the  herbivora  differ  in  many  respects  from 
those  of  the  carnivora.  In  the  first  place,  less  albumen  is  destroyed 
during  fasting  by  the  herbivora  than  is  the  case  in  the  carnivora.  Thus, 
while  in  the  example  given  above  a  dog  weighing  thirty-five  kilos  de- 
stroys daily  one  hundred  and  sixty-eight  grammes  of  albumen,  an  ox 
weighing  five  hundred  and  twenty-two  kilos  only  destroys  twelve  hundred 
and  seventy  grammes.  So,  also,  the  herbivora  on  feeding  with  carbo- 
hydrates and  fat  show  much  less  tissue  waste  than  the  carnivora.  In 
other  respects,  with  allowances  for  the  different  digestive  peculiarities  of 
carnivora  and  herbivora,  the  nutritive  process  may  be  said  to  be  similar. 

It  has  been  already  stated  that  foods  must  not  only  contain  repre- 
sentatives of  the  proteid,  carbohydrate,  and  fat  groups,  with  salts  and 
water,  but  the  different  constituents  must  be  present  in  definite  propor- 
tions, which  may,  however,  vary  according  to  the  demands  on  the  animal. 
The  proportion  of  albuminous  to  non-nitrogenous  matter  in  food,  i.e.,  the 
proportion  of  albumen  to  starch  and  fat,  is  spoken  of  as  the  nutritive 
proportion.  The  average  nutritive  proportion  is  attained  when  the  food 
contains  one  part  proteid  to  from  five  to  eight  parts  of  non-nitrogenous 
matter,  it  being  remembered  that  one  hundred  parts  fat  may  be  replaced 
by  one  hundred  and  seventy-five  parts  carbohydrates ;  1 :  2-4  is  spoken 
of  as  a  narrower  nutritive  proportion,  and  1:8-12  as  a  wider  nutritive 
proportion. 

The  natural  food  of  the  domesticated  herbivora  has  a  nutritive  pro- 
portion of  1:4-1:7;  thus,  ordinary  hay  has  a  proportion  of  1:5-1:Y, 
and,  although  it  may  be  regarded  as  the  normal  food  of  ruminants,  is  not 
suitable  when  there  is  a  demand  for  rapid  fat,  milk,  or  work  production. 
In  grass  the  proportion  is  only  1 :4-6,  and  on  such  foods  cattle  produce 
the  most  milk ;  young  cattle  thrive  on  it  and  rapidly  put  on  flesh.  Clover 
has  a  proportion  of  1:5-6,  but  on  account  of  its  large  percentage  of 
cellulose  is  not  completely  digested,  so  it  is  usually  combined  with  some 
more  concentrated  food.  Before  blossoming  clover  has  a  proportion  of 


FOOD  KEQUIKED  BY  THE  HEKBIVOEA.          685 

1 :4,  or  even  1:3,  and  its  use  then  entails  a  waste  of  valuable  proteids 
unless  combined  with  chopped  straw  so  as  to  bring  the  proportion  down 
to  1:5.  In  the  cereals  the  proportion  on  an  average  is  1:5-7,  being 
broader  in  barle}r  and  corn  than  in  oats,  r}re,  and  wheat ;  in  the  hulled 
fruits,  malt,  brewers' grains,  and  distillery  residues  the  proportion  is  1:3, 
and  in  rape-seed  ca-ke  1 : 1-2.  These  latter  fodders  are,  therefore,  only 
applicable  under  special  conditions.  After  this  recapitulation  we  may 
consider  the  principles  of  feeding  somewhat  more  in  detail. 

Animals  which  have  no  work  to  do  besides  growing  and  keeping  up 
their  nutrition  are  nourished  perfectly  well  b}^  grazing  if  the  grass 
is  abundant  and  of  proper  composition  ;  .this  is  the  case  for  sheep,  two- 
to  three-year-old  horses,  and  }*oung  cattle.  If  these  animals  are  stall- 
fed,  instead  of  being  put  to  grass,  on  account  of  the  perfect  quiet  and 
even  temperature,  the  nutritive  demands  are  reduced  ;  so  now  feeding 
with  hay  or  straw  with  some  nitrogenous  food  suffices.  A  similar  state 
of  affairs  holds  in  animals  which  are  stall-fed  without  being  worked,  such 
as  oxen  in  winter  months,  and  the  amount  of  food  may  here,  also,  be  con- 
siderably reduced.  The  data  showing  the  amount  of  food  required  are 
about  as  follows  : — 

For  unworked  animals,  for  ever}-  one  hundred  kilos  body  weight, 
2.5  kilos  of  solids  in  the  grasses  (green  fodder)  is  sufficient ;  therefore, 
for  the  herbivora,  for  every  one  hundred  kilos  body  weight,  ten  kilos  of 
grass,  containing  2.5  kilos  of  solids,  and  of  this  1.3  kilos  of  digestible 
matters,  is  sufficient.  In  this  amount  0.25  kilo  is  represented  by  albu- 
men, non-nitrogenous  extractive  one  kilo,  and  fat  0.05  kilo  ;  so  the  ratio 
of  the  amount  of  food  to  the  amount  of  digestible  matter  is  1 :4.2. 

Thus,  a  horse  weighing  five  hundred  kilos  may  preserve  a  nutritive 
equilibrium  on  a  daily  ration  of  seven  hundred  grammes  albumen,  two 
hundred  and  ten  grammes  fat,  three  thousand  seven  hundred  and  fifty 
grammes  starch  and  cellulose,  and  about  twenty  kilos  of  water  ;  the  ratio 
of  nitrogenous  to  non-nitrogenous  food  being  thus  1:5.5.  Starch  and 
fat  may  replace  each  other,  seventeen  parts  of  starch  being  equivalent  to 
ten  parts  of  fat.  In  the  horse,  the  carbohydrates  are  more  important 
heat-producing  foods  than  is  the  case  in  man.  Wolff  has  found  tliat  of 
the  heat  produced,  76  per  cent,  is  due  to  carbohydrates,  13.5  per  cent, 
to  proteids,  and  10.1  per  cent,  to  fats. 

In  a  general  way  it  may  be  said  that  for  each  kilo  of  body  weight 
the  herJbivora  requires  daily  one  hundred  and  fifty  grammes  albumen, 
fifty  grammes  fat,  and  seven  hundred  and  fifty  grammes  carbohydrates. 
Smaller  animals  require  proportionately  larger  amounts,  since  the  de- 
structive processes  are  more  active  in  them.  In  fattening  animals  the 
carbohydrates  must  be  increased  ;  in  milking  animals  the  albuminous 
food-constituents. 


686  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

Experiment  has  proved  that  cattle  preserve  a  nutritive  equilibrium 
when  the}-  receive  a  daily  ration  calculated  for  ten  hundred  kilos  of 
body  weight,  as  follows  :— 

19.5  kilos  clover-hay. 

3.7  "        "         "    13.0  kilos  oat-straw,  and  0.6  kilos  rape-seed  cake. 

2.6  "        "          "    14.2     "       "        "        "    0.5      " 

3.2  "        "         "    13.3     "  barley  "        "    0.6      " 

25.6  "  fodder-beets,  12.6     "  oat        "        "    1.0 

In  the  above  feeding  the  animals  digested  and  absorbed  for  ten  hun- 
dred kilos  body  weight  on  an  average  0.57  kilo  albumen  and  7.4  kilos  non- 
nitrogenous  matter;  hence,  the  nutritive  proportion  was  1:13.  The 
above  fodder  contains  on  an  average  0.05  kilo  phosphoric  acid,  0.1  kilo 
lime,  and  0.2  kilo  alkalies;  in  addition,  for  ten  hundred  kilos  body 
weight,  fifty -five  kilos  water  were  given. 

For  pregnant  animals  which  are  not  worked,  as  brood  mares,  pas- 
ture is  sufficient;  or  if  stall-fed,  hay  and  straw,  the  latter  with  some 
nitrogenous  food,  will  answer  if  the  total  composition  is  made  to  cor- 
respond with  that  of  grass.  If  the  grass  and  hay  are  not  of  the  proper 
composition  some  accessory  food  must  be  added.  Especial  reference 
must  be  paid  to  the  amount  of  albumen  and  salts  in  the  food,  such  as 
lime  and  phosphates,  as  of  special  importance  for  the  development  of  the 
osseous  system  of  the  young.  In  such  cases  some  albuminous  food  rich 
in  salts  is  necessary,  such  as  grains. 

Male  breeding  animals  which  do  not  work  must  have  their  food  so 
adjusted  that  they  do  not  put  on  fat;  not  that  the  amount  of  organic 
matter  may  be  reduced,  but  the  food  must  be  concentrated,  have  a  small 
percentage  of  indigestible  matter,  and  little  water  and  much  albumen.  Es- 
pecially in  the  coupling  season  must  the  food  be  rich  in  albumen  to  make 
up  for  the  losses  through  copulation.  Fat  stallions  and  bulls  are  not 
fruitful. 

Animals  for  labor  require  more  than  pasture  ;  they  require  a  large 
amount  of  albumen,  for  by  it  the  muscles  are  enabled  to  appropriate  a 
larger  amount  of  oxygen ;  so, also, fat  and  carboln'drates  must  be  increased, 
since  they  give  to  the  muscles  the  substance  which  is  consumed  in  muscular 
activity.  If  the  work  is  constant  the  carbon  of  muscles  must  always  be 
in  excess.  Voluminous  and  watery  food  must  be  avoided.  The  former 
distends  the  alimentary  canal,  and  so  interferes  with  respiration,  and  the 
latter  leads  to  an  accumulation  of  water  in  the  tissues,  and  reduces  the 
tension  and  elasticity  of  the  muscles.  So  the  food  must  be  concentrated, 
as  oats  and  barley,  which  are  especially  valuable  on  account  of  their  fat. 

Cattle  on  moderate  work  require  per  thousand  kilos  body  weight, 
from  0.7  kilo  to  1.6  kilos  albumen,  non-nitrogenous  matters  from  8.4  to 
12  kilos  ;  the  nutritive  proportion  should  thus  be  1 : 7.5. 


FOOD  REQUIRED  BY  THE  HERBIVORA.          687 

This  proportion  may  be  reached  in  the  administration  of  suitable 
amounts  of  hay  with  some  concentrated  food,  or  clover-hay  with  chopped 
straw.  When  severe  work  is  required  it  is  advisable  to  increase  the 
quantity  of  fat  given  (as  by  adding  some  oil-cake),  the  nutritive  propor- 
tion being  brought  to  1:6. 

Working  oxen  can  stand  a  larger  amount  of  raw  food  (hay,  etc.) 
than  horses.  If  rapid  work  is  required  of  horses,  a  rich  albuminous  food 
such  as  oats  must  be  given  ;  if  prolonged  work  is  demanded,  one  richer 
in  fat,  as  corn,  is  better. 

If  animals  are  fed  for  food  purposes  an  increase  in  the  solids  and 
digestible  matter  of  the  food  is  requisite ;  so  the  appetite  must  be 
stimulated,  and  yet  overloading  of  the  alimenta^  canal  avoided.  It  is, 
therefore,  advisable  gradually  to  increase  the  amount  of  the  usual  food, 
to  stimulate  the  secretion  by  small  quantities  of  salt,  if  possible,  to  aid 
digestion  by  a  previous  preparation  of  the  food,  such  as  b}*  giving  ground 
meal,  and  so  to  choose  the  foods  that  the  waste  of  the  organism  will  be 
at  a  minimum. 

At  the  commencement  of  such  fattening,  the  organism  must  be  made 
rich  with  albumen :  so  thin  animals  must  receive  a  large  amount  of 
digestible  food,  with  an  extra  proportion  of  fat  and  carbohydrates,  since 
we  have  found  that  under  such  circumstances  there  will  be  least  waste  of 
albuminoids.  This  is  accomplished  by  feeding  for  about  two  weeks  with 
2.5  kilos  albumen  and  12.5  kilos  non-nitrogenous  matters  per  thousand 
kilos  body  weight,  thus  giving  a  nutritive  proportion  of  1:5.  Then  the 
non-nitrogenous  matters  must  be  increased  to  from  12.5  to  16.25  kilos  per 
thousand  kilos  body  weight,  so  making  the  proportion  1 :6.5.  When  the 
economy  becomes  rich  in  albumen  and  then  commences  to  put  on  fat,  the 
albumen  of  the  food  may  be  increased  to  3.0  kilos,  making  a  proportion 
of  1 :5.5;  when  it  becomes  very  fat,  the  solids,  especially  the  indigestible 
solids,  must  be  reduced,  and  some  oil-cake  added  to  the  food. 

In  fattening  oxen  the  water  given  should  be  in  the  proportion  of 
4-5  :1  of  the  solids  given,  in  sheep  2-3  : 1. 

In  fattening  sheep  it  has  been  proved  that  highty  albuminous  foods 
are  especially  valuable.  Ground  beans  ma}^  be  used  for  this  purpose 
(0.5  kilo  daily)  combined  with  hay,  In  fattening  sheep  the  preparatory 
treatment  necessary  with  cattle  may  be  usually  dispensed  with,  and  the 
diet  more  rapidly  changed  from  one  poor  in  nitrogenous  matters  (1:5.5) 
to  one  rich  in  proteids  (1 : 4.5).  The  diet  for  sheep  must  not  be  too  rich 
in  water,  so  beets  are  not  as  valuable  as  with  cattle ;  the  best  results  are 
obtained  from  feeding  with  good  hay  and  a  corresponding  amount  of 
crushed  beans  or  cereals.  Sheep  fatten  more  rapidly  after  shearing  than 
before,  for  then  the  appetite  is  better  and  the  thirst  lees. 

Young  animals  which  are  designed  for  food  purposes  will  slowly  take 


688  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

on  flesh  in  a  good  pasture  ;  if  an  accumulation  of  fat  is  desired,  additional 
carbohydrates  and  fatty  food  must  be  given. 

As  a  rule,  the  hog  is  more  readily  fattened  than  the  sheep,  and  the 
latter  than  the  ox.  Race  is  also  of  influence.  Thin,  full-grown  hogs  at 
the  commencement  of  fattening  require  large  amounts  of  food,  forty  kilos 
of  solids  per  thousand  kilos  body  weight.  Good  results  are  obtained  by 
feeding  with  crushed  barley,  corn,  or  peas,  the  latter  especially,  if  mixed 
with  steamed  potatoes.  The  use  of  buttermilk  or  sour  milk  enables  the 
amount  of  food  to  be  reduced  and  still  give  satisfactory  results. 

For  milk  animals  the  conditions  of  food  have  been  already  consid- 
ered, and  a  good  pasture  is  all  that  is  required. 

When  stall-fed,  nutritive  change  is  reduced ;  when  food  corre- 
sponding to  pasture  is  given  the  quantity  of  milk  and  butter  is  increased. 

In  wool-producing  animals  a  larger  percentage  of  proteids  is  required 
in  the  food  than  in  cattle,  goats  requiring  less  than  sheep.  Experiment 
has  proven  that  sheep  (ninety-six  kilos  in  weight)  on  feeding  with  hay 
for  one  thousand  kilos  body  weight  require  daily  twenty-six  kilos,  and 
of  this  digest  1.32  kilos  albumen  and  10.53  kilos  non-nitrogenous  matters 
(with  0.322  kilo  fat).  On  such  feeding  the  weight  increased  somewhat, 
0.181  kilo  albumen  and  0.299  fat  (reckoned  for  one  thousand  kilos  body 
weight)  being  deposited.  The  nutritive  proportion,  therefore,  for  sheep 
should  be  1 :  9.3.  It  has  further  been  determined  by  Wendee  and  Hohen- 
heim  that  slight  loss  of  weight,  within  limits,  does  not  interfere  with 
wool  production,  especially  if  the  food  be  rich  in  proteids. 

By  chopping  food  mastication  is,  to  a  certain  extent,  facilitated,  but 
it  cannot  be  regarded  as  a  substitute  for  mastication,  since  the  mixing 
with  saliva  can  only  be  perfectly  performed  when  the  food  is  thorough^ 
masticated.  The  principal  object  in  chopping  food  is  to  enable  it  to  be 
mixed  with  other  materials  so  as  to  increase  its  tastefulness  and  digesti- 
bility, or  to  assist  in  the  administration  of  other  substances.  Chopping 
should  never  be  carried  so  far  as  to  permit  of  the  food  being  swallowed 
without  undergoing  a  certain  amount  of  mastication.  The  cereals  are 
especially  suited  for  administration  under  the  forms  of  meals  and  may 
be  readily  mixed  with  other  foods.  The  readily  digestible  grains,  of 
course,  do  not  need  to  be  ground,  but  in  the  form  of  meal  they  may  be 
mixed  with  less  digestible,  bulky  substances,  such  as  chopped  straw. 
Thorough  mastication  of  the  latter  is  so  attained  and  the  grain  gives 
taste  to  the  mixture,  without  which,  probably,  the  food  would  be  rejected. 
To  horses  and  sheep  all  grains  the  hulls  of  which  are  not  too  hard  and 
thick  may  be  given  uncrushed  by  mixing  with  chopped  straw  and  the  like 
as  long  as  their  organs  of  mastication  are  in  good  condition.  Barley  is 
best  given  to  sheep  when  roughly  ground,  while  the  seeds  of  the  legu- 
minous plants  and  corn  may  likewise  be  ground  for  sheep  and  horses. 


FOOD  REQUIRED  BY  THE  HERBIVORA.          689 

Grinding  of  oats  is  only  necessary  for  old  horses  or  those  in  which  the 
teeth  are  changing.  Oxen  and  hogs,  as  a  rule,  digest  the  ground  cereals 
better  than  the  whole  grains.  According  to  Lehinann,  of  the  entire 
grains  in  a  fourteen-months-old  ox  48.2  barley  and  19.6  per  cent,  oats 
remained  undigested.  In  a  five-months-old  ox  33.0  barley  and  6.5  per 
cent,  oats  remained  undigested. 

Even  after  mixing  with  chopped  straw  a  large  part  of  the  entire 
grains  escape  digestion  and  pass  through  the  faeces  almost  entirely 
unchanged,  and  still  possess  the  power  of  germination.  Of  one  hundred 
kilogrammes  of  the  unground  grains  fed  to  hogs  Lehmann  found  in  the 
faeces  50.6  kilos  of  oats,  49.8  kilos  of  rye,  54.8  kilos  of  barley,  and  4.8 
kilos  of  peas.  The  experiment,  therefore,  points  in  the  most  emphatic 
manner  to  the  administration  to  the  ox  and  hog  of  all  the  cereal  grains 
mealed  and  mixed  with  other  foods.  About  the  only  exception  to  this 
statement  is  found  in  the  case  of  oats.  The  chopping  of  dry  fodder 
enables  it  to  be  mixed  readily  with  large  amounts  of  more  tasty  sub- 
stances. So,  also,  the  j^oung,  tender,  highly  albuminous  green  foods 
may  be  chopped  and  mixed  with  less  nutritious  substances,  such  as  straw. 
The  transition  of  dry  to  green  feeding  and  the  reverse  is  facilitated  by 
the  mixture  of  the  green  fodder  with  dry,  chopped  straw.  Horses  should 
always  receive  good  hay  unchopped,  but  the  straws  of  the  cereals  should 
always1  be  given  in  a  chopped  state,  since  horses  will  only  take  the  hard 
straw  in  small  amounts.  Chopped  food  for  horses  should  not  be  shorter 
than  from  one  and  one-third  to  two  centimeters  in  length  of  each  piece, 
since  smaller  pieces  readily  lead  to  obstructive  colic,  especially  if  given 
with  meal  in  a  moist  condition.  For  the  ox,  straw  may  be  chopped  into 
pieces  two  and  one-half  to  three  centimeters  long,  and  mixed  well  with 
corn-meal  or  chopped  beets  or  potatoes  in  order  to  make  it  more  tasty. 

The  duration  of  the  interval  between  different  times  of  feeding  of 
the  domestic  animals  is  a  matter  of  considerable  importance.  Too  fre- 
quent feeding  should  be  avoided  on  account  of  the  shortening  of  the 
necessary  pauses  between  the  digestive  processes.  The  ruminants,  espe- 
cially, should  not  receive  more  than  at  most  three  meals  in  the  day,  so  as 
to  allow  time  for  rumination.  Horses  likewise  should  receive  three  meals 
and  hogs  from  three  to  four  meals  a  day.  On  the  other  hand,  the  inter- 
vals between  feeding  should  not  be  too  long,  on  account  of  the  great 
increase  of  hunger  so  produced  leading  to  faulty  mastication  and  imper- 
fect insalivation  of  the  food.  This  state  of  affairs  may  produce  much 
more  serious  disturbance  in  the  non-ruminants  than  in  the  ruminants. 
In  young  cattle  from  four  to  six  meals  may  be  given  a  day  on  account 
of  the  relatively  smaller  size  of  their  stomachs,  since  three  meals  scarcely 
furnish  enough  to  sustain  them.  So,  also,  when  the  fodder  is  especially 
fluid  the  meals  may  succeed  each  other  every  two  or  three  hours,  for  in 

44 


690 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


NORMAL  AMOUNTS  OF  FOOD  FOR  CATTLE,  HORSES,  SHEEP,  AND  SWINE. 

For  every  kilogramme  of  body  weight  the  following  amounts  of  digestible 
food-stuffs  must  be  contained  in  the  daily  ration: — 


N  I  T  R  0- 

NON-NlTRO- 

. 

SOLIDS. 

GENOUS 
M  A   T    - 

G  E  N  O  IT  S 

EXTRA  c  T- 

FAT. 

1 

•1 

TERS. 

IVE  MAT- 
TERS. 

| 

CLASS  OP  ANIMAL. 

a 

a 

g 

S 

£ 

a 

a 

a 

a 

5| 

£ 
f 

'2 

1 

1 

P 

a 

'3 

3 

i 

a 
I 

a 
S 

c: 
1 

J 

| 

i 

o 

f 

f 

§ 

s 

* 

§ 

% 

3 

% 

^ 

* 

Kilogrammes. 

1.   Young  Cattle. 

2-3  months  old,  75  kg. 

weight,  

21.0 

26.0 

23.5 

3.0 

5.0 

4.0 

9.5 

12.5 

11.0  1.5 

2.5 

2.0 

17.0 

1:4.0 

3-6    months  old,   150 

1 

kg.  weight,     .     .     . 

23.5 

27.0 

25.0 

3.0 

3.5 

3.0 

9.5 

12.0 

11.0  0.75 

1.25 

1.0 

15.0 

1:4.2 

6-12  months  old,  250 

kg.  weight,     .     .     . 

25.0 

30.0 

26.0 

2.0 

3.0 

2.5 

9.5 

12.0 

11.0  0.4 

0.8 

0.6 

14.1 

1:5.0 

12-18  months  old,  350 

kg.  weight,     .     .     . 

25.0 

30.0 

26.0 

1.8 

2.5 

2.0 

9.5 

11.0 

10.5,0.3 

0.5 

0.4 

12.9 

1:5.7 

18-24  months  old,  425 

1 

kg.  weight,     .     .     . 

25.0 

30.0 

26.0 

1.4 

1.8 

1.5 

9.0 

10.5 

9.5 

0.2 

0.4 

0.3 

11.3 

1:6.8 

2.  Oxen. 

At  rest  

15.0 

20.0 

18.0 

0.6 

09 

0.7 

5.5 

7.0 

6.5 

0.1 

0.2 

0.15 

7.35 

1:1.0 

Working,  .     .     .     .     . 

24.0 

28.0  26.0 

1.4 

1.8 

1.6 

8.0 

10.0 

9.0 

0.2 

0.4 

0.3 

10.9 

1:6.0 

Severe  working,     .     . 

24.0 

32.0 

28.0 

2.0 

2.8 

2.4 

10.0 

12.0 

11.0 

0.4 

0.6 

0.5 

13.9 

1:5.1 

S,  Fattening  Cattle. 

1st  period,      .... 
2d       " 

27.0 
260 

30.0 

9,90 

28.5 

9,7  5 

2.3 

9,  8 

3.0 
35 

2.5 
30 

11.0 

11  0 

12.5 
1?0 

12.0 
11  5 

0.5 

06 

0.7 
1  0 

0.6 

0  7 

15.1 
152 

1:5.4 
1-4  5 

3d       " 

250  '-2RO  9,«5 

95 

3  3 

97 

11  0 

11  5 

05 

08 

06 

14  8 

1-48 

4.  Milk  Cows. 

21.0 

32.0 

26.0 

2.2 

2.8 

2.5 

9.5 

12.0 

10.0 

0.35 

0.6 

0.4 

12.9 

1:4.4 

5.  Horses. 

Working 

21.0 

27.0 

24.0 

1.6 

2.0 

1  8 

80 

100 

90 

05 

08 

06 

11.4 

1:5.8 

Heavy  work,     .    .    . 

23.0 

30.0 

26.5 

2.5 

3.0 

2.8 

9.0 

12.0 

10.5 

0.6 

1.0 

0.8 

14.1 

1:4.5 

6.   Young  Sheep. 

5  -6  months  old,  28  kg. 

weight,  

28.0 

32,0 

30.0 

2.5 

3.5 

3.2 

9.5 

11.5 

10.5 

0.7 

1.0 

0.8 

14.5 

1:4.0 

6-8  months  old,  33-34 

kg.  weight,     .     .     . 

26.0 

28.027.0 

2.5 

2.8 

2.7 

8.5 

10.5 

9.5 

0.5 

0.8 

0.6 

12.8 

1:4.0 

8-11  months  old,  37- 

38  kg.  weight,    .     . 

23.5 

26.0 

25.0 

2.0 

2.5 

2:1 

7.5 

9.5 

8.5 

0.4 

0.8 

0.5 

11.1 

1:4.7 

11-15  months  old,  41 

kg.  weight,     .     .     . 

23.5 

25.0 

24.5 

1.5 

2.0 

1.7 

6.5 

8.5 

7.5 

0.3 

0.5 

0.4 

9.6 

1:5.0 

15-20  months  old,  42- 

43  kg.  weight,     .     . 

21.5 

25.0  23.5 

1.2 

i.r, 

1.4 

6.5 

8.5 

7.5 

0.25 

0.4 

0.3 

9.2 

1:6.0 

FOOD  REQUIRED  BY  THE  HERBIVORA. 


691 


NORMAL  AMOUNTS  OP  FOOD  FOR  CATTLE,  HORSES,  SHEEP,  AND  SWINE. 

(Continued.) 


N  I  T  R  O- 

NON-NlTRO- 

SOLIDS. 

GENOUS  ! 
M  A  T   - 

GE  NOUS 

EXTRA  c  T- 

FAT. 

3 

| 

TERS. 

IVE  MAT- 
TERS. 

1 

1 

CLASS  OF  ANIMAL. 

d 

| 

Q 

3 

d 

a 

g 

g 

q 

£ 

3 

| 

eg 

1 

3 
1 

a 
_§ 

1 

p 
I 

1 

g 

i 

V 

1 

a 

1 

3 

i 

f 

E 

1 

3 

1 

S 

§ 

B 

Kilogrammes. 

7.  Wool  Sheep. 

Coarse-wooled  sheep,  . 

19.0 

24.0 

22.0 

1.0 

1,5 

1.2 

6.5 

8.5 

7.5 

0.1 

0.3 

0.2 

8.9 

1:6.7 

Fine-wooled  sheep,     . 

21.5 

27.0 

24.5 

1.1 

1.7 

1.5 

7.5 

9.0 

8.5 

0.2 

0.4 

0.3 

10.3 

1:6.2 

8.  Rams. 

23.5 

27.0 

25.0 

2.0 

2,5 

2.2 

9.0 

12.0 

10.5 

0.4 

0.6 

0.5 

13.2 

1:5.3 

9.  Fattening  Sheep. 

27.0 

32.0 

29.0 

2.5 

3,5 

3.0 

11.0 

13.0 

12.0 

0.4 

0.6 

0.5 

15.5 

1:4.5 

2d       "      ..... 

25.0 

30.0 

27.0 

3.0 

4.0 

3.5 

11.012.0 

11.0 

0.5 

0.7 

0.6 

15.1 

1:3.5 

Non-Nitro- 

genous Ex- 

tractive 

10.  Young  Pigs. 

Matters  and 
Fats. 

2-3  months  old,  25  kg. 

weight,  

50.0 

58.0 

54.0 

,7.0 

8.0 

7.5 

26.6  31.0 

28.5 

3-5  months  old,  33-50 

kg.  weight,     .     .     . 

41.0 

47.0 

44.0 

5.0 

7.0 

6.0 

22.0 

26.0 

24.0 

5-6  months  old,  62-63 

kg.  weight,     .     .     . 

39.0 

43.0 

41.0 

4.0 

5.0 

4.5 

20.0 

24.0 

22.0 

6-8  months  old,  85  kg. 

weight,  

32.0 

38.0 

35.0 

3.0 

4.0 

3.5. 

18.020.0 

19.0 

8-12  months  old,  125 

kg.  weight,     .     .     . 

24.0 

30.0 

27.0 

2.5 

3.5 

3.0 

15.018.0 

16.5 

11.  Fattening  Pigs. 

1st  period,     .... 

45.0 

48.0 

46.0 

4.5 

6.0 

5.0 

24.5 

26.5 

26.0 

31.0 

1:5.2 

2d       "      

37.0 

45.0  40  0 

3.5'45 

4.5 

21.0 

24.5 

230 

27.0 

1:5.8 

3d       "      

26.0 

33.0 

30.0 

2.5 

3.5 

3.0 

17.0 

19.0 

18.0 

21.0 

1:6.0 

12.  Breeding  Pigs. 

(Sows  and  Boars),  .     . 

26.0 

32.0 

32.0 

1.5  2.0 

1.8 

1.25 

15.0 

14* 

15.8 

1:7.8 

this  condition  the  stomach  rapidly  empties  itself  and  the  feeling  of 
hunger  again  appears.  So,  also,  when  feeding  with  dry  fodder  is  com- 
menced it  is  better  at  the  beginning  to  give  at  least  four  different  meals, 
so  as  to  avoid  overdistention  and  filling  of  the  stomach  with  this  more 
bulky  food.  At  the  end  of  fattening  the  meals  may  be  increased  in 
number  and  reduced  in  amount,  digestion  of  small  amounts  of  readily 
digestible  foods  being  now  more  readily  accomplished. 


692  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


VI.  HUNGER  AND  THIEST. 

The  sensations  which  lead  to  the  prehension  of  solid  and  liquid 
foods  are  known  as  hunger  and  thirst.  It  was  previously  supposed  that 
hunger  was  a  local  sensation  which  was  produced  by  the  absence  of  food 
in  the  stomach.  Evidently  this  is  a  mistaken  idea,  else  would  the  rumi- 
nants never  experience  this  sensation,  for  in  them  the  stomach  is  never 
free  from  food,  even  when  death  occurs  from  starvation.  The  appear- 
ance of  hunger  coincides  with  absorption  of  the  matters  digested  at  the 
previous  meal.  Although  the  sensation  is  apparently  referred  to  the 
abdomen,  it  cannot  be  regarded  as  a  localized  sensation,  but  rather  as  a 
peculiar  modification  of  the  general  system  similar  to  that  produced  in 
dyspnoea;  nor,  indeed,  is  the  stomach  even  the  starting  point  of  hunger, 
for  the  pneumogastrics,  the  sensory  nerves  of  this  organ,  may  be  divided, 
and  if  the  animals  be  deprived  of  food  the  clearest  evidences  of  hunger 
are,  nevertheless,  capable  of  detection.  In  spite  of  this  fact,  the  sensation 
of  hunger  is,  nevertheless,  to  a  certain  extent  dependent  upon  the  con- 
dition of  the  stomach,  as  is  indicated  by  the  temporary  relief  of  hunger 
which  follows  introduction  into  the  stomach  of  matter  which  is  not  in 
the  slightest  respect  nutritious.  So,  again,  even  when  the  stomach  is 
filled  with  food,  if  through  any  disease  digestion  or  absorption  or  the 
passage  of  food  into  the  small  intestine  are  interfered  with  the  hunger 
may,  nevertheless,  be  intensely  felt;  and,  again,  even  after  a  hearty  meal 
digestion  may  be  complete,  and  the  stomach  empty  for  some  time  before 
the  sensation  of  hunger  appears. 

In  the  case  of  thirst  the  state  of  affairs  is  somewhat  similar,  except 
that  there  the  sensation  is  more  distinctly  localized  in  the  fauces  and 
may  be  relieved  by  the  application  of  moisture  to  that  part.  When  an 
animal  is  deprived  of  liquid,  the  blood,  from  the  continued  formation  of 
secretions  and  excretions,  rapidly  loses  its  normal  percentage  of  water. 
The  sensation  of  thirst  is  evidently  due  to  the  irritation  of  the  sensory 
nerves  of  the  mucous  membrane  of  the  pharynx  produced  by  the  drying 
of  the  mucous  membrane,  and  while  it  may  be  relieved,  as  already 
mentioned,  b}T  moistening  this  part,  the  arrest  of  thirst  is  only  temporary. 
But,  on  the  other  hand,  the  thirst  may  be  permanently  relieved  by  the 
injection  of  water  into  the  veins  and  even  by  enemata  of  water,  and 
while  thirst,  therefore,  has  a  local  expression,  like  hunger,  it  represents 
the  needs  of  the  econom}*-  for  water  ;  thirst  may  thus  be  abolished,  even 
although  no  water  enter  the  mouth.  Every  cause,  therefore,  which 
diminishes  the  proportion  of  fluid  in  the  blood,  whether  intense  heat  or 
exercise  which  favor  cutaneous  and  pulmonary  evaporation,  dropsies, 
abundant  hemorrhages,  or  diabetes,  all  lead  to  thirst ;  so,  also,  salts 
occasion  thirst  by  withdrawing  water  from  the  blood. 


SECTION    XIII. 
ANIMAL  HEAT. 

IT  has  been  seen  that  the  income  of  the  animal  body  is  represented 
by  complex  combinations  of  carbon,  hydrogen,  nitrogen,  and  oxygen,  and 
the  introduction  of  free  oxygen  in  respiration ;  the  outgo  of  the  body, 
on  the  other  hand,  is  represented  by  similar  combinations  of  the  same 
elements  in  t;lie  form  of  carbon  dioxide,  water,  and  urea. 

The  conclusion  is  thus  evident  that  the  absorbed  ox^ygen  has  within 
the  body  undergone  combination  with  carbon  and  hydrogen  with  the 
production  of  carbon  dioxide  and  water,  and  that  the  substances  intro- 
duced as  food  have  all  in  different  degrees  united  with  oxygen.  In  other 
words,  the  nutritive  processes  in  the  animal  body  are  represented  by  a 
series  of  oxidations  by  which  the  organic  food-products  are  restored  to 
the  inorganic  form.  Oxidation  of  any  kind  will  invariably  be  accom- 
panied by  a  production  of  heat,  and  we  thus  see  that  one  of  the  principal 
sources  of  the  heat  of  the  animal  body  is  to  be  looked  for  in  such  pro- 
cesses of  oxidation.  It  is  a  well-established  fact  that  the  combustion  of 
any  body,  whether  rapidly  or  slowly  produced,  is  accompanied  by  the 
evolution  of  a  fixed  quantity  of  heat,  provided  the  energy  be  not  other- 
wise employed.  Thus,  the  complete  combustion  of  one  gramme  of  sugar 
invariably  corresponds  to  the  development  of  four  heat-units.* 

If  this  combustion  takes  place  in  the  animal  body,  it  is  evident  that 
the  same  amount  of  heat  must  be  developed,  no  matter  what  may  be  the 
character  of  the  substances  developed  between  the  starting  point  and  the 
final  termination  of  the  process  of  oxidation. 

In  the  animal  body,  however,  such  processes  of  combustion  are 
rarely  as  complete  as  would  occur  in  the  incineration  of  food-stuffs 
outside  of  the  body.  Thus,  for  example,  in  albumen  the  process  of 
oxidation  results  in  the  formation  of  urea,  which  itself  is  capable  of 
still  further  oxidation.  '  Nevertheless,  it  ma}T  be  stated  with  a  tolerable 
degree  of  accuracy  how  much  heat  is  set  -free  in  such  processes  of 
oxidation  of  the  food-stuffs  in  the  animal  body.  Knowing  the  amount 
of  heat  developed  in  the  oxidation  of  one  gramme  of  albumen  and 
the  amount  developed  in  the  oxidation  of  a  proportionate  quantity  of 
urea,  deducting  the  latter  from  the  former  will  evidently  represent  the 

*  By  this  term,  heat-unit,  is  meant  that  amount  of  heat  which  is  required  to  raise  one 
kilogramme  of  water  from  0°  C.  to  1°  C. 

(693) 


694  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS 

degree  of  oxidation  occurring  in  the  animal  body.  This  factor  has  been 
estimated  as  corresponding  to  five  heat-units.  With  these  data  the 
amount  of  heat  developed  in  twenty-four  hours  may  be  readily  calculated. 
Thus,  taking  the  example  given  by  Fick,  the  income  of  the  body  was 
represented  in  round  numbers  by  one  hundred  and  twenty  grammes  of 
fat,  two  hundred  and  sixty-three  grammes  of  carbohydrates,  and  one 
hundred  and  seventeen  grammes  of  albumen,  with  the  excretion  of 
thirty-nine  grammes  of  urea.  The  combustion  of  one  gramme  of  fat  is 
represented  by  the  development  of  nine  and  six-tenths  heat-units,  and,  as 
already  seen,  one  gramme  of  carbohydrates  by  four  heat-units,  and  one 
gramme  of  albumen  by  five  heat-units.  The  total  amount  of  heat,  there- 
fore, developed  is  represented  by  120  X  9.6  -f  263  X  4  -f  1 17  X  5,  or,  in 
round  numbers,  two  thousand  eight  hundred  heat-units.  The  confirma- 
tion of  these  figures  and  their  influence  in  maintaining  the  heat  of  the 
animal  body  is  determined  by  calorimetric  experiments.  To  accomplish 
such  an  experiment,  first,  the  tissue  change  in  twenty-four  hours  must  be 
calculated ;  second,  the  amount  of  heat  liberated  by  the  body  in  that 
time ;  third,  the  average  temperature  of  the  animal  body  at  the  com- 
mencement and  end  of  the  experiment;  and,  fourth,  the  average  heat 
capacity  of  the  body.  Asa  rule,  the  difference  between  the  body  tem- 
perature at  the  commencement  and  end  of  such  experiments  is  so  slight 
as  not  to  deserve  attention,  and  the  amount  of  heat  set  free  in  twenty- 
four  hours  may  be  regarded  as  indicating  the  amount  of  heat  developed 
in  the  body. 

Such  experiments  do  not,  however,  serve  with  absolute  accuracy  to 
confirm  the  theoretical  figures  deduced  from  the  co-efficient  of  heat 
production  represented  above  as  belonging  to  the  different  food-stuffs. 
In  nearly  all  cases  there  is  an  apparent  loss  of  heat  over  what  should  be 
expected  from  these  data.  It  is  to  be  recollected,  in  the  explanation  of 
this  discrepancy,  that  the  energy  set  free  in  such  oxidations  ma}7  take 
on  the  form  either  of  heat  or  of  mechanical  work.  In  the  animal  body 
all  these  sources  of  loss  of  energy  occur.  All  forms  of  muscular  move- 
ment are  accompanied  by  liberation  of  energy,  and  a  continual  loss  of 
heat  is  taking  place  through  radiation  from  the  surface  of  the  body,  by 
conduction,  by  the  evaporation  from  the  skin  and  mucous  surfaces,  and 
by  the  warming  of  the  ingesta.  The  amount  of  heat  dissipated  by  the 
animal  body  in  a  condition  of  health  is  in  close  dependence  upon  the 
amount  produced,  upon  the  difference  in  temperature  between  the  animal 
body  and  the  surrounding  medium,  and  especially  upon  the  relationship 
between  the  external  surface  of  the  body  and  the  body  weight.  Thus, 
small  animals  for  each  kilogramme  of  the  body  weight  set  free  more  heat 
than  large  animals.  It  has  been  estimated  that  for  each  kilogramme  of 
body  weight  the  horse  in  each  hour  sets  free  two  and  one-tenth  heat- 


ANIMAL  HEAT.  695 

units ;  sheep,  two  and  six-tenths  heat-units ;  the  dog,  four  heat-units ; 
and  the  sparrow,  thirty-two  heat-units.  The  cause  of  this  difference  may 
be  found  in  the  fact  that  the  smaller  a  sphere  the  greater  is  its  superficial 
area  in  comparison  to  its  cubic  contents.  The  same  rule  applies,  also,  to 
the  irregular  form  of  the  animal  body,  in  which  the  smaller  it  is  in  pro- 
portion to  the  weight  of  the  animal  the  greater  will  be  its  superficial  area. 
It  is,  however,  from  the  external  surfaces  that  the  greatest  amount  of 
body  heat  is  dissipated,  and  it  is,  therefore,  seen  why  small  animals  lose 
proportionately  more  heat  than  larger  animals. 

Two  different  conditions  are  noted  in  reference  to  the  heat  which  is 
retained  in  the  animal  body,  and  which,  therefore,  causes  the  body  tem- 
perature. In  the  cold-blooded  animal  the  temperature  of  the  body  is 
not  constant,  but  varies  with  that  of  the  surrounding  medium,  rarely 
being  more  than  a  few  tenths  of  a  degree  above  it.  In  the  warm-blooded 
animals,  as  in  mammals  and  birds,  on  the  other  hand,  the  body  tempera- 
ture is,  as  a  rule,  higher  than  that  of  the  surrounding  medium,  and  is 
independent  of  variations  in  the  latter.  The  cause  of  this  difference  of 
body  heat  lies  in  the  difference  in  energy  of  the  tissue  changes.  In  the 
cold-blooded  animals  the  development  of  heat  is  so  slight  that  this 
amount  of  heat  is  at  once  given  up  to  the  cold  atmosphere.  If  the  ex- 
ternal temperature  be  increased,  this  dissipation  of  heat  is  accordingly 
diminished,  and  as  a  consequence  part  of  the  heat  produced  is  retained 
in  the  body  and  increases  its  temperature.  On  the  other  hand,  if  the 
external  temperature  falls,  the  amount  of  heat  dissipated  is  increased 
and  the  body  temperature  falls.  In  animals  with  a  constant  body  tem- 
perature the  amount  of  heat,  on  account  of  the  greater  energy  of  tissue 
change,  is  so  much  greater  that  but  a  part  alone  is  given  up  to  the  sur- 
rounding medium.  From  the  fact  that  the  source  of  temperature  is 
found  in  the  chemical  changes  occurring  in  the  tissues,  it  is  evident  that  the 
development  of  heat  will  be  greater  in  tissues  in  which  such  processes  are 
active  than  where  they  are  sluggish.  The  temperature  of  the  animal  body 
will,  therefore,  vary  in  different  localities  ;  it  will  be  greater  in  secreting 
glands  and  contracting  muscles ;  it  will  be  less  where  loss  of  heat  is 
favored,  and,  as  a  consequence,  the  exterior  surfaces  of  the  body  will 
possess  a  lower  temperature  than  the  inner  cavities. 

In  the  lungs  the  blood  gives  up  so  much  heat  to  the  air  that  the 
temperature  of  the  blood  in  the  left  side  of  the  heart  is  cooler  than  that 
of  the  right,  in  spite  of  the  development  of  heat  which  accompanies  the 
oxidation  of  haemoglobin.  With  this  exception  the  arterial  blood,  as 
being  less  exposed  to  loss  of  heat,  ma}',  as  a  rule,  be  stated  to  be  warmer 
than  venous  blood. 

The  temperature  of  an  organ  will,  therefore,  depend  upon  the  amount 
of  blood  circulating  through  it.  Under  certain  circumstances  the  venous 


696  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

blood  may  increase  in  temperature  over  that  of  the  arterial  blood  ;  such 
a  state  of  affairs  is  seen  in  the  blood  coining  from  the  contracting  muscles 
or  from  a  secreting  gland.  The  blood  by  its  continuous  circulation 
through  the  body  tends  to  equalize  the  body  temperature,  giving  up 
heat  to  tissues  which  are  cooler  than  itself  and  withdrawing  heat  from 
those  which  are  warmer.  The  mean  between  the  highest  and  lowest 
temperature  of  the  animal  body  is  spoken  of  as  the  body  temperature, 
and  is  generally  represented  by  the  temperature  taken  in  the  mouth  or  in 
the  rectum. 

The  following  figures  represent  the  mean  average  temperatures  of 
the  different  domestic  animals  : — 


Horse, 
Ox,  . 

37.50  to  380  C. 
.     380  to  38.50  C. 

Dog, 

38.50  c. 

Sheep, 
Chicken, 

390  to  400  C. 

420  C. 

Hog, 

390  to  400  c. 

Ass, 
Rabbit, 
Mouse, 
Cat, 
Goose, 
Pigeon, 

39.50  to  38°  C. 
390  to  39.50  C. 
41.10  C. 
38.50  to  390  C. 
41.50  C. 
420  C. 

While  these  figures  represent  the  average  body  temperature,  varia- 
tions within  narrow  limits  may  often  be  observed  even  in  perfectly 
healthy  individuals.  A  variation  of  one  degree  or  more  indicates  some 
failure  in  the  organism  or  some  departure  from  the  natural  process  of 
metabolism.  It  is,  therefore,  evident  that  the  mechanisms  which  regulate 
the  balance  between  the  production  and  loss  of  heat  must  be  extremely 
sensitive.  Such  a  regulating  mechanism  will  prevent  an  increase  of  the 
body  temperature  either  by  diminishing  the  production  or  increasing 
dissipation  of  heat,  or,  in  the  other  case,  by  increasing  the  production 
and  diminishing  the  loss. 

Heat,  as  already  indicated,  is  lost  to  the  body  by  conduction  to  the 
ingesta  and  egesta,  to  the  expired  air,  and  by  conduction  and  radiation 
from  the  skin  and  through  the  evaporation  of  fluid  from  the  surface  of 
the  body.  The  relative  amounts  of  heat  lost  by  these  different  channels 
have  been  calculated  by  Helmholtz  as  follows :  through  the  expired  air, 
5.2  per  cent.;  through  the  water  of  respiration,  14.7  per  cent. ;  through 
the  skin,  77.5  per  cent.  The  chief  means,  therefore,  of  heat  dissipation 
are  through  the  lungs  and  skin.  The  more  rapid  the  respiration  the 
greater  will  be  the  loss  of  heat,  and  in  animals  which  do  not  perspire  the 
lungs  will  represent  the  main  source  of  heat  dissipation.  In  other 
animals  the  skin  is,  no  doubt,  the  great  regulator  of  the  body  temper- 
ture.  The  more  blood  passes  through  the  cutaneous  vessels,  the  greater 
will  be  the  loss  of  heat  through  radiation,  the  greater  will  be  the  cuta- 


ANIMAL  HEAT.  697 

neous  secretion,  and,  as  a  consequence,  the  greater  will  be  the  loss  of 
heat  through  evaporation.  Everything,  therefore,  which  dilates  the 
cutaneous  blood-vessels  will  increase  the  heat  dissipation.  The  working 
of  the  mechanism  of  heat  regulation  through  increasing  heat  dissipation 
is  well  seen  in  the  case  of  exercise.  Every  muscular  contraction,  as 
already  pointed  out,  leads  to  an  increase  of  heat  production,  and,  as  a 
consequence,  the  blood  coming  from  a  contracting  muscle  may  be  several 
degrees  warmer  than  the  arterial  blood  supplied  to  it.  Nevertheless,  the 
body  temperature,  even  in  severe  exercise,  is  but  little  elevated  above  the 
average,  for  the  increased  exercise  leads  to  an  increased  demand  of 
oxygen  in  the  inspired  air,  and,  as  a  consequence,  respiration  is  increased 
and  the  amount  of  heat  eliminated  through  the  expired  air  thereby  aug- 
mented. The  action  of  the  heart  is  likewise  accelerated,  the  circulation 
through  the  skin  is  augmented,  perspiration  is  increased,  and  a  greater 
amount  of  heat  is  given  up  from  the  skin  by  radiation  and  by  the  evapo- 
ration of  the  perspiration.  By  this  means  enough  heat  is  lost  to  the 
animal  body  to  balance  the  increased  production. 

Increase  of  external  temperature  likewise  prevents  an  increase  in 
the  body  temperature  by  increasing  the  circulation  through  the  skin 
and  the  cutaneous  perspiration,  and  so  also  increases  the  loss  of  heat. 
On  the  other  hand,  if  the  external  temperature  is  reduced  the  cutaneous 
vessels  contract,  the  evaporation  of  perspiration  is  prevented,  and  again 
a  balance  is  struck  between  the  production  and  the  heat  dissipation. 

The  influence  of  the  nervous  system  on  the  temperature  of  the 
animal  body  is  both  directly  and  indirectly  exerted.  It  has  been  men- 
tioned in  a  previous  section  that  division  of  the  cervical  sympathetic 
nerve  is  followed  not  only  by  contraction  of  the  pupil,  but  also  by  an 
increased  temperature  of  the  corresponding  side  of  the  head  and  neck. 
If  this  experiment  be  performed  upon  a  rabbit  the  increase  of  tempera- 
ture is  so  great  as  to  be  readily  perceptible  to  the  touch ;  and  if  the  ears 
of  the  rabbit  be  examined  in  transmitted  light  the  blood-vessels  of  the 
auricle  on  the  side  of  section  of  the  sympathetic  will  be  found  to  be 
greatly  dilated.  Section  of  the  sympathetic,  therefore,  by  paralysis  of 
the  vaso-motor  nerves,  has  occasioned  dilatation  of  the  blood-vessels,  and 
the  consequent  increased  vascularity  facilitates  radiation  of  heat  and  so 
causes  a  perceptible  increase  in  the  temperature  of  the  part.  But  the 
increased  radiation  of  heat  is  also  attended  with  increased  heat  produc- 
tion ;  for  the  hypersemia  produced  by  vaso-motor  paralysis  is  accom- 
panied by  increased  nutritive  activity,  and  heat  production  is  thereby 
augmented.  Thus,  it  has  been  shown  by  Bidder  that  excision  of  a  part 
of  the  cervical  sympathetic  in  the  rabbit  is  followed  within  two  weeks  by 
a  marked  increase  in  the  size  of  the  ear  on  the  side  of  operation  ;  and 
excision  of  the  cceliac  plexus  has  been  said  to  produce  intense  hyperaemia 


698  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

of  the  stomach.  Numerous  instances  of  pathological  increase  of  nutri- 
tive activity  from  increased  blood  supply  and  consequent  increased  tem- 
perature will  doubtless  suggest  themselves. 

In  addition  to  this  indirect  influence  of  the  nervous  system  through 
the  vaso-motor  nerves  on  calorification,  the  central  nervous  system  is 
stated  to  both  directly  and  reflexly  govern  the  development  of  heat, 
though  much  of  the  evidence  brought  forward  as  to  a  special  nervous 
mechanism  for  regulating  animal  heat  is  imperfect.  Experiments  have 
chiefly  been  directed  toward  locating  special  heat-centres  in  various 
parts  of  the  brain.  Ott  claims  that  there  are  four  localities  in  the  brain 
irritation  of  which  increases  bodily  temperature  by  from  2.2°  to  3.3°  C. 
These  heat-centres  are  said  to  be  located  as  follows:  1.  In  front  of  and 
beneath  the  corpus  striatum.  2.  The  median  portion  of  the  corpora 
striata.  3.  Between  the  corpus  striatum  and  the  optic  thalamus.  4.  The 
anterior  inner  end  of  the  optic  thalamus.  A  heat-centre  is  also  claimed 
to  be  present  in  the  dog,  in  the  cortex  of  the  anterior  portion  of  the 
upper  surface  of  the  brain,  near  the  median  line,  the  locality  agreeing 
with  that  of  the  motor  centres  of  the  hind  limbs,  and  for  the  movements 
of  flexion  and  rotation  of  the  fore  limbs.  According  to  Wood,  section 
of  the  brain  between  the  pons  and  medulla  oblongata  causes  increased 
radiation  of  heat  and  diminished  heat  production,  due  to  the  cutting  of 
the  paths  of  communication  with  the  cerebral  heat-regulating  centre. 
There  seems  to  be  little  doubt  but  that  irritation  of  various  parts  of  the 
brain  does  lead  to  modifications  in  the  heat-producing  mechanisms 
of  the  body,  arid  that  fibres  in  connection  with  these  centres  decussate 
in  the  medulla;  but  as  to  whether  the  effects  produced  are  stimulating 
or  inhibitory,  whether  they  act  through  the  production  of  change  in 
circulation,  or  whether  they  directly  influence  the  chemical  operations 
concerned  in  the  production  of  heat,  is  quite  unknown. 


BOOK   II. 


THE  ANIMAL  FUNCTIONS. 


(699) 


SECTION    I. 
PHYSIOLOGY  OF  MOVEMENT. 

1.  THE  CONTRACTILE  TISSUES. — It  was  stated  that  the  function  of 
contractility  represents  one  of  the  fundamental  properties  of  protoplasm, 
and  in  the  simplest  forms  of  life,  consisting  of  undifferentiated  proto- 
plasm, as  in  the  structureless  amoeba,  the  contractilit}^  of  protoplasm 
renders  locomotion  possible.  The  first  attempt  at  localization  of  this 
function  of  contractility,  in  the  general  specialization  of  function  in  the 
development  of  the  animal  kingdom,  was  noted  in  the  development  of 
protoplasmic  prolongations  of  cells,  so-called  cilia,  which  in  numerous 
infusoria  constitute  organs  of  locomotion ;  in  various  shell-fish,  organs 
for  aiding  the  prehension  of  food  and  the  functions  of  respiration,  and  in 
the  higher  animals  for  producing  motion  of  particles  brought  in  contact 
with  them.  The  first  attempt,  therefore,  at  the  development  of  organs 
in  which  the  function  of  contractility  is  specialized  is  seen  in  the  develop- 
ment of  vibratile  cilia.  In  a  step  higher  in  the  progress  of  specialization, 
contractility  reaches  its  highest  degree  in  the  muscular  tissue,  which  may 
be  regarded  as  a  mass  of  protoplasm  inclosed  within  a  cylindrical  or 
polygonal  cell.  In  the  higher  animals  each  of  these  three  different 
representations  of  contractile  substances  are  met  with  :  undifferentiated 
protoplasm,  as  found  in  the  lymph-corpuscles,  white  blood-corpuscles, 
connective-tissue  corpuscles,  mucus-  and  pus-cells ;  ciliated  cells,  lining 
various  mucous  cavities  in  the  body  ;  and  muscular  tissues  of  the  striped 
and  unstriped  varieties. 

The  characteristics  of  motion  as  occurring  in  undifferentiated  proto- 
plasm and  ciliated  cells  have  already  been  studied.  The  conditions  of 
muscular  contractility  now  deserve  attention.  In  muscular  tissue  the 
contractile  substance  is  inclosed  in  a  tubular  sheath,  constituting  a  mus- 
cular fibre.  Muscular  fibres  may  be  either  striped  or  voluntary  fibres,  or 
unstriped  or  involuntary  fibres.  The  striped  or  voluntary  muscles,  which 
have  a  red  appearance,  constitute  the  great  mass  of  contractile  tissues 
of  the  body.  They  are  ordinarily  connected  with  the  bones,  and  are 
therefore  spoken  of  as  skeletal  muscles ;  their  contractions,  as*  a  rule,  are 
under  the  control  of  the  will.  Each  muscle-fibre  is  more  or  less  cylin- 
drical, varies  in  length  from  one  one-hundredth  to  one  six-hundredth  of 
an  inch,  and  consists  of  the  sarcolemma,  an  elastic  sheath,  probably  of  the 
nature  of  connective  -tissue,  with  transverse  partitions  which  stretch 

(701) 


702 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


across  the  fibre  at  regular  intervals  (membrane  of  Krause).  Within  this 
is  inclosed  the  sarcous  substance,  or  the  contractile  tissue  of  the  muscu- 
lar fibre,  which  is  a  broad,  highly  refractive,  doubly  refractive  disk,  and 
the  nuclei  or  muscle-corpuscles.  The  muscle-corpuscles  are  thus  within 
the  sarcolemma,  and  it  is  at  the  expense  of  their  protoplasm  that 


FIG.  271.— MUSCULAR  TISSUE,  AFTER  GERLACH.    '(Ellenberger.) 

1,  scheme  of  the  different  parts  of  striped  muscular  fibre;  S,  sarcolemma:  K,  nucleus:  2,  striation; 
F,  fibrillae  ;  N,  nerve ;  E,  nucleated  nerve-plate ;  2,  part  of  a  cross-section :  3,  isolated  fibrillae  ;  4,  highly 
magnified  fibril  of  insect  muscle :  A,  Krause- Amici's line;  B,  anisotropic  substance ;  C,  central  disk ;  D, 
isotropic  substance ;  5,  separation  of  disks ;  6.  cell  of  heart-muscle  of  frog ;  7,  embryonal  development  of 
muscular  fibre;  8,  cells  of  heart-muscle;  9,  cross-section  of  heart-muscle;  10,  unstriped  muscle-cells;  11, 
cross-seqtion  of  unstriped  muscle-cells;  12,  muscular  fibre  with  tendon;  13,  interfibrillar  muscular 
n«rvos. 

muscular  tissue  is  formed.  Between  the  contractile  disks  and  Krause 's 
membrane  is  a  transparent,  isotropic,  semifluid  laj'er  (the  lateral  disk 
of  Engelnrann),  which  is  composed  of  prismatic,  rod-shaped  elements, 
the  sarcous  elements  of  Bowman. 


PHYSIOLOGY  OF  MOVEMENT. 


703 


The  striated  appearance  of  muscular  tissue  is  due  to  the  arrange- 
ment of  the  sarcous  substance  in  alternate  light  and  dark  layers  or  disks. 

Each  muscular  fibre  is  made  up  of  a  large  number  of  primitive 
fibrillse  placed  side  by  side  and  united  by  a  semi-fluid  cement  substance, 
the  fibrillse  being  so  arranged  that  the  transverse  markings  lie  at  the 
same  level. 

The  muscular  corpuscles  in  the  muscular  fibres  of  man  and  most 


B 


B 


FIG.    272.— UNSTRIPED   MUSCULAR   TISSUE. 

(Ellenberger. ) 

A  and  B,  foetal  cells:  C,  H.  fullv  formed  fibre;  I, 
bundle  of  fibres ;  K,  cross-section  of  bundle  of  pale  muscular 
fibres. 


FIG.  273.— MUSCULAR  CELLS  FROM  THE 
MUSCULAR  COAT  OP  THE  STOMACH, 
ENLARGED  Two  HUNDRED  AND  FIFTY 
DIAMETERS.  (Ellenberger.) 

A,  elongated  nucleus ;  B,  pointed  ends  of  the  cells. 


vertebrates,  with  the  exception  of  the  tissue  of  the  heart,  are  situated  on 
the  surface  of  the  muscular  substance,  but  in  invertebrates  they  are 
usually  found  in  the  central  part  of  the  fibres.  The  muscular  fibres  are 
united  in  bundles  by  connective  tissue  and  terminate  in  tendons  which 
are  composed  of  connective-tissue  fibrillee. 

The  unstriped  muscular  fibres  are  composed  of  elongated  spindle- 
shaped  nucleated  cells,  which  are  contractile  in  one  direction.     These 


704 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


•""mil  HI'-. 

'it'UNUII  II  III"! 

j-Wftti  3«|M 

>»wiii  9  nm 

^mifi 


cells  are  arranged  in  bundles  connected  by  a  cement  substance ;  they  do 
not  terminate  in  tendons,  but  are  arranged  in  groups,  usually  in  the  form 
of  a  membrane ;  such  muscular  fibres  are  found  in  the  walls  of  the  ali- 
mentary canal,  in  the  walls  of  the  genito-urinary  passages,  in  the  bronchi, 
and  in  various  other  localities. 

(a)  The  Chemical  Composition  of  Muscle. — The  chemical  constit- 
uents found  in  muscles  differ  greatly  according  as  the  examination  is 
made  on  fresh,  living  tissue,  or  after  rigor  mortis  has  set  in.  All  mus- 
cles after  death  lose  their  irritability,  and  pass  from  their  flexible,  trans- 
parent condition  into  a  state  of  rigidity  and  opacity,  which  is  described 
under  the  general  term  of  rigor  mortis.  Analogy 
may  be  traced  in  this  respect  between  the  living 
and  dead  muscle  and  blood. 

Blood  in  the  process  of  coagulation  produces 
the  proteid  fibrin ;  muscle,  in  the  act  of  dying, 
produces  the  proteid  myosin. 

Before  taking  up  the  characteristics  of  these 
bodies,  further  comparison  of  the  characteristics 
of  living  and  dead  muscle  deserves  attention. 

In  the  first  place,  in  a  state  of  rest,  living 
muscle  has  an  alkaline  reaction ;  in  dead  muscle, 
and  in  muscle  in  contraction,  the  reaction  is  acid, 
due  to  the  development  of  paralactic  acid,  as  well 
as  acid  potassium  phosphate,  and  carbonic  acid. 

Living  muscle  is  to  a  certain  extent  trans- 
lucent, extensible,  and  elastic ;  dead  muscle  is 
opaque,  rigid,  inextensible,  and  has  lost  its  elas- 
ticity. The  main  difference,  however,  between 
living  and  dead  muscle  is  found  in  the  coagulation 
of  nvyosin  in  the  latter.  If  a  living  muscle  be 
freed  from  blood  by  repeated  washing  and  injec- 
tion of  saline  solution  through  its  blood-vessels,  be  then  frozen,  chopped 
up,  and  rubbed  up  in  a  mortar  with  four  times  its  weight  of  powdered 
ice,  containing  1  per  cent,  of  sodium  chloride,  a  mixture  is  obtained 
which,  below  the  freezing  point,  is  sufficiently  fluid  to  be  filtered.  This 
opalescent  filtrate  is  known  as  muscle-plasma,  and  remains  fluid  only 
while  kept  at  0°  C.  If  allowed  to  be  heated  above  this  point  it  is 
gradually  transformed  into  a  solid  jelly,  which  subsequently  separates 
into  a  clot  and  serum.  The  clot  is  myosin,  and  originates  in  the  doubly 
refractive  substance ;  the  serum  contains  serum-albumen  and  various 
extractives. 

If  a  muscle  which  has  already  passed  into  the  condition  of  rigor 
mortis  be  washed  with  water  so  as  to  remove  the  albumen  and  the  dif- 


i,   Ulllllllll 


FIG.  274.  — PRIMITIVE 
BUNDLE  FROM  THE  BI- 
CEPS BRACHII  OF  THE 
HORSE.  (Tereg.) 

A,  intermediary  disks :  B,  cen- 
tral disks ;  C,  dark  striation ;  D, 
light  striatiou. 


PHYSIOLOGY   OF   MOVEMENT.  705 

ferent  extractive  matters,  and  then  be  extracted  with  10  per  cent,  solu- 
tion of  sodium  chloride,  a  large  portion  of  the  muscular  tissue  will  be 
dissolved  and  will  form  a  viscid  fluid.  If  this  fluid  be  allowed  to  fall 
drop  by  drop  into  distilled  water  a  flocculent  precipitate  will  be  pro- 
duced ;  this  precipitate  is  likewise  myosin.  As  is  seen  from  its  method 
of  preparation,  myosin  is  a  globulin  which  is  soluble  in  strong  solution 
of  sodium  chloride,  and  which  may  be  precipitated  therefrom  by  dilution 
with  water.  Myosin,  like  other  globulins,  may  be  coagulated  by  heat, 
although  it  coagulates  at  a  lower  temperature  than  does  serum-albumen, 
its  point  of  coagulation  being  from  55°  to  60°  C.  It  is  coagulated  by 
alcohol  and  ma}'  be  precipitated  by  an  excess  of  sodium  chloride.  It  is 
through  the  action  of  dilute  acids  converted  into  syntonin,  or  acid  albu- 
men. Myosin  is,  therefore,  the  result  of  coagulation  of  the  proteid  of 
muscle-plasma. 

In  addition  to  myosin,  dead  muscle  contains  serum-albumen  and 
various  extractive  matters,  and  bodies  belonging  to  the  gelatin  group. 

In  living  muscle,  on  the  other  hand,  myosin  is  not  present,  but  some 
substances  or  substance  which  in  the  death  of  the  muscle  become  con- 
verted into  myosin,  just  as  the  fibrin  factors  present  in  living  blood  in 
the  act  of  coagulation  become  converted  into  fibrin. 

The  differences  already  alluded  to  between  living  and  dead  muscle 
are,  without  doubt,  caused  by  the  appearance  of  n^osm.  The  process 
of  coagulation  of  muscle,  however,  is  not  directly  comparable  to  that  of 
the  coagulation  of  the  blood,  for,  while  in  the  latter  case  the  alkalinity  is 
preserved,  in  the  former  case  the  alkaline  reaction  of  living  muscle 
gives  place  to  a  strongly  acid  reaction. 

Dr.  W.  D.  Halliburton  has  found  that  the  muscle-plasma  of  warm- 
blooded animals  is  a  j^ellowish,  viscid  fluid  of  alkaline  reaction,  which 
remains  uncoagulated  at  0°  C.,  and  at  the  temperature  of  the  air  sets 
into  a  jelly-like  clot,  on  the  subsequent  contraction  of  which  muscle-serum 
of  an  acid  reaction  is  squeezed  out. 

It  was  found,  however,  that  cold  is  not  the  only  agent  which  will 
prevent  the  formation  of  myosin,  but  that,  as  in  the  case  of  the  blood, 
solutions  of  certain  neutral  salts  will  act  similarly.  The  solutions  found 
most  convenient  to  use  were  a  10  per  cent,  solution  of  sodium  chloride, 
a  5  per  cent,  solution  of  magnesium  sulphate,  or  a  half-saturated  solution 
of  sodium  sulphate.  The  salted  muscle-plasma  was  prepared  either  by 
receiving  the  expressed  muscle-juice  into  excess  of  one  of  these  solutions, 
or  else  by  extracting  the  finely  divided  pieces  of  frozen  muscle  with  the 
solution  in  question. 

A  further  resemblance  between  salted  muscle-plasma  and  salted 
blood-plasma  must  be  noticed,  namely,  that  on  dilution  of  the  mixture 
of  muscle-plasma  and  salt-solution  with  water  the  influence  of  the  latter 

45 


706  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

in  preventing  coagulation  is  removed  and  a  clot  of  myosin  forms.  This 
is  first  a  jellying  through  the  whole  liquid  ;  the  clot  subsequently  con- 
tracts, squeezing  out  a  colorless  fluid  or  salted  muscle-serum ;  this  does 
not  occur  if  the  temperature  is  kept  about  0°  C.,  and  it  occurs  much 
more  quickly  at  the  temperature  of  the  body  than  at  that  of  the  air. 
The  formation  of  the  clot  at  36°  C.  takes,  as  a  rule,  five  or  ten  minutes; 
at  the  temperature  of  the  air,  several  hours.  The  formation  of  the  clot 
is  accompanied  by  the  development  of  an  acid  reaction  due  to  sarco- 
lactic  acid  ;  in  this  the  formation  of  myosin  contrasts  with  that  of  fibrin. 
The  resemblances  between  the  coagulation  in  muscle  and  in  blood  is, 
however,  so  striking  as  to  suggest  that  the  cause  is  similar;  namely,  a 
ferment  in  both  cases.  The  theory  most  generally  accepted  regarding 
the  formation  of  fibrin  is  that  it  is  the  result  of  a  ferment  action  on  a 
previously  soluble  proteid  of  the  globulin  class  occurring  in  blood- 
plasma,  called  fibrinogen ;  and  the  theory  Dr.  Halliburton  now  puts 
forward  is  that  myosin  is  also  the  result  of  a  ferment  action  on  a 
previously  soluble  globulin  occurring  in  a  muscle-plasma,  for  which  he 
proposes  the  name  myosinogen.  This  ferment  can  be  prepared  from 
muscle  in  the  same  way  as  Schmidt's  fibrin  ferment  is  prepared  from 
blood ;  muscle  is  kept  for  some  months  under  alcohol,  dried,  and 
*  extracted  with  water.  This  aqueous  extract  contains  the  ferment,  and 
on  adding  it  to  the  salted  muscle-plasma  coagulation  occurs  much  more 
quickly  than  if  water  alone  be  added.  Myosin  ferment  is  not  identical 
with  fibrin  ferment,  as  it  does  not  hasten  the  coagulation  of  salted  blood- 
plasma,  nor  does  the  fibrin  ferment  hasten  the  coagulation  of  muscle- 
plasma.  The  aqueous  solution  of  the  n^osin  ferment  gives  the  reaction 
of  a  proteid  of  the  albumose  class,  and  especially  of  that  variety  of 
albumose  to  which  Kiihne  and  Chittenden  have  given  the  name  deutero- 
albumose.  This  is  the  same  albumose  as  will  be  shown  presently  to 
exist  normally  in  the  muscle-plasma. 

The  proteids  of  muscle-plasma  can  be  separated  by  fractional  heat 
coagulation,  by  fractional  saturation  with  neutral  salts,  and  by  the 
occurrence  of  spontaneous  coagulation  and  the  separation  of  the  plasma 
into  clot  and  serum.  The  proteids  were  found  to  be  five  in  number;  the 
names  Dr.  Halliburton  proposes  for  them  and  their  chief  properties  are 
as  follow : — 

1.  Paramyosinogen. — This  forms  a  flocculent  heat  coagulum  at  47°  C. 
It  is  precipitated  from  its  solutions  in  an  uncoagulated  condition  (that 
is,  it  can  be  redissolved  in  weak  saline  solutions)  by  magnesium  sulphate 
or  sodium  chloride  ;  by  the  former,  when  the  percentage  of  salt  present 
reaches  37  to  50 ;  by  the  latter,  when  the  percentage  reaches  15  to  26. 
The  precipitate  so  obtained  occurs  in  white,  curd-like  flocculi.  It  is 
precipitated  also  by  dialyzing  out  the  salts  from  its  solutions. 


PHYSIOLOGY   OF   MOVEMENT.  707 

2.  Myosinogen. — This   is   coagulated   by    heat  ut  56°   C.,  and  the 
coagulum  so  formed  is  a  sticky  one.     It  is  precipitated  by  dialyzing  out 
the  salt  from  its  solutions ;  and  it  is  also  insoluble  in  magnesium  sulphate 
solutions  of  the  strength  of  60  to  94  per  cent,  and  in  saturated  solutions 
of  sodium  chloride.    Weak  acetic  acid  added  to  its  saline  solutions  gives 
a  characteristic  stringy  precipitate. 

3.  Myoglobulin. — This    resembles    serum-globulin   in   most   of    its 
properties.     It  is  coagulated  by  heat  at  63°  C.,  and  thus  differs  from 
serum-globulin,  which  is  coagulated  at  75°  C.     It  is  completely  precipi- 
tated   by    saturating   its    solutions    with   magnesium   sulphate,  sodium 
chloride,  or  by  dialyzing  the  salts  out. 

4.  Albumen. — This  appears  to  be  identical  with  serum-albumen. 

5.  Myo-albumose. — This  is  not  precipitated  by  heat,  by  copper  sul- 
phate, by  magnesium  sulphate,  or  sodium  chloride.     It  is  precipitated 
by  saturation  with  ammonium  sulphate;  \)y  nitric  acid  in  the  cold.     The 
precipitate  produced  by  nitric  acid  disappears  on  heating  and  reappears 
on  cooling.     It  also  gives  the  biuret  reaction — that  is,  a  pink  color — - 
with    copper    sulphate   and   caustic    potash.      This    proteid  is  closely 
associated  with  the  myosin  ferment. 

Peptones  and  alkali  albumen  do  not  occur  in -muscle-plasma. 

In  coagulation  of  the  muscle-plasma  the  first  two  proteids  go  to  form 
the  clot,  and  the  three  latter  remain  in  the  muscle-serum.  The  name 
paramyosinogen  is  given  to  the  first  on  the  list,  because,  although  it 
forms  part  of  the  clot,  it  seems  rather  to  be  accidentally  carried  down 
than  to  form  an  essential  part  of  the  m}'osin.  If  pure  solutions  of  para- 
myosinogen and  myosinogen  respectively  be  prepared  and  ferment  added 
to  each,  in  the  former  no  coagulation  occurs,  but  in  the  latter  myosin  is 
formed.  Moreover,  paramyosinogen  is  sometimes  absent,  or  only  present 
in  exceedingly  minute  quantities  in  the  muscle-plasma. 

Saline  extracts  of  rigid  muscle,  or  of  muscle  from  which  rigor  has 
passed  off,  differ  from  the  salted  muscle-plasma  in  being  of  an  acid  reac- 
tion, but  otherwise  very  closely  resemble  it.  Such  an  extract  contains 
the  same  five  proteids,  and,  on  dilution,  myosin  separates  as  it  does  from 
muscle-plasma;  pure  myosin,  also,  if  redissolved  in  a  10  per  cent,  magne- 
sium sulphate  or  sodium  chloride  solution  can  similarly  be  made  to 
undergo  a  recoagulation  on  dilution  and  addition  of  the  ferment.  More- 
over, this  recoagulation  resembles  in  all  particulars  the  coagulation  which 
takes  place  in  muscle-plasma  ;  it  is  first  a  jelly  ;  the  jelly  contracts,  squeez- 
ing out  a  colorless  fluid ;  it  is  inhibited  by  cold,  occurs  most  readily  at 
the  temperature  of  the  body,  is  accompanied  by  the  formation  of  sarco- 
lactic  acid,  and  is  hastened  by  the  addition  of  myosin  ferment.  In  this 
particular  we  have,  also,  an  important  difference  between  the  coagulation 
of  blood  and  of  muscle.  Fibrin  cannot  be  reconverted  into  fibrinogen  in 


708  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

the  same  way  as  myosin  can  be  converted  into  myosinogen,  which  will 
again  coagulate  with  the  formation  of  myosin.  The  ease  with  which 
myosin  can  thus  be  made  to  clot  and  unclot  outside  the  body  might 
seem  to  be  a  confirmation  of  Hermann's  view  that  a  similar  clotting  and 
re-solution  of  myosin  accompanies  the  contraction  and  relaxation  of 
muscle  during  life ;  in  other  words,  that  each  contraction  is  the  partial 
death  of  a  muscle.  We  must  remember  that  the  most  important  simi- 
larity between  rigor  mortis  and  contraction  is  the  formation  of  sarcolactic 
acid,  and  not  the  development  of  a  clot  of  nryosin  ;  in  fact,  as  a  muscle 
becomes  more  extensible  during  contraction,  it  becomes  in  a  sense  more 
liquid,  not  more  solid,  as  it  does  when  myosin  is  formed  post-mortem. 

Dr.  Halliburton  further  suggests  that  the  passing  off'  of  rigor  mortis 
is  due  to  the  reconversion  of  myosin  into  myosinogen,  brought  about  by 
the  pepsin  present  in  muscle.  For  when  muscle  becomes  acid  in  rigor 
mortis  the  pepsin  which  it  contains  is  enabled  to  act,  and  at  the  suitable 
temperature  (35°-40°  C.)  albumoses  and  peptones  are  formed  by  a 
process  of  self-digestion.  This  is  a  more  satisfactory  explanation  of  the 
disappearance  of  rigor  mortis  than  putrefaction,  for  rigor  mortis  occa- 
sionally persists  after  putrefaction  has  set  in,  and  at  other  times  disap- 
pears within  an  hour  after  death. 

The  chemical  processes  continually  occurring  in  living  muscle  also 
undergo  change  on  the  death  of  the  muscle.  It  has  been  found  that  liv- 
ing muscle  is  continually  appropriating  oxygen  from  the  arterial  blood 
and  setting  free  carbon  dioxide.  In  the  death  of  the  muscle  the  absorp- 
tion of  oxygen  ceases,  while  the  exhalation  of  carbonic  acid  may  continue 
for  a  certain  time,  even  if  the  dead  muscle  be  placed  in  an  atmosphere 
free  from  oxygen  ;  it  is,  therefore,  evident  that  in  the  act  of  death  or  in 
the  production  of  rigor  mortis  some  complex  compound  is  split  up  and 
carbon  dioxide  set  free. 

Living  muscle  is,  then,  alkaline  and  contains  in  solution  in  the  sub- 
stance of  its  fibres  a  coagulable  proteid  in  the  muscle-plasma. 

Dead  muscle,  on  the  other  hand,  is  acid  in  reaction  from  the  devel- 
opment of  sarcolactic  acid,  and  the  coagulable  plasma  has  become  con- 
verted into  a  solid  myosin  in  muscle-serum.  When  muscles  are  sub- 
jected to  the  vacuum  of  a  mercurial  air-pump,  a  certain  amount  of  gas, 
which  is  almost  solely  CO8,  is  extracted,  which  has  been  in  part  dissolved 
in  the  muscle-plasma  and  in  part  combined  with  its  salts.  In  muscles  in 
which  rigor  mortis  has  not  taken  place,  2.74  volumes  per  cent,  of  CO2 
represent  the  free  gas,  1.95  per  cent,  the  fixed  gas.  If,  however,  rigor 
mortis  be  produced,  then  15  volumes  per  cent,  of  CO2  may  be  obtained. 
Therefore,  in  rigor  mortis  a  large  amount  of  C0a  becomes  free,  but  this 
is  not  due  to  the  decomposition  of  carbonates  by  the  acid  formed  in  the 
same  process.  So  also  in  muscular  contractions  there  is  an  increase  in 


PHYSIOLOGY  OF   MOVEMENT. 


709 


the  amount  of  CO2  in  muscles  capable  of  withdrawal  by  the  air-pump 
amounting  to  12.08  per  cent,  by  volume  of  the  muscle.  The  other  con- 
stituents of  the  muscle  are  represented  in  the  following  table  (Charles) : — 

ANALYSES  OP  MUSCLE. 


COMPONENTS  IN  100  PARTS. 

Mean  of 
Human 
Muscle. 

Mean  of 
Muscle 
of  Mam- 
mals. 

Muscle 
of 
Birds. 

Muscle 
of  Fish. 

Muscle 
of 

Frogs. 

Water,      

73.50 

72.87 

73.00 

74.08 

80.43 

Solids  coagulated,  

26.50 

27.13 

27.00 

25.92 

19.57  . 

Albumen  (rnyosin,  etc.)  and  other 

derivatives,  sarcolemma,  vessels, 

nerves,  etc.,  insoluble  in  water. 

Soluble   albumens  or   albuminates  : 

Haemoglobin,     .          ... 

1.84 

2.17 

3.13 

3.61 

1.86 

Fat,      

3.27 

3.71 

1.94 

4.59 

0.10 

Gelatin,     

1.99 

3.16 

1.40 

4.34 

2.48 

Kreatin  

0.22 

0.18 

0.33 

0.28 

'Ash,     

3.12 

1.14 

1.30 

1.49 

The  constituents  of  muscle  are,  therefore,  nitrogenous,  non-nitroge- 
nous, and  inorganic.  Under  the  former  group  occur  myosin,  alkali 
albuminate,  and  serum-albumen,  with  extractives  such  as  kreatin,  sarkosin, 
sarkin,  xanthin,  and  carnin. 

Of  the  non-nitrogenous  bodies,  inosite,  fat,  and  glycogen  are  the  most 
important,  while  phosphoric  acid,  potassium,  sodium,  magnesium,  and 
lime  are  the  principal  inorganic  constituents. 

(b)  Muscular  Irritability. — The  principal  physiological  difference 
between  living  and  dead  muscle  is  that  the  former,  under  the  action  of 
various  stimuli,  is  thrown  into  contraction.  This  property  of  contraction 
results  from  what  is  termed  irritability  of  the  muscle. 

If  the  spinal  cord  and  brain  of  a  frog  be  destroyed  the  animal  remains 
perfectly  passive,  without  any  contraction  occurring  in  any  of  its  muscles. 
If,  however,  an}'  stimulus,  mechanical,  electrical,  or  thermal,  be  applied  to 
its  muscles  they  at  once  shorten,  and  it  is  only  on  the  onset  of  rigor 
mortis  that  this  power  disappears.  If  the  stimulus  be  applied  to  a  motor 
nerve-trunk  a  similar  state  of  contraction  is  produced. 

In  the  destruction  of  the  central  nervous  system  the  peripheral 
nerve-branches  have,  of  course,  not  been  destroyed,  and  yet  the  contrac- 
tility of  muscle  is  not  dependent  upon  the  stimulation  of  nerve-fibres 
distributed  to  it,  for  muscle,  like  other  forms  of  protoplasm,  possesses 
an  independent  excitability.  This  may  be  demonstrated  by  a  number  of 
different  methods.  In  the  first  place,  various  chemical  stimuli,  such  as 
ammonia^  lime-water,  etc.,  do  not  produce  muscular  contraction  when 
applied  to  motor  nerves,  but  do  evoke  contraction  when  directly  applied 
to  muscle.  Again,  in  various  muscles  it  is  impossible  to  recognize  the 


710  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

presence  of  nerve-filaments,  as  in  the  extremes  of  the  sartorius  muscle  of 
the  frog,  and  yet  in  them  stimulation  applied  directly  to  a  muscle  pro- 
duces contraction.  The  most  conclusive  evidence,  however,  of  the  inde- 
pendent irritability  of  muscles  is  found  through  the  use  of  the  poison, 
curare. 

This  substance,  a  South  American  arrow -poison,  possesses  the  prop- 
erty of  entirely  paralyzing  the  terminal  filaments  of  the  motor  nerves. 
If  an  animal,  such  as  the  frog,  be  poisoned  with  this  drug,  stimuli  ap- 
plied to  the  motor  nerves  will  be  entirely  incapable  of  producing  muscular 
contraction.  The  same  stimulus,  however,  applied  direct^  to  the  muscle 
still  produces  a  characteristic  normal  contraction.  This  poison  acts,  not 
on  the  nerve-trunks,  but  on  the  intra-muscular  terminations  of  the  nerves. 
This  fact  may  be  demonstrated  by  ligating  the  sciatic  artery  in  one  hind 
leg  of  the  frog  and  injecting  curare  into  the  dorsal  lymph-sac.  The 
poisoned  blood  will  then,  of  course,  circulate  in  every  part  of  the  body 
with  the  exception  of  the  limb  in  which  the  circulation  has  been  arrested. 
If  a  stimulus  be  then  applied  to  the  sciatic  nerve  of  the  non-poisoned 
limb  it  will  still  succeed  in  calling  forth  a  contraction,  even  although  the 
sciatic  trunk  has  been  exposed  to  the  action  of  curare.  Stimulation  of 
the  sciatic,  on  the  other  hand,  in  the  limb  in  which  the  circulation  has 
been  maintained,  and  in  which,  of  course,  the  poison  has  had  access  to 
the  nerve-filaments  produces  no  contraction,  while  local  stimulation  of 
the  muscle  does. 

Muscular  contraction  may  be  produced  by  various  stimuli,  acting 
either  indirectly  upon  the  muscle  through  its  motor  nerve,  or  directl}- 
by  being  immediately  applied  to  the  muscle  substance. 

Muscular  stimuli  may  be  either  chemical,  thermal,  mechanical,  or 
electrical.  All  chemical  substances,  such  as  acids  and  various  metallic 
salts,  which  alter  the  composition  of  muscle  are  muscular  stimuli. 
Variations  of  temperature  also  produce  muscular  contraction.  Thus,  if 
an  excised  frog's  muscle  be  heated  rapidly  to  about  28°  C.,  contraction 
commences  and  reaches  its  maximum  at  45°  C.  If  the  temperature  be 
raised  above  this  point  the  muscle  passes  into  a  condition  of  heat-rigor, 
due  to  the  coagulation  of  the  proteids  of  muscle.  Sudden  mechanical 
stimuli,  whether  applied  directly  to  the  muscle  or  indirectly  to  the  nerve, 
if  repeated  with  sufficient  rapidity,  also  produce  contraction  of  muscle. 
Strong  local  irritation,  as  by  a  blow,  produces  a  long-continued,  weal- 
like  contraction  of  the  part  stimulated. 

(c)  Th,e  Phenomena  of  Muscular  Contraction. — Muscular  contraction 
consists  in  the  shortening  of  muscle-fibres  in  the  direction  of  their  long 
axes,  with  a  proportionate  and  simultaneous  increase  in  their  transverse 
diameter.  Such  a  contraction  is  accompanied  by  a  number  of  phenomena, 
of  which  the  most  evident  is  the  change  in  form. 


PHYSIOLOGY   OF   MOVEMENT. 


711 


When  a  single  induction  shock  is  allowed  to  pass  through  the  motor 
nerve  of  a  muscle,  the  muscle  at  once  gives  a  single  short  contraction. 
The  phenomena  of  such  a  muscular  contraction  may  be  best  studied  on 

IF 


FIG.  275.— THE  NERVE-MUSCLE  PREPARATION.    (Stirling.) 
F,  lower  third  of  femur ;  S,  sciatic  nerve ;  I,  tendon  of  gastrocnemius  muscle. 

the  gastrocnemius  muscle  of  the  frog.  Various  contrivances  have  been 
devised  for  graphically  representing  the  results  of  the  muscular 
contraction.  The  simplest  method  is  to  support  the  knee-joint  of 
a  frog's  leg  in  a  clamp,  connecting  the  tendon  of  the  gastrocnemius  by 


Pro.  276.— ARRANGEMENT  OF  APPARATUS  IN  CONDUCTING  EXPERIMENTS  ON 
NERVE  AND  MUSCLE.    (Stirling.) 

B,  galvanic  battery;  K,  electric  key  in  primary  circuit  ;  P,  primary  coil  of  induction  machine; 
S,  secondary  coil  of  induction  machine  from  which  the  current  is  conducted,  when  the  key,  K',  is  open,  to 
the  electrode,  E,  on  which  rests  the  nerve,  n  ;  the  muscle,  M,  is  supported  by  a  clamp,  under  a  glass  shade, 
its  tendon  being  connected  by  a  thread  with  a  lever,  L.  writing  on  the  smoked  surface  of  a  revolving 
drum.  The  time-marker,  TM,  is  included  in  the  primary  circuit,  so  that  when  the  current  passes  through 
P,  by  closing  the  key,  K,  it  also  traverses  the  electro-magnet  of  the  time-marker  and  causes  a  record  of 
the  instant  of  stimulation  to  be  made  on  the  surface  of  the  drum.  S,  stand  supporting  moist  chamber ; 
W,  weight  by  which  muscle  is  extended,  and  which  is  lifted  in  the  contraction. 

means  of  a  thread  to  a  lever,  which  records  its  movements  on  a  rapidly 
moving  surface.  If  a  single  induction  shock  is  then  passed  through  the 
sciatic  nerve  or  directly  applied  to  the  muscle  the  so-called  muscle 
curve  will  be  obtained  (Figs.  275  and  276). 


FIG.  277.— THE  PENDULUM  MYOGRAPH.    (Foster.) 

The  figure  is  diagrammatic,  the  essentials  only  of  the  instrument  being  shown.  The  smoked-glass  plate.  A.  swings 
on  the  "seconds"  pendulum,  B,  by  means  of  carefully  adjusted  bearings  at  C.  Before  commencing  an  experiment  the 
pendulum  is  raised  up  to  the  right,  and  is  kept  in  that  position  by  the  tooth,  a.  catching  on  the  spring-catch,  h.  On  depress- 
ing the  catch,  ft,  the  glass  plate  is  set  free,  swings  into  the  new  position  indicated  by  the  dotted  lines,  and  is  held  in  that 
position  by  the  tooth,  at,  catching  on  the  catch,  bt.  In  the  course  of  its  swing  the  tooth,  n>,  coming  into  contact  with  the  pro- 
jecting steel  rod,  c,  knocks  it  on  one  side  into  the  position  indicated  by  the  dotted  line,  ct.  The  rod,  c,  is  in  electric  con- 
tinuity with  the  wire,  x,  of  the  primary  coil  of  an  induction  machine.  The  screw,  d,  is  similarly  in  electric  continuity 
with  the  wire,  y,  of  the  same  primary  coil,  both  rod  and  screw  being  insulated  by  the  ebonite  block,'  e.  As  long  as  r.  and  d 
are  in  contact,  the  circuit  of  the  primary  coil  is  closed.  When  in  its  swing  the  tooth,  a>,  breaks  this  contact,  the  circuit 
is  broken,  and  a  "  breaking  "  induction  shock  is  sent  through  the  electrodes  connected  with  the  secondary  coil  of  the  induc- 
tion machine  to  the  nerve.  The  lever,  I,  is  connected  with  the  tendon  of  the  muscle,  and  is  brought  to  bear  on  the  glass 
plate,  and  when  no  muscular  contraction  is  produced  in  the  swing  of  the  pendulum  traces  a  straight  line,  or  rather  an 
arc  of  a  circle.  When  the  muscle  is  stimulated  during  the  swing  of  the  pendulum,  the  muscle  curve  is  produced.  The 
tuning-fork,  only  partly  shown,  serves  to  mark  the  rapidity  of  motion  of  the  pendulum. 


(712) 


PHYSIOLOGY   OF   MOVEMENT. 


715 


Such  a  curve  (as  produced  by  the  pendulum  myograph,  Fig.  277) 
is  represented  in  Fig.  278.  To  study  the  characteristics  of  such  a  curve 
more  fully  certain  additional  apparatus  is  necessary.  In  the  first  place, 
it  is  necessary  to  know  the  rate  of  motion  of  the  recording  surface. 
This  'may  be  accomplished  by  means  of  a  recording  tuning-fork  writing 
on  the  traveling  surface.  It  is  further  necessary  to  indicate  the  instant 
at  which  the  nerve  or  muscle  receives  the  stimulus.  This  may  be  done 
by  including  an  electro-magnet  writing  on  the  traveling  surface  in  the 
current  through  which  the  stimulus  to  the  muscle  passes.  If  the  curve 
be  examined,  it  will  be  noticed  that  the  muscle  does  not  commence  to 
shorten  instantaneously  with  the  entrance  of  the  stimulus  into  the  nerve, 
but  an  appreciable  interval  elapses  after  the  application  of  the  stimulus 
before  contraction  commences.  This  interval  is  termed  the  latent  period  r 
and  is  usually  about  one-seventieth  part  of  a  second.  The  duration  of 
the  latent  period  will  depend  upon  the  distance  through  which  the  stimulus 


FIG.  278.— MUSCLE  CURVE  OBTAINED  BY  MEANS  OP  THE  PENDULUM  MYO- 

GKAPH.     (Foster.) 
(To  be  read  from  left  to  right.) 

o  indicates  the  moment  at  which  the  induction  shock  is  sent  into  the  nerve  ;  b,  the  commencement ;  c, 
the  maximum ;  and  d,  the  close  of  the  contraction.  The  two  smaller  curves  are  due  to  oscillations  of  the 
lever.  Below  the  muscle  curve  is  the  curve  drawn  by  a  tuning-fork,  making  one  hundred  and  eighty 
double  vibrations  a  second,  each  complete  curve,  therefore,  representing  1-180  of  a  second. 

has  to  pass  through  the  nerve  before  entering  the  muscle.  If  the  elec- 
trodes be  moved  along  the  sciatic  nerve  farther  from  the  muscle,  the 
latent  period  will  be  increased.  If  moved  down  closer  to  the  muscle, 
or  applied  directly  upon  the  muscle,  although  not  absent,  the  "duration 
of  the  latent  period  will  be  greatly  reduced  (Fig.  279).  It  is,  therefore, 
evident  that  while  part  of  the  latent  period  is  consumed  in  the  conduc- 
tion of  the  stimulus  through  the  nerve,  yet  a  considerable  fraction  of 
it  is  taken  up  in  changes  in  the  muscle  itself  which  precede  active  con- 
traction, and  this  process  occupies  the  greater  portion  of  the  latent 
period. 

When  the  stimulus  or  induction  shock  is  applied  to  the  nerve 
the  latent  period  is  partly  due,  in  the  first  place,  to  the  production 
of  a  nerve  impulse  in  the  nerve;  and,  second,  the  progression  of  that 
impulse  through  the  nerve  to  the  muscle  ;  and,  third,  the  changes  already 
alluded  to  which  occur  in  the  muscle  itself. 


714 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


In  the  second  case  the  rate  of  transmission  of  the  nerve  impulse  has 
been  placed  about  twenty-eight  meters  per  second.  After  the  latent 
period  has  been  completed  the  muscle  then  commences  to  shorten,  at  first 
slowly  and  then  more  rapidly,  and  then  again  more  slowly  until  the 
maximum  shortening  is  reached,  the  duration  of  active  contraction  occu- 
pying about  the  one-twentieth  part  of  a  second.  As  soon  as  the  maxi- 


FIG.  279.— DIAGRAMMATIC  CUKVES  ILLUSTRATING  THE  MEASUREMENT  OF  THE 

VELOCITY  OF  A  NERVOUS  IMPULSE.    (Foster.) 

(To  be  read  from  left  to  right.) 

The  same  nerve-muscle  preparation  is  stimulated  (1)  as  far  as  possible  from  the  muscle,  i'2)  as  near  as 
possible  to  the  muscle,  both  contractions  being  registered  in  the  same  manner  on  the  pendulum  myograph 

In  (1)  the  stimulus  enters  the  nerve  at  the  time  indicated  by  the  line,  a ;  the  contraction,  shown  by  the 
dotted  line,  begins  at  b> ;  the  whole  latent  period  is,  therefore,  indicated  by  the  distance  from  a  to  bl. 

In  (2)  the  stimulus  also  enters  the  nerve  at  a,  the  contraction  begins  at  b,  and  is  shown  in  the  un- 
broken line ;  the  latent  period,  therefore,  is  indicated  by  the  distance  from  a  to  b.  The  time  taken  up  in 
the  passage  of  the  nerve  impulse  in  the  length  of  nerve  between  1  and  2  is  indicated  by  the  distance  be- 
tween b  and  bt,  and  may  be  measured  by  the  tuning-fork  curve  below.  The  distance  between  these 
curves  is  exaggerated  for  the  sake  of  simplicity,  no  value  being  given  for  the  rate  of  vibration  of  the 
tuning-fork. 

mum  contraction  is  reached  relaxation  commences,  following  the  same 
general  course  as  in  shortening,  relaxing  first  slowly  then  more  rapidty, 
and  then  more  slowly  again,  the  general  duration  of  the  active  relaxation 
being  somewhat  longer  than  that  of  contraction.  Such  are  the  general 
characteristics  of  the  curve  of  a  single  muscular  contraction  produced 
by  a  single  stimulus. 

If  a  single  stimulus  be  allowed  to  follow  the  first  it  will  be  followed, 


FIG.  280.— TRACING  OF  A  DOUBLE  MUSCLE  CURVE. 

(To  be  read  from  left  to  right.) 


(Foster.) 


While  the  muscle  was  engaged  in  the  first  contraction  (whose  complete  course,  had  nothing  intervened. 
is  indicated  by  the  lower  line  in  the  muscle-curve)  a  second  induction  shock  was  thrown  in  at  such  a  time 
that  the  second  contraction  began  just  as  the  first  was  beginning  to  decline.  The  second  curve  is  seen  to 
start  from  the  first,  as  does  the  first  from  the  base  line. 

like  the  first,  by  a  single  muscular  contraction.  If  the  interval  between 
the  second  and  first  muscular  contraction  be  gradually  reduced,  a  point 
will  ultimately  be  reached  in  which  the  second  stimulus  enters  the  nerve 
before  the  contraction  produced  by  the  first  has  passed  off.  The  result 
will  be  that  the  muscle  will  undergo  a  second  shortening,  and  such  a 


PHYSIOLOGY   OF   MOVEMENT. 


715 


curve  will  be  produced  as  is  represented  by  Fig.  279.  The  two  con- 
tractions are  thus  added  together  and  the  total  shortening  may  be  nearly 
double  that  produced  by  a  single  contraction  (Fig.  280). 

If  a  third  stimulus  is  then  allowed  to  pass  into  the  nerve  before  the 
second  contraction  has  passed  off,  a  third  contraction  will  be  added  to 
the  second,  and  so  on  in  the  case  of  the  fourth,  fifth,  or  more.  It  will 
be,  however,  noticed  that  while  the  second  contraction  may  be  nearl}7  or 
quite  as  extensive  as  the  first,  the  third  and  fourth  progressively  decrease 
in  extent,  until  finally  simply  a  broken  line  without  any  extensive  increase 
in  contraction  will  indicate  the  entrance  of  the  separate  stimuli,  the 
stimuli  merely  serving  to  keep  up  the  contraction  already  produced. 

When  the  stimulation  ceases  the  muscle  then  rapidly  passes  into  a 
condition  of  rest,  relaxation  occurring  very  rapidly. 


^      I 


FIG.  281.— MUSCLE  THROWN  INTO  TETANUS  WHEN  THE  PRIMARY  CURRENT  OF 
AN  INDUCTION  MACHINE  is  REPEATEDLY  BROKEN  AT  INTERVALS  OF  SIX- 
TEEN IN  A  SECOND.  (Foster.) 

(To  be  read  from  left  to  right.) 

The  upper  line  is  that  described  by  the  muscle.  The  lower  marks  time,  the  intervals  between  the  ele- 
vation indicating  seconds.  The  intermediate  line  shows  when  the  shocks  were  sent  in,  each  mark  corre- 
sponding to  a  shock.  The  lever,  which  describes  a  straight  line  before  the  shocks  are  allowed  to  fall  into 
the  nerve,  rises  almost  vertically  (the  recording  surface  moving  slowly)  as  soon  as  the  first  shock  enters  the 
nerve  at  a.  Having  risen  to  a  certain  height  it  begins  to  fall  again,  but  in  its  fall  is  raised  once  more  by 
the  second  shock,  and  that  to  a  greater  height  than  before.  The  third  and  succeeding  shocks  have  similar 
effects,  the  muscle  continuing  to  become  shorter,  though  the  shortening  at  each  shock  is  less.  After  a 
while  the  increase  in  the  total  shortening  of  the  muscle,  though  the  individual  contractions  are  still  visible, 
almost  ceases.  At  b  the  shocks  cease  to  be  sent  into  the  muscle,  the  contractions  almost  immediately  disap- 
pear, and  the  lever  forthwith  commences  to  descend.  The  muscle  being  only  slightly  loaded,  the  relaxa- 
tion is  very  slow. 

When  the  separate  stimuli  do  not  follow  each  other  more  rapidly 
than  sixteen  in  a  second,  the  contraction  produced  by  one  stimulus  has 
had  time  to  undergo  partial  relaxation  before  the  following  stimulus 
enters ;  as  a  consequence,  the  point  of  the  lever  traces  a  broken  line  on 
the  traveling  surface  (Fig.  281). 

If,  however,  the  stimuli  follow  each  other  more  rapidly  than  this,  an 
apparently  constant  shortening  is  produced,  in  which  no  variation  what- 
ever in  length  can  be  made  out.  The  gradual  production  of  this  state 
of  affairs  indicates  that  this  apparent^  constant  and  uniform  contraction 
is,  nevertheless,  made  up  of  a  large  number  of  individual  contractions 
added  to  each  other.  Such  a  condition  is  spoken  of  as  tetanus,  and  the 


716  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

curve  produced  in  such  a  tetanic  muscular  contraction  is  represented  ira 
Fig.  282. 

Tetanic  contraction  requires  for  its  production  at  least  a  greater 
number  than  sixteen  stimuli  per  second.  It  may  thus  be  most  readily 
produced  by  the  employment  of  a  rapidly  interrupted  induction  current.. 

Tetanus  may,  however,  also  be  produced  by  mechanical  stimulation,, 
provided  the  impulses  succeed  each  other  with  sufficient  rapidity.  In  the 
case  of  chemical  stimulation  tetanus  is  the  ordinary  expression  of  mus- 
cular contraction. 

It  is  thus  evident  that  the  tetanic  contraction  is  composed  of  a  series 
of  vibrations  of  the  muscular  fibre,  and,  as  would  be  expected  from  this 
statement,  is  accompanied  by  the  production  of  a  musical  note,  the  pitch 
of  the  note  depending  upon  the  number  of  vibrations  of  the  muscular 
fibre.  Wherever  the  muscle  is  artificially  thrown  into  tetanus,  as  by  the 
action  of  an  interrupted  induced  current,  the  number  of  vibrations, 
of  course,  corresponds  to  the  number  of  contractions,  these  depending 


a- 

FIG.  282.— TETANUS  PRODUCED  WITH  THE  ORDINARY  MAGNETIC  INTERRUPTER 
OF  AN  INDUCTION  MACHINE,  THE  RECORDING  SURFACE  MOVING  SLOWLY. 
(Foster.) 

(To  be  read  from  left  to  right.) 

The  interrupted  current  being  thrown  in  at  a,  the  lever  rises  rapidly,  but  at  b  the  muscle  reaches  the 
maximum  of  contraction.  This  is  continued  until  at  c,  when  the  current  is  shut  off  and  relaxation 
commences. 

upon  the  number  of  interruptions  of  the  current,  and,  as  a  consequence,, 
the  number  of  vibrations  of  the  muscle  and  the  corresponding  note  pro- 
duced have  a  pitch  which  corresponds  in  vibration  to  these  data. 

When  the  ear  is  placed  over  a  muscle  which  is  thrown  into  contrac- 
tion by  means  of  the  will  a  musical  tone  is  likewise  appreciated.  This 
serves  to  indicate  that  even  in  a  single  sharp  contraction  of  a  muscle 
through  the  action  of  the  will,  that  apparent  single  contraction  is  made 
up  of  a  number  of  contractions,  and  every  single  muscular  movement 
of  the  animal  body  is,  therefore,  of  the  nature  of  a  tetanus. 

The  musical  note  heard  indicates  that  the  rate  of  vibration  is  19.5 
per  second. 

We  may  now  study  the  changes  which  occur  in  contracting  muscle 
in  somewhat  more  detail.  The  most  obvious  is,  of  course,  the  change  of 
form.  Such  a  change  of  form  is  represented  by  a  decrease  in  the  long 
axis  of  a  muscle,  the  shortening,  perhaps  amounting  to  three-fifths,  of  the 
length  of  the  muscle,  with  a  corresponding  increase  in  the  cross  diameter. 


PHYSIOLOGY   OF   MOVEMENT. 


717 


There  is  no  actual  change  in  bulk  in  muscular  contraction,  the  increase  in 
thickening  being  almost  precisely  proportionate  to  the  decrease  in  length. 


This  fact  may  be  demonstrated  by  connecting  the  sciatic  nerve  of  a  frog's  leg 
with  the  poles  of  an  induction  machine  and  then  placing  the  leg  in  a  bottle  filled 
with  dilute  saline  solution,  in  the  stopper  of  which  is  inserted  a  capillary  tube, 
pare  should  be  taken  that  no  air-bubbles  are  present  in  the  bottle,  that  the  bottle 
is  filled,  and  that  the  fluid  ascends  up  a  certain  distance  in  the  capillary  tube.  If 
the  leg  is  then  thrown  into  contraction  by  passing  a  current  through  the  wires, 


718  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

the  level  of  the  fluid  in  the  capillary  tube  will  remain  almost  constant,  thus  indi- 
cating an  absence  of  change  in  the  bulk  of  muscle,  for  a  decrease  would,  of  course, 
be  indicated  by  a  fall  of  fluid,  and  increase  of  bulk  would  raise  the  fluid  in  the 
capillary  tube.  By  extremely  accurate  measurements  a  slight  actual  decrease  in 
volume  may  be  made  out.  Thus,  Valentine  has  determined  that  a  muscle  with  a 
volume  of  two  thousand  seven  hundred  and  six  cubic  centimeters  in  contraction 
in  tetanus  is  reduced  to  two  thousand  seven  hundred  and  four  cubic  centimeters, 
while  its  specific  gravity  increases  from  1061  to  1062. 

When  a  muscle  is  thrown  into  contraction,  it  does  not  occur  sim- 
ultaneously in  all  the  muscle-fibres.  If  a  muscle-fibre  be  placed  under  a 
microscope  and  then  thrown  into  contraction  a  wave  of  undulation  may 
be  seen  to  be  rapidly  propagated  from  one  end  of  the  fibre  to  the  other. 
This  wave  is  especially  sensible  if  the  muscular  fibre  is  fixed  at  each 
extremity.  If  a  long  muscle,  such  as  the  sartorius  of  the  frog,  have 
its  motor  nerve-filaments  paralyzed  by  curare,  and  the  muscle  then 
thrown  into  contraction  by  stimulating  one  extremity  with  an  induction 
current,  the  wave  of  contraction  travels  so  slowly  as  almost  to  be 
capable  of  being  seen  by  the  eye.  If  such  a  muscle  be  supported 


FIG.  284.— CURVE    ILLUSTRATING   THE  PROPAGATION    OF    THE  WAVE    OF 
MUSCULAR  CONTRACTION.    (Marcy.) 

The  lower  of  the  two  straight  lines  represents  the  point  of  the  lever  resting  on  the  muscle  nearest  the 
point  of  stimulation.  If  the  time  between  the  moment  of  commencing  contraction  at  this  spot  and  that  of 
commencing  contraction  at  the  spot  on  which  the  second  lever  rests  be  measured  by  counting  the  vibra- 
tions of  the  tuning-fork,  the  rate  of  progression  of  the  contraction  may  be  determined. 

horizontally  and  two  light  levers  be  placed  at  a  distance  from  each  other 
bearing  on  the  muscle  and  writing  over  each  other  on  a  recording  sur- 
face (Fig.  283),  if  the  muscle  be  then  thrown  into  contraction  by  direct 
stimulation  the  levers  will  not  be  elevated  simultaneously,  but  a  curve 
similar  to  that  represented  in  Fig.  284  will  be  produced.  By  measur- 
ing the  distance  between  the  commencement  of  these  two  contractions 
and  knowing  the  rate  of  movement  of  the  recording  surface,  the  rate 
of  progression  of  the  wave  ma}^  be  calculated.  If,  instead  of  stimulating 
the  muscle,  the  nerve  (in  such  an  experiment)  be  stimulated,  if  no  curare 
have  been  given  both  levers  will  be  simultaneously  elevated. 

According  to  Bernstein,  the  rate  of  progression  in  the  muscles  of 
cold-blooded  animals  of  the  wave  of  contraction  is  about  two  to  three 
meters  per  second.  Its  rate  of  progression  is  much  more  rapid  in  the 
case  of  warm-blooded  animals. 


PHYSIOLOGY   OF   MOVEMENT. 


719 


The  irritability  of  muscle  is  subject  to  great  variation,  and  a  single 
irritant  is,  under  different  circumstances,  capable  of  producing  different 
results.  In  an  excised  muscle  the  irritability  rapidly  disappears,  although 
it  persists  much  longer  in  the  muscles  of  cold-blooded  animals  than  in 
warm-blooded.  In  the  latter  case  the  irritability  of  warm-blooded 
muscles  may  be  somewhat  prolonged  if  the  animal  be  artificially  cooled 
before  death. 

Temperature  is  of  great  influence  on  the  irritability  of  muscle,  both 
an  increase  or  decrease  above  the  normal  temperature  of  the  muscle  being 
followed  by  a  decrease  in  irritability.     Again,  through  repeated  contrac- 
tion the  muscle  loses  its  power  of  being  thrown 
into  contraction ;  it  is  then  said  to  be  in  a  con- 
dition of  fatigue,  due  either  to  the  insufficient 
supply  of  nutritive  substances  or  to  the  accumu- 
lation of  the  products  of  decomposition,  which, 
as  has  been  experimentally  demonstrated,  pro- 
duce  a  hurtful  action  upon  the   muscle-fibres. 
In   all   probability   both   of  these   factors   are 
concerned  in  fatigue. 

When  a  contracting  muscle  is  examined 
under  the  microscope  marked  changes  in 
structure  may  be  made  out.  If  a  living  mus- 
cular fibre  of  an  insect,  for  example,  which  is 
especialty  fitted  for  such  study,  be  examined 
under  the  microscope  while  contracting,  a  wave 
of  contraction,  as  already  mentioned,  may  be 
seen  traveling  along  the  surface  of  the  fibre, 
while  at  the  same  time  the  transverse  striations 
approach  each  other.  In  the  contracted  portion 
each  disk  has  become  shorter  and  broader,  while 
the  band  which  in  a  relaxed  muscle  is  light, 
in  a  contracted  muscle  becomes  dark,  and  the 
band  which  in  a  relaxed  muscle  was  dark  in  the 
contracted  muscle  becomes  light  (Fig.  285). 

In  the  process  of  contraction  chemical  changes  occur ;  these  have 
been  already  to  a  certain  extent  indicated.  The  muscle  in  which  reaction 
was  alkaline,  in  contraction  becomes  acid  through  the  development  of 
sarcolactic  acid,  which  may  even  be  excreted  by  the  kidneys.  During  its 
contraction  the  muscle  absorbs  more  oxygen  from  the  blood  than  during 
its  stage  of  rest,  and,  as  a  consequence,  venous  blood  from  a  resting 
muscle  contains  8.5  per  cent.,  that  from  a  contracting  muscle  12.8  per 
cent,  less  oxygen  than  the  arterial  blood ;  while  the  venous  blood 
from  a  resting  muscle  contains,  as  an  average,  6.7  per  cent.,  that  from  a 


FIG.  285.— MUSCULAR  FIBRE 
UNDERGOING  CONTRAC- 
TION, AFTER  ENGL.E- 
MANN.  (Foster.) 

The  muscle  is  that  of  Telephorus 
melanurus  treated  with  osmie  acid. 
The  fibre  at  c  is  at  rest,  at  a  the  con- 
traction begins,  at  b  it  has  reached  its 
maximum.  The  right-hand  side  of 
the  figure  shows  the  same  fibre  as 
seen  in  polarized  light. 


720  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

contracting  muscle  10.8  per  cent,  more  carbon  dioxide  than  arterial  blood. 
The  amount  of  oxygen  consumed,  as  may  be  noticed  from  these  figures, 
bears  no  relationship  to  the  amount  of  carbon  dioxide  liberated  ;  whence 
it  follows,  as  already  stated,  that  the  formation  of  carbon  dioxide  in  a 
contracting  muscle  is  not  a  simple  process  of  oxidation,  but  rather  the 
splitting  up  of  some  complex  compound. 

During  contraction  the  glycogen  of "  the  muscles  becomes  reduced, 
while,  on  the  other  hand,  there  is  an  increase  in  the  amount  of  kreatin 
obtainable  from  the  contracted  over  that  found  in  the  resting  muscle. 

The  question,  What  is  the  source  of  the  carbon  dioxide  and  lactic 
acid  developed  by  a  contracting  muscle?  may,  perhaps,  be  answered  by 
the  statement  that  they  are  derived  neither  from  the  albuminous  nor  fatty 
constituents  of  the  muscle,  but  from  the  carbohydrates,  especially  from 
the  glycogen,  which  may  even  entirely  disappear  during  the  stage  of 
•contraction  of  a  muscle,  even  although  the  amount  of  nitrogenous  decom- 
position products  in  the  muscle  is  not  increased  and  the  amount  of  fat 
not  diminished.  From  the  greater  demand  of  oxygen  by  a  contracting 
muscle  we  find,  as  a  consequence,  a  greater  increase  in  the  supply  of  the 
arterial  blood  furnished  to  a  muscle  in  contraction. 

When  a  muscle  contracts,  its  arterioles  dilate,  more  blood  passes 
through  the  muscle,  and,  as  a  consequence,  the  removal  of  the  increased 
carbon  dioxide  formed  is  facilitated.  It  would  appear  from  this  that 
the  source  of  muscular  force  is  found,  not,  as  was  formerly  supposed,  in 
the  breaking  up  of  albuminoids,  but  in  the  chemical  changes  occurring 
in  muscle  which  are  evidenced  by  the  breaking  up  of  the  carbohydrates. 

This  statement  may  appear  contradictory  to  common  experience, 
which  teaches  that  animals  fed  with  albuminoids  do  more  work  than 
those  fed  on  a  diet  less  rich  in  albuminoids.  Our  studies  on  nutrition 
have,  however,  indicated  that  a  large  supply  of  albuminous  matter 
renders  possible  the  use  of  the  larger  amount  of  carbohydrates.  This 
will,  perhaps,  explain  the  fact  that  well-nourished  herbivora  are  able 
to  develop  more  force  than  the  apparently  much  more  powerful  carnivora, 
and  that  the  activity  of  muscle  does  not  increase  the  breaking  up  of 
albuminates  but  increases  the  elimination  of  carbon  dioxide.  The  few 
examples  in  which  muscular  work  is  accompanied  by  an  increased 
excretion  of  urea,  such,  for  example,  as  may  be  occasionally  seen  in  the 
horse,  are  only  to  be  accounted  for  by  the  insufficiency  of  the  quantity 
of  carbohydrates  administered  in  the  food,  this  insufficiency  necessi- 
tating a  destruction  of  the  proteids  for  the  development  of  force. 

As  might  be  supposed  from  the  above,  every  muscular  contraction  is 
accompanied  by  an  elevation  of  temperature.  Such  a  heat  production 
may  be  determined  experimentally  by  a  thermometer,  and,  in  a  general 
way,  it  may  be  stated  that  within  certain  limits  the  greater  the  work 


PHYSIOLOGY  OF  MOVEMENT.  721 

demanded  of  a  muscle,  in  other  words,  the  greater  the  resistance  to  be 
overcome,  the  greater  will  be  the  amount  of  heat  production ;  and,  as  a 
consequence,  in  a  contracting  muscle,  not  only  is  energy  liberated  but 
heat  is  developed,  which  is  capable  of  being  converted  into  actual  energy. 
The  heat  development  of  a  contracting  muscle  is  not  only  dependent 
upon  the  amount  of  work  done,  but  also  on  the  tension  of  the  muscle, 
and  the  heat  production  reaches  its  maximum  when  the  tension  exerted 
on  the  muscle  is  so  great  that  it  is  not  able  to  contract. 

Since  a  muscle  in  contracting  is  capable  of  lifting  a  weight,  it  is, 
therefore,  likewise  capable  of  accomplishing  work.  The  amount  of 
work  will  depend  upon  the  size  of  the  weight,  upon  the  distance  to  which 
the  weight  is  lifted,  and  upon  the  time  during  which  this  lifting  con- 
tinues. It  was  found  that  the  degree  of  contraction  was  proportionate 
to  the  degree  of  stimulation.  Therefore,  the  maximum  amount  of  work 
capable  of  being  produced  by  a  muscle  is  accomplished  when  the 
maximum  weight  is  lifted.  The  amount  of  work  which  a  muscle  may 
perform  is,  therefore,  equal  to  the  product  of  the  weight  lifted  and  the 
height  to  which  it  is  lifted  :  thus,  if  a  muscle  contracts  where  no  load  is 
present,  it  accomplishes  no  work;  or,  if  it  be  loaded  beyond  the  point  at 
which  the  load  may  be  lifted,  again  no  work  is  accomplished.  If 
the  weight  be  gradually  increased,  even  although  it  may  be  lifted,  the 
height  to  which  that  lift  is  accomplished  becomes  reduced,  and,  as 
a  consequence,  the  work  diminishes. 

The  amount  of  work  which  a  muscle  may  accomplish  is  greater  in 
proportion  to  the  transverse  section  of  the  muscle,  for  the  longer 
the  muscle  the  greater  is  the  shortening,  and,  accordingly, the  higher  the 
lift.  In  muscles  within  the  animal  body  the  amount  of  shortening 
which  they  may  attain  is  never  capable  of  reaching  the  maximum 
obtained  in  a  similar  excised  muscle.  The  force  with  which  a  muscle 
contracts  is  greater  at  the  commencement  of  contraction,  and,  when 
a  muscle  begins  to  contract,  it  can,  therefore,  lift  the  largest  load.  If  a 
muscle  loaded  with  a  weight  be  stimulated  with  a  rapidly  interrupted 
induction  current,  after  the  muscle  has  once  contracted  no  further 
lift  is  produced  and  no  external  work  is  evident;  but  if  the  muscle 
sustain  a  weight  at  the  height  to  which  it  raised  it,  the  amount  of  work, 
in  this  case  the  amount  of  energy  developed  by  the  prolonged  contrac- 
tion of  the  muscle,  is  converted  into  heat. 

When  a  muscle  is  stimulated  with  a  feeble  induced  current  and  the 
current  then  gradually  increased  in  strength,  it  will  be  found  that 
the  height  to  which  the  load  may  be  lifted  increases  with  the  strength 
of  the  stimulus. 

(d)  TKe  Electrical  Phenomena  in  Muscle. — If  the  gastrocnemius 
muscle  of  the  frog  be  excised  and  its  tendinous  insertions  cut  off,  and  two 

46 


722  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

points  of  this  surface,  or  the  longitudinal  surface  of  the  muscle  and  the 
transverse  section,  be  connected  by  non-polarizable  electrodes  with  a  sen- 
sitive galvanometer,  at  the  moment  of  making  the  contact  a  deflection 
of  the  galvanometer  needle  will  take  place,  indicating  the  presence  of  a 
galvanic  current.  The  strongest  effect  is  produced  when  one  point  of 
the  transverse  section  and  one  point  of  the  longitudinal  surface  are  con- 
nected with  a  galvanometer;  even  single  fibres,  nevertheless,  if  brought 
into  connection  with  a  galvanometer  also  develop  galvanic  currents.  The 
direction  of  the  current  is  from  the  longitudinal  section  through  the  con- 
ducting wires  to  the  transverse  section  ;  within  the  muscle  itself  the 
current  passes  from  the  transverse  to  the  longitudinal  section.  The 
nearer  the  one  electrode  is  to  the  equator  and  the  other  to  the  centre  of 
the  transverse  section  the  stronger  will  be  the  current,  while  the  current 
becomes  more  feeble  when  one  electrode  is  approached  to  the  outer  sur- 
face and  the  other  to  the  edge  of  the  transverse  section. 

The  existence  of  a  muscle  current  may  further  be  proved  by  an 
experiment  which  is  termed  the  rheoscopic  frog.  If  the  gastrocnemius 
muscle  of  a  frog  be  prepared  with  a  long  piece  of  sciatic  nerve  still  in 
connection  with  it,  and  the  end  of  the  nerve  be  placed  over  another 
excised,  fresh  gastrocnemius  muscle,  so  as  to  be  in  contact  with  its  trans- 
verse and  longitudinal  surfaces,  contraction  of  the  muscle  connected  with 
the  nerve  occurs  at  the  moment  of  contact.  A  single  contraction  is, 
however,  only  produced,  but  if  the  nerve  be  removed  from  the  muscle  a 
second  contraction  occurs ;  thus  pointing  out  that  the  current  circulating 
through  the  muscle  is  a  constant  current  and  may  serve  to  stimulate  other 
muscles  or  nerves  at  the  moment  of  breaking  and  making  the  contact. 
If  a  muscle  be  prepared  as  before,  connected  with  a  galvanometer,  and  be 
found  to  yield  a  strong  galvanic  current,  if  the  muscle  be  then  thrown 
into  tetanus  by  electrical  stimulation  of.the  muscle  itself,  or  of  its  motor 
nerve,  the  needle  of  the  galvanometer  will  be  found  to  swing  back  to 
zero,  indicating  the  disappearance  of  the  muscle  current;  such  a  state 
of  affairs  is  spoken  of  as  the  negative  variation  of  the  muscle  current. 

2.  THE  APPLICATIONS  OF  MUSCULAR  CONTRACTILITY. — The  contractility 
of  muscles  serves  especially  to  produce  changes  in  form  of  the  animal 
body  by  which  single  members  are  thrown  out  of  their  condition  of 
equilibrium  and  changes  of  location  in  the  animal  parts  thus  produced ; 
or  in  the  case  of  the  unstriped  muscles  to  diminish  the  capacity  of  the 
various  cavities  of  the  animal  body.  Hence,  muscles  may  be  classified 
into  two  different  groups  :  those  without  a  definite  origin  and  insertion, 
and  those  in  which  definite  origin  and  insertion  are  present.  To  the  first 
group  belong  the  hollow  muscles  surrounding  the  urinary  bladder,  gall- 
bladder, uterus,  heart;  intestinal  canal,  blood-vessels,  ureters,  etc.  In 
such  instances  the  muscular  fibres  are  unstriped  and  involuntary  and  are 


PHYSIOLOGY  OF  MOVEMENT.  723 

arranged  in  several  layers,  an  oblique,  circular,  and  longitudinal  layer 
being  in  nearly  all  cases  distinguishable ;  all  these  sets  of  fibres  acting 
simultaneously,  the  result  is  to  diminish  the  capacity  of  the  cavity  which 
they  inclose.  They  thus  aid  in  various  motions  of  animal  life,  such  as 
the  propulsion  of  the  blood  from  the  heart  and  in  assisting  its  onward 
passage  through  the  arteries,  the  evacuation  of  the  bladder  and  rectum, 
the  emptying  of  the  pregnant  uterus,  and  various  other  operations  which 
have  been  already  alluded  to.  In  addition  to  this  group  of  muscles,  the 
sphincters  likewise  have  no  definite  origin  or  insertion,  but  are  found  at 
the  various  openings  of  the  body,  whether  the  anus,  urethra,  or  mouth, 
and  several  other  localities.  The  muscular  fibres  of  the  sphincters  are 
circular,  and  by  their  contraction  serve  to  close  the  orifices  of  these 
several  openings. 

Of  the  muscJes  with  definite  origin  and  insertion,  either  the  origin  is 
fixed  or  both  origin  and  insertion  may  be  movable.  In  many  cases  be- 
longing to  the  former  of  these  groups  the  origin  is  only  fixed  during 
muscular  action;  thus,  in  the  case  of  the  palato-pharyngeal  muscles  their 
characteristic  action  is  only  rendered  possible  by  the  fixation  of  their 
origin  through  the  contraction  of  the  levator  palati  muscle. 

Again,  both  origin  and  insertion  may  be  movable,  the  part  moved 
being  usually  under  the  control  of  the  will.  Thus,  in  the  case  of  the 
sterno-mastoid  muscle,  through  its  contraction  the  head  may  be  depressed 
or  the  chest  elevated. 

Movement  of  the  animal  parts  or  of  the  entire  animal  body  is  ren- 
dered possible  through  the  manner  in  which  the  skeletal  muscles  are 
inserted  in  the  long  bones  by  which  lever  motion  is  possible,  the  bones 
being  regarded  as  levers,  the  joint  as  the  fulcrum,  the  insertion  of  the 
muscle  the  point  of  application  of  the  power,  and  the  centre  of  gravity 
of  the  bone  with  the  resistances  overcome  by  its  motion  as  the  load. 

Thus,  muscles  arising  in  one  bone  and  inserted  in  another  will,  in 
their  contraction,  either  move  both  bones  toward  each  other,  or,  if  one  be 
fixed,  will  approach  the  movable  to  the  fixed  bone.  From  the  definition 
of  the  power-arm  of  a  lever,  it  is  evident  that  in  general  the  direction  of 
muscles  relative  to  the  levers  on  which  they  act  is  very  disadvantageous, 
since  their  course  is  almost  always  more  or  less  parallel  to  the  bony  levers. 
This  parallelism  is  diminished  by  the  swelling  of  the  articular  extremi- 
ties and  by  the  development  of  more  or  less  marked  eminences,  such  as 
the  olecranon  or  the  trocanters,  or  by  the  presence  of  sesamoid  bones. 
In  movements  of  flexion,  however,  this  parallelism  becomes  diminished 
according  to  the  degree  of  flexion,  so  that,  therefore,  at  the  termination 
of  the  act  of  flexion  the  muscles  are  more  favorably  situated  for  the  de- 
velopment of  power.  Certain  muscles,  however,  such  as  the  muscles  of 
mastication,  the  flexors  of  the  head,  the  psoas  muscles,  and  the  abductors 


724 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


and  adductors  of  the  arm  have  their  insertion  almost  perpendicular  to 
the  bones  on  which  they  act. 

Although  all  three  classes  of  levers  are 
met  with,  in  general  the  lever  of  the  first  class 
comes  into  play  in  movements  of  extension,  and 
that  of  the  third  class  in  movements  of  flexion. 

A  lever  may  be  defined  as  an  inflexible  bar 
capable  of  being  freely  moved  about  a  fixed  point  or 
line,  which  is  called  the  fulcrum.  In  the  first  class 
of  lever  the  fulcrum  lies  between  the  weight  and  the 
power,  and  may  be  illustrated  by  a  common  crowbar 
or  a  pair  of  scissors.  In  levers  of  the  second  class 
the  weight  lies  between  the  fulcrum  and  the  power, 
and  may  be  illustrated  by  the  wheelbarrow  or  nut- 
cracker. In  the  third  class  of  lever  the  power  falls 
between  the  fulcrum  and  the  weight,  and  may  be 
illustrated  by  a  pair  of  fire-tongs  or  sheep-shears 
CFig.  286.) 


F 


A 


A 


A 


(l) 


(2) 


(3) 


FIG.  286.— THREE  CLASSES  OF  LEVERS.  (Landois.) 

W,  weight;  F,  fulcrum;  P,  power;  l,in  levers  of  first  class  the  fulcrnm 
is  between  the  power  and  the  weight ;  2,  in  levers  of  second  class  the  weight 
falls  between  the  power  and  fulcrum  ;  3,  in  levers  of  third  class  the  power  is 
applied  between  the  fulcrum  and  weight.  The  index  shows  the  direction  in 
which  the  power  acts. 


FIG.  287.— DIAGRAMS  SHOW- 
ING THE  MODE  OF  AC- 
TION OP  THE  THRKE 
ORDERS  OF  LEVERS, 
NUMBERED  FROM  ABOVE 
DOWNWARD,  ILLUS- 
TRATED BY  THE  ACTION 
OF  THE  ELBOW-JOINT. 
(Yeo.) 


In  considering  the  development  of  power  by  the  use  of  levers,  the  relation- 
ship between  the  power-  and  the  weight-arm  has  to  be  considered.     The  power- 


FIG.  288.— PARTIAL  COHTSACTIOIC  or  BICEPS.    (Perrier.) 

arm  of  the  lever  may  be  defined  as  the  perpendicular  distance  from  the  line  in 
which  the  power  acts  to  the  fulcrum  ;  the  weight-arm,  the  perpendicular  distance 


PHYSIOLOGY  OF  MOVEMENT. 


725 


from  the  line  in  which  the  weight  acts  to  the  fulcrum.  The  law  of  the  lever  may 
be  expressed  as  follows  :  A  power  will  support  a  weight  as  many  times  as  great  as 
itself  as  the  power-arm  is  times  longer 
than  the  weight-arm.  Thus,  for  ex- 
ample, in  a  lever  of  the  first  class,  if  we 
suppose  that  the  power-arm  be  ten 
times  as  long  as  the  weight-arm,  a 
weight  of  one  pound  at  the  extremity 
of  the  power-arm  will  support  a  weight 
of  ten  pounds  at  the  extremity  of  the 
weight-arm.  It  must  be  recollected, 
however,  in  the  case  of  the  lever,  as  in 
every  other  machine,  what  is  gained  in 


FIG.    289.— COMPLETE    CONTRACTION    OF 
BICEPS.    (Perrier.) 


FIG.  290.— MOTION  OP  HEAD  AS  ILLUSTRA- 
TING ACTION  OF  LEVER  OF  FIRST  CLASS. 
(  Beclar  d.) 

a,  fulcrum  of  the  lever,  c  b  ;  a  b  is  the  weight-arm,  for 
the  head  tends  to  fall  forward  by  its  own  weight  acting  ia 
the  line,  r.  This  U  prevented  by  the  contraction  of  the 
muscles  of  the  baelt  of  the  neck  acting  on  the  power-arm,  c  a, 
in  the  line,  F. 


power  is  lost  in  velocity,  artd  vice  versa.  Thus,  in  the  case  of  the  third  class  of 
lever,  power  is  exchanged  for  velocity.  This  may  be  well  represented  in  the 
movement  of  flexion  of  the  human  forearm  (Figs.  288  and  289).  The  fulcrum 
is  there  found  in  the  elbow-joint,  the  power  is  the  insertion 
of  the  biceps  muscles  in  the  bone  of  the  forearm  in  front  of 
the  joint,  the  weight  is  carried  by  the  hand.  In  this  arrange- 
ment it  is  evident  that  slight  motion  at  the  insertion  of  the 
biceps  will  be  greatly  multiplied  in  the  case  of  the  hand. 
Thus,  say  that  the  distance  from  the  elbow-joint  to  the  tip  of 
the  hand  is  eighteen  inches,  the  dis- 
tance from  the  elbow-joint  to  the 
point  of  insertion  of  the  biceps  one 
inch,  motion  of  one  inch  at  the  inser- 
tion of  the  biceps  will  produce  motion 
at  the  hand  of  an  arc  of  a  circle  whose 
cord  is  eighteen  inches  The  forearm 
is,  therefore,  in  this  action  an  example 
of  the  third  class  of  lever. 

In  general,  in  the  animal  body, 
the  point  of  application  of  the  power 
developed  by  muscular  contraction 
lies  near  the  fulcrum :  hence  the 
conditions  favor  the  production  of  velocity  of  movement  at  the  expense  of  power, 
for  the  power-arm  is  always  shorter  than  the  weight-arm. 

The  conditions  are,  however,  reversed  in  the  case  of  the  extensor  muscles  of 
the  limbs  when  in  contact  with  the  ground.  Here  the  joint  nearest  to  which  the 
muscle  is  inserted  is  the  point  of  application  of  the  weight,  and  the  fulcrum  is  the 


FIG.  291.— MOTION  ILLUSTRATING  ACTION   OF 
LEVERS  OF  THE  THIRD  CLASS.    (Btclard.) 

The  fulcrum  is  at  a,  the  power  from  contraction  of  gastroc- 
nemhu  muscle,  acting  in  the  line,  d  e,  la  applied  at  c,  while  the 
weight  (of  the  body)  aete  in  the  line,  o  b.  acia  thus  the  power- 
arm,  a  b  the  weight-arm. 


726  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

joint  above,  far  from  the  insertion  of  the  muscle.  Hence,  the  power-arm  is 
greatly  increased.  Thus,  in  the  horse,  while  the  foot  is  on  the  ground  in  the  con- 
traction of  the  extensors  the  point  of  application  of  the  weight  is  in  the  hock- 
joint,  the  point  of  application  of  the  power  in  the  caleaneum,  where  the  extensors 
are  inserted,  and  the  pastern -joint  the  fulcrum  ;  hence  the  power-arm  is  long,  and, 
although  motion  is  slow,  it  is  accompanied  by  a  corresponding  increase  in  power. 
If,  however,  the  hind  foot  is  not  on  the  ground,  but  is  extended  as  in  kicking,  then 
the  fulcrum  is  in  the  hock-joint,  and  the  power-arm  is  now  short  and  power  is 
exchanged  for  velocity. 

The  first  class  of  levers  may  be  represented  in  such  movements  as  in  nodding 
the  head,  where  the  fulcrum  is  the  articular  surface  of  the  atlas,  the  weight  being 
found  in  the  back  of  the  head  when  the  throat  muscles  contract,  in  the  front  of 
the  head  when  the  posterior  neck  muscles  contract  (Fig.  290).  Movement  due  to 
the  action  of  levers  of  the  second  class  is  seen  when  the  body  is  raised  up  on  tiptoe 
by  the  muscles  of  the  calf  (Fig.  291). 

All  three  orders  of  levers  may  come  into  play  in  the  action  of  the  human 
elbow-joint.  Thus,  the  first  class  is  illustrated  when  the  forearm  is  extended  on 
the  arm  through  the  contraction  of  the  triceps  muscles ;  in  this  instance,  the  hand 
is  the  weight,  the  elbow -joint  the  fulcrum,  and  the  insertion  of  the  triceps  in  the 
olecranon  the  power  (see  upper  diagram  Fig.  287). 

If  the  hand  rest  on  the  table  and  the  body  be  raised  on  it,  then  the  hand 
is  the  fulcrum,  the  triceps  is  the  power,  and  the  humerus,  at  its  articulation  in 
the  elbow-joint,  the  weight,  thus  illustrating  the  action  of  a  lever  of  the  second 
class  (see  middle  diagram  287).  The  third  order,  as  already  mentioned,  comes 
into  play  when  the  forearm  is  flexed  on  the  arm. 

In  the  horse  the  extensors  of  the  forearm  (A  Z>,  B  D,  and  G  D,  Fig. 
292)  act  as  levers  of  the  first  class,  the  power-arm  being  the  distance 
between  the  summit  of  the  olecranon  and  the  centre  of  the  humero- 
radial  articulation,  which  forms  the  fulcrum,  while  the  weight-arm  is 
represented  by  the  length  of  the  radius.  In  man  the  triceps  brachialis 
(B,  Fig.  293),  which  is  the  analogue  of  the  olecranon  muscles  of  quad- 
rupeds, acts  also  as  a  lever  of  the  first  class,  the  power-arm,  however, 
being  much  shorter  in  man.  In  the  posterior  extremity  of  the  horse 
(Fig.  294),  the  glutens  medius,  the  fascia  lata,  the  triceps  cruralis,  the 
Mfemero-calcaneus,  the  vastus  externus,  etc.,  are  also  examples  of  the 
first  class  of  levers.  In  the  case  of  the  gluteus  medius  (A  B,  Fig.  294) 
the  power-arm  is  the  distance  from  the  trochanter  to  the  centre  of  the 
acetabular  articulation,  which  is  the  fulcrum,  while  the  weight-arm  is  the 
length  of  the  femur.  For  the  gastrocnemius  the  power-arm  is  the 
distance  from  the  summit  of  the  caleaneum  to  the  centre  of  the  hock- 
joint,  which  is  the  fulcrum,  while  the  weight-arm  is  the  length  of  the 
metatarsus.  The  first  class  of  levers  is  thus  mainly  represented  by  the 
extensors. 

Levers  of  the  third  class  are  mainly  represented  by  the  flexors.  In 
the  anterior  extremity  of  the  horse  (Fig.  295)  the  infraspinatus,  the 
biceps  flexor,  the  metacarpal  flexor,  and  the  flexor  pedis  are  all  examples 
of  muscles  whose  action  operates  through  levers  of  the  third  class,  in 
each  instance  the  power  acting  between  the  fulcrum  and  the  weight.  In 
operations  of  levers  of  the  third  class  power  is  exchanged  for  velocity 
of  motion,  from  the  fact  that  tlie  power-arm  is  alwa}~s  shorter  than  the 


PHYSIOLOGY  OF  MOVEMENT. 


727 


weight-arm.  In  the  posterior  extremity  of  the  horse  (Fig.  296)  the 
superficial  gluteus  muscle  and  the  ischio-tibial  muscles  are  levers  of  the 
third  class. 

Levers  of  the  second  class  are  more  rarely  met  with.     In  the  horse 


FIG.    292.— ANTERIOR     Ex-      FIG.    293.— SUPERIOR      EX- 


TREMITY OF  THE  HORSE 
IN  EXTENSION.    (Colin.) 

AD,  BD,  and  CD.  lines  of  action 
of  the  triceps  extensor  brachii,  scapulo- 
•ulnaris,  and  aconeus  muscles.  E  F, 
flexor  brachii.  G  II,  line  of  action  of 
flexor  pedis  muscles. 


TREMITY  OF  MAN.  (Colin.) 

A  C,  line  of  action  of  the  biceps 
flexor.    B,  triceps  extensor. 


FIG.  294.— POSTERIOR  EX- 
TREMITY OF  THE  HORSE 
IN  EXTENSION.  (Colin.) 

AB,  line  of  action  of  gluteus 
medius.  C  D,  line  of  action  of  triceps 
extensor.  E  F,  line  of  action  of  gas- 
trocnemius.  Gil,  line  of  action  of 

metatarsal  flexor. 


the  gastrocnemius  acts  through  a  lever  of  the  second  class  when  the  foot 
is  in  contact  with  the  ground.  Then  the  fulcrum  is  at  the  point  of  con- 
tact of  the  foot  with  the  ground,  the  power-arm  is  the  distance  from 
the  calcaneum  to  the  ground,  the  weight-arm  the  distance  from  the 


728 


PHYSIOLOGY  OP  THE  DOMESTIC  ANIMALS. 


astragalo-tibial  articulation  to  the  ground,  and  the  resistance  is  the  weight 
of  the  body.  This  mode  of  action  of  the  gastrocnemius  is  more  evident 
in  man  (Fig.  297)  when  the  weight  of  the  body  is  raised  on  the  toes 
through  the  action  of  this  muscle.  In  the  anterior  extremity  of  quad- 
rupeds the  extensors  of  the  forearm  (A  D,  B  D,  and  C  D,  Fig.  292)  also 
act  through  levers  of  the  second  class  when  the  foot  is  on  the  ground, 


FIQ.  295.— THE  ANTERIOR  EXTREMITY 
OF  THE  HORSE  IN:  FLEXION.    (Colin.) 

A  B,  line  of  action  of  infraspinatus.  C  D,  line 
of  action  of  biceps  flexor.  E  F,  line  of  action  of 
metacarpal  flexor.  G  II,  line  of.  action  of  flexor 
pedis. 


FIG.  296.— POSTERIOR  EXTKEBIITY  OF 
THE  HORSE  IN  FLEXION.  (Colin.) 

A  B,  line  of  action  of  superficial  gluteus 
muscle.  C  D,  line  of  action  of  ischio-tibial 
muscles.  E  F,  line  of  action  of  metatarsal 
flexor.  G  H,  lines  of  action  of  flexors  of  foot. 


their  action  serving  then  to  flex  the  humero-radial  articulation,  instead 
of  extending  it,  as  occurs  when  they  act  with  the  foot  in  the  air. 

The  movements  of  the  different  parts  of  the  animal  body  depend 
upon  the  union  of  the  different  parts  of  the  skeleton  with  each  other  and 
the  mode  of  insertion  of  the  muscles.  The  movable  parts  of  the  skeleton 
are  designated  as  joints,  the  relative  positions  of  the  bones  forming  a 


PHYSIOLOGY  OF  MOVEMENT. 


729 


joint  being  determined  by  muscular  action ;  for  when  by  the  action  of 
muscular  force  the  positions  of  the  bones  are  changed,  the  original 
position  is  not  regained  in  the  cessation  of  that  force. 

The  form  of  the  joint,  in  which  two  bones  are  united  end  to  end,  is 
subject  to  considerable  variation,  depending  on 
and  governing  the  direction  in  which  the  move- 
ment may  take  place.  The  articular  extremities 
of  the  bone  are  covered  with  articular  cartilage, 
surrounded  by  closed  serous  sacs  containing 
a  serous  fluid,  the  synovia,  which  tends  to 
diminish  friction  between  the  movable  parts. 
Since  the  space  between  articular  surfaces  con- 
tains only  the  synovial  fluid,  it  ma}^  be  regarded 
as  a  vacuum,  and  atmospheric  pressure  is  itself 
sufficient  to  keep  the  articular  surfaces  in  con- 
tact, even  sustaining  the  entire  weight  of  the 
limbs  and  thus  sparing  muscular  action.  The 
movement  between  the  joint  ends  is  not  only 
governed  by  the  character  of  the  joint,  which 
we  will  find  may  be  resolved  into  several  differ- 
ent types,  but  is  further  restricted  by  the  cap 
sular  ligament  which  holds  the  joints  in  appo- 
sition and  by  the  tendinous  bands  which 
surround  them,  in  all  cases  only  those  move- 
ments being  possible  in  which  the  articular 
surfaces  remain  in  contact. 

The  articulations  are  divided  into  three 
classes :  the  immovable  articulations,  or  the 
synarthroses ;  the  mixed,  or  amphiarthroses ; 
and  the  movable,  or  diarthroses. 

To  the  first  class  belong  the  sutures  and 
other  articulations  where  the  surfaces  of  the 
bones  are  in  almost  direct  contact,  not  sepa- 
rated by  a  synovial  cavity,  and  immovably 
connected  with  each  other.  In  the  second  class 
the  osseous  surfaces  are  connected  together  ^ 
by  disks  of  fibro-cartilage,  as  between  the  bodies 

AB  C,  line  of  action  of  biceps  flexor. 

of  the  vertebrae,  or  the  articulating  surfaces  are   (A  !eyer  of  third  class.)   E,  gastroc- 

nemius. 

covered   with   fibro-cartilage,   partly   lined    by 

synovial  membrane,  and  bound  together  by  external  ligaments,  as  in  the 

sacro-iliac  and  pubic  symphyses. 

The  third  class  includes  the  greatest  number  of  joints  in  the  animal 
bod}',  and  as  mobility  is  their  distinguishing  characteristic  they  are  the 


ITY  OF  MAN. 


EXTREM- 

(Colin.) 


730  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

only  ones  with  which  we  are  concerned.  Four  different  varieties  of  this 
form  of  joint  have  been  described,  according  to  the  kind  of  motion 
permitted  in  each. 

a.  The  Rotatory  Joint,  or  Diartlirosis  Eotatoria. — In  this  class  of 
joint  the  movement  is  limited  to  rotation,  the  joint  being  formed  by  a 
pivot-like  process  turning  within  a  ring  or  the  ring  on  the  pivot,  the  ring 
being  formed  partly  of  bone  and  partly  of  ligament.     The  articulation 
of  the  atlas  and  the  occiput  is  an  example  of  such  a  joint.    In  the  elbow- 
joint  a  similar  rotatory  articulation  is  met  with,  where  in  the  radio-ulnar 
articulation  the  ring  is  formed  by  the  lesser  sigmoid  cavity  and  the  orbicular 
ligament  while  the  head  of  the  radius  rotates  within  the  ring.     Only  in 
animals  in  whom  pronation  and  supination  of  the  hand  are  possible  does 
this  movement  occur ;  it  is,  therefore,  absent  in  the  horse  and  ox.     In 
general,  it  may  be  said  that  in  animals  provided  with  the  clavicle  this 
motion  of  supination  and  pronation  is  usually  present. 

b.  The  Ball  and  Socket  Joint,  or  the  Enarthrosis. — In  this  joint  motion 
in  all  directions  is  possible,  and  it  is  formed  by  the  reception  of  the 
globular  head  of  a  long  bone,  into  a  deep,  cup-like  cavity,  hence  called 
ball  and  socket,  the  parts  being  kept  in  apposition  by  a  capsular  ligament 
and   accessory  ligamentous  bands.     The  hip-  and  shoulder-  joints  are 
examples  of  this  class. 

c.  The  Hinged  or  Ginglymous  Joint. — In  this  form  motion  is  only 
possible  in  one  plane  and  only  in  two  directions,  forward  and  backward, 
the  articular  surfaces  being  moulded  to  each  other  in  such  a  way  that  a 
solid  cylinder  moves  within  a  greater  or  lesser  segment  of  a   hollow 
cylinder.     The  joint  between  the  ulna  and  the  humerus  is  a  most  perfect 
example  of  a  ginglymous  joint,  while  the  joints  between  the  phalanges 
and  between  the  inferior  and  superior  maxillary  bones  of  the  carnivora 
are  other  examples.     The  pastern-joint  of  the  horse  is  a  modified  form 
of  this  joint  and  is  often  spoken  of  as  a  screw-joint. 

d.  The  Gliding  Joints,  or  the  Arthrodia. — In  this  class  motion  of  a 
gliding  character  takes  place.    Such  joints  are  formed  by  the  approxima- 
tion of  plane  surfaces,  or  one  slightly  concave,  the  other  slightly  convex, 
movement  between  them  being  limited  by  the  ligaments  or  the  osseous 
processes   surrounding   the   articulation.      Such  articulations  are  seen 
between  the  vertebra,  metatarsal  and  tar  sal  bones,  and  others. 

The  forces  which  move  the  joints  are  found  in  the  contraction  of 
striped  muscular  fibres.  The  extent  of  contraction  for  which  the  muscle 
is  capable  depends  upon  its  length,  and  therefore  we  speak  of  long  and 
short  muscles.  A  muscle  whose  function  it  is  to  bring  its  points  of 
origin  and  insertion  nearer  to  each  other  must  necessarily  be  a  long 
muscle,  while  the  muscles  whose  contraction  only  leads  to  slight  change 
of  place  are  usually  short  muscles.  It  will  always  be  found  that  the 


PHYSIOLOGY   OF   MOVEMENT.  731 

length  of  the  muscle-fibre  corresponds  to  the  degree  of  movement  which 
the  muscle  has  to  produce.  It  does  not  necessarily  follow  that  a  muscle 
whose  points  of  origin  and  insertion  are  widely  separated  should  be  a 
long  muscle,  since  the  interval  between  these  two  points  may  be  largely 
taken  up  by  tendons. 

3.  ANIMAL  LOCOMOTION. — The  essential  factor  for  animal  locomotion 
consists  in  the  movement  of  the  centre  of  gravity  of  the  body.  By  the 
term  "  the  centre  of  gravity  "  is  understood  the  point  about  which  all 
the  matter  composing  the  body  may  be  balanced.  The  attraction  of 
gravit}'  tends  to  draw  every  particle  of  matter  downward  in  a  vertical 
line.  The  factors  of  this  force  may  be,  therefore,  regarded  as  the  sum  of 
an  almost  infinite  number  of  parallel  forces,  each  of  which  is  acting  upon 
one  of  the  molecules  of  which  that  body  is  composed.  Just  as  the 
resultant  of  the  force  exerted  by  two  horses  harnessed  to  a  swingle-tree 
is  equal  to  the  sum  of  the  forces  exerted  by  the  horses  but  applied  at  a 
single  point  at  or  near  the  centre  of  the  swingle-tree,  so,  also,  the  sum 
of  the  forces  of  gravity  may  be  regarded  as  acting  upon  a  single  point 
which  is  near  the  centre  of  gravity  of  that  body.  In  other  words,  the 
weight  of  the  body  may  be  considered  as  concentrated  at  the  centre  of 
gravity.  When  the  centre  of  gravity  is  supported  the  whole  body  will 
be  in  a  state  of  equilibrium ;  or  when  the  line  of  direction  of  the  force 
of  gravity,  which  is  thus  a  vertical  line  passing  through  the  centre  of 
gravity,  falls  within  the  base  of  the  bod}',  or  base  on  which  the  body 
stands,  it  is  then  said  to  be  stable. 

In  all  regular  bodies  the  centre  of  gravity  will  coincide  with  the 
central  point,  while  in  irregular  bodies  it  will  be  nearest  to  that  part  in 
which  the  greatest  weight  is  concentrated.  As  the  centre  of  gravity  of 
the  animal  body  is  within  the  body  it  can  be  directly  supported.  The 
stability  of  the  body  will  be  greater  the  broader  the  base  and  the  nearer 
the  centre  of  gravity  to  the  support.  The  animal  body  when  standing  is, 
however,  only  at  best  in  a  state  of  unstable  equilibrium ;  for  when  slightly 
displaced  from  its  position  of  equilibrium,  it  tends  to  fall  still  farther 
from  that  position,  owing  to  the  fact  that  the  disturbance  has  lowered 
the  centre  of  gravity,  and  equilibrium  is  not  restored  until  it  reaches  its 
lowest  possible  point.  An  animal  in  a  recumbent  position  is  in  a  state 
of  neutral  equilibrium  ;  when  its  position  is  changed  it  tends  neither  to 
return  to  its  former  position  nor  to  fall  farther  from  it.  Stable  equi- 
librium is  when  a  bod}'  is  so  supported  that  when  slightly  displaced  from 
its  position  of  equilibrium  it  tends  to  return  to  that  position.  Such  a 
condition  can  only  occur  when  displacement  raises  the  centre  of  gravity. 
The  pendulum  is  an  example  of  stable  equilibrium. 

Standing  is  thus  a  condition  of  unstable  equilibrium  in  which  the 
centre  of  gravity  is  supported  from  the  fact  that  the  line  of  direction 


732  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

falls  within  the  base  of  the  figure.  The  mechanism  of  standing  differs  in 
bipeds  and  quadrupeds.  In  man  the  centre  of  gravity  lies  within  the 
pelvis,  about  one  and  a  half  millimeters  in  front  of  the  promontory  of  the 
sacrum.  In  the  erect  attitude  of  man  the  feet  are  directed  outward 
(forming  an  angle  of  about  fifty  degrees),  so  increasing  the  base  of 
support,  the  heels  touching,  the  knees  extended,  the  thighs  rotated 
externally,  and  the  pelvis  and  trunk  bent  slightly  backward,  the  arms 
hanging  at  the  side. 

In  the  act  of  standing,  the  body  not  being  rigid,  balancing  must 
be  aided  by  the  assistance  of  the  contraction  of  various  muscles.  In  a 
certain  number  of  joints  the  action  of  ligaments  in  the  erect  position 
assists  the  maintenance  of  the  upright  posture  ;  thus,  in  the  attitude 
already  described,  where  the  knees  are  extended  to  the  utmost,  the 
trunk  thrown  back,  and  the  head  balanced,  the  anterior  hip-ligaments 
are  rendered  tense,  and  the  knee-  and  hip-joint  remained  fixed  without 
&i\y  etfort  upon  the  part  of  the  joint-muscles.  In  the  position  known  as 
"  standing  at  ease"  the  weight  of  the  body  rests  mainly  on  one  leg,  the 
other  forming  simply  a  support  to  assist  the  muscles  around  the  support- 
ing ankle.  In  this  position  the  joints  are  not  kept  locked  by  the  tension 
of  the  ligaments,  for  the  pelvis  is  now  somewhat  oblique,  so  as  to  bring 
it  directly  over  the  head  of  the  femur.  Varying  tension  in  the  muscles 
serves  to  preserve  the  balance  and  prevent  fatigue.  In  the  erect  posture 
the  ankle  supports  the  weight  of  the  body;  the  line  of  gravity  falling 
slightly  in  front  of  the  axis  of  rotation  of  the  ankle-joint,  the  tendency 
is  thus  for  the  body  to  fall  forward  at  the  ankles;  this  is,  however, 
checked  by  the  calf-muscles,  which  keep  the  parts  nearly  in  position  of 
exact  equilibrium.  In  the  erect  position,  the  ankle-joint  being  neither 
flexed  nor  extended  to  the  utmost  forward  or  backward,  motion  must  be 
prevented  by  muscular  contraction.  Lateral  motion  at  the  ankle-joint 
is  prevented  by  the  malleoli.  When  the  knee-joint  is  completely  ex- 
tended no  muscular  action  is  required  to  prevent  it  from  bending,  be- 
cause the  line  of  gravity  then  passes  in  front  of  the  axis  of  rotation  and 
the  weight  of  the  body  tends  to  bend  the  knee  backward.  Although  the 
ligaments  which  exert  their  contraction  behind  the  axis  of  rotation  tend 
to  render  this  impossible,  ordinarily  the  position  is  maintained  by  mus- 
cular action  so  exerted  that  the  line  of  gravity  passes  slightly  behind 
the  axis  of  the  knee,  the  tendency  thus  produced  of  the  knee  to  bend 
being  checked  by  the  extensor  muscles  of  the  thigh. 

In  the  hip-joint  the  line  of  gravity  falls  behind  the  line  uniting  the 
joint.  When  the  person  is  erect,  the  tendency  thus  produced  of  the 
body  to  fall  backward  is  prevented  by  the  ileo-femoral  ligament.  If, 
however,  the  knee  is  not  extended  to  the  full  extent  the  line  of  gravity 
passes  a  little  behind  the  axis  of  rotation  of  that  joint,  and  the  pelvis 


PHYSIOLOGY  OF  MOVEMENT.  733 

being  slightly  flexed  on  the  femora,  the  axis  of  the  joint  lies  a  little 
behind  the  line  of  gravity,  and  the  inclination  thus  produced  to  fall 
forward  is  prevented  by  the  glutei  muscles,  which  are  likewise  concerned 
in  regaining  the  erect  posture  after  bending  the  trunk  forward.  The 
motions  between  the  pelvis  and  vertebrae  are  practical^  so  slight  as  to  be 
disregarded,  and  the  vertebral  column,  with  the  exception  of  the  motions 
existing  between  the  head  and  the  upper  cervical  vertebrae,  may  be  re- 
garded as  a  rigid  column.  Between  the  occiput  and  atlas  lateral  and 
rotatory  motions  are  "possible  to  a  considerable  extent,  so  that  balancing 
the  head  is  rendered  possible  only  by  co-ordinated  muscular  contractions, 
since  no  ligaments  are  present  which  can  fix  the  occipito-atlantoid  artic- 
ulation. 

Sitting  is  that  position  of  equilibrium  where  the  body  is  supported 
on  the  tubera  ischii.  The  line  of  gravity  may  pass  either  in  front  of  the 
tubera  ischii,  in  which  the  body  must  be  supported  by  some  fixed  object, 
or  the  line  of  gravity  may  fall  behind  the  tubera  in  the  backward  pos- 
ture, in  which  case  falling  backward  may  be  prevented  by  leaning  upon 
a  support  or  by  the  counter-weight  of  the  extended  legs.  In  sitting 
erect  the  line  of  gravity  falls  between  the  tubera  themselves,  and  but 
slight  muscular  action,  such  as  is  required  in  the  balancing  of  the  head, 
is  sufficient  to  maintain  equilibrium. 

In  quadrupeds  the  four  limbs  act  like  four  columns,  as  in  a  chair  or 
table,  in  supporting  the  centre  of  gravity  of  the  body,  so  that  the  base 
of  support  is  a  parallelogram  whose  corners  are  represented  by  the  point 
of  contact  of  the  feet  with  the  ground,  and  which  is  about  four  times  as 
long  as  it  is  broad.  In  consequence  of  the  greater  base  of  support,  equi- 
librium is  more  readily  preserved  in  quadrupeds  than  in  bipeds.  The 
centre  of  gravity  in  the  large  quadrupeds,  such  as  the  horse,  ox,  etc.,  lies 
at  the  intersection  of  a  line  passing  vertically  behind  the  xyphoid  carti- 
lage and  one  passing  horizontally  through  the  end  of  the  second  third 
of  the  sterno-vertebral  diameter.  In  the  small  quadrupeds,  such  as  the 
dog,  the  centre  of  gravity  is  located  somewhat  more  anteriorly.  From 
the  fact  that  the  centre  of  gravity  lies  below  the  vertebrae  in  quadrupeds, 
in  the  erect  position  the  tendency  of  the  weight  at  the  centre  of  gravity 
is  to  curve  the  vertebral  column  inward.  This  is  prevented  by  both  mus- 
cular action  and  ligamentous  support.  The  fore  extremities  and  scapula 
are  only  attached  to  the  trunk  through  muscular  and  ligamentous  con- 
nections which  are  continually  on  a  stretch  and  so  serve  to  render  the 
shoulder-blade  immovable,  while  by  means  of  the  greater  serrati  muscles 
the  trunk  is  supported  as  in  a  sling,  so  that  it  cannot  be  pushed  forward 
against  the  shoulder-blade.  In  the  posterior  extremities  the  relationships 
differ  in  that  the  single  bones  are  not,  as  in  the  fore  extremities,  verti- 
cally over  each  other.  Here,  also,  the  erect  oosition  is  maintained  through 


734  PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 

muscular  action.  When  the  body  is  uniformly  supported  on  all  four 
extremities,  in  the  fore  limbs  the  line  of  direction  passes  from  the  shoulder 
through  the  centre  of  the  elbow-joint  in  the  axis  of  the  forearm,  through 
the  centre  of  the  knee-joint  in  the  axis  of  the  ulna,  through  the  centre 
of  the  pastern-joint  perpendicular  to  the  ground  behind  the  ball  of  the 
foot.  Three  principal  angles  are  thus  formed  whose  degree  depends 
partly  on  the  angle  between  the  scapula  and  vertebrae  and  partly  on  the 
relative  lengths  of  the  different  bones. 

In  the  case  of  the  anterior  extremity  the  line  of  direction  of  the 
lower  bones  is  almost  vertical,  but  in  the  case  of  the  upper  bones  becomes 
considerably  inclined  ;  thus,  the  scapulo-humeral  angle  tends  constantly 
to  become  smaller  and  smaller  on  account  of  the  depression  of  the 
superior  extremity  of  the  scapula  and  by  the  projection  anteriorly  of 
the  scapulo-humeral  articulation.  This  depression  and  projection  are 
hindered  by  the  action  of  numerous  muscles.  The  most  important 
muscle  concerned  in  the  fixation  of  the  upper  extremity  is  the  serratus 
magnus,  which,  arising  in  numerous  fan-shaped  bundles  from  the  five 
posterior  cervical  vertebrae  and  the  first  eight  ribs,  converges  to  be 
inserted  in  the  ventral  surface  of  the  scapula.  This  muscle,  with  its 
fellow,  serves  as  a  muscular  sling  in  which  the  body  is  supported 
between  the  fore  limbs,  the  axis  of  motion  of  the  shoulder-blade  pass- 
ing through  its  insertion  in  the  scapula. 

The  superior  extremity  of  the  scapula  is  sustained  by  the  rhomboid 
muscles,  which  draw  it  upward,  as  well  as  by  the  trapezius,  which  tend  to 
elevate  and  advance  this  bone,  so  opposing  the  depression  of  the  scapula 
through  the  weight  of  the  trunk.  These  muscles  thus  give  fixity  to  the 
scapula.  Further,  the  anterior  projection  of  the  scapulo-humeral  angle 
is  prevented  by  the  greater  and  lesser  pectoral  muscles,  which  by  their 
contraction  tend  to  retract  this  angle.  The  obliquity  of  the  humerus 
tends  to  become  exaggerated  during  standing  as  well  as  at  each  act  of 
striking  the  foot  upon  the  ground.  The  pectoralis  major  and  the  infra- 
spinalis  muscles,  as  well  as  the  coraco-radii,  tend  to  prevent  this,  the  latter 
muscle  being  especially  efficacious,  acting  not  only  as  a  muscle,  but  a 
band  of  unyielding  tendinous  material  running  through  it  enables  it  to 
act  as  a  ligament  preventing  exaggerated  flexion  of  the  humerus  on  the 
shoulder.  That  the  coraco  radii  should  fulfill  this  function  it  is  neces- 
sary that  its  insertion  in  the  inferior  extremit}7  should  be  fixed.  This 
fixity  is  accomplished  by  the  five  olecranon  muscles.  At  the  elbow-joint 
the  lower  end  of  the  humerus  is  fixed  by  the  strong  lateral  ligaments ; 
reduction  of  the  elbow  angle  being  prevented  by  the  fixation  of  the 
olecranon  through  the  contraction  of  the  extensors  of  the  forearm, 
and  anterior  deviation  by  the  tendinous  expansion  of  the  long  flexor  of 
the  forearm,  its  tension  increasing  with  the  weight  on  the  shoulder. 


PHYSIOLOGY  OF  MOVEMENT. 


735 


Below  the  humerus  the  bones  lie,  with  the  exception  of  the  phalanges, 
in  an  almost  vertical  line,  flexion  being  prevented  by  the  five  extensors 
of  the  forearm.  The  metacarpus  continues  the  vertical  column  of  which 
the  forearm  forms  the  superior  segment,  its  flexion  being  prevented  by 


Q 


FIG.  298.— ANTERIOR  EXTREMITY  OF  THE 
HORSE  IN  EXTENSION.    (Colin.) 

AD,  BD,  and  C  D,  lines  of  action  of  the  triceps  exten- 
sor brachii,  scapulo-ulnaris,  and  aconeus  muscles.  E  F, 
flexor  brachii.  G  H,  line  of  action  of  flexor  pedia  mus- 
cles. 


FIG.  209.— POSTERIOR  EXTREMITY  OF  THE 
HORSE  IN  EXTENSION.    (Colin.) 

AB,  line  of  action  of  glutens  medius.  CD,  line  of 
action  of  triceps  extensor.  E  F,  line  of  action  of  gas- 
trocnemius.  G  If,  line  of  action  of  metatarsal  flexor. 


the  extensor  inserted  in  its  carpal  extremity,  and  which  receives  in  about 
the  middle  of  its  fleshy  belly  an  aponeurotic  cord  fixed  superiorly  to  the 
external  tuberosity  of  the  humerus.  In  the  phalangeal  region  the  direc- 
tion of  the  bony  support  now  becomes  oblique,  and,  while  its  obliquity 


736  PHYSIOLOGY  OF  THE   DOMESTIC   ANIMALS. 

constantly  tends  to  become  exaggerated  by  the  weight  which  the  upper 
extremity  supports,  it  never  passes  certain  limits  on  account  of  the  pres- 
ence of  the  spiral  ligament  of  the  pastern-joint.  Without  this  ligamentous 
support  muscular  action  would  be  insufficient  to  prevent  extreme  flexion, 
but  by  means  of  the  ligament,  which  in  the  horse  and  ruminant  is  composed 
of  powerful  non-elastic  tendinous  fibres,  represented  in  the  carnivora  by 
muscular  fibre,  the  support  of  the  body  is  rendered  possible  without 
fatigue. 

In  the  case  of  the  posterior  limbs  great  deviation  from  the  vertical 
is  met  with,  and  that  their  obliquity  should  be  restrained  within  certain 
limits  considerable  muscular  effort  is  required  and  the  mechanical  dispo- 
sitions of  the  power  is  more  complex  (Fig.  298)  than  in  the  case  of  the 
thoracic  members.  In  the  hind  leg  four  angles  are  met  with,  viz. :  in 
the  hip-joint,  the  knee-joint,  the  hock-joint,  and  the  pastern-joint,  the 
degree  of  these  angles  being  governed  by  the  angle  which  the  axis  of  the 
femur  makes  with  the  vertebrae  and  the  position  in  which  the  hind  foot 
is  placed.  In  the  resting  position  of  the  hind  extremity  the  line  of  direc- 
tion of  the  body  weight  passes  from  the  centre  of  the  hip-joint  vertically 
downward  to  the  centre  of  the  hock-joint,  and  then,  deviating  about  10° 
from  the  direction  of  the  metatarsus,  passes  behind  the  pastern-joint 
to  the  ground.  The  pelvis  is  very  oblique  relatively  to  the  trunk  in  the 
horse,  ox,  and  most  ruminants  and  carnivora.  The  femur  is  obliquely 
connected  with  the  pelvis,  downward  motion  of  the  pelvis  and  backward 
motion  of  the  femur  from  the  body  weight  being  prevented  by  the 
abdominal  recti  muscles,  whose  tendons,  being  inserted  in  the  pelvis,  by 
their  tension  tend  to  draw  the  hip-joint  anteriorly.  The  gluteal  muscles, 
arising  from  the  ilium  and  passing  over  the  hip-joint  to  the  femur,  act 
in  the  same  direction,  not  only  preventing  forcing  backward  of  the  hip- 
joint,  but  in  its  contraction  pressing  the  hip-joint  forward.  The  leg  is, 
like  the  femur,  flexed,  its  obliquity  being  limited  by  the  tension  of  the 
tendons  of  the  extensor  muscles,  which  pass  over  the  anterior  surface  of 
the  knee-joint,  by  the  ligaments  of  the  knee-joint,  and  by  the  tibio-tarsal 
muscle,  which  in  the  solipedes  throughout  its  entire  length  consists  of  a 
strong  aponeurotic  band,  thus  being  analogous  in  its  action  to  the  coraco- 
radial  muscle  of  the  anterior  extremity.  The  flexion  of  the  metatarsus 
on  the  leg  is  limited  especially  by  the  gastrocnemius  muscles  and:  by  the 
superficial  flexor  of  the  phalanges,  which  in  the  suspensory  ligament 
becomes  reduced  to  a  cylindrical  cord  and  flattened  out  at  its  passage 
over  the  summit  of  the  calcaneum.  The  inclination  of  the  phalanges  on 
the  metatarsus  is  prevented  by  a  ligamentous  suspensory  apparatus 
similar  to  that  of  the  anterior  extremity. 

From  the  above  it  is  seen  that  the  extremities  in  standing  support 
the  body  only  by  muscular  effort,  principally  that  of  the  extensors. 


PHYSIOLOGY   OF  MOVEMENT.  737 

Although  the  flexors  participate  in  many  joints,  as  an  example  of  which 
it  is  only  necessary  to  mention  the  coraco-radial,  which,  as  already  stated, 
offers  resistance  to  the  flexion  of  the  arm  on  the  forearm,  this  action  is 
only  rendered  possible  when  the  radius  is  fixed  by  the  olecranon  muscles. 
The  support  of  the  head  in  standing  in  the  case  of  quadrupeds  is  accom- 
plished mainly  by  the  ligamentum  nucae,  which,  originating  in  the  spinous 
processes  of  the  dorsal  vertebrae,  terminates  in  the  occipital  protuber- 
ance, being  connected  at  the  same  time  with  all  the  cervical  vertebrae. 

While  standing  quietly  the  weight  of  the  horse  is  supported  by  both 
of  the  fore  legs  and  only  one  hind  leg,  the  other  hind  leg  being  flexed  and 
only  the  tip  of  the  toe  touching  the  ground.  By  this  means  the  muscles 
of  the  posterior  extremity  which  are  concerned  in  the  act  of  standing 
are  enabled  to  rest,  the  weight  being  borne  alternately  at  varying  inter- 
vals by  the  opposite  hind  legs.  From  the  fact  that  the  centre  of  gravity 
in  quadrupeds  lies  nearer  to  the  anterior  than  the  posterior  extremities, 
the  fore  limbs  sustain  the  greater  part  of  the  weight  of  the  body.  In 
riding  two-thirds  of  the  weight  of  the  rider  are  borne  by  the  anterior 
extremities  and  one-third  by  the  posterior. 

In  every  form  of  animal  locomotion  the  position  of  the  centre  of 
gravity  of  the  body  in  space  is  changed,  inertia  tending  to  continue  the 
motion  inaugurated  by  the  muscular  contraction  until  friction,  resistance 
of  the  atmosphere,  or  opposed  muscular  action  arrests  it. 

In  man,  movements  of  locomotion  are  much  simpler  than  in  quad- 
rupeds, and  will,  therefore,  be  first  analyzed.  The  movements  in  man 
consist  in  walking,  running,  and  jumping.  In  the  act  of  walking  in  man, 
by  the  alternate  action  of  each  leg  the  centre  of  gravit3r  is  advanced  so 
that  at  each  step  there  is  a  moment  in  which  the  body  rests  vertically  on 
the  foot  of  one  leg  (say  the  right),  while  the  other  (the  left)  is  inclined 
obliquely  behind  with  the  heel  raised  and  the  toe  resting  on  the  ground. 
Then  the  latter,  slightly  flexed  to  avoid  touching  the  ground,  is  swung 
forward  like  a  pendulum,  and  the  toe  of  the  moving  leg  (the  left) 
then  brought  to  the  ground.  On  this  point,  as  a  fulcrum,  the  body  is 
moved  forward  by  a  propulsive  act  of  the  supporting  leg  (the  right),  the 
centre  of  gravity  becoming  thus  advanced  until  it  lies  vertically  over  the 
leg  (the  left)  which  has  last  touched  the  ground.  The  body  then  rests 
vertically  on  the  left  foot,  the  right  now  being  directed  obliquely  back- 
ward. The  propulsive  movement  of  the  active  leg,  the  one  concerned  in 
pushing  the  body  off  the  ground,  gives  sufficient  impetus  to  the  centre 
of  gravity  to  carry  it  by  inertia  beyond  the  vertical  line  on  the  passive 
or  supporting  leg,  so  that  this  movement  from  inertia  assists  in  swinging 
forward  the  active  leg  until  it  advances  a  step  beyond  the  passive  sup- 
porting leg  (Fig.  299).  Hence,  after  the  act  of  walking  is  once  started, 
inertia  is  largely  instrumental  is  maintaining  the  motion,  and  but  slight 

47 


738 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS.. 


muscular  exertion  is  required  in  walking  on  level  ground.  In  ascending 
an  incline,  however,  the  active  limb  has  at  each  step  to  elevate  the  weight 
of  the  body  by  extending  the  knee-  and  ankle-joint  by  the  thigh-exten- 
sors and  calf-muscles,  therefore  greatly  increasing  the  muscular  power 
required.  During  walking  the  trunk  leans  toward  the  active  leg,  owing 
to  the  contraction  of  the  glutei  muscles  and  the  tensor  fascia  lata,  and  is 
inclined  slightly  forward  to  overcome  the  resistance  of  the  air.  The 
more  anteriorly  the  trunk  is  advanced  the  more  the  centre  of  gravity  of 
the  body  tends  to  lie  in  the  line  of  the  active  leg,  and,  consequently,  the 
stronger  is  the  forward  propulsion  of  the  body.  Hence,  in  rapid  walk- 
ing the  body  is  more  bent  forward  than  in  slow  walking.  During  the 
advancing  of  the  passive  leg  the  trunk  rotates  on  the  head  of  the  active 
femur  and  is  compensated  by  the  arm  of  the  side  of  the  oscillating  leg 


FIG.  300.— THE  DIFFERENT  POSITIONS  OF  THE  LEGS  OF  MAN  IN  WALKING, 

AFTER  WEBEK. 

A,  the  propelling  le£ ;  B,  the  "  pendulum  "  leg. 

swinging  in  the  opposite  direction,  while  that  on  the  other  side  swings 
in  the  same  direction  as  the  oscillating  leg. 

Running  is  distinguished  from  walking  by  the  fact  that  at  a  certain 
moment  the  body  is  raised  in  the  air,  neither  leg  touching  the  ground. 
In  walking,  on  the  other  hand,  both  feet  rest  on  the  ground  for  the 
greater  part  of  the  step.  In  running  the  active  leg,  as  it  is  forcibly  ex- 
tended from  a  flexed  position,  gives  the  body  the  necessary  impetus,  the 
active  leg  leaving  the  ground  before  the  swinging  foot  has  reached  the 
ground.  There  is  thus  an  interval  during  which  both  feet  are  off  the 
ground,  and  as  each  foot  comes  to  the  ground  it  executes  a  new  swing 
without  waiting  for  the  pendulous  swing  which  occurs  in  walking. 

In  jumping  the  propulsion  of  the  bod}'  takes  place  from  both  feet 


PHYSIOLOGY   OF   MOVEMENT.  739 

simultaneously.  A  running  jump  ma}'  be  made  higher  or  broader  than 
a  standing  jump  from  the  additional  impetus  acquired  through  inertia. 

4.  THE  GAITS  OF  THE  HORSE. — Although  the  acts  of  locomotion  in 
quadrupeds  are  much  more  complicated  than  in  man,  they  may  be  all 
reduced  to  variations  of  three  main  t}7pes — the  walk,  the  trot,  and  the 
gallop.*  Since  in  quadrupeds  the  centre  of  gravity  lies  in  front  of  the 
centre  of  the  trunk,  it  can  only  be  advanced  by  power  acting  from  the  hind 
extremities,  the  fore  legs  being  concerned  simply  in  supporting  the  trunk. 
In  the  horse  the  posterior  extremities  are  especialty  fitted  for  this  act  by 
the  angular  character  of  their  joints,  so  that  in  the  action  of  the  extensor 
muscles  the  hind  legs  become  considerably  longer,  and  the  foot  remain- 
ing in  contact  with  the  ground,  through  the  contraction  of  the  extensors 
the  result  must  be  to  advance  the  upper  extremity  of  the  leg  forward ; 
and  the  greater  the  angles  of  the  posterior  extremity,  the  farther  the 
trunk  will  be  advanced  in  the  straightening  of  the  hind  leg.  The 
extremity,  which  in  the  commencement  of  the  extension  of  the  hind 
leg  was  behind,  will  now  be  advanced  so  as  to  support  the  trunk,  exactly 
as  has  been  found  to  be  the  case  with  the  swinging  leg  of  the  walking 
man,  which,  immediately  after  the  impulse  of  the  active  leg,  swings  for- 
ward, and  then  on  its  part  assumes  the  role  of  the  propulsive  leg,  while 
the  previously  active  leg  now  becomes  passive.  The  force  of  the  shock 
communicated  to  the  trunk  by  the  hind  legs  will  be  somewhat  diminished 
by  the  oblique  insertions  of  the  extremities  and  by  the  angles  between 
the  single  bones  of  the  hind  leg,  while  in  the  fore  extremities  the  shock 
of  the  foot  striking  the  ground  will  be  diminished  by  the  soft  parts, 
muscles  and  fascia,  which  connect  the  shoulder-blade  to  the  trunk. 

Before  taking  up  the  consideration  of  the  different  gaits  of  the 
horse  the  characters  and  mode  of  production  of  the  different  movements 
in  the  individual  limbs  first  deserve  attention,  taking  up,  first,  the  move- 
ments of  the  fore  leg  and  then  of  the  hind  leg : — 

The  animal  being  supposed  to  be  in  the  erect  position,  before  move- 
ment of  the  fore  leg  takes  place  the  body  weight  is  first  shifted,  through 
the  contraction  of  the  pectoral  muscles,  aided  b}^  the  latissimus  dorsi,  to 
the  opposite  extremity.  The  shoulder  being  elevated  by  the  rhomboid 
and  trapezius  muscles,  flexion  commences  with  the  contraction  of  the 
levator  humeri,  approximating  the  humerus  to  the  scapula  and  diminish- 
ing the  shoulder  angle.  The  principal  reduction  in  the  length  of  the 

*  In  the  account  of  the  different  movements  in  the  gaits  of  the  horse  the  author  has 
mainly  followed  the  analysis  published  by  Bruchmiiller, "  Lehrbuchder  Physiologie,"  Oes- 
terreicher  Vierteljahresschrift  fur  Veterinarkunde ,  liii,  1880,  pp.  97-120,  based  on  instan- 
taneous photography.  Acknowledgment  is  also  due  to  Colin,  "  Traite  de  Physiologie 
Comparee ;•"  Munk,  "  Physiologie  des  Menschen  und  der  Saugethiere ;"  Boehm,  Archiv 
fur  Wissenschaftliche  und  Praktische  Thierheilkunde,  Bd.  xiii  and  xiv  ;  and  Schmidt- 
Miilheim,  "  Physiologie  der  Haussaugethiere." 


740 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


axis  of  the  fore  leg  occurs  through  the  flexion  of  the  knee-joint,  which  is 
elevated  and  advanced  by  the  action  of  the  coraco-radial  and  humero- 
radial  muscles  ;  then  by  the  action  of  the  flexors  of  the  carpus  and  digit 
the  fetlock  and  pastern-joints  are  flexed. 


FIG.  301.— POSTERIOR  EXTREMITY  OF  THE 
HORSE  IN  EXTENSION.    (Colin). 

A  B,  line  of  action  of  gluteus  medius.  C  D,  line  of 
action  of  triceps  extensor.  E  F,  line  of  action  of  gas- 
trocnemius.  G  H,  line  of  action  of  metatarsal  flexor. 


FIG.  302.— ANTERIOR  EXTREMITY  OF  THE 
HORSE  IN  EXTENSION.    (Colin). 

AD,  BD,  and  CD.  lines  of  action  of  the  triceps  exten- 
sor brachii,  scapulo-ulnaris,  and  aconeus  muscles.  E  f. 
flexor  brachii.  G  H,  line  of  action  of  flexor  pedis  mus- 
cles. 


Extension  of  the  fore  leg  is  the  reverse  of  the  preceding  motions 
and  serves  to  open  out  the  angles  reduced  in  flexion  and  so  increase  the 
length  of  the  axis  of  the  limb.  Extension  is  still  further  the  reverse  of 
flexion  in  that  the  motion  commences  in  the  pastern-joint,  instead  of  in 


PHYSIOLOGY   OF   MOVEMENT.  741 

the  shoulder,  through  the  action  of  the  extensor  pedis,  which,  with  the 
metacarpal  extensors,  converts  the  angle  of  the  pastern-joints  into 
a  straight  line,  the  axis  of  the  phalanges  forming  an  angle  anteriorly 
with  the  axis  of  the  metacarpus.  Simultaneously  with  this  movement 
the  knee  becomes  extended,  the  axis  of  the  metacarpus  forming  a 
straight  line  with  that  of  the  radius,  this  movement  also  being  accom- 
plished by  the  contraction  of  the  metacarpal  extensors.  Finally,  the  fore- 
nnn  returns  to  its  extended  position  in  a  line  with  the  upper  arm,  partly 
through  the  action  of  the  ligaments  of  the  elbow-joint  and  partly  from 
the  contraction  of  the  five  olecranon  muscles.  During  this  forward 
motion  of  the  foot  in  extension  the  humerus  leaves  its  position  of  flexion, 
and  the  foot  striking  the  ground,  the  fore  limb  again  becomes  vertical, 
and  by  the  action  of  the  pectoral  latissimus  dorsi  muscles  the  body  weight 
is  again  transferred  to  it.  The  lever  motion  of  the  muscles  producing 
these  movements  is  seen  in  Figs.  301  and  302.  Instead,  however,  of  the 
simple  motions  of  flexion  and  extension  above  described,  which 
occur  when  one  forefoot  is  simply  raised  from  the  ground  and  again 
returned  to  the  same  spot,  the  flexed  forearm  and  carpus  may  be  carried 
beyond  the  vertical  line  through  the  extension  of  the  humerus  by  the 
contraction  of  the  various  extensors,  aided  by  the  abductors  of  the 
humerus,  while  at  the  same  time  the  posterior  angle  of  the  scapula 
is  drawn  backward  and  downward  by  the  contraction  of  the  rhomboid 
and  trapezius  muscles.  At  first,  in  the  forward  motion  of  the  lower  end 
of  the  humerus  flexion  is  increased,  but  the  farther  it  advances  forward 
and  the  more  the  scapula  rotates  backward  the  more  the  shoulder  angle 
becomes  opened,  and,  under  the  action  of  the  adductors  of  the  humerus, 
directed  outward  and  upward,  so  that  the  extensors  of  the  lower  joints 
are  put  on  the  stretch  and  their  contraction  converts  the  flexion  of  the 
limb  into  extension,  the  fore  leg  thus  describing  a  pendulum-like 
motion,  and  in  its  extended  position  is  directed  forward  and  downward 
and  strikes  the  ground  in  front  of  its  previous  position  (Fig.  303).  Then, 
from  the  impulse  communicated  to  the  trunk  from  the  hind  legs,  the 
weight  of  the  body  is  gradually  transferred  to  the  fore  leg,  which, 
the  foot  remaining  on  the  ground,  gradually  becomes  more  and 
more  vertical  from  the  forward  motion  on  it  of  the  trunk  (Fig.  304). 
As,  however,  the  inertia  of  the  moving  body  carries  the  shoulder  beyond 
the  vertical,  the  axis  of  the  fore  limb  is  then  directed  downward 
and  backward,  the  assumption  of  this  position  being  aided  by  the 
forward  rotation  of  the  scapula,  while  the  extensors  of  the  forearm  (the 
foot  being  fixed  on  the  ground)  not  only  sustain  the  elbow-  and  shoulder- 
joints,  but,  by  their  contractions,  give  an  additional  forward  impetus  to 
the  body.  The  extreme  extended  position  of  the  limb  puts  the  flexors 
of  the  lower  joints  on  the  stretch  and  so  leads  to  their  contraction,  and 


742  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

the  limb,  passing  now  into  flexion,  again  describes  its  forward  pendulum 
motion,  the  point  of  support  of  the  scapula  being  the  centre  of  rotation, 
while  the  hoof  describes  an  arc  of  a  circle.  On  the  other  hand,  while 


FIG.  303.— OSCILLATION  OF  THE  FLEXED  FORE  LEG.    (Colin.) 
The  hoof  describes  an  arc  of  a  circle,  C  B  A,  the  cord,  C  A,  being  a  measure  of  the  extent  of  oscillation. 

the  foot  is  on  the  ground  the  shoulder  describes  the  arc  of  a  circle  and 
the  centre  of  rotation  is  in  the  foot.  The  combination  of  these  two 
movements  in  both  fore  legs  is  seen  in  Fig.  305. 


J) 

F-io.  304.— OSCILLATION  OF  THE  EXTENDED  FORE  LEG.    (Colin.) 

The  foot  being  on  the  ground  at  I),  the  shoulder  describes  an  arc  of  a  circle,  ABC. 

In  the  case  of  the  hind  leg  flexion  likewise  results  in  a  shortening 
of  the  axis  of  the  leg  and  the  reduction  of  the  angles  between  the  dif- 
ferent bones.  The  weight  being  thrown  on  the  opposite  extremity  by 


PHYSIOLOGY  OF  MOVEMENT. 


743 


the  contraction  of  the  adductors,  the  femur  is  approached  to  the  ilium 
by  the  contraction  of  the  rectus  and  lumbar  and  iliac  psoas  muscles,  the 
knee  being  elevated  anteriorly  by  the  ischio-tibial  muscle  and  the  hock- 
joint  flexed  by  the  contraction  of  the  metatarsal  flexor,  whose  tendinous 
portion,  when  the  stifle-joint  is  flexed,  becomes  tensed  and  mechanically 
repeats  the  action  on  the  joint  below,  the  digital  region  being  flexed  on 
the  metatarsus.  As  a  consequence  of  these  flexions,  produced  almost 
simultaneously,  the  axis  of  the  limb  becomes  shorter,  is  raised  from  the 
ground,  and  advanced  in  a  more  or  less  oblique  line.  That  the  foot  may 
again  be  placed  on  the  ground  the  above  muscles  must  relax  and  their 
antagonists  contract.  First  the  femur  is  extended  on  the  pelvis  by  the 
action  of  the  glutens  maximus,  whose  principal  trochanteric  branch  acts 
as  a  lever  of  the  first  class.  The  leg  is  then  extended  on  the  thigh  by 


FIG.  305.—  OSCILLATION  OF  THE  ANTERIOR  EXTREMITIES.    -(Colin.) 

The  figure  shows  that  while  one  fore  leg  is  describing  the  pendulum  motion  the  other  is  acting  as  a 


e     gure  sows  tat  we  one  ore  eg  s    escrng  te  penuum  moton  te  oter  is  acting  as  a 
support,  while  the  right  fore  foot  describes  the  arc,  </  /(,  the  left  shoulder  describes  the  arc,  at  hi  <•!,  from  the 

on  of  the  hind  legs.    Then  the  right 
in  one  complete  step  are  shown  at 


, 

impulse  given  to  the  centre  of  gravity  of  the  body  through  the  extension  of  the  hind  legs.    Then  the  right 
shoulder  describes  the  arc,  df  eJ  ft.    The  six  positions  of  the  left  leg  i 


abed  e/,  the  centre  of  gravity  having  been  advanced  from  m  to  n. 

the  rotuleus  muscles,  the  metatarsus  in  its  turn  regaining  its  position  on 
extension  through  the  contraction  of  the  gastrocnemius,  the  digital  region 
being  extended  by  the  phalangeal  extensors.  The  lever  action  of  the 
muscles  which  produce  these  motions  is  seen  in  Figs.  249  and  251. 

In  movements  of  progression  each  hind  limb  alternately  serves  to 
give  an  impetus  to  the  body  by  passing  into  a  condition  of  extreme  ex- 
tension, the  foot  being  on  the  ground,  and  then,  passing  into  a  condition 
of  flexion,  describes  a  pendulum  motion  through  the  air  until  the  foot 
again  strikes  the  ground  in  front  of  the  position  which  it  left.  The  pen- 
dulum motion  commences  with  flexion  of  the  hip-joint  and  forward  motion 
of  the  lower  end  of  the  femur  followed  by  flexion  of  the  other  joints. 
The  greater  the  advance  of  the  knee  the  greater  the  tension  of  the  ex- 
tensors, until  the  limb  becomes  extended  and  its  increased  length  brings 


744  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

the  foot  to  the  ground,  the  axis  of  the  limb  being  now  directed  obliquety 
downward  and  forward.  The  body  weight  is  then  shifted  to  this  limb 
through  the  action  of  the  adductors,  the  limb  again  passing  into  a  more 
or  less  marked  position  of  flexion.  The  croup  muscles  then  contracting, 
the  pelvis  is  advanced,  assisted  by  the  extensors  of  the  femur,  which  find 
a  fixed  point  in  the  knee,  while  at  the  same  time  the  gastrocnemius 
muscle,  contracting,  opens  the  angle  of  the  hock-joint  and  elevates  the 
pelvis  from  the  increase  in  the  length  of  the  axis  of  the  limb.  Through 
these  motions  the  line  of  the  hind  leg  gradually  becomes  vertical,  passes 
the  perpendicular,  and  is  then  directed  downward  and  backward  from 
the  advance  communicated  to  the  body  (Fig.  306).  When  the  highest 


FIG.  306.— OSCILLATION  OF  THE  EXTENDED  HIND  LEG.    (Colin.) 

The  foot  being  on  the  ground  at  D,  the  hip-joint  describes  an  arc  of  a  circle,  ABC,  the  lines  A  D, 
B  D,  and  C  D  representing  the  changing  axis  of  the  hind  leg. 

degree  of  extension  is  reached  the  weight  is  shifted  to  the  opposite  limb, 
and  after  complete  flexion  the  pendulum  motion  is  repeated. 

In  these  motions  the  hind  leg  does  not  move  in  the  plane  of  the  line 
of  direction ;  in  rapid  movement  the  knee  and  tip  of  the  foot  are  some- 
what everted  through  the  action  of  the  iliacus  muscle  until  the  foot 
strikes  the  ground.  In  slow  motions,  on  the  other  hand,  especially  when 
bearing  heavy  weights,  the  knee  is  directed  inward  from  the  action  of 
•the  adductors  and  tension  of  the  femoral  fascia,  while  the  hock  is  everted, 
thus  turning  the  toe  toward  the  median  line. 

(a)  The  Walk. — In  walking  the  body  is  supported  by  two  legs  while 
the  other  two  are  describing  the  pendulum  motion,  the  support  being 
alternately  on  diagonal  feet  and  then  on  the  two  feet  of  the  same  side  ; 


PHYSIOLOGY  OF  MOVEMENT.  745 

but  as  the  impulse  of  the  supporting  feet  is  not  simultaneously  pro- 
duced, four  strokes  of  the  hoof  are  heard  with  each  step,  but  at  unequal 
intervals ;  for  when  the  support  comes  from  the  two  feet  on  the  same 
side  the  preservation  of  equilibrium  compels  a  more  rapid  shifting  of 
the  body  weight  to  the  opposite  side  than  when  the  diagonal  limbs  are 
in  action. 

If  we  commence  the  consideration  of  the  act  of  walking  in  quadru- 
peds at  the  moment  in  which  the  one  hind  leg  after  completing  its  pen- 
dulum motion  comes  again  to  the  ground,  then  it  occupies  a  position  in 
which  the  axis  of  the  limb  is  directed  from  behind  forward  and  from 
above  downward.  The  centre  of  gravity  in  consequence  of  the  propul- 
sive movement  advances,  the  leg  and  trunk  describe  an  arc  of  a  circle 
around  the  foot  as  a  centre,  so  that  the  axis  of  the  leg  gradually 
becomes  vertical  and  then  advances,  and  the  axis  now  tends  to  become 


FIG.  307.— THE  WALK.    (Colin.) 

directed  from  before  backward  and  from  above  downward.  At  this 
moment  active  contraction  of  the  extensor  muscles  occurs  and  the  leg 
which  was  the  supporting  member  now  becomes  an  active  propulsive 
member.  It  leaves  the  ground,  becomes  flexed,  and  swings  forward, 
the  femoral  articulation  now  being  the  centre  of  movement  and  the  foot 
describing  an  arc  of  a  circle  until  it  becomes  advanced  in  front  of 
its  point  of  support.  It  then  strikes  the  ground  and  the  movements 
are  repeated  (Fig.  307).  At  the  moment  when  the  hind  leg  is  thus 
swinging  forward  the  fore  leg  of  the  opposite  side  is  likewise  advanced, 
the  movement  commencing  as  soon  as  the  propulsive  hind  leg  is  in  a 
vertical  line.  Through  the  forward  movement  of  the  trunk  the  line  of 


746  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

direction  of  the  fore  extremity  becomes  changed,  so  that  instead  of  being 
vertical  it  is  directed  from  above  downward  and  from  before  backward. 
The  foot  must,  therefore,  be  raised  from  the  ground  and  advanced  in  the 
direction  in  which  the  trunk  is  moving,  and,  striking  the  ground,  again 
becomes  vertical  at  the  moment  when  the  pendulous  hind  leg  strikes  the 
ground.  At  the  moment,  then,  when  the  fore  leg  becomes  vertical,  the 
propulsive  movement  in  the  opposite  hind  leg  occurs.  Then  the  motion 
commences  in  the  opposite  hind  leg  and  fore  leg,  the  alternation  of  the 
limbs  being  perfectly  regular.  Thus,  suppose  the  right  hind  foot  to  be  the 
propulsive  foot,  the  left  fore  foot  is  extended  on  the  ground,  the  left 
hind  leg  is  swinging  forward,  and  the  right  fore  foot  is  just  leaving  the 
ground,  the  body  thus  being  supported  on  a  diagonal  pair  of  feet.  Then 
the  right  hind  foot  leaves  the  ground,  the  left  fore  foot  is  on  the  ground, 
the  limb  having  passed  the  vertical  line,  the  left  hind  leg  is  giving  the 
impulse  to  the  body,  while  the  right  fore  foot  is  swinging  forward.  The 
body  is  then  supported  on  unilateral  feet,  the  support  being  of  shorter 
duration  than  in  the  first  case.  Hence,  in  walking,  there  is  always  at 
any  one  time  an  anterior  and  a  posterior  limb  in  the  air  and  an  anterior 
and  posterior  limb  acting  as  a  support,  the  limbs  being  raised  and  replaced 
in  such  an  order  that  of  the  two  limbs  in  the  air  one  is  alwaj^s  in  advance 
the  half  of  its  course  over  the  other,  while  of  the  supporting  limbs  in 
one  the  line  of  the  support  is  vertical  when  the  other  first  reaches  the 
ground.  • 

In  quadrupeds  the  length  of  the  step  is  measured  by  the  distance 
between  the  track  formed  by  each  separate  foot,  so  that  it  is,  therefore, 
twice  as  extensive  as  in  man.  When  the  hind  feet  reach  the  foot-prints 
of  the  fore  feet  it  is  twice  as  long  as  the  base  of  support,  i.e.,  the  dis- 
tance between  the  pairs  of  feet  at  rest.  As  the  motion  in  walking  in 
quadrupeds  is  produced  by  the  action  of  the  diagonal  extremities,  the 
centre  of  gravity  is  first  moved  to  one  side  and  then  returned  to  the 
centre  and  then  cast  to  the  opposite  side.  The  duration  of  the  step  is 
dependent  upon  the  duration  of  the  swinging  of  the  leg.  The  higher  an 
animal  raises  its  leg,  the  shorter  is  the  pendulum  and  the  more  rapidly  it 
swings. 

The  rapidity  of  motion  in  the  walk  in  the  horse  varies  front  one  to 
two  meters  in  the  second.  In  drawing  heavy  weights  or  in  a  very  slow 
walk  the  relative  movement  of  the  feet  is  somewhat  different  from  that 
detailed  above.  Then  the  elevation  of  each  foot  is  delayed  until  the  sup- 
porting feet  are  firmly  on  the  ground ;  the  body  is  then  always  supported 
on  three  limbs,  by  which  equilibrium  is  better  preserved.  The  same 
sequence  of  movement  is,  however,  preserved. 

(6)  The  Amble. — The  amble  is  a  modification  of  the  walk,  and  is 
seen  in  the  dromedary,  giraffe,  and  occasionally  in  ruminants,  and  more 


PHYSIOLOGY  OF  MOVEMENT.  747 

seldom  still  in  the  horse.  It  is  characterized  by  the  fact  that  the  eleva- 
tion of  the  second  leg  on  the  same  side  occurs  sooner  than  in  the  walk. 

The  walk  merges  into  the  amble  when,  the  body  being  supported  by 
the  two  legs  on  the  same  side,  the  two  opposite  legs  are  elevated  simul- 
taneonsty  instead  of  separately,  as  in  the  walk  (Fig.  308). 

In  the  walk  the  fore  leg  is  alwa}Ts  one-half  the  extent  of  its  move- 
ment behind  the  hind  leg  on  the  same  side,  while  in  the  amble  both  legs 
on  one  side  move  together,  so  that,  therefore,  there  is  a  regular  change 
between  the  feet  on  each  side  of  the  body.  Consequently,  in  the  amble 
the  centre  of  gravity  is  first  shifted  to  the  one  side  and  then  to  the 
other,  the  length  of  the  step  in  the  amble  and  walk  being  the  same.  But 
from  the  fact  that  the  supporting  limbs  are  on  the  same  side  of  the  body, 
to  preserve  equilibrium  the  movements  must  be  more  rapidly  performed 


FIG.  308.— THE  AMBLE.    (Colin.) 

than  in  the  walk.  The  gait  is,  therefore,  a  faster  one,  the  greater  rapidity 
of  the  pace  being  accomplished  by  the  reduction  of  the  time,  which  cor- 
responds to  the  half  of  the  duration  of  the  movement  of  one  leg,  since  on 
each  side  one-fourth  of  the  time  is  saved.  The  rate  of  movement  in 
pacing  may  approach  that  of  the  trot,  the  velocity  often  rising  to  three 
meters  per  second.  Since  the  two  unilateral  propulsive  and  the  two 
swinging  feet  always  move  together,  and  are  always  at  one  time  in  the 
same  phase  of  motion,  the  swinging  feet  strike  the  ground  together,  so 
that  after  one  pace  but  two  strokes  of  the  feet  have  been  heard. 

In  the  rack,  which  is  simply  a  modification  of  pacing,  the  uni- 
lateral feet  act  together,  but  the  hind  leg  in  propulsion  is  somewhat 
later  than  the  fore  foot  of  the  same  side  in  leaving  the  ground.  Four 
strokes  of  the  feet  are  heard  in  this  gait,  two  rapidly  following  sounds 
when  the  feet  of  one  side  strike  the  ground,  separated  by  a  longer  interval 


748  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

from  the  two  rapid  sounds  when  the  feet  of  the  opposite  side  strike  the 
ground. 

It  has  been  seen  that  in  the  movement  of  locomotion  in  man  there 
are  two  periods  of  time  in  which  both  feet  are  on  the  ground  and  only 
one  interval  in  which  only  one  foot  is  in  contact  with  the  earth.  In 
running,  on  the  other  hand,  there  is  a  moment  in  which  one  of  the  legs 
is  raised  up  while  the  other  is  still  performing  the  pendulum  motion,  and, 
consequently,  both  legs  are  at  one  time  in  the  air.  This  interval  is,  how- 
ever, much  shorter  than  that  in  which  both  feet  are  on  the  ground. 

(c)  The  Trot. — The  form  of  locomotion  seen  in  the  horse  and  more 
seldom  in  the  ox  and  other  quadrupeds  which  corresponds  to  the  act  of 
running  in  man  is  termed  the  trot,  in  which  the  fore  leg  completes  its 
movement  with  the  diagonal  hind  leg ;  so  that  in  the  trot  the  diagonal  feet 
and  hind  limbs  at  the  same  moment  leave  the  ground  and  at  the  same 


FIG.  309.— THE  TROT.    (Colin.) 

moment  again  reach  it.  Therefore,  in  the  trot  two  strokes  of  the  feet 
on  the  ground  are  heard  at  each  step.  In  the  fast  trot  an  interval  occurs 
between  this  double  stroke  of  the  feet  against  the  ground  in  which  the 
body  is  moving  through  the  air  with  all  four  feet  raised  from  the  ground. 
This  interval  is  variable,  usually  being  about  half  the  time  that  the 
feet  are  in  contact  with  the  ground. 

In  the  trot  the  impulse  is  communicated  to  the  pelvis  from  each  hind 
leg  alternately,  so  tending  to  strain  the  articulation  between  the  sacrum 
and  vertebrae.  This  is,  however,  reduced  to  a  minimum  by  the  contrac- 
tion of  the  ilio-spinalis  of  the  opposite  side. 

In  a  very  fast  trot  the  second  pair  of  feet  leave  the  ground  as  soon 
as  the  first  pair  have  reached  the  vertical  position.  Each  step  in  the  trot 
is  twice  as  long  as  the  step  in  the  walk,  in  rapid  trotting  the  hind  feet 


PHYSIOLOGY  OF  MOVEMENT.  749 

striking  the  ground  considerably  in  front  of  the  track  of  the  fore  feet  and 
the  velocity  of  motion  rising  to  from  eight  to  twelve  meters  per  second. 
The  walk  turns  into  the  trot  when,  the  body  being  supported  on  two 
diagonal  feet,  the  opposite  hind  foot  rapidly  leaves  the  ground  and 
swings  forward  so  that  it  strikes  the  ground  simultaneously  with  the 
diagonal  fore  foot,  or  by  one  hind  foot,  as  soon  as  it  strikes  the  ground, 
rapidly  passing  into  extension  simultaneously  with  the  diagonal  fore 
foot. 

(d)  The  Gallop. — The  more  the  long  axis  of  the  body  coincides 
with  the  axis  of  the  propelling  hind  legs,  the  greater  is  the  propulsive 
power  of  the  legs.  The  angle  between  the  hind  legs  and  the  body  may 
be  increased  by  elevation  by  means  of  the  fore  legs,  and  in  the  act  of 
galloping  the  fore  legs  are  raised  up,  while  the  main  propulsive  power 
comes  from  the  hind  legs,  so  that  the  gallop  is  a  series  of  jumps:  Accord- 
ing to  the  rapidity  of  the  gallop  or  run  of  quadrupeds,  four  strokes  of 
the  feet  on  the  ground  are  heard  in  a  slow  gait  or  canter,  three  in  the 
ordinary  run,  and  two  in  running  at  full  speed.  Ordinarily,  the  legs  of 
the  two  sides  of  the  body  do  not  act  simultaneously,  and,  according 
as  the  right  or  the  left  hind  leg  is  extended  farthest  behind,  one  speaks 
of  a  right-  or  a  left-handed  gallop.  Thus,  in  the  right-handed  run,  the 
left  hind  leg,  stretched  far  under  the  body,  first  in  its  extension  gives  the 
impulse  to  the  body,  the  right  hind  leg  at  this  moment  swinging  forward 
to  add  the  impulse  of  its  extension  a  moment  later,  while  both  fore  feet  are 
off  the  ground,  swinging  forward,  the  left  being  the  farthest  advanced  in 
commencing  extension,  while  the  right  fore  leg  is  still  flexed.  Then,  while 
the  left  hind  leg  is  still  on  the  ground,  though  extended  far  behind  the 
body,  the  right  hind  leg  strikes  the  ground  and  adds  its  impulse  in 
extension,  while  the  extended  left  fore  foot  approaches  the  ground  and 
the  swinging  right  fore  foot  passes  into  extension.  Then  the  left  fore 
foot,  reaching  the  ground,  acts  as  a  support  on  which  the  weight  of  the 
body  is  sustained,  both  hind  legs  being  extended  behind  the  body,  the  left 
being  farthest  extended,  while  the  extended  right  fore  foot  is  just  about 
to  touch  the  ground.  Finally,  the  right  fore  leg  reaches  the  ground  and 
receives  the  weight  of  the  body,  while  flexion  commences  in  the  left  fore 
leg,  both  hind  legs  being  now  flexed  under  the  body,  the  left  hind  foot 
being  somewhat  the  farthest  advanced. 

At  this  moment  the  left  fore  foot  is  raised  and  the  right  fore  leg, 
which  alone  sustains  the  weight  of  the  body,  leaves  the  ground  after 
having  passed  the  vertical,  the  body  being  then  entirely  free  from  all 
support,  the  fore  legs  flexed,  and  the  hind  legs  drawn  under  the  body, 
the  left  first  reaching  the  ground. 

Thus,  there  is  a  moment,  in  which,  alternately,  each  limb  alone  sus- 
tains the  weight  of  the  body,  and  a  moment  in  which  both  hind  legs  are 


750  PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 

propelling  the  body,  and  one  in  which  both  fore  legs  are  supporting  it. 
In  the  analysis  of  the  movements  of  the  limbs  in  the  run  the  greatest 
confusion  has  existed  as  to  the  functions  of  the  fore  limbs  ;  this  has  now, 
thanks  to  instantaneous  photography,  been  cleared  up.  In  the  first 
place,  it  is  seen  that  at  one  time  the  body  is  entirely  clear  from  the 
ground,  and  that  the  weight  of  the  body  is  not  received  on  one  or  both 
of  the  fore  legs,  but  on  one  hind  leg,  advanced  under  the  body  so  that 
the  foot  is  nearly  under  the  centre  of  gravity.  In  the  second  place,  the 
fore  legs  do  not  serve  merely  as  "  props  or  stilts  "  for  the  support  of  the 
body  in  motion,  but  are  themselves  also  propelling  organs.  At  first 
sight  this  might  seem  impossible,  for  the  insertion  of  the  fore  limbs, 
acting  on  the  body  at  rest,  and  being  inserted  in  front  of  the  centre  of 
gravity,  could  not  advance,  but  only  elevate  it,  as  in  rearing.  In  the 
running  animal,  however,  the  propulsion  from  the  hind  legs  advances  the 
centre  of  gravity,  but  at  the  same  time  tends  to  lower  it,  and  if  the  fore 
feet  were  immovable,  the  animal  would  tend  to  fall  forward  on  its  head. 
This  is  prevented  by  the  shifting  of  the  fore  feet,  while  at  the  same 
time  a  distinct  upward  impulse  is  communicated  to  the  centre  of  gravity. 
This  may  be  seen  in  Mr.  Muybridge's  photographs,  where  there  is  a 
distinct  elevation  of  the  body  at  each  time  the  fore  legs  leave  the  ground. 
The  centre  of  gravity  of  the  body  is  thus  acted  on  \)y  two  forces,  one 
from  the  hind  legs  tending  to  advance  and  lower  it,  the  other  from  the  fore 
legs  tending  to  elevate  it ;  the  resultant  of  these  two  forces  will  evidently 
be  a  diagonal  between  the  two ;  and  the  upward  lift  from  the  fore  feet 
will  more  than  compensate  the  downward  tendency,  and  the  bod}-  will 
be  lifted  and  advanced. 

In  this  gait  but  two  strokes  of  the  feet  are  heard,  the  first  pro- 
duced by  the  contact  of  the  left  hind  leg,  lengthened  by  the  fall  of  the 
right  hind  foot,  the  second  by  the  contact  of  the  left  fore  foot  with  the 
ground,  lengthened  by  the  fall  of  the  right  fore  foot.  The  interval 
between  the  first  and  second  sounds  is  very  short,  that  between  the 
second  and  first,  while  the  hind  legs  are  swinging  through  the  air,  some- 
what longer.  The  length  of  the  strides  in  the  full  run  may  amount  to 
six  or  seven  meters,  and  a  velocity  of  nearly  fifteen  meters  per  second 
be  attained. 

In  a  slower  run  or  gallop  three  strokes  of  the  feet  are  heard,  the 
body,  as  in  the  trot,  being  supported  on  the  diagonal  limbs.  The  differ- 
ence of  this  gait  from  the  trot  consists  in  the  fact  that  in  the  latter  the 
support  on  the  diagonal  limbs  is  equally  prolonged,  while  in  the  gallop 
the  support  on  one  pair  is  longer  than  on  the  other.  A  conception  of 
this  gait  is  obtained  if  it  is  imagined  that  one  pair  of  feet  are  acting  as 
in  the  trot,  the  other  as  in  the  movement  of  jumping. 

1.  In  this  gait,  when  right-handed,  the  left  hind  leg  is  extended  on 


PHYSIOLOGY   OF   MOVEMENT.  751 

the  ground  and  gives  the  forward  impetus  to  the  bod}1 ;  the  right  hind 
leg  and  left  fore  leg  are  swinging  forward,  while  the  flexed  right  fore  leg 
is  being  advanced.  2.  The  right  hind  foot  and  left  fore  foot  then  strike 
the  ground  and  receive  the  weight  of  the  body ;  the  left  hind  leg  is 
extended  behind  the  body  and  about  to  leave  the  ground,  while  the  fully 
extended  right  fore  leg  is  advanced.  3.  Then  the  right  fore  leg  reaches 
the  ground  and  sustains  the  weight  of  the  body  until  the  limb  is  vertical ; 
the  left  hind  leg  leaves  the  ground,  and  the  flexed  right  hind  leg  and  left 
fore  leg  are  swinging  forward.  Finally,  the  right  fore  foot  leaves  the 
ground,  the  leg  being  strongly  flexed,  and  the  bod}T  moves  through  the 
air  from  the  impetus  from  the  left,  aided  by  the  right,  hind  leg.  The 
three  strokes  of  the  hoof  correspond  to  the  three  actions  described 
above  as  1,2,  and  3.  The  pause  between  the  first  and  second  sounds  is 
short,  that  between  the  second  and  third  still  shorter,  while  between  the 
third  and  first,  and  while  the  body  is  moving  through  the  air,  the  pause 
is  considerably  longer. 

In  this  gait,  as  in  the  run  and  long  jump,  and  occasionally  in  the 
high  jump,  the  weight  of  the  body  when  it  first  reaches  the  ground  is 
not  received  on  the  fore  legs,  but  through  rapid  flexion  the  hind  legs 
first  touch  the  ground. 

In  the  canter  the  action  of  all  the  limbs  is  much  slower,  the  verte- 
bral column  being  more  raised,  the  gait,  therefore,  more  resembling  the 
high  than  the  long  jump.  The  fall  of  the  diagonal  feet  is  separated  by  a 
short  interval ;  so  in  the  canter  four  strokes  of  the  hoofs  are  heard. 

The  plates  following  page  921,  through  the  kind  permission  of  Pro- 
vost Pepper,  of  the  University  of  Pennsylvania,  and  Mr.  Muybridge,  are 
reproduced  from  the  elaborate  series  of  instantaneous  photographs  made 
by  Mr.  Muybridge  in  the  University  of  Pennsylvania. 

5.  OTHER  MOVEMENTS  IN  THE  HORSE. — (a)  Rearing. — In  the  act  of  rear- 
ing the  fore  part  of  the  body  becomes  raised  up  on  the  hind  extremities, 
so  that  the  vertebral  column  leaves  the  horizontal  direction  and  becomes 
nearly  vertical.  The  first  stage  of  rearing  consists  in  the  fixation  of  the 
hind  legs,  the  elevation  of  the  neck  and  head,  and  the  contraction  of  the 
back  and  lumbar  muscles,  by  which  the  vertebral  column  becomes  rigid  ; 
then  the  elevation  of  the  fore  legs  commences  with  a  slight  bowing  of 
the  extremities  and  subsequent  powerful  extension,  by  which  the  feet  are 
raised  up  from  the  ground  and  become  flexed.  Then  there  is  a  powerful 
contraction  of  the  back  muscles  (the  ilio-spinal,  the  gluteal  muscles,  and 
the  ischio-tibial  muscles),  the  anterior  extremit}7  of  the  vertebral  column 
is  somewhat  raised  up,  its  elevation  being  assisted  by  the  drawing  down 
of  the  pelvis  by  means  of  the  lumbar  muscles,  so  that  the  weight  of  the 
body  is  now  borne  by  the  flexed  hind  legs  (Fig.  310).  The  vertebral 
column  ordinarily  does  not  quite  reach  the  vertical  line,  but  yet  the  line  of 


752 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


direction  of  the  centre  of  gravity  may  fall  behind  the  hind  legs,  and  then 
the  animal  falls  over  backward.  In  rearing,  the  fore  legs  and  hind  legs 
are  parallel  to  each  other  and  always  somewhat  diagonal ;  likewise,  both 
fore  legs  are  not  elevated  simultaneously,  but  one  somewhat  precedes  the 


FIG.  310.— REARING.    (Colin.) 

A  B,  line  of  action  of  ilio-spinal  muscles :  F  G,  glutens  maximus ;  D  C,  ischio-tibial 
pyramidal  prolongation  of  the  vastus. 


luscles;  DE, 


other.  The  return  to  the  normal  condition  is  accomplished  by  the  drop- 
ping of  the  head  and  neck,  the  return  of  the  fore  legs  from  their  flexed 
to  the  extended  condition,  so  that  gravitation  alone  is  sufficient  to  cause 


PHYSIOLOGY   OF   MOVEMENT. 


753 


the  body  to  return  to  its  natural  position  supported  on  all  four  of  its 
extremities. 

(6)  Kicking. — By  this  term  is  understood  the  elevation  and  violent  ex- 
tension of  the  hind  legs,  with  raising  of  the  posterior  part  of  the  vertebral 


column.  The  first  stage  of  this  act  consists  in  the  extension  of  the  neck 
and  the  dropping  of  the  head  toward  the  ground  between  the  firmly  ex- 
tended fore  legs,  while  the  hind  legs  are  flexed  by  the  powerful  contrac- 
tion of  the  back  muscles,  which  find  a  fixed  point  of  support  in  the  last 

48 


754  PHYSIOLOGY   OF   THE    DOMESTIC   ANIMALS. 

cervical  vertebrae.  The  pelvis  and  posterior  part  of  the  vertebral  column 
is  raised,  this  elevation  being  assisted  by  and  coinciding  with  the  sudden 
extension  of  the  hind  legs,  the  feet  leaving  the  ground  and  being  ex- 
tended by  the  muscles  of  the  upper  joint  of  the  leg,  the  lower  joints 
likewise  being  subsequently  extended.  Here,  also,  both  fore  feet  are  not 
parallel  on  the  ground,  but  one  is  somewhat  advanced  in  front  of  the 
other.  The  hind  foot  on  the  diagonal  side  is  somewhat  sooner  raised, 
and,  therefore,  further  extended  than  the  other  (Fig.  311).  In  this  act 
the  centre  of  gravity  never  nearly  approaches  the  line  of  direction  of  the 
fore  legs,  so  that  this  position  can  be  maintained  but  for  an  instant,  the 
trunk  sinking  again  by  its  own  weight,  and  is  supported  by  the  hind 
legs,  which  are  now  flexed  and  drawn  under  the  body. 

(c)  Lying  Down  and  Rising  Up. — The  first  stage  of  lying  down  in 
the  horse  consists  in  the  backward  motion  of  the  fore  feet  and  the  for- 
ward motion  of  the  hind  feet,  thus  greatly  reducing  the  base  of  support. 
A  sudden  flexion  of  the  fore  legs  then  occurs,  so  that  the  animal  falls  on 
its  knees ;  then  the  hind  legs  become  flexed,  so  that  the  posterior  surface 
of  the  tibiae  touches  the  ground.     The  act  of  lying  down,  therefore,  in 
the  horse  is   practically  falling   down.      While  lying   one  side  of  the 
body  completely  touches  the  ground,  the  limbs  being  extended  from  the 
body  either  in  slight  flexion  or  in  complete  extension.     In  rising  up  the 
extended  extremities  are  drawn  to  the  body,  and  by  the  unilateral  action 
of  the  trunk  muscles  the  body  is  brought  in  such  a  position  that  the 
chest  and  abdomen  are  in  contact  with  the  ground,  the  fore  feet  are  then 
extended  on  the  ground,  and  a  fixed  point  for  the  back  muscles  thus  being 
acquired,  the  contraction  of  these  muscles  draws  the  pelvis  forward,  so 
that  the  hind  legs  are  now  enabled  to  bring  the  feet  against  the  ground, 
and  by  sudden  extension  of  all  the  legs  the  bod}'  is  raised  up. 

(d)  Walking  Backward. — In  walking  backward  in  the  horse  the  head 
and  neck  are  elevated,  the  spinal  column,  through  the  contraction  of  its 
muscles,  rendered  rigid,  and  the  fore  legs  in  a  somewhat  flexed  condition 
are  directed  from  above  backward  and  downward,  and  then,  in  contact 
with  the  ground,  gradually  extended,  being  assisted  by  the  contraction 
of  the  pectoralis  major  and  latissimus  dorsi,  serve  to  push  the  body  back- 
ward from  the  flexed  hind  legs.     The  backward  movement  occurs  by  the 
alternate  movement  of  the  diagonal  feet ;  thus,  it  may  commence  with 
the  fixation  and  extension  of  the  right  fore  foot,  then  the  left  hind  foot, 
then  the  left  fore  foot,  and  then  the  right  hind  foot.     The  foot  which  is 
raised  up  is,  however,  again  placed  on  the  ground  and  commences  to  act 
as  a  supporting  member  before  the  foot  which  is  next  elevated  has  left 
the  ground.     Consequently,  support  continues  on  three  feet  at  one  time, 
and  the  period  of  support  lasts  much  longer  than  that  of  forward  move- 
ment.  Walking  backward  in  quadrupeds  is,  therefore,  an  extremely  slow 


PHYSIOLOGY   OF   MOVEMENT.  755 

gait.     In  this  act  the  centre  of  gravity  is  not  moved  directly  forward, 
but  oscillates  from  side  to  side. 

(e)  Swimming. — In  swimming  the  trunk  is  almost  entirely  immersed 
in  the  water,  the  neck  extended,  and  the  head  held  high.  The  horse 
swims  readily,  since  its  lungs  contain  a  large  amount  of  air,  and  the  rapid 
movement  of  the  limbs  gives  to  the  body  an  impulse  in  a  horizontal 
direction,  the  weight  of  the  body  being  largely  overcome  by  the  buoy- 
ancy of  the  water.  The  movement  of  the  feet  consists  in  rapid  pen- 
dulum-like motions  from  before  backward,  and  the  forward  motion  of 
the  body  results  from  the  resistance  which  the  water  offers  to  the  back- 
ward movement  of  the  feet.  The  swimming  motions  in  the  horse  occur 
regularly  in  the  same  direction  on  each  side  of  the  body. 

The  power  developed  by  any  mechanical  contrivance  is  estimated 
by  the  weight  multiplied  by  the  height  to  which  it  may  be  raised  in  one 
second  ;  this  is  described  as  a  kilogram  meter.  Animals,  therefore,  may 
be  regarded  as  machines,  since  they  possess  the  power  of  raising  a  weight 
to  a  certain  height.  Likewise,  the  motion  of  a  weight  on  a  level  surface 
is  to  be  regarded  as  a  production  of  work,  and  whose  movement  equals 
the  sum  of  all  the  resistances  which  have  to  be  overcome  by  the  animal 
and  the  velocity  produced.  The  power  of  a  horse  is  placed,  as  an  average, 
at  sixty  kilogram  meters,  an  ox  at  sixty  kilogram  meters,  and  an  ass  at 
thirty -six  kilogram  meters.  The  average  velocity  communicated  to  the 
weight  in  work  continued  for  several  hours  each  day  has  been  placed  in 
the  horse  at  1.25  meters,  the  ox  0.8  meter,  and  the  ass  0.8  ;  consequently 
the  unit  of  power  in  the  horse  has  been  placed  at  sevent3r-five  kilogram 
meters,  in  the  ox  forty-seven,  and  ass  twenty -nine:  so  that,  therefore,  one 
horse-power  would  mean  a  power  which  would  be  able  to  raise  seventy- 
five  kilograms  one  meter  high  in  one  second.  In  referring  these  figures 
to  the  body  of  animals,  it  has  been  calculated  that  the  development  of 
power  in  animals  in  one  hour,  reckoned  for  each  kilogram  of  body 
weight,  is — 

In  the  horse,         .        .        .        .        .940  kilogram  meters. 

"     "   mule, 800 

"     "   ass; 640  " 

"     "   ox,     t        .    ,    .        .        .        .620 

"     "   man, 560        "  " 

In  the  application  of  animal  power  in'  hauling,  or  in  employing  the 
horse  as  a  draught  animal,  resistance  has  to  be  overcome,  since  the  centre 
of  gravity  must  be  advanced  by  the  power  exerted  by  the  hind  extremi- 
ties (Fig.  312).  In  general,  the  hauling  power  of  an  animal,  as  in  all 
motors,  is  governed  by  the  mass  moved,  therefore  through  the  weight 
of  the  animal  and  through  the  velocity  communicated.  The  power  thus 
acts  in  two  relationships,  through  the  overcoming  of  the  resistance  of  the 


756 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


weight  and  the  transference  of  the  velocity  of  the  animal  to  the  moving 
mass.  All  the  arrangements  of  the  hind  extremities  are  especial!}'  favor- 
able for  the  production  of  power;  thus,  reduction  of  the  anterior  pelvic 
angle,  accompanied  by  powerful  development  of  the  hips  and  lumbar 
muscles.  In  animals,  therefore,  with  short  bones,  slight  angularity,  and 
short  muscles  the  conditions  are  most  favorable  for  drawing  heavy 
weights,  while  animals  with  long  bones,  long  muscles,  and  highly 
angular  joints  are  especially  adapted  for  speed.  The  position  of  the 
centre  of  gravit}*  in  the  animal  body  is  especially  of  influence  in  the 
developing  power.  Since  the  body  weight  is  the  moving  force  its 


FIG.  312.— HAULING  FROM  A  COLLAR.    (Colin.) 

The  line,  A  B,  indicates  the  direction  of  the  resultant  of  the  propelling  forces  through  the  lines,  A  D 

and  B  C. 

action  will  be  the  more  developed  the  farther  forward  the  centre  of 
gravity,  since  in  this  way  the  power-arm  of  the  lever  will  be  increased. 
Consequently,  draught  animals  sink  the  head  and  neck.  The  power 
developed  by  horses  has  been  estimated  by  raising  a  certain  weight 
to  a  certain  height  by  a  rope  passing  over  a  pulley.  Experiments  so 
made  have  shown  that  a  moderately  strong  horse  may  raise  a  weight 
of  ninety-five  kilos  in  one  second  to  0.8  meter  high,  from  whence  horse- 
power of  seventy-six  kilogram  meters  has  been  deduced.  In  the  same 
way  the  power  'of  an  ox  has  been  found  to  be  forty-seven  and  an  ass 
twenty-nine  kilogram  meters.  In  drawing  a  weight,  the  full  power  of  an 


PHYSIOLOGY   OF   MOVEMENT. 


757 


animal  is  never  employed,  but  there  is  always  a  certain  amount  of  loss 
from  friction  and  other  causes.  As  most  of  the  contrivances  which  are 
employed  to  enable  horses  to  draw  weight  consist  of  attachments  which 
applies  the  weight  to  the  horse's  shoulders,  the  weight  falls  in  front  of  the 
centre  of  gravity  of  the  body,  and  the  animal  may  thus  be  regarded  as 
pushing  the  weight ;  and  as  the  mass  moved  is  the  animal's  body  plus  the 
applied  weight,  the  greater  the  latter  the  more  the  centre  of  gravity  of  the 
common  mass  will  be  advanced.  Hence,  in  drawing  heavy  weights  the 
fore  limbs  will  be  behind  the  common  centre  of  gravity,  and  they,  also, 
in  their  extension  will  aid  in  propelling  the  body. 

6.  SPECIAL  MUSCULAR  MECHANISMS. —  The  Voice. — By  the  term  voice 
is  meant  the  sound  produced  in  man  and  the  higher  animals  through  the 
vibration  of  the  column  of  air  forced  by  the  contraction  of  the  thorax 
between  the  vibrating  vocal  cords  of  the  larynx.  Speech,  of  which  man 


FIG.  313.— THE  HUMAN  LARYNX,  AS  SEEN  FIG.  314.— POSITION  OF  THE  HUMAN  VOCAL 

WITH  THE  LARYNGOSCOPE.  (Landois.)  CORDS  ON   UTTERING  A   HIGH  NOTE. 

L.,  tongue  :  £.,  epiglottis:   V.,  valleculla;  R.,  glottis;  (LandoiS.) 

L.  i\,  true  vocal  cords  ;  S.  M.,  sinus  Morgagni :  L.  r>.  s., 
false  vocal  cords :  P.,  position  of  pharynx :  S.,  cartilage 
of  Santorini;  W.,  cartilage  of  Wrisberg  ;  S.  p.,  sinus 
pyriformes. 

alone  is  capable,  consists  in  certain  modifications  of  the  vocal  sounds 
by  the  parts  situated  above  the  larynx;  that  is,  the  pharynx,  mouth,  soft 
palate,  nasal  fossae,  tongue,  teeth,  and  lips.  Speech  may,  therefore,  be 
described  as  articulate  voice. 

Voice  is  produced  by  the  imparting  of  the  vibrations  of  the  vocal  cords 
to  the  column  of  air  within  the  respiratory  organs.  The  means  by  which 
this  is  accomplished  is  entirely  analogous  to  that  by  which  sound  is 
produced  in  reed  instruments.  The  vocal  cords  consist  of  free  rims  of 
highly  elastic  membrane  whose  tension  may  be  varied  by  muscular  action 
and  whose  edges  may  be  approximated  or  separated  (Figs.  313  and  314). 
When  the  edges  of  the  vocal  cords  are  in  close  contact,  through  a  strong 
muscular  expiratory  motion  the  air  below  the  vocal  cords  becomes 
greatly  condensed  and  finally  its  tension  is  sufficient  to  overcome  the 
resistance  of  the  closed  vocal  cords;  when  the  vocal  cords  are  thus 


758  PHYSIOLOGY   OF  THE  DOMESTIC   ANIMALS. 

separated  air  passes  between  them,  and,  consequently,  rarefaction  of  the 
air  below  takes  place,  while  the  cords  being  elastic,  their  tension  serves 
to  again  readily  overcome  the  propulsion  of  the  air  from  the  contraction 
of  the  thorax.  As  a  consequence,  the  edges  of  the  vocal  cords  are  set 
into  rapid  vibration  and  these  vibrations  are  communicated  to  the  column 
of  air  both  below  and  above  the  vocal  cords,  and  as  a  result  a  sound 
which  is  due  to  these  vibrations  is  produced  ;  the  vibrations  of  condensa- 
tion and  rarefaction  of  the  air  are  the  principal  causes  of  the  tone,  while 
the  cavities  above  the  vocal  cords  fulfill  the  part  of  resonators. 

Sounds  produced  in  this  way,  like  other  musical  sounds,  may  vary 
in  regard  to  their  pitch,  intensity,  and  quality.  The  pitch  of  the  sound 
will  depend  upon  the  length  of  the  vocal  cords,  the  shorter  the  vocal 
cords,  the  more  rapid  are  the  vibrations  and  the  higher  the  pitch  of  the 
note  produced.  The  pitch  of  the  note  is  further  dependent  upon  the 
degree  of  tension  of  the  vocal  membrane.  As  in  the  case  of  musical 
instruments  of  a  similar  nature,  stringed  instruments,  or  reed  instru- 
ments, the  pitch  of  the  note  is  proportionate  to  the  square  root  of  the 
tension.  In  man  and  other  mammals  in  whom  vocal  cords  are  present, 
the  pitch  of  the  note  may,  therefore,  be  modified  by  varying  degrees  of 
tension  of  the  vocal  cords  through  the  action  of  different  muscles. 

The  intensity  of  the  sound  depends  primarily  upon  the  strength  of 
the  blast  of  air,  so  that,  therefore,  the  more  vigorous  the  expiration,  the 
greater  will  be  the  amplitude  of  the  vibration  of  the  vocal  cords  and  the 
greater  will  be  the  intensity  of  the  sound,  while  the  action  of  the  dif- 
ferent resonators  of  the  vocal  organs,  through  the  sympathetic  vibrations 
induced  in  their  cavities  by  the  vibration  of  the  column  of  air  set  into 
motion  by  the  swaying  vocal  cords,  is  added  to  the  fundamental  tone 
that  is  produced  and  its  intensity  is  modified. 

The  timbre,  or  quality  of  the  vocal  sounds,  as  in  other  musical  in- 
struments, depends  upon  the  over-tones  or  harmonics  which  accompany 
the  fundamental  note.  Changes  in  the  shape  of  the  different  resonating 
cavities  of  the  vocal  organs  will,  by  modifying  the  prominence  of  dif- 
ferent over-tones,  account  for  the  difference  in  the  voice  of  different 
animals. 

The  mode  of  production  and  the  character  of  the  voice  differ  very 
greatly  in  different  members  of  the  animal  kingdom.  Voice  may  be  pro- 
duced in  all  vertebrates  possessed  of  lungs  and  la^nges,  while  in  fishes, 
where  the  respiration  is  branchial  and  not  pulmonary,  the  production  of 
voice  is  impossible.  In  invertebrates  the  sounds  produced  in  such  great 
variet}^  are  in  no  respect  analogous  to  the  voice,  since  they  are  produced 
by  entirety  different  mechanisms.  Thus,  insects  produce  sounds  (which 
are  especially  distinguished  for  their  acuteness)  either  by  the  rapid 
movement  of  their  wings,  as  in  flies  and  bees,  or  by  rubbing  their  legs 


PHYSIOLOGY   OF   MOVEMENT. 


759 


on  their  wing-cases,  or  their  wing-cases  on  each  other  or  on  the  thorax 
or  abdomen.  In  humming  insects  sound  may  be  produced  by  forcing 
the  expired  air  from  their  stigmata,  which  are  provided  with  muscular 
rods  and  which  are  thus  thrown  into  vibration,  so  that  in  this  group  of 
insects,  represented  by  the  humming-bees  and  many  dioptera,  the  closest 
analogy  exists  between  the  production  of  sound  and  the  production  of 
voice  in  the  vertebrates. 

IB 


Libr 


L.ibr 


FIG.  315.— INFERIOR  LARYNX  OF  THK  TURKEY.    (Griitzner.) 

A,  during  voice  production :  B,  in  free  respiration.  (In  At  and  J5'  the  anterior  wall  is  removed.) 
m.st.tr.,  sterno-tracheal  muscles  in  contracted  condition  in  A  and  A> ;  Tr.,  trachea;  v,  Tr.  R., 
united  tracheal  rings,  forming  the  tympanum  with  its  antero-posterior  bridge,  S. ;  B.  Sp.,  bronchi ;  m.  t. «., 
external  tympanic  membrane ;  m.  1. 1..  internal  tympanic  membrane  stretched  out  flat  in  B  and  Bf,  in  A 
and  Al  forming  sharp  folds  in  the  lumen  of  the  bronchi;  L.  ibr.,  interbronchial  ligament;  b.,  band  run- 
ning to  the  dorsal  wall  of  the  trachea. 

Animals  below  insects,  as  radiates  and  mollusks,  are  all  entirely 
incapable  of  sound.  Among  reptiles,  certain  of  them,  such  as  frogs, 
lizards,  and  other  batrachians,  possess  true  vocal  organs.  Among  am- 
phibians the  frog  has  a  larynx  provided  with  muscles,  which  produces  a 
sound  of  varying  pitch,  dependent  upon  the  strength  of  the  muscular 
contraction  and  the  force  of  the  expiratory  blast.  The  range  of  such 
vibrations  is,  however,  extremely  limited.  In  the  Rana  esculenta  there 
is  on  each  side  of  the  angle  of  the  mouth  a  membranous  bag  which  may 


760  PHYSIOLOGY  OF   THE   DOMESTIC   ANIMALS. 

be  inflated  with  air,  and  whose  wralls,  being  thin  and  membranous,  are 
thrown  into  vibration,  and,  together  with  the  column  of  air  contained  in 
the  oral  chamber,  aid  in  producing  the  characteristic  resonance  of  the 
croaking  of  the  frog  (Fig.  315). 

In  birds  the  vocal  organs  are  double,  a  larynx  situated  at  the  upper 
termination  of  the  trachea  and  a  syrinx  at  its  bifurcation  constituting 
a  true  vocal  organ.  Two  folds  of  mucous  membrane,  or  three  in  the  case 
of  song-birds,  project  into  each  bronchus,  and  are  so  acted  on  by  muscles 
as  to  vary  their  tension  and  adapt  them  to  the  production  of  voice.  The 
superior  larynx  acts  only  as  an  accessory  in  the  production  of  sound. 
The  number  and  complexity  of  the  muscular  fibres  acting  on  these 
membranes  varies  in  proportion  to  the  range  of  voice.  In  the  gallinacea 
simply  a  trace  of  muscular  fibre  can  be  recognized ;  but  one  pair  of 
muscles  is  found  in  the  eagle,  three  pairs  in  the  paroquet,  while  five 
pairs  are  found  in  song-birds.  These  muscles  have  a  common  origin  in 
the  trachea,  and  their  other  extremities  are  inserted  into  the  first  ring  of 
the  bronchus.  In  addition  to  these  intrinsic  muscles  there  are  others 
concerned  in  varying  the  length  of  the  trachea,  so  as  to  alter  the  length 
of  the  vocal  tube  and,  therefore,  the  pitch  of  the  note  produced.  The 
superior  organ,  -or  the  larynx,  is  entirely  negative  in  the  production  of 
sound,  and  the  performance  of  tracheotomy  below  the  larynx  produces 
but  slight  modification  in  the  character  of  the  sound  produced. 

In  mammals,  as  is  well  known,  the  greatest  variation  exists  in  the 
character  of  the  sounds  produced.  The  organs  for  the  production  of 
sound  are  here  the  larynx  and  the  upper  resonating  chambers,  varying  in 
shape  and  general  character  among  each  other,  although  in  all  built  on 
the  same  general  plan  as  in  man.  The  variations  in  the  voice  are 
dependent  upon  modifications  in  the  larynx,  in  the  depth  of  the  nasal 
chambers,  the  shape  of  the  pharynx,  of  the  various  sinuses,  and  the 
formation  of  the  mouth  and  of  the  laryngeal  ventricles.  Sound  is,  how- 
ever, primarily  due  in  all  cases  to  the  vibrations  transmitted  to  the 
column  of  air  by  the  swaying  to  and  fro  of  the  vocal  cords.  The  superior 
or  false  vocal  cords  of  man  are  absent  in  many  species  of  mammals. 
The  glottis  of  the  horse  is  distinguished  by  the  formation  of  a  semi-lunar 
fold  of  mucous  membrane  below  the  epiglottis,  which  serves  to  form  a 
funnel-shaped  cavity.  The  laryngeal  ventricles  are  also  well  developed. 
The  voice  in  the  horse  is  produced  by  a  succession  of  interrupted  expira- 
tory movements,  the  tension  of  the  vocal  cords  gradually  diminishing 
during  each  complete  expiration,  so  that,  therefore,  the  first  sounds 
produced  have  a  higher  pitch  than  the  last;  the  superior  ventricles  are 
wanting  (Fig.  316). 

The  larynx  of  the  ass  differs  but  slightly  from  that  of  the  horse. 
Here,  also,  there  are  two  vocal  cords,  the  ventricles  are  well  developed, 


PHYSIOLOGY  OF  MOVEMENT. 


761 


but  the  opening  to  them  is  narrow.  The  voice  of  the  ass  is  characterized 
by  the  fact  that  it  commences  in  an  inspiratory  movement  in  the  produc- 
tion of  a  sound  of  high-pitch  and  it  terminates  in  expiration  in  the 
production  of  a  deeper  sound. 

The  larynx  of  ruminants  offers  considerable  differences  to  that  of 
solipedes.  The  glottis  is  short,  and  the  vocal  cords  can  scarcely  be  dis- 
tinguished from  the  lining  membrane  of  the  larynx,  and  there  are  no 
ventricles.  The  voice  in  ruminants  is,  therefore,  more  imperfect  than  in 
the  horse,  and  consists  of  a 

sound  of  low  pitch  capable  of  ifljFmafr  t       5' 

but  little  variation  (Fig.  317). 

In  the  hog  below  the  epi- 
glottis is  found  a  large,  mem- 
branous sack,  which  fulfills  the 
purpose  of  a  resonator,  greatly 


Fia.  316.— LARYNX    OF    THE    HORSE 
FROM  ABOVE  AND  BEHIND.  (Muller.) 

a  at,  thyroid  cartilage;  b  b,  arytenoid  car- 
tilages; cc',  arytenoid  muscles;  d dt,  aryepiglottic 
folds;  e,  epiglottis.  1  V,  posterior  crico-arytenoid 
muscles;  2  I',  oblique  arytenoid  muscles;  33f, 
superior  thyro-arytenoid  muscles;  44',  true  vocal 
cords ;  5,  glottis ;  6,  ventricles  of  larynx. 


FIG.  317.— LARYNX  AND  HYOID  BONE  OF  Ox. 

(Milller.) 

1,  2,  3,  arms  of  the  hyoid  bone  :  4.  thyroid  cartilage ;  5,  body 
of  the  hyoid  bone;  5'  and  5",  fork  of  the  hyoid  bone;  6,  arytenoid 
cartilages ;  7,  epiglottis ;  8,  cricoid  cartilage ;  9,  posterior  crico- 
arytenoid  muscles ;  10,  trachea. 


strengthening  the  intensity  of  the  voice  and  giving  to  it  its  peculiar 
character.  In  the  hog  the  inferior  vocal  cords  are  inserted  into  the 
tracheal  border  of  the  thyroid  cartilage  and  the  arytenoid  cartilages 
are  fused  together,  the  vocal  cords  are  rudimentary,  the  ventricles  are 
deep  and  communicate  with  the  interior  of  the  larynx  only  by  a  narrow 
slit.  Two  characters  of  sound  may  be  produced  by  the  hog,  the  one 
of  low  pitch,  a  grunt,  which  is  the  habitual  sound,  while  another  of  very 
high  pitch  is  only  produced  when  the  animal  is  maltreated  or  excited. 
In  the  dog  the  vocal  cords  are  well  developed,  while  the  false  vocal 


762  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

cords  are  scarcely  perceptible;  the  ventricles  are  ample,  but  their 
openings  are  very  narrow.  The  voice  in  dogs  is  capable  of  greater  scope 
than  in  other  of  the  domestic  animals,  with  the  exception,  perhaps,  of 
the  cat,  which  is  characterized  by  an  almost  equal  development  of  the 
upper  and  lower  vocal  cords. 

The  mechanism  of  the  production  of  the  voice,  therefore,  depends 
upon  the  expulsion  of  a  blast  of  air  between  two  free  membranous  rims, 
which  are  thus  thrown  into  vibration  and  whose  tension  and  position  are 
capable  of  modification.  The  change  in  the  position  and  tension  of  the 
vocal  cords  is  accomplished  through  the  action  of  the  laryngeal  muscles. 
The  laryngeal  muscles  fulfill  a  double  function.  In  respiration,  as  has 
been  already  mentioned,  the  glottis  is  widened  during  inspiration  and 
the  vocal  cords  tend  to  approach  each  other  during  expiration.  In  the 
production  of  voice  the  vocal  cords  are  almost  always  in  close  contact. 

The  glottis  may  be  dilated  by  the  action  of  the  crico-arytenoid 
muscles.  When  they  contract  the  arytenoid  cartilages  are  drawn  back- 
ward, downward,  and  toward  the  middle  line,  so  that,  therefore,  the 
vocal  processes  in  which  the  vocal  cords  are  inserted  must  be  separated. 
A  large  triangular  space  is  thus  formed  between  the  vocal  cords 
as  in  inspiration. 

The  glottis  is  constricted  by  the  contraction  of  the  transverse 
arytenoid  muscles,  which  extend  from  both  outer  surfaces  of  the 
arytenoid  cartilages  along  their  entire  length.  When  these  muscles, 
together  with  the  oblique  arytenoid,  contract,  the  arytenoid  cartilages 
are  approximated  and  the  glottis  closed.  During  the  production  of 
voice  the  vocal  processes  of  the  arytenoid  cartilages  must  be  closely 
approximated,  and  to  accomplish  this  it  is  necessary  that  they  be  rotated 
inward  and  downward.  This  result  is  brought  about  through  the 
contraction  of  the  thyro-arytenoid  muscles,  which  are  imbedded  in  the 
substance  of  the  vocal  cords,  and  when  they  contract  they  so  rotate  the 
arytenoid  cartilages  that  the  vocal  processes  turn  inward.  The  glottis 
is,  therefore,  narrowed  to  a  mere  slit  in  the  anterior  part,  while  a 
triangular  space  through  which  respiration  takes  place  remains  open 
posteriorly. 

The  vocal  cords  vary  in  tension  according  to  the  degree  of  con- 
traction of  the  crico-thyroid  muscles,  which  pull  the  thyroid  cartilage 
downward  and  forward.  At  the  same  time  the  crico-arytenoid  muscles 
act  upon  the  arytenoid  cartilages,  drawing  them  slightly  backward  and 
maintaining  them  in  that  position. 

In  the  production  of  voice,  not  only  must  the  vocal  cords  be  thrown 
into  tension  in  the  manner  above  described,  but  the  triangular  space  of 
the  respiratory  part  of  the  glottis  between  the  arytenoid  cartilages  must 
likewise  be  closed.  This  is  accomplished  by  the  contraction  of  the 


PHYSIOLOGY  OF  MOVEMENT. 


763 


transverse  and  oblique  arytenoid  muscles,  added  to  the  contraction  of 
the  internal  thyro-arytenoids.  At  the  same  time  a  concave  margin 
is  produced  in  the  vocal  cords  through  the  action  of  the  crico-tl^roid 
and  the  posterior  crico-arytenoids  (Figs.  318,  319,  and  320). 


FIG.  318.— ACTION  OF  THE  MUSCLES  OF 
THE  LARYNX.  (Beaunis.) 

The  dotted  lines  indicate  the  new  positions  as- 
sumed by  the  thyroid  cartilage  in  the  action  of  the 
crico-thyroid  muscles. 

1,  cricoid  cartilage:  2,  arytenoid  cartilage:  3, 
thyroid  cartilage ;  4,  true  vocal  cord  ;  5,  new  position 
of  the  thyroid  cartilage ;  6,  new  position  of  the  vocal 
cords.  ' 


FIG.  319.— SCHEMATIC  HORIZONTAL  SECTION  OF 
THE  LARYNX.    (Landois.) 

I,  position  of  the  horizontally  divided  arytenoid  cartilages 
during  respiration ;  from  their  anterior  processes  run  the  con- 
verging vocal  cords.  The  arrows  show  the  line  of  action  of  the 
posterior  crico-arytenoid  muscles,  resulting  in  the  assumption  of 
the  positions  indicated  by  the  dotted  Hues,  II,  H. 


FIG.  320.— SCHEME  OF  THE    CLOSURE    OF  THE   GLOTTIS  BY  THE  THYRO- 
ARYTENOID  MUSCLES.    (Landois,) 

II,  II,  position  of  the  arytenoid  cartilages  during  quiet  respiration  ;  the  arrows  indicate  the  direction 
of  muscular  traction.    1 1,  the  position  of  the  arytenoid  cartilages  after  the  muscles  contract. 

The  thyro-arytenoid  muscle  is  the  one  which  principally  causes 
variations  in  the  tension  of  the  vocal  cords  and,  consequently,  variations 
in  the  pitch  of  the  sounds. 

When  the  muscles  acting  on  the  vocal  cords  relax  the  vocal  cords 
themselves  likewise  relax  from  the  reduction  of  the  extending  force,  and 


764  PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 

the  elasticity  of  the  displaced  thyroid  and  arytenoid  cartilages  corner 
into  play  and  causes  them  to  assume  their  original  position.  The  thyro- 
arytenoid  and  the  lateral  crico-arytenoids  may  likewise  serve  to  produce 
relaxation  of  the  vocal  cords. 

To  recapitulate :  the  tension  of  the  vocal  cords  is  principally  due  to 
the  crico-thyroid  and  the  posterior  crico-arytenoids  ;  the  narrowing  of 
the  respiratory  part  of  the  glottis  is  accomplished  by  the  transverse  and 
oblique  arytenoids  ;  and  the  narrowing  of  the  vocal  glottis  is  accom- 
plished by  the  contraction  of  the  thyro-arytenoid  and  the  lateral  crico- 
arytenoids,  the  former  muscle  likewise  increasing  the  tension  of  the 
vocal  cords. 

With  the  exception  of  the  crico-thyroid  all  the  intrinsic  muscles  of 
the  larynx  are  supplied  by  the  inferior  laryngeal  nerve.  The  superior 
laryngeal  nerve  supplies  the  crico-thyroid,  and  is  at  the  same  time 
the  sensory  nerve  of  the  mucous  membrane  of  the  larynx. 

For  the  mechanism  of  articulated  speech  the  reader  is  referred  to 
text-books  on  human  physiology. 


SECTION  II. 
THE  PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM. 

THE  different  functions  of  the  animal  body  have  been  found  to 
require  for  their  fulfillment  divers  structures  different  in  location  and  in 
mode  of  action.  In  any  one  of  the  single  functions  of  the  animal  body, 
such,  for  example,  as  the  contraction  of  a  muscle,  a  number  of  processes 
are  concerned ;  thus,  the  inauguration  of  the  muscular  contraction 
requires  the  conduction  to  a  muscle  of  a  stimulus.  The  muscle  in  con- 
tracting uses  up  a  large  supply  of  oxygen  and  liberates  more  carbon 
dioxide  and  other  retrograde  products.  Increased  muscular  contraction, 
therefore,  necessitates  a  supply  to  the  muscle  of  a  larger  amount  of 
arterial  blood  and  the  removal  from  the  body  through  the  lungs  and  kid- 
neys of  the  products  of  the  waste  of  muscular  tissue.  Muscular  activity, 
therefore,  implies  accelerated  circulation,  accelerated  respiration,  and 
increased  excretion.  A  similar  complexity  may  be  traced  in  all  the  other 
different  functions  of  the  animal  body.  Each  modification  or  even  mani- 
festation of  function  implies  a  reflection  upon  the  activity  of  other  asso- 
ciated processes.  This  co-ordination  of  operations,  which  may  be  widely 
different  in  character  and  yet  closely  interdependent,  is  accomplished  by 
means  of  the  nervous  system.  The  primaiy  object  of  the  nervous  system 
is,  therefore,  to  link  together  different  and  widely  distant  organs,  and 
thus  act  as  the  regulator  of  the  actions  of  the  animal  body. 

In  animals  where  specialization  of  function  has  not  yet  appeared  no 
such  communication  between  different  parts  of  the  body  is  required,  and, 
as  a  consequence,  in  such  no  nervous  system  is  present.  As  we  found 
that  the  organs  of  circulation  were  largely  dependent  for  their  degree  of 
development  on  the  complexity  of  the  alimentary  apparatus,  so  it  may 
be  found  that  in  a  general  way  the  nervous  system  is  developed  in  pro- 
portion to  the  muscular  system.  This  indicates  one  of  the  main  func- 
tions possessed  by  the  nervous  apparatus  for  controlling  and  modifying 
movement.  This  is,  however,  but  one  side  of  the  importance  of  the 
nervous  system. 

In  the  nervous  system  is  developed  in  the  highest  degree  the  func- 
tion of  automatism.  By  this  term  is  meant  the  power  possessed  by  the 
lowest  forms  of  protoplasm  of  receiving  impulses  from  without  and  modi- 
fying them  into  efferent  impulses,  which  may  take  on  the  form  of  motion 
as  their  most  usual  manifestation.  It  is  thus  seen  that  automatism 

(765) 


766  PHYSIOLOGY   OF  THE  DOMESTIC  ANIMALS. 

implies  at  least  four  different  operations — the  conduction  of  afferent 
impulses,  the  reception  and  conversion  of  these  afferent  into  efferent 
impulses,  and  the  liberation  again  and  conduction  of  efferent  impulses. 

In  the  scheme  of  specialization  of  function  it  would  only  be  expected 
that  for  the  division  of  labor  we  should  also  find  that  these  operations 
become  separated  and  located  in  different  structures.  We  find,  therefore, 
the  nervous  system,  in  accordance  with  this  purpose,  divided  into  organs 
of  conduction  and  organs  of  receiving  and  liberating  nervous  impulses. 

The  organs  for  transmitting  nerve  impulses  constitute  the  nerves. 
The  organs  for  modifying  and  liberating  nerve  impulses  are  found  in  the 
ganglia  or  nerve-cells  of  the  nervous  system. 

The  scheme  of  the  nervous  system,  therefore,  implies  the  presence 
on  the  periphery  of  a  receptive  organ  for  receiving  external  impressions. 
Such  an  organ  is  represented  by  the  terminal  filaments  of  the  sensory 
nerves,  or,  rather,  the  nerves  of  general  or  special  sense.  It  implies  a 
means  of  communication  between  this  external  receptive  organ  and  the 
nervous  ganglia  at  a  distance,  the  latter  possessing  the  power  of  receiv- 
ing the  impressions  transmitted  from  the  exterior  through  the  afferent 
sensory  nerves.  Such  a  receptive  ganglion  is  again  in  connection  with  a 
cell  or  collection  of  cells  in  which  the  automatic  powers  are  especially 
developed,  and  which,  therefore,  modify  the  impressions  coming  from 
without  and  convert  them  into  efferent  impressions.  The  latter  are  con- 
ducted from  the  centre  through  the  efferent  or  motor  nerves  to  various 
peripheral  organs,  whether  to  the  terminal  plates  in  the  muscular  tissue 
or  to  glands,  blood-vessels,  or  the  other  structures  of  the  animal  body'. 

Like  all  other  organic  systems,  the  nervous  system  becomes  more 
complicated  and  diversified,  reaching  a  higher  stage  of  perfection  in  pass- 
ing from  the  lowest  forms  of  animal  life,  in  which  it  first  appears,  to  the 
higher  examples  of  the  animal  series. 

In  the  protozoa,  the  lowest  subdivision  of  the  animal  kingdom,  a 
nervous  system  in  the  sense  in  which  we  have  described  it,  as  constituted 
of  nerve-cells  and  nerve-fibres,  is  entirely  absent.  The  undifferentiatecl 
protoplasm  fulfills  all  the  purposes  of  the  nervous  system  as  demanded 
by  the  needs  of  such  an  organization. 

In  the  animals  belonging  to  the  group  of  infusoria,  where  we  find  the 
first  appearance  of  the  development  of  organs  as  seen  in  the  contractile 
cilia  as  organs  of  locomotion,  the  nervous  system  has  not  appeared,  the 
movement  of  such  organs  being  dependent  simply  upon  the  automatic 
properties  of  the  undifferentiated  protoplasm  ;  and  we  find  as  an  illus- 
tration of  this  that  even  in  animals  higher"  in  the  scale,  where  ciliated 
organs  are  commonly  found,  that  such  are  independent  of  the  nervous 
system. 

In  the  star-fish  is  found  the  first  clear  evidence  of  nerve  fibres  and 


PHYSIOLOGY   OF   THE   NEKVOUS   SYSTEM. 


767 


cells  connected  together  to  receive  and  convey  impression  (Fig.  321). 
It  consists  of  a  ring  around  the  mouth  composed  of  five  ganglia  of  equal 
size  with  radiating  nerves.  From  this  circle  delicate  fibres  may  be  traced 
into  the  different  rays.  In  lower  zoophytes  all  traces  of  the  nervous 
system  is  wanting,  and  in  them  the  functions  of  nutrition  are  accom- 
plished through  the  operations  of  undifferentiated  protoplasm. 

In  the  mollusks  the  nervous  system  has  reached  a  somewhat  higher 
form  of  development,  and  two  or  more  ganglia  are  found  located  around 
the  gullet  and  communicating  by  nerve-fibres  with  other  ganglia  in  dif- 
ferent regions  of  the  body,  sending  off  nerves  to  the  different  organs. 
Usually  in  the  mollusks  there  is  a  cir- 
cular ganglion  located  in  the  cephalic 
side  of  the  animal  and  two  abdominal 
ganglia  placed  below  the  oesophagus 


FIG.  322.— NERVOUS  SYSTEM  OF  A  GAS- 

TEKOPOD  MOLLUSK.    (Perrier.) 
c,  cerebroid  ganglia ;  p,  pedal  ganglia ;  o,  otocysts ; 

FIG.   321.— NERVOUS    SYSTEM    OF   THE   STAR-       v>  vl'vll,  ganglia  of  second  oesophageal  collar ;    f,  ten- 
FISH.     (Carus.)  tacles ;  y,  eyes ;  x,  excrement. 

and  united  to  the  cephalic  ganglion  and  the  cesophageal  ring  (Fig.  322). 
These  ganglia  are  frequently  connected  with  others  whose  locations  will 
vary  in  different  species. 

In  the  articulata,  represented  by  the  insects,  annelida,  and  crusta- 
ceans, the  nervous  system  has  become  symmetrical  (Fig.  323). 

The  ganglia  which  compose  the  nervous  system  may  be  arranged 
in  pairs  on  each  side  of  the  median  line  of  the  bod}*,  each  pair  corre- 
sponding to  a  segment  of  the  body,  extending  throughout  its  entire 
length  and  united  to  each  other  so  as  to  form  a  longitudinal  chain 
of  ganglia,  which  are  connected  further  by  transverse  commissures. 
Sometimes  the  ganglia  consist  of  a  single  median  row.  Usually  one  of 
the  ganglia  is  more  voluminous  than  the  others,  and  being,  as  a  rule, 
located  in  the  anterior  extremity  of  the  animal,  might  be  compared  to 


768  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

the  brain  of  vertebrates.  Such  a  comparison  is  warranted  by  the  fact 
that  when  nerves  of  special  sense  are  present  they  invariably  originate 
from  this  collection  of  nerve-cells.  Where  a  distinct  cephalic  gan- 
glion is  present  it  is  situated  above  the  oesophagus,  while  all  the  other 
portions  of  the  ganglionic  chain  lie  on  the  ventral  side  of  the  body,  the 
commencement  of  the  chain  being  connected  with  the  cephalic  ganglion 


FIG.  323.— NERVOUS  SYSTEM  OP  AN  ARTICULATE.    (Perrier.) 

by  a  collection  of  circular  fibres  around  the  gullet  and  spoken  of  as  the 
oesophageal  collar. 

The  number  of  ganglia  in  the  articulata  is  very  variable ;  there  may 
be  twelve  or  fifteen  pairs  or  but  three.  The  larger  the  number  of 
ganglia,  the  greater  their  tendency  to  fusion  along  the  middle  line. 

In  all  invertebrates  the  nervous  system  is  composed  of  such  a  series 
of  separate  and  distinct  ganglia,. 


PHYSIOLOGY   OF   THE   NEKVOUS   SYSTEM. 


769 


In  vertebrates  the  nervous  system  has  reached  a  much  higher  stage 
of  development,  and  here  is  placed  above  the  digestive  canal,  in  contra- 
distinction to  the  position  which  it  occupies  when  present  in  the  inverte- 
brates, and  is  usually  inclosed  within  a  bony  or  cartilaginous  cavity ;  it 
is  divided  into  a  cephalic  portion,  confined  within  the  cranium,  connected 
to  a  long  trunk  of  nerve-cells  inclosed  within  the  vertebral  canal,  con- 
stituting the  spinal  cord  (Fig.  324).  From  this  central  nervous  system, 


B 


FIG.    325.— BRAIN    OF    PERCH,    AFTER   CUVIER.     (Rymer 
Jones. ) 

A,  cerebellum;  B,  cerebrum :  C.  olfactory  ganglion;  i,  olfactory  nerves; 
D,  optic  ganglion;  G,  supplementary  lobe;  H,  transverse  fibres  in  the  walls  of 
the  cerebral  ventricle;  N,  commissure  of  the  optic  nerves;  P,  Q,  R,  S,  T,  U, 
the  third,  fourth,  fifth,  sixth,  seventh,  and  eighth  pair  of  cerebral  nerves. 


RH. 


VIII. 


FIG.  324.  — BRAIN  AND 
SPINAL  CORD  OF  MAN. 
(Carpenter.) 


FIG.  326.— BRAIN  OF  FROG  SEEN  FROM  ABOVE.     (JVv/w.) 

L.  OLF,  olfactory  lobes ;  L.H,  hemispherical  lobe  (fore-brain) ;  VIII,  lobe 
of  the  third  ventricle;  L.O,  optic  lobes  (mid-brain) ;  CELL,  cerebellum  (hind- 
brain)  ;  OBL,  medulla  oblongata ;  RH,  rhomboidal  sinus. 


both  from  the  brain  and  spinal  cord,  originate  series  of  fibres  which 
fulfill  the  functions  of  conduction  of  both  motor  and  sensory  impulses 
and  which  extend  to  all  parts  of  the  body.  In  connection  with  this  sys- 
tem, which  is  spoken  of  as  the  cerebro-spinal  system,  there  is  usually  found 
a  more  or  less  independent  series  of  ganglia,  which  constitutes  the 
sympathetic  system. 

While  such  a  cerebro-spinal  system  characterizes  all  vertebrates,  it  is 

49 


770  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

capable  of  great  variations  in  development  in  different  members  of  this 
group.  In  fishes  and  reptiles  the  brain  is  less  developed  than  in  higher 
members,  no  convolutions  are  found  on  its  surface,  and,  while  the  cere- 
bral hemispheres  are  not  highly  marked,  the  optic  and  olfactory  lobules 
are  usually  comparatively  voluminous,  while  the  cerebellum  of  reptiles 
and  fishes  is  reduced  to  a  single  lobe  (Figs.  325  and  326). 

In  birds  the  hemispheres  or  cerebral  lobes  are  still,  as  in  the  mam- 
mals, the  most  voluminous  portions  of  the  brain,  but  here,  also,  no  con- 
volutions are  found  and  the}^  are  not  closely  united  to  each  other,  since 
the  corpus  callosnm,  as  well  as  the  pons  varolii,  is  absent  (Fig.  327). 

In  birds  the  analogue  of  the  tubercula  quadrigemina,  which  are  four 
in  number  in  the  mammals,  are  here  reduced  to  two,  and,  therefore,  receive 
the  name  of  the  tubercula  bigemina  or  optic  lobes,  and  are  visible  at  each 
side  of  the  brain  when  looked  at  from  above. 


T- 
-cM 


I.  II. 

FIG.  327.— BRAIN  OF  BIRD  (Falco  buteo).    (Nuhn.) 

I,  view  of  upper  surface.    II,  view  of  lower  surface :  cbr,  cerebrum ;   </,  corpora  quadrigemina,  or 
bigemina;  cbll,  cerebellum;  nbl,  medulla  oblongata;  //,  hypophysis;  opt,  optic  nerve. 

In  birds  the  cerebellum  is  likewise  reduced  to  a  single  median  lobe, 
and  is  entirely  uncovered  \)j  the  cerebrum,  and  being  single  it  possesses 
no  lateral  hemispheres;  the  pons  varolii,  or  the  transverse  fibres  which 
serve  as  a  commissure  for  the  cerebellar  hemispheres,  as  in  mammals,  is 
likewise  absent. 

The  characteristics  of  the  mammalian  brain  will  be  subsequently 
alluded  to. 

The  nervous  system  is  composed  of  central  masses  which  are  in 
constant  communication  with  different  parts  of  the  body  by  means  of 
peripheral  prolongations  which  act  as  organs  of  conduction.  The 
nervous  system  exists,  therefore,  under  two  forms — the  central,  composed 
largely  of  the  so-called  nervous  ganglia,  or  nerve-cells,  and  the  organs  of 
conduction,  or  nerve-fibres.  As  already  indicated,  the  peripheral  termi- 
nations of  the  nerves  are  likewise  in  connection  with  corpuscular  bodies, 


PHYSIOLOGY   OF   THE   NEKVOUS   SYSTEM. 


771 


which  vary  in  accordance  with  the  character  of  the  nerves  with  which 
they  are   in   communication.     The   nerves   or   nerve-fibres   are   simply 


FIG.  328.— BRAIN  AND  NERVOUS  SYSTEM  OF  DIFFERENT  ANIMALS,  NATURAL 
SIZE.    (Thanhoffer.) 

1,  brain  of  ape:  2.  domestic  cat;  3.  squirrel :  4.  water-rat:  5.  mole:  6.  fox :  7.  qnail :  8,  nervous  sys- 
tem of  horned  beetle ;  9,  perch ;  />/,  suprapharyngeal  ganglion :  h<l.  abdominal  ganglion :  vd,  end  ganglion ; 
b,  oesophagus:  e.  nervous  cord  connecting  the  pharyngeal  ganglion:  Crh,  cerebrum:  <-bl.  cerebellum; 
mobl,  medulla  oblongata;  olf,  olfactory  tract;  /«.  optic  lobes:  Ch,  hemispherical  lobes:  I-IX  (in  Fig.  9), 
cerebral  nerves :  wl,  vagus  ganglion ;  br.  branchial  nerves :  10,  nervous  system  of  the  snail ;  Jy,  supra- 
pharyngeal ganglion ;  ag,  infrapharyngeal  ganglion. 


772  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

organs  of  conduction,  and  the  nerve-cells,  in  which  each  nerve  at  each 
end  terminates,  are  for  receiving  and  liberating  impulses. 

Nerves  may  be  of  two  kinds:  afferent  or  centripetal  nerves,  which 
are  concerned  in  the  carrying  of  impulses  from  the  exterior  to  the  cen- 
tral organs  ;  such  nerves  are  frequently  spoken  of  as  sensory  nerves : 
and  efferent  or  centrifugal,  which  carry  impulses  from  the  central 
portions  of  the  nervous  system  to  the  exterior ;  such  nerves  are  motor 
nerves. 

These  two  distinctions  between  nerves  are  not  based  on  an}-  differ- 
ence in  anatomical  structure,  but  are  simply  functional  differences,  since 
it  has  been  found  by  experiment  that  nerves  ma}T  carry  impulses  in 
either  direction,  and  by  dividing  a  motor  and  sensory  nerve  and  con- 
necting the  divided  extremities  of  the  one  with  the  other  the  sensory 
nerve,  after  union  has  taken  place,  may  now  carry  motor  impulses  and 
the  motor  sensory  impulses. 

The  essential  part  of  the  nerve-trunk  is  the  so-called  axis  cylinder, 
which  is  composed  of  a  thin  filament  of  undifferentiated  protoplasm  in 
no  way  different,  as  far  as  ma}'  be  determined,  from  that  found  in  other 
examples  of  free  protoplasm.  This  protoplasmic  centre,  which  is  com- 
posed of  a  number  of  fine  fibrils  and  constitutes  the  axis  cylinder,  is 
always  covered  by  a  thin,  transparent  membrane,  which  is  termed  the 
primitive  sheath.  In  many  instances  this  is  the  only  covering  to  the 
ultimate  fibrils  of  the  nerve,  such  nerves  being  called  non-medullated 
nerve-fibres;  in  others,  which  are  called  medullated  nerves,  within  this 
primitive  sheath,  and  surrounding  directly  the  fibrils  of  the  axis  cjdin- 
der,  is  found  a  thick  layer  of  double  refractive  substance,  which  is  termed 
the  medullary  sheath  or  white  substance  of  Schwann  (Fig.  329). 

Each  nerve-trunk  consists  of  bundles  of  nerve-fibres  held  together 
by  fibrous  connective  tissue  called  the  epineurium,  in  which  are  the 
blood-vessels  with  which  the  nerve-trunk  is  supplied,  lymphatics,  and 
numerous  fatty  cells.  The  neurilemma  closely  resembles  sarcolemma  in 
its  character;  when  subjected  to  long  boiling  botli  yield  gelatin. 

Ganglioiiic  cells  or  nerve-corpuscles  vary  greatly  in  size.  They  may 
be  spherical,  ovoid,  pyramidal,  or  of  other  shapes,  and  send  off  usually 
numerous  branched  processes,  which  serve  to  characterize  the  cells  as 
multipolar  nerve-cells.  No  cell-membrane  is  to  be  detected,  but  the  gan- 
glia are  of  soft  consistence,  containing  numerous  granules  and  pigment 
matter. 

The  nucleus  is  ordinarily  well  developed  and  is  disproportionate^ 
large  to  the  size  of  the  cell.  Two  nucleoli  are  nearly  always  present. 
One  of  the  processes  of  the  ganglion  is  always  unbranched  and  forms  the 
axis  cylinder  of  the  nerve  originating  or  terminating  in  such  a  nerve-cell. 
A  nerve,  therefore,  may  be  regarded  simply  as  a  process  of  the  nerve- 


PHYSIOLOGY   OF   THE   NERVOUS    SYSTEM. 


773 


cell,  the  white  substance  of  Schwann  being  added  after  the  separation  of 
the  nerve-filament  from  the  ganglion. 


FIG.  329.— THE  STRUCTURE  OF  NERVOUS  TISSUE.    (Landois.) 

1,  primitive  fibrilla ;  2,  axis  cylinder ;  3.  Remak's  fibres :  4,  medullated  varicose  fibre ;  5,  6,  medul- 
lated  fibre,  with  Schwann's  sheath :  C.  neurilemma ;  t,  t,  Ranvier's  nodes ;  h,  white  substance  of 
Schwann;  d,  cells  of  the  endoneurium  ;  a,  axis  cylinder :  x,  myelin  drops;  7,  transverse  section  of  nerve- 
fibre  ;  8,  nerve-fibre  acted  on  with  silver  nitrate :  I.  nvultipolar  nerve-cell  from  spinal  cord ;  z,  axial 
cylinder  process :  y,  protoplasmic  processes — to  the  right  of  it  a  bipolar  cell :  II,  peripheral  ganglionic  cell, 
with  a  connective-tissue  capsule ;  III,  ganglionic  cell,  with,  o,  a  spiral,  and,  w,  straight  process  ;  m,  sheath. 

The  branched  processes  of  nerve-cells  are  not,  as  a  rule,  concerned 
in  the  formation  of  other  nerve-trunks  except  in  the  bipolar  or  multi- 
polar  cells,  but  are  concerned  in  bringing  in  communication  other 


774:  PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 

adjacent  cells,  so  that  impulses  may  be  conducted  from  one  to  the  other. 
In  the  peripheral  ganglia  connective-tissue  corpuscles  surround  the 
nerve-cells. 

I.      CHEMICAL      AND      PHYSICAL      CHAKACTEKISTICS      OF      NERVOUS 

TISSUES. 

The  composition  of  nervous  tissue  varies  according  as  the  examina- 
tion is  made  of  the  white  matter  of  the  cerebrum  or  of  the  spinal  cord, 
or  of  the  gray  matter.  The  following  table  represents  their  average 
composition : — 

CHEMICAL  COMPOSITION  OP  NERVOUS  TISSUE. 

Gray  Matter.    White  Matter. 
Water,       .        .'  .        .        .        .    81.6  68.4 

Solids,        .        ...        .        .        .     18.4  31.6 

Proteids,  55.4  24.7 


Lecithin,    . 

Cholesterin  and  fats, 

Cerebrin,  . 

Substances  insoluble  in  ether, 

Salts,          .'..., 


17.2  9.9 

18.7  52.1 

0.5  9.5 

6.7  3.3 

1.5  0.5 


When  brain-matter  is  incinerated  the  greater  part  of  the  phosphorus 
of  the  lecithin  becomes  phosphoric  acid,  and  the  ash,  hence,  has  an  acid 
reaction.  The  following  is  the  composition  of  the  ash  of  one  hundred 
grammes  brain  after  removing  lecithin : — 

SO4K2,  0.411 

KC1 2.524 

K2HPO4, 0.266 

Ca3P208, 0.013 

MgHP04, 0.084 

Na2HP04, 1.752 

Na2CO3 1.148 

Excess  CO2, 0.082 

FeP2O8, 0.010 

6.290 

The  reaction  of  the  gray  matter  during  life  is  said  to  be  acid  from 
the  presence  in  the  ganglionic  masses  of  lactic  acid.  The  reaction  of 
the  white  matter  is  neutral  or  alkaline. 

From  the  above  table  it  is  seen  that  more  than  half  the  solids  in  the 
gray  matter  and  about  one-fourth  the  solids  in  the  white  matter  of  the 
nerve-centres  consist  of  proteids,  and  yet  our  knowledge  of  these  bodies 
is  very  imperfect. 

The  proteids  consist  of  albumen,  which  is  found  in  the  axis  cylinder 
and  in  nerve-cells;  it  is  soluble  in  water  and  coagulates  at  75°  C.;  a 
globulin-like  substance,  which  may'  be  extracted  by  means  of  a  10  per 
cent,  solution  of  common  salt,  and  which  is  precipitated  by  dilution  with 
water  and  by  saturation  with  salt;  and  alkali  albuminate,  which  remains 


CHARACTERISTICS   OF   NERVOUS   TISSUES.  775 

in  solution  when  a  10  per  cent,  salt  solution  of  brain  is  boiled;  it  may 
be  precipitated  after  filtering  by  the  addition  of  acetic  acid. 

Nuclein,  also,  is  found,  especially  in  the  gray  matter;  while  in  the 
sheath  of  nerve-fibres  after  the  removal  of  the  fatty  matters  by  boiling 
alcohol  and  ether  a  nitrogenous  body  is  found  which  is  termed  neuro- 
keratin,  and  which  in  its  composition  appears  closety  related  to  keratin 
and  is  especially  characterized  by  the  sulphur  (2.93  per  cent.)  which  it 
contains. 

Neurokeratin  is  not  affected  in  gastric  or  pancreatic  digestion ;  it 
swells  in  caustic  potash  and  strong  sulphuric  acid,  but  only  dissolves  in 
these  liquids  when  boiled. 

Gelatiu  is  likewise  found  in  nerves,  but  is  evidently  derived  simply 
from  the  connective  tissue  of  their  sheaths. 

Fats  are  present  in  large  amounts,  especially  in  the  white  matter  and 
in  the  white  substance  of  Schwann,  which  appears  to  be  almost  solely  of 
a  fatty  nature. 

The  specific  constituents  of  the  brain  and  nerves  are  of  a  highly 
complex  character  and  may  be  divided  into  two  groups — those  which 
contain  phosphorus  in  combination  and  those  which  are  free  from  phos- 
phorus. As  an  example  of  the  first  of  these,  protagon  may  be  mentioned, 
which,  discovered  by  Liebreich,  has  been  regarded  by  many  chemists, 
not  as  a  distinct  body,  but  as  a  mixture  of  lecithin,  a  phosphorized  fat, 
with  cerebrin,  a  nitrogenous,  non-phosphorized  body.  Experiments  by 
Gamgee  have,  however,  apparently  proven  that  protagon  is  a  definite 
chemical  body,  soluble  in  cold  alcohol  with  difficulty,  readily  soluble  in 
warm  alcohol  and  ether.  To  this  substance  Gamgee  attributes  the  em- 
pirical formula  C160H308X5P035.  It  forms  a  clear  solution  with  glacial 
acetic  acid. 

Cerebrin  is.  an  example  of  the  special  brain-constituents  which  are 
free  from  phosphorus;  it  appears,  however,  that  cerebrin,  as  described 
by  Mu'ller,  is  not  a  distinct  body,  but  a  mixture  of  cerebrin,  homocere- 
brin,  and  encephalin. 

The  entire  subject  of  the  organic  constituents  of  the  nervous  sj'stem 
needs  to  be  re-examined,  since  on  any  matter  where  such  diametrically 
opposite  opinions  are  held  the  error  on  both  sides  must  be  considerable. 

Like  the  muscular  tissue,  nervous  substance  when  passive  has  a 
neutral  or  even  faintly  alkaline  reaction  ;  after  prolonged  stimulation  or 
functional  activit}T,  produced  in  any  wa}T,  the  reaction  becomes  acid. 

After  death  the  reaction  likewise  becomes  acid  and  the  nerves  become 
more  solid,  thus  resembling  the  similar  changes  which  occur  in  muscle, 
and,  although  not  thoroughly  investigated,  in  all  probability  are  due  to  a 
similar  process. 

Nerve-fibres  are  free  from  elasticit}',  and  if  divided  do  not  retract  : 


776  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

their  cohesion,  due  to  their  connective-tissue  constituents,  is  consider- 
able. It  has  been  found  that  a  weight  of  one  hundred  and  ten  to  one 
hundred  and  twenty  pounds  was  required  to  rupture  the  sciatic  nerve  of 
a  man  at  the  popliteal  space.  The  nerves  lengthen  very  considerably 
before  breaking  ;  they,  therefore,  are  extensible. 

II.    NERVOUS  IRRITABILITY. 

As  in  the  case  of  muscle,  nerves  are  capable  of  having  their  func- 
tional activity  called  into  play  by  various  stimuli ;  they  are,  therefore, 
said,  like  muscles,  to  possess  the  power  of  irritability. 

Stimuli  which  call  nervous  activity  into  existence,  like  muscular 
stimuli,  may  be  either  mechanical,  thermal,  chemical,  electrical,  or  physi- 
ological, by  which  is  meant  the  normal  stimuli  which  excite  the  nervous 
system  in  living  bodies. 

In  the  case  of  the  nervous  system  the  influence  of  various  stimuli 
may  be  made  evident,  either  by  allowing  them  to  act  upon  motor 
nerves,  when  the  contraction  of  the  muscles  evoked  will  indicate  the 
stimulation  of  the  nerve ;  or,  in  the  case  of  sensory  nerves,  by  the  pain 
produced  on  their  application. 

A  mechanical  irritant  produces  stimulation  of  the  nerves  by  pro- 
ducing change  in  the  molecular  arrangement  of  the  nerve-particles.  If 
the  mechanical  stimulus,  which  may  be  of  the  nature  of  a  blow,  pressure, 
pinching,  and  stretching,  be  sufficiently  severe  the  nerve  may  then  become 
completely  and  permanently  destroyed,  and  then  lose  its  power  at  that 
point  of  conducting  impressions.  A  single  mechanical  stimulation  of  a 
motor  nerve  will  produce  a  single  contraction  of  a  muscle.  If  the  stimuli 
be  repeated  rapidly  at  short  intervals  the  contractions  may,  as  in  the 
case  of  electrical  stimulation,  be  blended  together,  and  when  the  stimuli 
succeed  each  other  more  frequently  than  sixteen  in  the  second  a  prolonged 
tetanic  contraction  is  produced. 

The  action  of  variations  in  temperature  on  nerve-trunks  is  somewhat 
similar  to  that  exerted  on  muscles. 

If  the  nerve  of  a  frog  be  heated  to  45°  C.  its  excitability  is  first 
increased  and  then  diminished,  and  the  higher  the  temperature  the 
greater  the  excitability  and  the  shorter  its  duration.  If  the  temperature 
be  raised  above  60°  the  medullary  substance  becomes  disorganized  and 
the  nerve  loses  its  excitability.  Sudden  application  of  cold  or  heat  acts 
as  a  stimulus,  and  may  cause  muscular  contraction.  Increase  of  tempera- 
ture above  45°  produces  tetanus  with  rapid  exhaustion  of  the  nerve. 

Anything  which  will  rapidly  change  the  chemical  composition  of  a 
nerve-trunk  may  act  as  a  nerve  stimulus,  and,  although  such  stimuli  may 
at  first  increase  a  nerve's  excitability,  they  rapidly  diminish  its  irrita- 
bility and  often  result  in  complete  nervous  paralysis. 


NERVOUS   IRRITABILITY.  777 

Rapid  desiccation  of  nerves  by  abstracting  the  water  comes  under 
the  head  of  a  chemical  stimulus.  Sugar,  urea,  glycerin,  and  many  metallic 
salts  likewise  act  as  stimuli  and  often  produce  paralysis. 

Nerves  may  likewise  be  thrown  into  activity  by  the  application  of 
the  electrical  current,  whether  on  employing  the  constant  or  induced 
current.  When  a  constant  current  is  allowed  to  enter  a  nerve  a  single 
contraction  is  produced  at  the  moment  of  application  of  the  current, 
and  no  other  apparent  effect  is  evident  until  the  current  is  broken.  The 
breaking  of  the  current  again  causes  a  contraction  to  occur.  So,  also,  in 
sudden  increase  or  decrease  in  the  strength  of  a  constant  current 
passing  through  a  nerve  the  same  effect  will  be  produced  as  on  making 
or  breaking  the  current. 

When  a  constant  current  which  is  too  feeble  to  produce  a  contraction 
is  allowed  to  pass  into  a  nerve,  and  the  strength  of  a  current  then 
gradually  increased,  the  degree  at  which  the  contraction  is  produced  is 
spoken  of  as  the  minimal  stimulus.  As  the  current  increases  in  strength 
the  degree  of  contractions  produced,  at  first  rapidly  and  then  more 
slowly,  increases  until  a  maximum  is  reached ;  such  a  stimulus  is  spoken 
of  as  the  maximal  stimulus.  As  a  rule,  the  effect  produced  by  making 
the  current  is  more  powerful  than  when  the  current  is  broken. 

Nerves  are  more  sensitive  to  electrical  stimuli  than  muscles,  and  a 
current  which,  applied  directly  to  a  muscle,  may  be  too  feeble  to  produce 
contraction  may  throw  the  muscle  into  contraction  when  allowed  to  pass 
through  its  motor  nerve.  When  a  strong  current  is  allowed  to  pass 
through  a  motor  nerve  for  some  time  and  the  circuit  then  suddenly 
broken,  instead  of  a  single  contraction  the  muscle  will  be  thrown  into 
tetanus ;  such  a  condition  is  especially  produced  when  the  positive  pole, 
or  anode,  is  nearest  to  the  muscle,  while,  when  the  negative  pole,  or 
cathode,  is  nearest  to  the  muscle,  tetanus  occasionally  follows  the  making 
of  the  current.  This  effect  is  to  be  explained  by  the  production  of 
a  condition  which  is  known  as  electrotonus,  which  will  be  alluded  to 
directly. 

When  a  stimulus  is  applied  to  any  part  of  a  motor  nerve  a 
condition  of  increased  excitation  is  produced  and  the  impulse  travels 
along  the  nerve,  the  direction  of  the  motion  depending  upon  the 
character  of  the  terminal  organs  with  which  the  nerve  is  in  communica- 
tion. When,  therefore,  a  motor  nerve  is  stimulated  the  impulse  travels 
to  the  periphery ;  when  the  nerve  terminates  on  a  cutaneous  surface  it 
travels  toward  the  centre,  although  it  must  be  understood  that  nerves 
maj^  conduct  impulses  in  either  direction  and  even  carry  impulses 
simultaneously  in  different  directions  without  interfering  with  each 
other. 

The  rate  of  conduction  of  nerve  impulses  is  about  twenty-seven 


778  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

and  a  quarter  meters,  or  ninety  feet,  per  second,  in  both  motor  and 
sensory  nerves,  and  is  influenced  by  various  conditions.  Reduced 
temperature  or  a  great  increase  in  temperature  reduces  the  velocity  of 
nerve  impulse.  Anelectrotonus  decreases  the  velocity  of  conduction, 
while  kathelectrotonus  increases  it. 

The  conduction  of  nerve  impulse  is  destroyed  by  all  conditions 
which  injure  the  nerve,  as  \yy  section,  ligature,  compression,  or  the  use 
of  chemical  agents  which  destroy  its  excitability  at  any  part  of  its 
course,  by  the  removal  of  blood,  or  by  the  action  of  certain  poisons,  as 
curare,  which  destroys  the  conductivity  of  the  terminal  motor-nerve 
filaments. 

When  a  nerve  is  subjected  to  continued  stimulation  the  irritability 
of  the  nerve  rapidly  diminishes ;  such  a  nerve  is  said  to  be  exhausted  or 
to  be  in  a  condition  of  fatigue.  A  nerve  in  which  exhaustion  has 
occurred  may  again  regain  its  activity,  provided  the  stimulation  has  not 
been  too  excessive  or  too  greatly  prolonged. 

In  cold-blooded  animals  stimulation  may  be  much  more  severe  and 
protracted  without  producing  exhaustion  than  in  warm-blooded  animalsr 
and,  while  nerves  are  more  slowly  affected  than  muscles,  the  recovery  of 
the  former  is  more  slowly  accomplished  than  in  the  latter. 

When  a  nerve-fibre  is  separated  by  section  from  the  central  nervous 
system  the  condition  of  the  nerve  will  vary  according  as  to  the  function 
of  the  nerve.  Provided  a  nerve  be  in  connection  with  the  nerve-centres 
which  govern  its  nutritive  processes,  it  may  be  divided  at  any  part  of  its 
course  and  degeneration  of  the  nerve  will  only  occur  in  those  parts  which 
have  been  separated  from  the  nutritive  centre.  Thus,  for  example,  if  a 
motor  nerve  be  divided  the  peripheral  extremity  of  the  nerve  will 
become  disorganized,  while  the  part  still  in  connection  with  the  spinal 
cord  will  remain  intact. 

If  a  purely  sensory  nerve  be  divided  it  would  at  first  appear  that 
the  same  condition  prevailed ;  and  if,  again,  a  mixed  nerve  be  divided 
the  peripheral  part  of  the  nerve,  including  all  its  branches,  will  degenerate, 
while  the  central  parts  will  remain  intact. 

The  centres  governing  the  nutrition  of  motor  and  sensory  nerves 
are  not,  however,  as  might  appear  from  the  above  statements,  the  same. 

If  the  anterior  root  of  a  spinal  nerve  be  divided  before  it  joins  the 
posterior  root  the  motor  fibres  in  the  spinal  nerve  formed  by  the  union 
of  this  anterior  and  posterior  root  will  degenerate,  while  the  portion 
remaining  in  connection  with  the  cord  will  remain  intact.  If  the  pos- 
terior root  be  divided  between  the  spinal  cord  and  its  ganglion  the  part 
of  the  nerve  lying  between  the  point  of  division  and  the  spinal  cord  will 
degenerate,  while  the  peripheral  portions  of  the  part  between  the  point 
of  section  and  the  posterior  ganglion  will  remain  intact.  This  indicates 


ELECTBICAL   PHENOMENA   IN   NEKVES. 


779 


that  the  nutrition  of  motor  nerves  is  controlled  by  the  ganglia  in  the 
spinal  cord,  while  the  ganglion  on  the  posterior  root  controls  the  nutri- 
tion of  the  sensory  fibres.  Such  ganglia  controlling  nutrition  are  spoken 
of  as  trophic  centres,  and  nerves,  therefore,  which  are  separated  from 
their  trophic  centres  undergo  permanent  degeneration.  The  nature  of 
the  influence  exerted  by  trophic  centres  is,  however,  entirely  unknown 
(Fig.  330). 

If  a  nerve  be  divided  and  the  divided  ends  again  brought  into  con- 
tact Ity  means  of  sutures,  regeneration  takes  place,  and  after  a  varying 
time  the  nerve  is  again  capable  of  conducting  impulses. 

A  B  C  D 


FIG.  830.— DIAGRAM   OF  THE  ROOTS  OF  A  SPINAL  NERVE  SHOWING  THE 
EFFECTS  OF  SECTION.    (Landois.) 

The  black  parts  represent  the  degenerated  parts.    A,  section  of  the  nerve-trunk  beyond  the  ganglion ;  . 

B,  of  the  anterior  root,  and  C,  of  the  posterior  root ;  D,  excision  of  the  ganglion ;  a,  anterior,  p,  posterior 
roots ;  g,  ganglion. 

III.      THE  ELECTRICAL  PHENOMENA  IN  NERVES. 

As  in  muscles,  evidence  of  the  presence  of  a  constant  electrical 
current  rna3r  be  found  in  nerves.  If  a  section  of  a  nerve  be  removed 
from  the  body  and  placed  upon  non-polar izable  electrodes  in  connection 
with  a  sensitive  galvanometer,  a  strong  electrical  current  may  be  observed 
when  the  transverse  section  of  the  nerve  is  placed  in  contact  with  one 
of  the  electrodes  and  the  surface  in  connection  with  the  other.  The 
current  will  then  pass  from  the  longitudinal  section  to  the  transverse 
section;  or,  in  other  words,  the  natural  surface  will  be  positive  and  the 
artificial  surface  negative.  The  nearer  one  electrode  is  to  the  equator, 
and  the  other  to  the  centre  of  the  transverse  section,  the  stronger  will  be 
the  current  produced,  and  when  two  points  on  the  surface  at  equal 
distance  from  the  equator  are  connected  with  the  galvanometer  no 
current  is  obtained.  The  electro-motor  force  of  the  strongest  nerve- 
current  has  been  placed  at  0.02  of  the  Daniells'  element. 

Like  muscle,  again,  the  natural  current  of  nerve  undergoes  a 
negative  variation  when  the  nerve  is  artificially  stimulated.  If  a  section 
of  nerve  be  so  connected  with  a  galvanometer  as  to  develop  a  strong 
current,  and  it  then  be  stimulated  either  by  the  application  of  electricity 
or  a  chemical  or  mechanical  stimulus,  the  nerve-current  will  be  found  to 


780  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

disappear.  This  negative  variation  travels  toward  both  ends  of  the 
nerve,  and,  like  the  production  of  the  negative  variation  of  muscle- 
current,  is  due  to  the  rapid  succession  of  interruptions  of  the  origin  of 
the  current. 

The  statement  as  regards  the  negative  variation  of  the  nerve- 
current  when  the  nerve  is  stimulated  by  an  electrical  current  requires 
some  modification.  The  statement  holds  when  the  induced  current, 
either  in  single  or  rapid  shocks,  is  employed.  If  the  constant  current 
be  applied  to  a  nerve  which  is  in  connection  with  the  galvanometer  the 
effect  on  the  nerve-current  will  depend  upon  the  direction  of  the  stimu- 
lating current. 

If  the  constant  current  be  passed  through  a  nerve  outside  of  the 
part  in  connection  with  the  electrodes  of  the  galvanometer,  so  that  its 
current  coincides  in  direction  with  that  of  the  nerve-current  (descending 
current),  the  deflection  of  the  galvanometer  needle  will  be  increased 
instead  of  decreased ;  such  a  state  of  affairs  is  spoken  of  as  the  positive 
phase  of  electrotonus,  and  is  directly  proportional  in  its  intensity  to  the 
length  of  nerve,  the  strength  of  the  galvanic  current,  and  the  nearness 
of  application  of  the  stimulus  to  the  section  of  the  nerve  in  connection 
with  the  galvanometer.  If,  now,  the  direction  of  the  constant  current 
be  reversed,  so  as  to  cause  the  constant  current  to  pass  in  the  opposite 
direction  to  the  nerve-current,  the  latter  will  be  diminished ;  such  a 
condition  is  spoken  of  as  the  negative  phase  of  electrotonus.  By  the 
production  of  electrotonus  by  means  of  such  a  constant  polarizing 
current  the  excitability  of  the  nerve  is  greatly  modified,  not  only  in  the 
part  through  which  the  current  is  passing,  but  throughout  the  entire 
extent  of  the  nerve.  It  has  been  found  that  at  the  positive  pole  the 
excitability  is  diminished;  this  condition  is  spoken  of  as  anelectro- 
tonus ;  at  the  negative  pole  the  excitability  is  increased  and  forms  the 
region  of  kathelectrotonus,  the  variation  in  irritability  being  most 
marked  in  the  neighborhood  of  the  poles  and  decreasing  in  proportion 
to  the  distance  from  the  poles. 

Between  the  poles  of  the  polarizing  current  a  point  exists  where  the 
region  of  over-stimulation  and  under-stimulation  meet,  and  where,  con- 
sequently, the  excitability  of  the  nerve  is  unchanged ;  such  a  point  is 
spoken  of  as  the  neutral  point,  and  with  a  weak  current  lies  nearer  the 
anode  and  with  a  strong  current  nearer  the  kathode. 

The  production  of  this  condition  serves  to  explain  the  character  of  con- 
tractions produced  on  making  and  breaking  a  constant  current  in  a  motor 
nerve.  When  a  constant  current  is  allowed  to  pass  through  a  motor 
nerve,  or,  in  other  words,  when  a  current  is  closed,  the  point  of  greatest 
stimulation  is  located  at  the  negative  pole  and  spreads  from  this  point 
throughout  the  remainder  of  the  nerve.  As  a  consequence,  when  the 


GENERAL  PHYSIOLOGY  OF  NERVE-CENTRES.        781 

current  is  closed  the  stimulation  occurs  only  at  the  negative  pole  at  the 
moment  when  electrotonus  takes  place.  On  the  other  hand,  with  the 
breaking  shock,  or  when  the  current  is  opened,  the  point  of  greatest 
stimulation  is  at  the  anode  and  coincides  with  the  disappearance  of  the 
electrotonus. 

The  contraction  which  is  produced  on  opening  and  closing  a  constant 
current  varies  not  only  with  the  direction  but  with  the  strength  of  the 
current.  Very  feeble  currents  produce  a  contraction  only  on  the  closing 
of  the  current,  both  with  an  ascending  and  descending  current,  from  the 
fact  that  the  occurrence  of  kathelectrotonus  produces  a  greater  effect  on 
the  irritability  of  the  nerve  than  the  disappearance  of  anelectrotonus. 
When  the  current  is  increased  in  strength  contractions  are  produced 
both  on  opening  and  on  closing  the  current  with  either  an  ascending  or 
descending  current.  If,  again,  the  current  is  greatly  increased,  contrac- 
tion is  only  produced  on  closing  the  descending  current  and  on  opening 
an  ascending  current.  This  is  to  be  explained  by  the  fact  that  with  very 
strong  currents  the  entire  intra-polar  portion  of  the  electrotonic  nerve  is 
incapable  of  conducting  an  impulse,  and,  as  a  consequence,  ascending 
currents  can  cause  only  an  opening  contraction.  These  results  may  be 
expressed  in  the  following  table,  in  which  R  =  rest,  C  =  contraction  : — 

Ascending.  Descending. 

On  On  On  On 

Closing.      Opening.       Closing.     Opening. 

Weak,  .    C  R  C  R 

Medium,  .     C  C  C  C 

Strong,  .     R  C  C  R 

IV.  GENERAL  PHYSIOLOGY  OF  THE  NERVE-CENTRES. 

The  nervous  system,  as  already  indicated,  consists  of  a  combination 
of  ganglion  cells  united  together  by  nerve-fibres.  The  second  element 
of  the  nervous  tissue,  or  nerve-cell,  is  a  mass  of  protoplasm  supplied 
with  a  nujleus  and  nucleolus,  from  which  originate  at  least  two  proto- 
plasmic strands  or  nerve-fibres,  which  serve  to  bind  the  different  elements 
of  the  nervous  system  together.  Unfortunately,  it  is  not  possible  to  ob- 
tain as  decisive  results  by  experimentation  as  to  the  functions  of  the 
nerve-centres  as  may  be  determined  as  regards  the  nerve-fibres. 

The  properties  of  the  central  organs  of  the  nervous  S37stem  can, 
therefore,  be  only  indirectly  determined.  The  nerve-centres,  by  which  is 
meant  simply  a  collection  of  nervous  ganglia,  may  be  divided  into  two 
general  classes ;  one  group  is  located  on  the  surface  of  the  body,  and  it 
is  adapted  to  the  reception  of  stimuli  originating  in  various  external 
influences  brought  to  bear  on  the  body  surface  ;  the  other  group  of 
nerve-centres  is  located  in  the  central  nervous  system,  so-called, — in  other 
words,  the  spinal  cord  and  brain,  or  the  cerebro-spinal  axis.  In  addition 


782  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

to  these  two  groups  various  so-called  sporadic  ganglia  are  also  to  be 
found  in  different  parts  of  the  body,  whose  functions,  while  in  the  main 
of  the  same  character  as  all  nerve-cells  wherever  found,  differ  according 
to  the  functions  of  the  organs  with  which  they  are  in  connection  ;  they 
will  subsequently  receive  attention. 

The  external  ganglia,  or  the  so-called  nerve-corpuscles,  vary  in  char- 
acter according  to  the  nature  of  the  stimulus  which  it  is  their  function 
to  receive.  They  may  be  distributed  over  the  skin  surface  and  are 
litted  for  recognition  of  tactile  and  thermic  changes,  or  they  may  be 
specialized  for  receiving  special  sensations  ;  in  such  cases  they  constitute 
the  organs  of  special  sense. 

In  addition  to  these  terminals  of  nerves,  which,  it  will  be  recog- 
nized, are  simply  in  connection  with  afferent  nerves,  another  set  of  nerve- 
corpuscles  is  in  connection  with  the  peripheral  terminations  of  the  motor 
nerves  and  act  as  organs  of  distribution  for  motor  impulses.  In  this 
group  fall  the  nerve-plates  on  the  voluntary  muscles  and  the  ganglionic 
cells  in  the  walls  of  the  intestinal  tube. 

The  central  nervous  ganglia,  located  in  the  cerebro-spinal  axis,  pos- 
sess the  power  of  developing,  first,  reflex  action ;  second,  automatism  ; 
third,  inhibition ;  fourth,  augmentation  ;  fifth,  co-ordination.  These  will 
be  alluded  to  in  detail. 

Nervous  centres  are  capable  of  receiving  impulses  brought  to  them 
through  afferent  nerves,  multiplying  them,  and  reflecting  the  impulses  so 
changed  through  an  efferent  nerve.  A  reflex  action,  therefore,  requires 
for  its  expression  an  afferent  nerve,  starting  from  some  receptive  sur- 
face, some  stimulus  applied  to  that  receptive  surface,  a  nervous  centre, 
and  an  efferent  nerve. 

1.  REFLEX  ACTION. — Reflex  actions  may  occur  in  a  number  of  dif- 
ferent ways.  The  impulse  reaching  the  centre  through  a  sensory  nerve  may 
be  reflected  through  a  motor  nerve  and  produce  muscular  contraction. 
Such  muscular  movements,  occurring  reflexty  as  the  result  of  stimuli,  are 
entirely  involuntary  and  independent  of  the  will.  Such  reflex  actions  are 
almost  innumerable  and  form  an  important  part  of  the  organic  acts  of  a 
living  animal.  As  examples  may  be  mentioned  the  involuntary  weep- 
ing which  almost  instantly  follows  the  applications  of  a  stimulus  to  the 
conjunctiva,  the  movements  of  the  limbs  which  occur  on  tickling  the 
soles  of  the  feet  during  sleep,  movements  of  vomiting  which  occur  when 
the  soft  palate  or  pharynx  are  mechanically  irritated, coughing  following 
irritation  of  the  larj'ngeal  or  trachea  1  mucous  membrane,  and  a  large 
number  of  other  movements  (Fig.  331). 

The  spinal  cord  offers  the  best  example  of  the  production  of  reflex 
motor  actions,  and,  in  fact,  reflex  action  may  be  said  to  be  the  main 
function  of  the  spinal  cord  and  its  ganglionic  cells  may  be  regarded  as 


GENEKAL  PHYSIOLOGY  OF  NERVE-CENTRES.        783 

collections  of  reflex  centres.  The  special  characters  of  reflex  action  as 
produced  by  the  conduction  of  a  stimulus  through  the  spinal  cord  will 
subsequently  receive  attention  more  in  detail.  At  present  a  general 
outline  of  the  production  of  such  reflex  action  is  all  that  is  needed. 

If  in  an  animal  the  cerebrum  be  removed  by  section  from  the 
spinal  cord, — and  such  an  experiment  may  be  best  performed  on  a  cold- 
blooded animal, — stimuli  applied  to  varying  parts  of  the  body  surface 
will  result  in  the  production  of  muscular  movement.  If  in  a  frog  the 
cerebrum  be  removed  by  a  section  forming  a  tangent  to  the  anterior 
part  of  the  t}'mpanic  membrane,  the  frog  will  apparently  be  in  a  normal 
condition,  as  far  as  its  posture  is  concerned.  If  after  the  shock  of  the 
operation  has  passed  away  the  toe  of  such  a  frog  be  pinched,  the  animal 
will  jump;  or,  in  other  words,  conduction  of  the  sensory  impulse  to  the 
spinal  cord  is  reflected  in  the  complicated  co-ordinated  movement  of 
jumping.  It  is  evident,  therefore,  that  the  sensory  impulse  is  not  simply 
reflected  from  the  nerve-cell,  but  that,  reaching  the  nerve-cell,  it  may 
there  be  converted  into  afferent  impulses 
which  may  be  of  the  most  complex  character. 

Coughing  and  sneezing,  also,  are  illustra- 
tions of  this  statement,  where  the  slightest 
mechanical  irritation  of  various  parts  of  the 
respiratory  mucous  membrane  may  produce 
complex  muscular  movements  which  are  out 
of  all  proportion  in  their  complexity  and 

vigor  to  the  afferent  impulses  which  inaugu-     FlG-  331.— SCHEME  OF  A  RE- 
FLEX ARC.    (Landois.) 

rate     them.          While     this     1S,     hOWeVer,     tO      a        S,  skin;    M,  muscle;    N,  nerve-cell,  with 

aj\  afferent,  and  ef,  efferent,  fibres. 

certain  degree  true,  within  limits  the  nature 

of  the  efferent  impulse  is  dependent  upon  the  nature  of  the  afferent 

impulse. 

If  after  removing  the  cerebrum  from  a  frog  the  flank  of  the  animal 
be  gently  stroked,  muscular  movement  will  occur  simply  as  feeble 
twitching  of  the  muscles  at  the  point  of  stimulation.  If  the  stimulus 
be  increased  in  intensity  the  neighboring  muscles  are  also  implicated, 
and  a  still  further  increase  in  severity  in  irritation  may  lead  to  the 
implication  of  nearly  all  the  muscles  of  the  bod}r. 

A  connection  may  also  be  recognized  between  the  locality  of  stimu- 
lation and  the  nature  of  the  resulting  movement;  thus,  stimulation  of 
the  larynx  will  invariably  cause  coughing  ;  of  the  mucous  membrane  of 
the  nostril,  sneezing;  of  the  mucous  membrane  of  the  eye,  weeping  and 
lachrymation,or,  to  go  back  to  the  lower  animals,  reflex  action  following 
from  a  stimulus  applied  to  the  skin  of  the  brainless  frog  will  be  so 
adapted  as  to  remove  the  irritating  body.  Thus,  if  a  scrap  of  paper 
moistened  with  acid  be  placed  on  the  right  flank  of  such  a  frog,  the 


784  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

right  foot  will  be  gradually  drawn  up  and  swept  over  the  point  of 
stimulation  to  remove  the  stimulus.  The  apparently  purposeful  char- 
acter of  such  an  action  is  still  more  strongly  manifested  if  in  such  an 
experiment  the  right  foot  be  firmly  held ;  after  a  few  ineffectual  con- 
tractions of  the  muscles  of  the  right  leg  the  left  leg  will  then  be  drawn 
up  to  remove  the  offending  body.  In  all  cases,  therefore,  except  in  those 
of  the  very  simplest  character,  the  resulting  motion  produced  reflectively 
from  a  stimulus  is  out  of  all  proportion  in  complexity  to  the  nature  of 
the  stimulation.  This  complexity  is  much  more  marked  when  the 
stimulus  is  applied  to  the  terminal  corpuscles  of  sensory  nerves,  as  in 
the  case  above  alluded  to. 

If  the  stimulation  be  applied  to  a  sensory  nerve-trunk  the  character 
of  the  resultant  reflex  action  is,  as  a  rule,  of  simpler  character ;  or,  at 
least,  is  to  a  certain  extent  free  from  the  apparent  purposeful  character 
noticed  above.  Thus,  for  example,  if  an  induced  current  be  applied  to 
the  central  end  of  a  divided  sciatic  nerve  general  convulsive  movements 
are  produced,  but  no  apparently  co-ordinate  attempt  to  remove  the 
stimulus  can  be  detected,  even  with  the  employment  of  the  weakest  cur- 
rent. It,  therefore,  is  evident  that  the  character  of  the  reflex  action 
depends  upon  the  nature  of  the  locality  of  application  and  intensity  of 
the  afferent  impulses. 

2.  AUTOMATISM. — By  automatism  is  meant  the  power  possessed  by 
nerve-centres  of  apparently  originating  nervous  impulses.  It  is,  how- 
ever, difficult  to  draw  a  line  between  so-called  automatic  action  and 
reflex  action.  Thus,  the  act  of  respiration,  which  is  a  favorable  example 
of  the  so-called  automatic  action,  is  in  all  probability  due  to,  or,  at  any 
rate,  largely  governed  by,  the  character  of  the  impulses  brought  to  that 
centre  through  the  various  afferent  nerves.  So,  again,  the  regulation  of 
the  calibre  of  the  blood-vessels,  which  is  controlled  by  the  automatic 
power  of  the  vaso-motor  centre,  is  again  largely  modified  by  the  nature 
of  the  afferent  impulses  brought  to  it. 

The  clearest  example  of  pure  automatic  action  is  to  be  found  in  the 
pulsations  of  the  excised  heart.  As  was  seen  in  the  chapter  on  circula- 
tion, the  heart  might  be  removed  from  a  cold-blooded  animal  and  yet 
preserve  for  many  hours  its  power  of  rhythmical  contraction,  and  it 
was  demonstrated  that  such  automatic  action  was  the  result  of  the 
function  of  the  nervous  ganglia  found  in  the  heart. 

So,  also,  the  movements  of  the  alimentary  canal  were  described  as 
of  an  automatic  character,  for  although  their  character  is  influenced  by 
the  contents  of  the  intestinal  tube,  just  as  the  movements  of  the  heart 
might  be  influenced  by  various  afferent  impulses,  the  movements  of  the 
intestine  may  occur  in  an  empty  condition  of  the  bowel  or  they  may  be 
absent  when  the  canal  is  filled.  In  the  spinal  cord,  therefore,  centres 


GENERAL  PHYSIOLOGY  OF  NERVE-CEXTBES.        785 

are  found  which  are  capable  of  regularly  and  rhythmically  governing 
complex  movements,  and,  to  that  extent,  it  is  automatic  :  the  brain, 
however,  as  the  seat  of  mental  activity,  perception,  volition,  thought, 
and  memory,  is  the  highest  expression  of  the  automatic  functions  of 
nervous  centres.  The  automatic  functions  of  the  cerebrum  will  sub- 
sequently receive  consideration  in  detail. 

3.  INHIBITION. — In   a   number  of  examples  which  were   given   as 
illustrations  of  reflex  action,  as  is  well  known,  the  will  by  its  exertion 
may  prevent  the  appearance  of  the  ordinary  reflex  result  of  the  stimulus. 
Thus,  for  example,  touching  the   e3'eball  tends  to  result  in  the   pro- 
duction of  winking  ;  touching  the  throat,  movements  of  vomiting  and 
coughing ;  tickling  the  soles  of  the  feet,  contractions  of  the  muscles  of 
the  legs.     All  of  these,  as  is  well  known,  may  be  controlled  by  a  volun- 
tary impulse. 

One  of  the  clearest  illustrations  of  such  inhibition  of  reflex  action 
and  of  its  development  by  education  is  seen  in  the  mechanism  of  defae- 
cation.  In  the  lower  animals  defaecation  is  a  purety  reflex  action  and,  as 
was  described,  results  from  the  contact  of  the  faecal  mass  with  the 
mucous  membrane  of  the  rectum. 

In  infants,  likewise,  the  same  state  of  affairs  occurs.  By  education 
the  will-power  is  capable  of  inhibiting  the  operations  which  result  in 
defaecation,  or,  in  other  words,  checking  the  action  of  the  nerve-cells 
which  control  the  co-ordinated  movements  in  this  process. 

A  number  of  other  illustrations  might  be  given,  of  which,  perhaps, 
the  clearest  instance  is  seen  in  the  action  of  the  heart. 

If  the  pneumogastric  nerve  be  stimulated  in  an  animal  in  whom  the 
heart  is  beating  in  a  normal  manner  with  an  interrupted  current,  the 
heart  is  almost  immediately  slowed  and  may  even  be  brought  to  a  stand- 
still ;  such  a  result  is  explained  by  the  statement  that  the  pneumogas- 
tric contains  cardio-inhibitory  fibres  whose  stimulation  arrests  the 
automatic  action  of  the  motor  ganglia  of  the  heart. 

4.  AUGMENTATION. —  In  contradistinction  to  inhibition  an  afferent 
impulse  may  increase  action  of  nerve-centres.     Thus,  for  example,  the 
vaso-motor  centre  located  in  the  floor  of  the  fourth  ventricle  controls 
the  calibre  of  the  blood-vessels  and  keeps  their  walls  in  a  state  of  con- 
traction.    The  action  of  the  vaso-motor  centre  may,  however,  be  aug- 
mented through  various  afferent  impulses,  the  most  striking  of  which  is 
seen  in  the  great  increase  of  blood  pressure  which  follows  stimulation 
of  sensory  nerves  in  curarized  animals. 

5.  CO-ORDINATION. — By  this  term  is  meant  the  power  possessed  b}' 
the  cells  of  the  central  nervous  system  of  combining  complex  muscular 
movements  ordinarily  of  a  reflex  nature.     Thus,  for  example,  the  act  of 
deglutition  necessitates  co-ordinate  action  of  a  large  number  of  different 

50 


786 


PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 


groups  of  muscles,  which  must  in  their  contraction  follow  each  other  in  a 
certain  definite  sequence;  so,  also,  the  act  of  coughing  requires  the  associa- 
tion of  a  number  of  different  muscular  movements.  Numerous  other  illus- 
trations might  be  given  of  the  combination  of  complex  movements  which 
are  governed  by  so-termed  co-ordinating  centres ;  that  is,  a  collection  of 
ganglia  located,  usually,  in  the  spinal  cord  or  medulla  oblongata  which 
govern  certain  specific  movements. 

V.  THE  FUNCTIONS   OF  THE  SPINAL  COED. 

The  spinal  cord  is  contained  within  the  vertebral  canal  and  is  com- 
posed of  white  matter  externally  and  gray  matter  internally,  inclosed  in 
membranous  sheaths  of  which  the  pia  mater  is  adherent  to  the  white 

A         A 
1 


L  — 


...  L 


p 

FIG.  332.—  TRANSVERSE  SECTION  OP  THE  SPINAL  CORD.    (Landois.) 

In  the  centre  is  the  butterfly-form  of  the  gray  matter  surrounded  by  white  matter,    p,  posterior,  and 
nterior  horns  of  the  gray  matter  ;    PR  posterior  roots,  A 
the  white  anterior,  L  L  the  lateral,  P  P  the  posterior  columns. 


matter  ;  externally  is  found  the  dura  mater,  which  lines  the  vertebral 
canal  and  forms  a  protective  coat  for  the  cord,  while  between  the  two  is 
found  the  arachnoid  membrane. 

The  white  matter  of  the  spinal  cord  is  composed  of  nerve-fibres 
arranged  longitudinally  and  divided  into  the  so-called  anterior,  lateral, 
and  posterior  columns  by  the  passage  of  the  roots  of  the  spinal  nerves. 
The  anterior  fissure  is  a  depression  which  separates  the  two  anterior 
columns  of  the  cord,  which  are  bounded,  therefore,  on  one  side  by  the 
fissure  and  on  the  other  by  the  points  of  origin  of  the  anterior  spinal 
nerve-roots. 

The  anterior  fissure  does  not  extend  down  to  the  gray  matter,  which 
composes  the  centre  of  the  cord,  but  is  separated  from  it  by  the  white 
commissure. 


FUNCTIONS   OF  THE   SPINAL  COED.  787 

Between  the  origins  of  the  anterior  and  posterior  nerve-roots  are 
found  the  lateral  columns,  while  the  posterior  columns  are  found  between 
the  origin  of  the  posterior  nerve-roots  and  the  posterior  fissure,  which  is 
deeper  than  the  anterior,  extending  completely  down  to  the  gray  matter, 
and  filled  up  by  an  inner  layer  of  pia  mater  (Fig.  332). 

In  certain  regions  of  the  cord  each  posterior  column  may  be  subdi- 
vided into  an  inner  part  lying  next  the  fissure,  the  poster o-median,  or 
column  of  Goll,  and  a  larger  part  next  the  posterior  nerve-roots,  the 
postero-external  or  column  of  Burdach. 


or 


FIG.  333.— TRANSVERSE  SECTION  OF  THE  SPINAL,  CORD  IN  THE  CERVICAL 
REGION,  AFTER  BE  VAN  LEWIS.    (Yeo.) 

A,  anterior  gray  column ;  a,  anterior  white  column  ;  I,  lateral  white  column;  ac,  anterior  commis- 
sure :  ar.  anterior  roots ;  of,  anterior  median  fissure ;  il,  intermedio-lateral  gray  column ;  vc,  vesicular 
column  of  Clarke :  P,  posterior  gray  column  ;  p,  posterior  white  column :  ptn,  posterior  median  column  ; 
pc,  posterior  commissure  :  cc,  central  canal ;  pr,  posterior  roots ;  pf,  posterior  median  fissure ;  ae  and  ai, 
external  and  internal  anterior  vesicular  columns ;  *y,  substantia  gelatinosa, 

The  white  matter  of  the  spinal  cord  is  composed  of  medullated  fibres, 
in  which  the  sheath  of  Schwann  is  absent,  arranged  for  the  most  part 
longitudinally.  The  nerve-fibres  of  the  nerve-roots  have  an  oblique 
course,  passing  from  the  gray  matter  through  the  columns  to  form  spinal 
nerves ;  transverse  fibres,  also,  are  found,  which  unite  the  different  col- 
umns of  the  spinal  cord  and  connect  the  gray  matter  with  the  columns 
of  the  cord. 

The  gray  matter  is  composed  of  collections  of  nerve-cells  arranged 
in  the  form  of  two  crescents,  the  convex  surfaces  of  which  are  united  by 
the  graj7  commissure.  In  the  centre  of  the  graj7"  commissure  runs  the 


788 


PHYSIOLOGY   OF   THE  DOMESTIC   ANIMALS. 


central  canal,  which  passes  from  the  floor  of  the  fourth  ventricle 
downward  and  is  lined  by  a  layer  of  cylindrical  epithelial  cells. 

The  cells  of  the  gray  matter  of  the  spinal  cord  differ  greatly  in  size, 
those  in  the  anterior  horn  being  much  the  largest.  The  gray  matter  is, 
also,  like  the  white  matter,  arranged  in  columns,  although  the  distinc- 
tion between  these  columns  may  be  less  readily  demonstrated.  Thus, 
the  anterior  and  posterior  horns  form  the  anterior  and  posterior  gray 
columns,  while  between  the  two  lies  the  lateral  column. 

The  distribution  of  white  and  gray  matter  varies  in  shape  in  differ- 
ent portions  of  the  spinal  cord.  In  the  cervical  region  the  lateral  white 
columns  are  large,  the  anterior  horn  of  the  gray  matter  is  wide  and 


&• — 


FIG.  334.— TRANSVERSE  SECTION  OF  THE  SPINAL  CORD  IN   THE  LUMBAR 
REGION,  AFTER  BEVAN  LEWIS.    ( Tco.) 

(For  references  see  description  under  Fig.  333.) 

large,  while  the  posterior  horn  is  narrow  and  the  transverse  diameter  of 
the  cord  is  the  longest  (Figs.  333, 334  and  335).  In  the  dorsal  region  both 
cornua  are  narrow  and  of  nearly  equal  breadth,  while  the  cord  is  smaller 
and  C3'lindrical. 

In  the  lumbar  region  the  gray  matter  is  largest  in  amount,  while  the 
lateral  columns  are  small  and  the  central  canal  is  nearly  in  the  middle  of 
the  cord. 

As  a  rule,  the  anterior  horn  of  gra3^  matter  is  shorter  and  broader, 
and  does  not  extend  so  near  to  the  surface  of  the  cord  as  does  the  pos- 
terior horn,  which  is  more  pointed,  longer,  and  narrower,  and  usually 
extends  nearer  to  the  surface. 


FUNCTIONS   OF  THE  SPINAL   COED. 


789 


The  spinal  cord  is  not  only  the  path  of  conduction  of  nerve  impres- 
sions from  the  periphery  of  the  brain  and  the  reverse,  but  is  also  the 
seat  of  a  large  number  of  nervous  centres  which  are  capable  of  acting 
as  reflex  centres,  or  even  of 
originating  impulses. 

The  functions  of  the  spinal 
cord  are,  therefore,  to  be  con- 
sidered— first,  as  a  collection 
of  nerve-centres,  and,  second, 
as  a  conductor  of  afferent  and 
efferent  impulses. 

(a)  The  Spinal  Cord  as  a 
Collection  of  Nerve- Centres.— 
It  has  been  already  stated  that 
reflex  action  requires  for  its 
performance  afferent  and  effer- 
ent nerve-fibres  and  a  nerve- 
centre,  and  the  spinal  cord  has 
been  mentioned  as  the  main 
seat  of  the  centres  of  reflex 
action. 

When  the  spinal  cord  is 
divided  in  an  animal,  the  ap- 
plication of  a  stimulus  to  its  skin  produces  muscular  movements  of 
the  most  diverse  kinds,  depending,  as  already  indicated,  upon  the 
nature,  intensit}',  and  the  locality  of  the  stimulus. 

The  histology  of  the  spinal  A 

cord  indicates  that,  from  the 
direct  communication  of  the 
posterior  roots  (which  have 
been  found  to  be  paths  of  con- 
duction of  sensation)  through 
the  gray  commissure  with  the 
anterior  roots  (which  have  been 
found  to  be  the  paths  of  motor 
impulses),  afferent  impulses 
reach  the  spinal  cord  through 
the  sensory  nerves  and  are 
directty  conducted  to  nerve- 
centres,  which  again  are  in  communication  with  motor  nerves.  It  is, 
therefore,  evident  that  afferent  impulses  are  brought  directly  to  nerve- 
cells,  which  again  communicate  the  modified  nerve  impulse  to  motor 
nerves  (Fig.  336).  In  the  spinal  cord  such  centres  of  reflex  action. may  be 


FIG.  385.— TRANSVERSE  SECTION  OF  THE  SPINAL 
CORD  IN  THE  DORSAL,  REGION.  AFTER 
BEVAN  LEWIS.  (Yeo.) 

(For  references  see  description  under  Fig.  333.) 


M 


FIG.  336.— SECTION  OF  A  SPINAL  SEGMENT, 
SHOWING  A  UNILATERAL  AND  CROSSED 
REFLEX  ACTION.  (Landois.) 

A,  anterior,  and  P,  posterior  surfaces ;   M,  muscle ;  S,  skin ;  G, 
ganglion. 


790  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

readily  proved  by  the  entire  failure  to  evoke  reflex  movements  after 
destruction  of  the  cord.  Thus,  while  reflex  movements  are  produced 
with  the  greatest  readiness  in  frogs  in  whom  the  cerebrum  has  been 
removed,  if  the  spinal  cord  be  then  disorganized  by  passing  an  instrument 
down  the  vertebral  canal  all  reflex  movements  are  then  impossible,  even 
although  the  nerves  possess  their  power  of  conductivity  and  the  muscles 
their  power  of  contraction. 

To  appreciate  the  functions  of  the  spinal  cord  as  a  collection  of 
centres  for  producing  reflex  action  we  have  only  to  recall  the  statements 
made  on  the  nervous  system  as  met  with  in  the  lowest  articulata,  in 
which  we  have  a  collection  of  nervous  matter,  ganglionic  in  its  nature 
and  comparable  to  the  medulla  spinalis  of  vertebrates,  with  afferent 
fibres  running  to  and  efferent  fibres  running  from  these  ganglia.  Such  a 
type  of  nervous  system  is  seen  in  the  star-fish.  If  an  irritation  be  ap- 
plied to  an  extremity  of  the  limb  of  a  star-fish  a  sentient  impression  is 
conducted  along  the  sensory  nerve  to  the  ganglionic  centres,  and  a  motor 
impulse  goes  out  along  the  motor  nerve  and  contraction  of  the  muscles 
supplying  the  body  results.  Sovif  a  decapitated  centipede  be  placed 
upon  the  ground  it  begins  to  make  forward  locomotive  efforts  as  soon  as 
the  impression  is  made  upon  the  sentient  extremities  of  the  nerves  dis- 
tributed to  its  feet ;  this  impression  is  conveyed  to  the  spinal  ganglia, 
and  motor  impulses  are  sent  out  along  each  one  of  the  legs  and  loco- 
motion results.  If  it  comes  in  contact  with  an  obstacle,  however,  as 
high  as  itself  it  will  mount  over  it,  but  if  higher  it  will  butt  against  it 
its  decapitated  extremity  until  all  nervous  force  is  exhausted,  when  it 
becomes  quiet.  Still  more  striking  phenomena  are  present  when,  after 
decapitation,  the  remainder  of  the  body  be  cut  in  two ;  if  then  the 
halves  of  the  body  be  placed  upon  the  ground  locomotive  efforts  will 
continue  in  each,  but  they  will  not  be  harmonious.  All  these  movements 
depend  upon  physical  excitation,  and  in  some  instances  they  require  to 
be  excited  by  the  elements  in  which  the  animal  naturally  moves.  Thus, 
if  we  take  a  decapitated  water-beetle  and  place  it  upon  the  floor  no 
motion  results,  but  place  it  in  water  and  it  begins  to  move  with  vigor. 
The  above  are  examples  of  reflex  action,  and  result  from  excitation  of 
sentient  surfaces  and  the  conduction  of  that  irritation  to  a  nervous 
ganglion,  and  the  reflection  of  that  stimulation  through  a  motor  nerve. 

It  has  been  mentioned  that  the  impulses  reaching  the  cord  through 
a  single  sensory  nerve  may  spread  to  the  adjacent  receptive  ganglia, 
and  so  lead  to  the  transmission  of  motor  impulses  through  a  number 
of  different  motor  nerves.  Ordinarily  the  degree  of  reflex  action  is  in 
proportion  to  the  stimulus. 

Under  certain  conditions  the  irritability  of  the  spinal  cord  may  be 
so  modified  that  a  gentle  stimulus  may  produce  excessive  stimulation  of 


FUNCTIONS  OF  THE   SPINAL   COED.  791 

the  motor  ganglia  of  the  cord,  and  so  produce  violent  convulsive  move- 
ments; or  the  receptivity  of  the  cord  may  be  obtunded  through  disease 
or  through  the  action  of  various  poisons,  and  the  most  violent  stimulus 
now  fail  to  evoke  any  reflex  action.  As  an  example  of  the  first  condition 
strychnine  furnishes  a  most  striking  illustration. 

If  a  frog  be  poisoned  with  strychnine  and  the  cerebrum  removed,  a 
degree  of  stimulation  which  otherwise  would  produce  but  a  feeble  or 
perhaps  even  no  reflex  action  now  produces  tetanic  contractions.  Such 
a  result  indicates  that  in  the  spinal  cord  every  sensible  fibre  is  in  direct 
communication  through  the  gray  substance  with  every  motor  fibre. 

In  the  frog  at  breeding  seasons  the  spinal  cord  is  in  a  physiological 
state  of  overexcitation ;  the  frog  is  found  at  this  time  clinging  obstinately 
to  pieces  of  bark  or  stone,  just  as  it  does  to  the  body  of  the  female  in 
the  act  of  copulation.  Such  a  condition  may  be  produced  by  gentle 
stimulations  of  the  skin  of  the  sternum  and  of  the  thumb  of  the  frog,  in 
which  an  increase  of  sensibility  exists.  Here  the  result  is  to  be  attributed 
not  only  to  the  increased  receptivity  of  the  spinal  cord,  but  also  to  the 
increased  sensitiveness  of  the  receptive  surfaces. 

In  the  normal  condition  of  animals,  whether  mammals  or  cold- 
blooded animals,  in  whom  the  brain  has  been  separated  from  the  spinal 
cord,  reflex  action  only  takes  place  through  the  application  of  irritants 
of  a  certain  intensity  and  a  certain  duration. 

Single  electric  shocks  as  a  rule  produce  no  result,  but  if  repeated 
sufficiently  often  produce  a  reflex  action  ;  such  single  impulses  are  con- 
ducted to  the  spinal  cord  and  there  become  added  to  each  other  by  what 
is  known  as  a  process  of  summation  until  a  maximum  result  is  attained. 
If,  then,  the  number  of  stimulations  per  second  be  increased  or  the  de- 
gree of  stimulation  be  made  more  severe  no  further  increase  in  the  reflex 
action  is  possible. 

Pfliiger  has  formulated  the  following  laws  of  reflex  action  : — 

1.  The  reflex  movement  occurs  on  the  same  side  on  which  the  sen- 
sory nerve  is  stimulated,  while  only  those  muscles  contract  whose  nerves 
arise  from  the  same  segment  of  the  spinal  cord. 

2.  If  the  reflex  occur  on   the  other  side  only  the   corresponding 
muscles  contract. 

3.  If  the  contractions  be  unequal  upon  two  sides,  then  the  most 
vigorous  contractions  always  occur  on  the  side  which  is  stimulated. 

4.  If  the  reflex  excitement  extend  to  the  other  motor  nerves,  those 
nerves  are  also  affected  which  lie  in  the  direction  of  the  medulla  oblon- 
gata. 

5.  All  the  muscles  of  the  body  may  be  thrown  into  contraction. 
(Landois.) 

In  the  human  body  are  found  mechanisms  which  may  inhibit  or 


792  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

control  reflex  action,  before  mentioned,  as  produced  after  a  mechanical . 
irritation  of  the  conjunctiva.  Tickling  of  the  feet  leads  to  an  inclination 
to  movement;  this  also  is  a  reflex  action,  and,  as  is  well  known,  such  a 
movement  may,  by  an  exertion  of  the  will,  be  suppressed,  such  a  sup- 
pression being  an  inhibition  of  reflex  action.  This  voluntary  control  of 
reflex  action  may  be  educated  to  a  certain  extent,  but  only  within  certain 
limits. 

If  the  stimulus  be  severe  and  frequently  repeated  reflex  action 
occurs  in  spite  of  the  effort  of  the  will  to  prevent  it.  On  the  other  hand, 
numerous  reflex  actions  are  entirely  beyond  the  control  of  the  will ;  thus 
the  contraction  of  the  iris  and  parturition  are  reflex  actions  over  which 
the  will  has  no  control. 

It  may  be  demonstrated  by  experiment  that  a  spinal  nervous  mech- 
anism exists  for  the  purpose  of  keeping  reflex  action  in  control.  If  the 
cerebrum  be  removed  from  a  frog  on  a  line  with  the  anterior  edges  of  the 
tympanic  membrane  reflex  action  may  be  readily  produced. 

The  best  method  of  studying  the  influence  of  different  agents  on  the 
production  of  reflex  action  is  that  of  Tiirck,  of  Vienna. 

The  frog,  from  which  the  cerebrum  has  been  removed,  should  be 
suspended  vertically  by  the  nose,  and  if  after  the  shock  of  the  operation 
has  passed  away  the  tip  of  one  toe  be  dipped  in  a  solution  of  sulphuric 
acid  it  will  be  rapidly  withdrawn ;  the  duration  of  immersion  before  the 
foot  is  withdrawn  may  be  taken  as  indicating  the  degree  of  reflex 
activity  of  the  spinal  cord.  After  each  immersion  the  foot  should  be 
dipped  into  distilled  water,  so  as  to  wash  off  the  excess  of  acid  and  pre- 
vent constant  corrosion  of  the  skin.  If  the  time  be  determined  which 
elapses  before  the  foot  is  withdrawn  from  the  acid  in  the  frog  from  whom 
the  cerebrum  has  been  removed,  and  the  cerebro-spinal  axis  be  then  again 
divided  on  a  line  tangent  to  the  posterior  borders  of  the  tympanic 
membranes  and  the  toe  be  again  immersed  in  acid,  it  will  now  be  found 
that  the  foot  is  withdrawn  after  a  much  shorter  interval  than  in  the 
previous  experiment.  This  result  would  indicate  that  in  some  portion 
of  the  cerebro-spinal  axis  between  the  lines  of  the  two  incisions  is  located 
a  mechanism  which  has  for  its  function  the  controlling  of  reflex  action. 

If  in  another  frog  the  cerebrum  be  removed  and  the  time  of  immer- 
sion in  the  acid  determined  before  reflex  action  takes  place,  and  now  one 
of  the  optic  lobes  be  exposed  and  irritated,  as  by  placing  a  crystal  of  com- 
mon salt  in  contact  with  it,  it  will  be  found  that  the  frog  will  retain  its 
foot  in  the  acid  for  a  much  longer  time  than  before,  or  may  even  entirely 
fail  to  remove  it.  That  this  result  is  due  to  the  stimulation  of  the 
inhibitory  apparatus  and  not  to  a  paralysis  of  reflex  mechanism  is 
proved  by  the  fact  that  if  the  spinal  cord  be  now  divided  below  the 
med.ulla  oblongata  the  foot  will  be  as  promptly  withdrawn,  or  even  more 


FUNCTIONS  OF  THE  SPINAL  COED.  793 

rapidly,  from  the  acid  than  before  ;  such  a  mechanism  is  spoken  of  as 
Setschenow's  inhibitory  centre. 

Reflex  action  may,  likewise,  be  inhibited  by  stimulation  of  sensory 
nerves.  As  an  example  of  this  may  be  mentioned  the  familiar  experi- 
ence of  our  ability  to  arrest  a  sneeze  by  compressing  the  skin  of  the  nose 
over  the  exit  of  the  nasal  nerve. 

Reflex  action  does  not  take  place  when  strong  electrical  irritation  is 
applied  to  the  trunk  of  a  sensory  nerve, but  tetanus  results;  while,  on  the 
other  hand,  a  much  weaker  stimulation  of  the  skin,  either  chemical  or 
mechanical,  will  readily  produce  reflex  movement.  This  would,  perhaps, 
indicate  that,  together  with  the  sensitive  fibres,  inhibitoiy  nerves  pass  in 
the  trunks  of  the  nerve  to  the  spinal  cord. 

The  reflex  functions  of  the  spinal  cord  may  be  looked  upon  as  one 
of  the  preservative  influences  of  the  animal  body,  guarding  all  the  inlets 
and  outlets  of  the  economy.  Through  it  the  movements  of  respiration 
are  permitted  to  occur  during  the  hours  of  sleep  and  waking.  Let  this 
reflex  action  be  lost  in  the  medulla,  and  respiration  ceases,  the  contents 
of  the  rectum  are  involuntarily  evacuated,  the  useful  operation  of  wink- 
ing, by  which  the  conjunctiva  is  kept  moist  and  the  eye  is  protected,  is 
lost,  and  the  acts  of  coughing  and  sneezing,  so  important  for  removing 
foreign  substances,  would  be  alike  impossible. 

The  movements  of  the  intestinal  canal,  although  not  entirely  de- 
pendent upon  reflex  action,  are  in  a  certain  degree  due  to  it.  Many  of 
the  phenomena  which  we  consider  as  voluntary  may  be  classed  among 
those  which  are  reflex  m  their  nature,  as  when,  in  walking,  we  may 
unconsciously  pass  around  an  obstacle  in  our  path,  or  unconsciously 
perform  many  acts  which  are  apparently  purely  voluntary  in  nature. 

As  already  mentioned,  reflex  actions  are  not  solel}7  motor  in  nature, 
but  may  result  in  the  production  of  changes  in  secretion,  in  the  distribu- 
tion of  blood  to  a  part,  or  in  changes  in  nutrition.  Illustrations  of 
excito-secretory  phenomena  are  very  numerous. 

If  we  touch  the  tongue  with  irritating  or  sapid  substances  the  secre- 
tion of  saliva  begins  to  flow  through  the  instrumentality  of  the  lingual 
nerve ;  the  impression  is  conveyed  to  the  medulla  oblongata,  whence  an 
efferent  impulse  is  emitted  through  the  chorda  t3'inpani,  as  a  result  of 
which  the  blood-vessels  supplying  the  submaxillaiy  gland  are  dilated  and 
an  increased  flow  of  saliva  is  produced.  It  has  also  been  found  that  if 
we  stimulate  the  oral  cavity  the  gastric  secretion  is  poured  out  in  large 
quantities,  indicating  the  action  of  condiments  and  spices  in  conditions 
of  feeble  digestion. 

The  reflex  vaso-motor  results  are  clearly  evident  as  examples  of 
reflex  action.  If  a  sensory  nerve  is  stimulated  the  tonic  action  of  the 
vaso-motor  centre  is  increased,  and  the  blood-vessels  of  the  body  are 


794  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

contracted  through  the  reflection  of  that  impulse  from  the  spinal' cord 
through  the  efferent  vaso-motor  nerves  to  the  muscles  composing  the 
walls  of  the  arterioles.  In  vaso-motor  reflex  action  phenomena  of  inhibi- 
tion are  likewise  capable  of  demonstration.  Thus,  the  vaso-motor  centre 
in  the  bod\^,  which  is  a  purely  reflex  centre,  may  be  inhibited  by  stimuli 
passing  through  certain  nerves.  If  the  so-called  depressor  nerve  be 
stimulated  the  vaso-motor  centre  in  the  medulla  is  inhibited  and  dilata- 
tion of  the  blood-vessels  ensues,  as  is  evidenced  by  the  great  fall  of  blood 
pressure.  So,  also,  certain  nerves  when  stimulated  lead  to  a  dilatation 
of  the  blood-vessels  by  inhibition,  in  all  probability,  of  the  ganglia  con- 
tained within  their  walls.  Such  a  reflex  inhibition  of  vaso-motor  action 
is  seen  in  the  case  of  the  chorda  tympani,  already  referred  to,  in  the  reflex 
stimulation  of  the  nervi  errigentes,  and  a  number  of  other  instances. 

As  an  example  of  changes  in  nutrition  clue  to  reflex  action,  illustra- 
tions are  not  as  readily  found ;  what  is  spoken  of  as  sympathy  is  an 
example,  however,  of  changes  in  nutrition  of  reflex  nature.  Surgeons 
are  well  aware  that  when  disease  of  an  inflammatory  character  exists  in 
one  eye  it  is  not  unusual  to  find  the  eye  of  the  other  side  becoming 
affected  in  a  similar  manner,  purely  in  a  reflex  manner ;  as  a  proof  of  this 
ma3T  be  mentioned  that  extirpation  of  the  diseased  eye  is  almost  invariably 
followed  by  a  cure  of  the  disease  in  the  remaining  one.  So,  also,  section  of 
the  supraorbital  branch  of  the  fifth  pair  of  nerves  leads  to  disturbances  in 
the  cornea  which  are  of  a  nutritive  character  and  which  are  probably 
due  to  some  disturbances  of  the  reflex  control  of  nutrition. 

It  has  been  already  mentioned  that  in  the  spinal  cord  are  located  a 
number  of  collections  of  cells  which  have  for  their  function  the  control 
of  certain  complicated  co-ordinate  movements ;  such  centres  exert  their 
action  in  a  reflex  manner  by  the  modification  which  they  produce  on  the 
afferent  impulses  brought  to  them.  These  centres  retain  their  activity 
even  after  the  spinal  cord  has  been  removed  from  the  medulla  by  section, 
but  all  are  to  a  certain  extent  controlled  by  the  action  of  higher  reflex 
centres  found  in  the  medulla  oblongata  and  cerebrum. 

The  following  represents  the  most  important  of  these  collections  of 
nerve-centres  : — 

First,  vaso-motor  centres  which  control  the  calibre  of  the  blood- 
vessels are  found  in  the  floor  of  the  fourth  ventricle  of  the  medulla 
oblongata  and  distributed  throughout  the  entire  spinal  axis,  as  is 
evidenced  by  the  fact  that  the  dilatation  of  the  blood-vessels  which 
follows  division  of  the  spinal  cord  below  the  medulla  is  only  transitory, 
the  blood-vessels  regaining  their  normal  tone  as  the  shock  of  the  opera- 
tion passes  off.  If,  however,  the  spinal  cord  be  entirely  destroyed,  the 
blood-vessels  become  then  permanently  paralyzed. 

It  is  probable  that  in  the  cerebro-spinal  axis  are  likewise  found 


FUNCTIONS  OF  THE   SPINAL    COED.  795 

vasodilator  centres.  It  thus  appears  that  the  calibre  of  the  blood- 
vessels in  the  bod}'  is  regulated  by  a  collection  of  centres  located  in  the 
central  nervous  system. 

Second,  the  cilio-spinal  centre;  this  collection  of  nerve-cells  is 
located  in  the  lower  cervical  portion  of  the  cord ;  its  functions  will  be 
again  alluded  to.  The  other  centres,  as  of  defalcation,  micturition,  etc., 
have  been  already  mentioned. 

(b)  The  Spinal  Cord  as  an  Organ  of  Conduction. — It  has  been  seen 
in  the  consideration  of  reflex  action  that  modes  of  communication  exist 
between  the  different  nerve-cells  in  the  spinal  cord.  It  is  also  evident 
that  in  the  spinal  cord  must  exist  paths  of  conduction  of  sensory  im- 
pulses reaching  the  cord  through  the  posterior  roots  of  the  spinal 
nerves  to  the  brain,  and  of  the  conduction  of  motor  impulses  from  the 
brain  through  the  anterior  spinal  roots  to  the  muscles.  For  when  the 
spinal  cord  is  divided,  or  when  it  is  altered  by  disease  or  injury,  the 
parts  which  receive  their  nerves  from  the  portion  of  the  spinal  cord 
situated  below  that  part  are  paralyzed,  both  as  regards  sensation  and 
motion.  Impressions  made  upon  these  parts  are  no  longer  appreciated 
and  voluntary  movements  can  no  longer  occur  in  them,  even  although 
reflex  action  may  still  be  present.  When  the  spinal  cord  is  divided 
above  the  points  of  origin  of  the  nerves  coming  to  the  muscles  of  respi- 
ration, respiration  is  interfered  with ;  thus,  if  the  spinal  cord  is  divided 
between  the  last  cervical  and  the  first  dorsal  vertebrae,  all  the  respiratory 
muscles,  with  the  exception  of  the  diaphragm,  are  paralyzed.  If  the 
spinal  cord  is  divided  above  the  origin  of  the  phrenic  nerve,  then  the 
diaphragm  is  likewise  paralyzed  and  death  occurs  from  asphyxia.  From 
these  facts  it  is  evident  that  the  spinal  cord  is  the  means  of  communica- 
tion between  the  exterior  and  the  brain,  and  we  haAre  now  to  consider 
the  paths  which  different  impulses  follow  in  passing  from  the  centre  to 
the  peripherj'  and  the  reverse. 

In  the  first  place,  it  would  be  scarcely  conceivable  that  the  irritation 
from  any  localized  portion  of  the  skin  surface  could  communicate 
a  definite  localized  sensation  to  the  brain  if  the  afferent  impulse  was 
compelled  to  travel  through  the  lab}Trinthine  communications  of  the 
gray  cells  of  the  spinal  cord.  Nor,  again,  could  we  suppose  that 
a  single  muscle  could  be  thrown  into  contraction  by  the  will  by  passing 
through  the  same  complicated  net-work  of  cells  and  fibres.  It  would  be 
much  more  natural  to  look  for  the  paths  of  communication  between  the 
voluntary  muscles  and  the  brain  on  the  one  side  and  the  sensory  end 
organs  and  the  brain  on  the  other  in  the  white  columns  of  the  cord.  It 
does  not  follow  from  this  fact  that  the  spinal  cord  may  be  regarded  as  a 
bundle  of  white  fibres  connecting  the  periphery  with  the  brain.  Were 
this  the  case  we  should  expect  that  the  spinal  cord  would  increase  in 


796  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

size  in  proportion  to  the  number  of  nerves  entering  into  it ;  and  that> 
therefore,  the  spinal  cord  should  be  largest  in  the  cervical  portion  and 
gradually  taper  down  to  a  point  in  the  lumbar  region,  as  if  each  spinal 
nerve  were  a  direct  loss  to  the  fibres  of  the  spinal  cord.  Such  is  not, 
however,  the  fact. 

Sections  of  the  spinal  cord  taken  at  different  parts  of  its  length 
indicate  that  the  gray  matter  of  the  cord  increases  with  the  amount  of 
nerve-fibre  passing  into  each  part  of  the  cord,  and  that,  therefore,  the 
largest  amounts  of  gray  matter  are  found  in  the  lumbar  and  cervical 
regions  at  the  points  of  origin  of  the  nerves  for  the  lower  and  upper 
extremities  ;  while,  if  the  proportionate  area  of  the  lateral  columns  is  com- 
pared, it  will  be  found  that  there  is  a  steady  increase  in  the  sectional  area 
of  this  portion  of  the  cord  from  the  lumbar  to  the  cervical  region.  This 
fact  would  indicate  that  the  latter  regions  are  the  main  paths  of  con- 
duction between  the  brain  and  the  periphery.  The  proportion  between 


FIG.  337.— DIAGRAM  OF  THE  ABSOLUTE   AND  RELATIVE   EXTENT  OF  THE 
GRAY  MATTER  AND  OF   THE  WHITE  COLUMNS,   IN  SUCCESSIVE  SEC- 
TIONAL, AREAS,  AS  WELL  AS  THE  SECTIONAL  AREAS  OF  THE  NERVE- 
ROOTS.     (Landois. ) 
N  B,  nerve-roots;  A  C,  L  C,  P  C,  anterior,  lateral,  and  posterior  columns;  Gr,  gray  matter. 

different  parts  of  the  spinal  cord  in  the  different  regions  and  the  different 
areas  of  the  spinal  nerves  are  indicated  in  the  diagram  (Fig.  337). 

In  addition  to  the  anatomical  division,  already  alluded  to,  into 
anterior,  lateral,  and  posterior  columns,  the  white  fibres  of  the  spinal 
cord  have  been  divided  into  several  secondary  columns,  according  to 
their  functions.  In  addition  to  the  experimental  method,  to  be  alluded 
to  directly,  this  grouping  of  the  longitudinal  fibres  of  the  spinal  cord 
into  different  systems  has  been  reached  through  facts  acquired  through 
the  study  of  the  degeneration  of  certain  parts  after  specific  injury  and 
through  the  developmental  history  of  the  cord  in  the  embryo.  Thus, 
injury  of  certain  parts  of  the  brain  is  followed  by  a  secondary  descending 
degeneration  of  certain  nerve-fibres  (Tiirck) ;  section  of  the  cord  causes 
ascending  degeneration  of  certain  fibres  (Schieferdecker)  ;  and  Flechsig 
showed  that  the  fibres  of  the  brain  and  cord  in  the  embryo  became 


FUNCTIONS   OF   THE   SPINAL   COED. 


797 


covered  with  myelin  at  different  periods  of  development,  those  receiving 
their  myelin  last  which  had  the  longest  course.  On  the  data  obtained  by 
this  method  Flechsig  mapped  out  the  following  system  (Landois)  : — 

1.  In  the  anterior  column  lie  the  (a)  uncrossed,  or  direct  pyramidal 
tract  (a  in  Fig.  338),  and,  external  to  it,  (6)  the  anterior  ground-bundle, 
or  anterior  radicular  zone. 

2.  In  the  posterior  column  he  distinguishes  (c)  (roll's  column,  or  the 
postero-median  column,  and  (d)  Burdach's  funiculiis  cuneatus,  the  pos- 
terior radicular  zone,  or  the  postero-external  column. 

3.  In  the    lateral   columns    are 
(e)  the  anterior  and  (/)  the  lateral     - 

mixed    paths,    (g)    the    lateral     or  Mlllllill!!llll'===^^^  ,.   <z* 

crossed  pyramidal  tract,  and  (h)  the 
direct  cerebellar  tract.  The  rela- 
tions of  these  fibres  in  the  cervical 
region  are  shown  in  Fig.  339. 


FIG.  338.— SCHEME  OF  THE  CONDUCTING 
PATHS  IN  THE  SPINAL  AT  THE  THIRD 
DORSAL  NERVE,  AFTER  FLECHSIG. 
(Landois.) 

The 

posterior 

*,  anterior  column  ground-bundle;   c,  Go'll's  column; 
postero-external   column ;    e  and  /,  mixed  lateral  paths  ; 
h,  direct  cerebellar  tracts. 


e  black  part  is  the  gray  matter,     v,  anterior,  hw, 
or  roots  ;  a,  direct,  and  g,  crossed  pyramidal  tracts ; 


FIG.  339.— SECTION  OF  THE  CERVICAL,  POR- 
TION OF  THE  SPINAL,  CORD,  SHOWING 
BY  DIFFERENCES  OF  SHADING  THE 
WHITE  TRACTS  SUPPOSED  TO  BE 
FUNCTIONALLY  DISTINCT.  (Yeo.) 

A,  anterior,  P,  posterior  median  fissures :  dp,  direct 
pyramidal,  cp,  crossed  pyramidal  tracts ;  dc,  direct  cere- 
bellar, pm,  posterior  median  column  (Goll) ;  az,  anterior, 
pz,  posterior  root-zones. 


Of  these  columns,  as  we  shall  find  directly,  the  pyramidal  tracts  may 
be  traced  to  the  anterior  pyramids  of  the  medulla  oblongata,  where  each 
lateral  pyramidal  tract  crosses  to  the  opposite  side,  through  the  pons  to 
the  middle  third  of  the  crusta,  thence  to  the  internal  capsule,  where 
they  diverge  like  the  rays  of  a  fan  through  the  white  matter  of  the 
cerebrum  to  the  central  convolutions. 

The  direct  cerebellar  fibres  may  be  traced  to  the  cerebellum,  reaching 
it  through  the  restiform  body  from  Clarke's  column  of  gray  cells,  thus 
directly  connecting  part  of  the  fibres  of  the  posterior  roots  with  the 
cerebellum. 


798 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


The  other  systems  of  fibres  terminate  in  the  medulla  oblongata,  the 
column  of  Goll  serving  to  connect  part  of  the  fibres  of  the  posterior 
roots  with  the  gray  nuclei  of  the  funiculi  graciles  of  the  medulla 
oblongata;  and  the  column  of  .Burdach  the  posterior  roots  through  the 
restiform  body  with  the  vermiform  process  of  the  cerebellum,  while  the 
anterior  and  lateral  mixed  columns  communicate  with  the  formatio 
reticularis  of  the  medulla  oblongata. 

Of  these  columns  the  pyramidal  tract,  the  cerebellar  tract,  and  the 
column  of  Goll  are  the  only  ones  which  steadily  increase  in  size  as  the 
medulla  oblongata  is  approached. 


eaop 


FIG.  340.— COURSE  OF  THE  FIBRES  IN  THE  SPINAL,  CORD,  AFTER  F.  FLESCII. 

(Thanhoffcr.) 

Ms,  anterior  horn  ;  ffn,  posterior  horn ;  my,  anterior  root ;  m(j,  1,  2,  3,  fibrous  bundles  of  the  anterior 
root;  kg,  posterior  root;  hy,  1,  2,  fibrous  bundles  of  the  posterior  root:  mlp,  direct  pyramidal  tract;  olp, 
crossed  pyramidal  tract ;  oak,  lateral  ground-bundle ;  eaop,  direct  cerebellar  tract ;  nmk,  anterior  ground- 
bundle  ;  he,  central  canal:  Co,  intermedio-lateral  column  of  Clarke ;  G,  funiculus  gracilis  of  Goll ;  B, 
funiculus  cuneatus  of  Burdach ;  x,  oblique  bundles  of  fibres. 

If  we  trace  by  means  of  the  microscope  the  origins  and  terminations 
of  the  spinal  nerves  it  will  be  found  that  the  posterior  roots  of  the 
spinal  nerves  pass  through  the  white  substance  of  the  cord  to  reach  the 
posterior  gray  column,  in  which  they  break  up  into  fine  twigs,  uniting 
with  the  ganglia  of  the  cord,  although  their  mode  of  connection  with 
the  cells  is  not  capable  of  ready  detection.  Having  entered  the  cord. 
the  fibres  of  the  posterior  nerve-roots  are  seen  to  divide  into  three 
different  bundles. 

The  fibres  of  the  anterior  roots  may  likewise  be  divided  into  three 


FUNCTIONS   OF   THE   SPINAL   CORD. 


799 


pm.f 


different  bundles:  1.  The  median  bundle,  represented  by  the  black  line 
in  the  figure  (Fig.  340),  partly  enters  into  direct  union  with  the  cells  of 
the  anterior  horn,  while  part  passes  through  the  gray  matter  to  enter  the 
anterior  commissure  and  pass  to  the  opposite  side  of  the  cord,  to  termi- 
nate, in  part,  in  the  cells  of  the  anterior  horn  on  this  side  and  partly  to 
pass  directly  into  the  anterior  white  columns.  2.  The  central  bundle  of 
motor  fibres  passes  in  part  through  the  anterior  horn  without  forming 
any  connection  with  its  cells,  to  be  lost  in  the  posterior  horn,  where,  in 
all  probability,  through  union  with  ganglionic  cells  it  is  in  communica- 
tion with  the  fibres  of  the  posterior  roots ;  the  other  part  of  this  bundle 
directly  unites  with  the  cells 
of  the  anterior  horn.  3.  The 
lateral  bundle  is  likewise 
partly  in  direct  communica- 
tion with  the  gray  matter  of 
the  anterior  horn  and  partly 
runs  up  in  the  lateral  columns 
of  the  cord  (Fig.  341). 

Further  examinations  of 
sections  of  the  cord  (right 
half  of  above  figure)  show 
that  the  direct  and  crossed 
pyramidal  tracts  of  opposite 
sides  of  the  cord  are  in  com- 
munication by  means  of  fibres 
passing  through  the  gray  sub- 
stance into  the  anterior  com- 
missure, and  that  the  direct 
cerebellar  column  communi- 
cates with  Clarke's  gray  col- 
umn and  the  latter  with  the 
column  of  Goll  on  the  same 
side  of  the  cord. 

Some  of  the  fibres  of  the  posterior  roots  pass  upward  in  the  posterior 
column.  The}'  thus  form  longitudinal  commissures  between  the  different 
ganglia  and  make  up  the  greater  part  of  the  posterior  columns.  These 
commissural  fibres  are  evidently  concerned  in  upward  conduction  of  sen- 
sations, for  when  the  cord  is  divided  they  undergo  ascending  degeneration. 

The  lateral  fibres  from  the  posterior  root  ascend  obliquely  and  divide 
in  the  posterior  horn,  with  whose  cells  they,  in  all  probability,  communi- 
cate, though  part  of  these  fibres  may  be  traced  as  far  as  the  anterior 
horns.  The  inner  bundle  has  been  traced  to  the  posterior  commissure  ; 
its  further  course  or  termination  is  unknown. 


FIG.  341.— DIAGRAM  ILLUSTRATING  THE  PATHS 
PROBABLY  TAKEN  BY  THE  FIBRES  OF  THE 
NERVE-ROOTS  ON  ENTERING  THE  SPINAL 
CORD,  AFTER  SCHAFER.  (YeO.) 

a.m./,  anterior  median  fissure ;  p.m./,  posterior  median  fissure ; 
c.c,  central  canal ;  SR,  substantia  gelatinosa  of  Rolando ;  a  a,  fu- 
niculi  of  anterior  root  of  a  nerve ;  p,  funiculus  of  posterior  root  of  a 
nerve.  By  following  the  fibres  1,  2,  3,  etc.,  their  course  through  the 
gray  matter  of  the  spinal  cord  may  be  traced. 


800 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


It  is  thus  seen  that  the  white  fibres  of  the  spinal  cord  are  not  in 
direct  communication  with  the  nerve-roots,  but  only  connect  different 
segments  of  the  spinal  cord.  In  each  segment  of  the  spinal  cord  are  to  be 
found  nerve-centres  for  the  afferent  and  efferent  nerves  of  definite  regions 
of  the  bod}r,  and  commissural  fibres  connecting  that  segment  with  other 
segments  of  the  cord  and  with  the  brain  (Fig.  342). 

Leaving  these  anatomical  considerations  of  the  moment,  we  have 
now  to  examine  the  data  as  to  the  paths  of  conduction  of  motor  and 
sensory  impulses  through  the  spinal  cord  attained  through  experiments 
performed  upon  the  spinal  cord.  The  method  of  such  experiments  con- 
sists in  attempting  to  make  isolated  sections  of  different  parts  of  the 
cord  and  determine  the  interference  of  function  which  results  from  such 
mutilations.  The  difficulty  of  such  experiments  is  twofold  :  In  the  first 


FIG.  342.— DIAGRAM  ILLUSTRATING  THE  VARIOUS  CHANNELS  THROUGH 
WHICH  A  MOTOR  CELL  OF  THE  CORD  MAY  BE  CALLED  INTO  ACTION. 
(Ranney.) 

A.H,  anterior  horn ;  C.P.C,  crossed  pyramidal  column :  P,  posterior  horn ;  B,  column  of  Burdach ; 
G,  column  of  Goll ;  1,  fibre  for  painful  sensations  ;  2,  fibre  for  tactile  sensations ;  3,  motor  cell ;  4,  motor 
fibres ;  5,  fibre  from  opposite  cerebral  hemisphere  going  to  cell,  3 ;  6,  ganglion  on  posterior  nerve-root ; 
7,  fibre  from  cerebral  hemisphere  of  same  side  going  to  motor  cell,  3. 

place,  it  is  difficult  to  separate  the  temporary  result,  due  to  the  shock  of 
the  operation,  and  the  permanent  results ;  and,  in  the  case  of  sensation  in 
the  lower  animals,  to  distinguish  between  reflex  action  and  purely  volun- 
tary movements.  In  the  second  place,  it  is  almost  impossible  to  make  a 
section  of  any  isolated  portion  of  the  spinal  cord  without  more  or  less 
damaging  the  adjacent  portions.  Thus,  for  example,  it  is  almost  impos- 
sible to  cut  tran  sversety  the  posterior  white  columns  of  the  cord  without 
at  the  same  time  more  or  less  injuring  the  gray  matter.  This  difficulty 
applies  to  isolated  sections  attempted  on  all  parts  of  the  spinal  cord. 
Nevertheless,  a  number  of  valuable  results  have  been  obtained  by  this 
method. 

In  the  first  place,  it  has  been  found  that  section  of  the  cord  causes 
immediate  loss  of  both  sensation  and  motion  in  all  parts  supplied  by 


FUNCTIONS   OF   THE  SPINAL   COED.  801 

nerves  which  arise  behind  the  point  of  injury,  with  temporary  vaso-motor 
paralysis.  The  remote  effects  are  secondary  descending  degeneration  in 
the  crossed  and  direct  pyramidal  tracts  and  ascending  degeneration  in 
the  postero-internal  columns.  If  the  section  is  made  on  one  lateral  half 
of  the  spinal  cord  (hemisection)  paralysis  of  voluntary  movement  and 
vaso-motor  paralysis  occur  on  the  side  of  the  operation  in  the  parts 
below,  with  loss  of  sensation  on  the  side  opposite  to  the  injury  and 
increased  sensitiveness  on  the  side  of  operation,  with  the  exception  of 
a  limited  area  of  anaesthesia  in  the  part  supplied  by  the  sensory  nerves 
destroyed  in  the  operation.  There  is  also  the  usual  ascending  and 
descending  degeneration,  the  former  also  appearing  in  the  column  of 
Goll  on  the  opposite  side. 

If  a  longitudinal  section  is  made  through  the  posterior  fissure  of  the 
cord  in  the  median  line,  little  if  any  loss  of  motion  results  (some  fibres 
of  the  p3rramidal  tract  cross  in  the  anterior  commissure),  but  a  consider- 
able reduction  of  sensibil^.  If  the  posterior  white  columns  are  di- 
vided there  is  considerable  loss  of  the  tactile,  temperature,  and  muscle 
senses,  although  the  sensation  of  pain  may  still  be  felt;  no  loss  of  motion 
results.  If  the  antero-lateral  columns  of  white  fibres  be  divided  there  is 
a  loss  of  voluntary  motion  in  a  corresponding  part  of  the  same  side  of 
the  body.  Such  a  loss  of  motion,  provided  the  gray  matter  be  not  inter- 
fered with,  is  temporary,  and  indicates  that  the  gray  matter  may  take  on 
the  function  of  conduction,  ordinarily  carried  on  by  the  white  columns, 
past  the  seat  of  injury. 

The  respiratory  and  vaso-motor  fibres  also  pass  through  the  antero- 
lateral  white  columns.  If  the' gray  matter  and  the  posterior  white 
columns  be  divided  sensory  or  tactile  impulses  no  longer  reach  the 
brain,  showing  that  sensory  impulses  travel  in  these  parts. 

These  facts  would  indicate  that  sensory  impulses  entering  the 
posterior  roots  of  the  spinal  nerves  pass  for  a  certain  distance  in  the 
posterior  columns  and  then  cross  over  to  the  gray  matter  of  the 
opposite  side  to  ascend  to  the  cerebrum  in  the  lateral  column  in  front  of 
the  pyramidal  tract,  while  some  may  pass  into  the  posterior  column  and 
others  ascend  in  the  gray  matter;  the  fibres  concerned  in  the  conduc- 
tion of  "  muscular  sense  "  apparently  do  not  decussate  until  the  medulla 
is  reached :  or  the}7  may  pass  to  the  cerebellum  by  the  direct  cerebellar 
tract  and  posterior  columns  to  the  restiform  body  and  thence  to  the 
cerebellum. 

On  the  other  hand,  voluntary  motor  impulses  after  having  crossed 
in  the  pons  varolii  and  medulla  oblongata  descend  in  the  antero-lateral 
columns  of  white  fibres  (crossed  pyramidal  tracts)  to  leave  the  cord 
through  the  anterior  roots  of  the  spinal  nerves,  after  forming  communi- 
cation with  the  motor  cells  of  the  anterior  cornua.  The  direct  pyramidal 

51 


802 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS, 


FIG.  343.— DIAGRAM  OF  A  SPINAL  SEGMENT  AS  A  SPINAL  CENTRE  AND  CON- 
DUCTING MEDIUM,  AFTER  BRAMWELL.    (Landois.) 

B,  right,  Bl,  left  cerebral  hemispheres:  M  O,  medulla  oblongata:  1,  motor  tract  from  right  hemi- 
sphere, largely  decussating  at  M  O.  and  passing  down  the  lateral  column  of  the  cord  on  the  opposite  side 
to  the  muscles  M  and  Ml ;  2,  motor  tract  from  left  hemisphere :  S.  Si,  sensitive  areas  011  the  left  side  of 
the  hody  ;  3,  31,  the  main  sensory  tract  from  the  left  side  of  the  body :  it  decussates  shortly  after  enter- 
ing the  cord :  82.  S3,  sensitive  arena,  and  41,  4,  tracts  from  the  right  side  of  the  body.  The  arrows 
indicate  the  direction  of  the  impulses. 


FUNCTIONS    OF   THE  BRAIN. 


803 


tract  descending  in  the  anterior  column  may  either  supply  the  muscles 
which  always  act.  together  on  both  sides  of  the  body;  or,  according  to 
other  observers,  they  cross  in  the  anterior  commissure  to  join  the  lateral 
pyramidal  tract  (Fig.  343). 

The  paths  of  conduction  of  motion  and  sensation  will  again  receive 
attention  when  the  upward  connections  of  the  different  columns  of  the 
cord  have  been  traced. 

VI.   THE  FUNCTIONS   OF   THE  BKAIN. 

In  its  earliest  stage  of  development  the  l/rain  simply  consists  of  the 
dilated  extremity  of  the  medullary  tube  formed  by  the  turning  in  of  the 
medullary  folds  of  the  ectoderm.  Almost  immediately  after  the  closure 
of  the  medullary  canal  its  anterior  termination  is  seen  to  become  differ- 
entiated into  three  bilateral  symmetrical  vesicular  dilatations,  which  are 
the  starting  points  of  the  fore-,  mid-,  and  hind- 
brain.  From  the  fore-brain  the  cerebral  lobes 


ETmfi 


PH. 


FIG.  344.— DIAGRAM  OF 
THE  CEREBRAL  VES- 
ICLES OF  THE  BRAIN 
OF  A  CHICK  AT  THE 
SECOND  DAY  OF  IN- 
CUBATION, AFTER  CA- 
DIAT.  ( Yeo.) 

1,  2,  3,    cerebral    vesicles;    0, 
optic  vesicles. 


FIG.  345.— DIAGRAM  OF  A  VERTICAL  LONGITUDINAL  SECTION 
OF  A  DEVELOPING  BRAIN  OF  A  VERTEBRATE  ANIMAL, 

SHOWING  THE  RELATIONS  OF  THE  THREE  CEREBRAL 

VESICLES  TO  THE   DIFFERENT   PARTS  OF  THE  ADULT 
BRAIN,  AFTER  HUXLEY.    (  Yeo.) 

OJf,  olfactory  lobes;  F.M,  the  foramen  of  Monro;  C.S,  corpus  striatnm ;  T7i, 
optic  thalamus;  Pn,  pineal  glands;  M  b,  mid-brain;  Cb,  cerebellum;  J/.O,  medulla 
oblongata;  Jimp,  cerebral  hemispheres;  ThE,  thalamencephalon ;  Py,  pituitary 
body;  C.Q,  corpora  quadrigemina;  C.C,  crura  cerebri ;  P.V,  pons  varo'lii ;  I-YII, 
regions  from  which  spring  the  cranial  nerves;  1,  olfactory  ventricle;  2.  lateral  ven- 
tricle; 3,  third  ventricle;  4,  fourth  ventricle. 


develop  as  two  hemispherical  vesicles  (prosencephalori),  which,  in  the 
brain  of  the  highest  mammals,  so  increase  in  size  upward  and  backward 
as  to  cover  more  or  less  completely  the  remainder  of  the  primary  cere- 
bral vesicle,  the  mid-,  and  hind-  brain,  so  that  the  mid-brain,  composed 
of  the  optic  thalamus,  corpora  quadrigemina,  and  corpora  striata 
(mesencephalon),  lies  beneath  the  hemispheres.  From  the  hind-brain 
originate  the  cerebellum,  pons  varolii,  and  the  medulla  oblongata 
(myelencephalon).  At  first  all  these  parts  consist  of  thin-walled  vesicles 
communicating  with  each  other  and  with  the  interior  of  the  central 
canal  of  the  spinal  cord  (Figs.  344,  345  and  346). 

In  higher  stages  of  development  the  walls  of  these  cerebral  vesicles 
become  not   only  thicker  and   their  cavities  smaller  and  smaller,  but 


804 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


elevations  (gyri)  and  depressions  (sulci),  convolutions  and  fissures,  form 

so  as  to  give  to  the  brain  its  characteristic 
appearance,  the  degree  of  external  com- 
plexity differing  in  different  classes  of 
animals. 

In  fact,  the  strongest  point  in  favor 
of  the  high  importance  of  the  cerebrum, 
and  especially  its  connection  with  the 
mental  functions,  is  seen  in  the  progressive 
complexity  of  its  surface  in  passing  from 
the  lower  to  the  higher  animals. 

In  fishes,  amphibia,  and  reptiles  the 
cerebral  cortex  is  smooth,  and  but  a  faint 
trace  of  the  formation  of  fissures  is  to 
be  seen  in  birds.  In  the  lowest  mammals 
also  the  hemispheres  are  smooth,  as  in  the 
marsupials,  the  lowest  rodents,  if  not  also 
in  the  lowest  so-called  quadrumana,  as  in 
the  lemurs.  But,  ascending  to  the  higher 
orders  of  mammals,  the  hemispheres  be- 
come more  and  more  sulcated  on  the 
surface,  until  the  ridges  or  convolutions 
become  more  and  more  numerous  and 
complex  as  we  reach  the  highest  mammals 
or  the  highest  genera  in  the  several  orders. 
The  cerebral  convolutions  may  be 
said  to  be  characteristic  of  the  brains  of 
mammals,  and  may  be  considered,  firstly,  in  regard  to  their  general 
plan,  and,  secondly,  their  relative  complexity  within  that  plan. 

The  highest  degree  of  complexity  of  the  cerebral  convolutions  is  seen  in  the 
brain  of  man,  of  which  the  most  important  are  represented  in  the  following 
diagrams  (Figs.  347,  348,  349).  Each  cerebral  hemisphere  is  subdivided  on  its 
external  surface  into  five  lobes — the  frontal,  parietal,  occipital,  ternporo-sphenoidal, 
and  island  of  Reil. 

In  the  (1)  frontal  lobe  are  found  three  convolutions — the  superior,  central, 
and  inferior  frontal  convolutions.  Behind  these  comes  the  ascending  frontal,  sepa- 
rated from  them  by  the  precentral  fissure  and  bounded  posteriorly  by  the  fissure  of 
Rolando,  which  forms  the  anterior  boundary  of  (2)  the  parietal  }ol>e,  the  latter  being 
limited  below  by  the  fissure  of  Sylvius  and  behind  by  the  parieto-occipital  fissure. 
In  this  lobe  are  found  the  ascending  parietal  convolutions  immediately  behind  the 
fissure  of  Rolando,  supramarginal  convolution  arching  around  the  posterior 
extremity  of  the  fissure  of  Sylvius,  and  the  angular  gyrus  arching  around  the  end 
of  the  first  temporo-sphenoidal  fissure. 

(3)  The  temporo-splienoidal  lobe,  bounded  in  front  by  the  fissure  of  Sylvius, 
contains  three   horizontal  convolutions,  superior,  middle,  and  inferior  temporo- 
sphenoidal  convolutions,  the  first  two  being  separated  by  the  parallel  sulcus. 

(4)  The  occipital  lobe  is  separated   from  the  parietal  lobe  by  the  parieto- 
occipital  fissure,  and  likewise  contains  three  convolutions  on  its  outer  surface, — the 
superior,  middle,  and  inferior  occipital  convolutions. 


FIG.  346.— DIAGRAM  OF  A  HOR- 
IZONTAL SECTION  OF  A 
VERTEBRATE  BRAIN,  AFTER 
HUXLEY.  (Yeo.) 

Olf,  Olfactory  lobes  ;  L.t,  lamina  termi- 
nalis;  C.S,  corpus  striatum ;  T h,  optic  thal- 
amus ;  Pn,  pineal  gland;  Mb,  mid-brain; 
Cb,  cerebellum;  M.O,  medulla  oblongata; 
1,  olfactory  ventricle;  2,  lateral  ventricle; 
3,  third  ventricle ;  4,  fourth  ventricle :  -f- 
itar  e  tertio  ad  quartum  ventriculum  ;  F.M, 
foramen  of  Monro ;  11,  optic  nerves. 


FUNCTIONS   OF  THE  BRAIN. 


805 


(5)  The  central  lobe,  or  island  of  Reil,  consists  of  five  or  six  short,  straight 
convolutions  (gyri  operti)  radiating  out  and  back  from  the  anterior  perforated  spot, 
and  can  only  be  seen  when  the  margins  of  the  fissure  of  Sylvius  are  separated. 

On  the  inner  surface  of  each  hemisphere  is  the  gyrus  fornicatus,  or  convo- 
lution of  the  corpus  callosum,  which  terminates  posteriorly  in  the  gyrus  uncinatus 
or  gyrus  hippocampi.  Above  is  the  marginal  convolution,  which  is  simply  the 
inner  surface  of  the  frontal  and  parietal  convolutions,  while  the  inner  surface  of 
the  ascending  parietal  convolution  is  termed  the  quadrate  lobe,  or  prseeuneus. 
The  parieto-occipital  fissure  terminates  in  the  calcarine  fissure  and,  running  back- 
ward in  the  occipital  lobe,  incloses  the  wedge-shaped  lobule, — the  cuneus. 

The  importance  of  an  acquaintance  with  the  principal  cerebral  convolutions 
as  here  sketched  will  be  seen  when  the  functions  of  the  cerebral  cortex  are 
considered. 


FIG.  347.— LEFT  SIDE  OF  THE  HUMAN  BRAIN  (DIAGRAMMATIC).    (Landois.) 

Y  frontal,  P  parietal,  O  occipital,  T  temporo-sphenoidal  lobes ;  S  fissure  of  Sylvius ;  S'  horizon- 
tal, S"  ascending  ramus  of  S;  c,  sulcus  centralis,  or  fissure  of  Rolando;  A  ascending  frontal  and  B 
ascending  parietal  convolutions:  f\  superior,  Fo  middle,  and  F3  inferior  frontal  convolutions;  f\ 
superior  and  /2  inferior  frontal  fissures;  /s,  sulcus  fraecentralis :  P,  superior  parietal  lobule;  Pg, 
inferior  parietal  lobule,  consisting  of  Po,  supramarginal  gyrus,  and  Pg',  angular  gyrus ;  ip,  sulcus  inter- 
parietal  is  ;  cm,  termination  01"  calloso-marginal  fissure;  Oi  first,  Oo.  second,  O?  third  occipital  convolu- 
tions; po.  parieto-occipital  fissure;  o,  transverse  occipital  fissure;  o2,  inferior  longitudinal  occipital 
fissure;  TI  first,  T2  second,  T3  third  temporo-sphenoidal  convolutions;  <j  first,  f2  second  temporo- 
sphenoidal  fissures. 


In  most  ruminants  the  convolutions  are  arranged  in  the  form  of 
parallel  folds,  extending  from  the  front  to  the  back  of  each  hemisphere, 
but  are  much  more  complicated  than  in  the  carnivora,  where  the  surface 
of  the  hemispheres  is  divided  into  four  pairs  of  antero-posterior  convo- 
lutions, distributed  around  the  upper  end  of  the  S3^1vian  fissure  and 
passing  from  the  frontal  to  the  parieto-temporal  lobe  (Fig.  350), 


806 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


In  the  ruminants  traces  of  the  fissure  of  Rolando  may  be  detected, 
but  in  none  of  the  ruminants,  rodents,  marsupials,  or  even  carnivora, 
with  the  exception  of  the  seal,  is  there  to  be  found  a  backward  prolonga- 
tion of  the  lateral  ventricle  forming  a  posterior  cornu. 

In  the  quadrumana  the  plan  of  the  arrangement  of  the  cerebral  con- 
volutions to  a  certain  extent  resembles  that  seen  in  the  cerebrum  of  man. 

The  characteristics  of  this  organization  are  found — first,  in  the 
existence  of  the  occipital  lobe,  with  the  prolongation  into  it  of  the  lateral 
ventricle;  second,  the  fissures  occupy  the  position  of  the  fissures  of  the 
human  brain,  of  which  the  most  important  are  the  fissure  of  Rolando, 
dividing  the  frontal  from  the  parietal  lobe,  the  parieto-occipital  fissure 


lens 
al 

.id 


FIG.  348.— MEDIAN  ASPECT  OF  THE  RIGHT  HEMISPHERE.    (Landois.) 

CC,  corpus  callosum  divided  longitudinally;  Gf,  gyrus  fornicatus;  H,  gyrus  hippocampi;  7;,  sulc 
hippocampi;  U,  unoinate  gyrus ;  cm,  calloso-marginal  fissure ;  Fj,  first  frontal  convolution;  c,  termir 
portion  of  fissure  of  Rolando ;  A,  ascending  frontal  convolution ;  B,  ascending  parietal  convolution  a: 
paracentral  lobule;  Pi',  praecuneus,  or  quadrate  lobule ;  Oz,  cuneus ;  Po,  parieto-occipital  fissure ;  o,  trans- 
verse occipital  fissure;  oc,  calcarine  fissure;  oct,  superior,  oclt,  inferior  ramus  of  the  same;  D,  gyrus 
descendens ;  T4,  gyrus  occipito-temporalis  lateralis  (lobulua  fusiformis) ;  T5,  gyms  occipito-temporalis 
medialis  (lobus  lingualis). 

distinguishing  the  occipital  from  the  parietal  lobe  ;  and,  third,  the  fissure 
of  the  hippocampi,  formed  by  the  folding  inward  of  the  cerebral  substance 
along  the  posterior  cornua.  In  the  higher  monkeys  numerous  other 
fissures  complicate  the  cerebral  surfaces  and  to  a  certain  extent  corre- 
spond with  the  arrangement  of  the  convolutions  in  the  human  brain.- 
In  all  these  may  be  recognized  certain  primary  frontal,  parietal,  occipital, 
and  temporal  convolutions,  which  have  a  general  longitudinal  direction. 
As  a  rule,  the  cerebral  hemispheres  are  more  convoluted  in  the  larger 
species  of  any  group  of  mammals  than  in  the  smaller  species  of  the 
same  group.  For  example,  in  the  pachydermata  the  highest  degree  of 
complexity  of  the  convolutions  is  found  in  the  elephant. 


FUNCTIONS   OF   THE   BKAIN. 


807 


The  basal  ganglia  likewise  depend  for  their  degree  of  development 
upon  the  position  of  the  animal  in  the  zoological  series.  Thus,  the 
corpora  quadrigemina  are,  as  their  name  implies,  divided  into  four  emi- 
nences in  all  mammals,  the  anterior  pair  being  larger  in  herbivora  and 
the  posterior  in  carnivora. 

In  birds,  reptiles,  and  fishes  they  consist  only  of  a  single  pair  of 
ganglionic  masses,  and  are  termed  the  corpora  bigemina,  or  optic  lobes. 


FIG.  349.— ORBITAL  SURFACE  OF  THE 
LEFT  FRONTAL  LOBE  AND  THE 
ISLAND  OF  REIL,  THE  TIP  OF 
THE  TEMPORO  -  SPHENOIDAL 
LOBE  REMOVED  TO  SHOW  THE 
LATTER.  (Landois.) 

17,  convolution  of  the  margin  of  the  longitu- 
dinal fissure ;  O,  olfactory  fissure,  with  the  olfac- 
tory lobe  removed  ;  TR,  triradiate  fissure  ;  HI  and 
lift,  convolutions  of  the  orbital  surface ;  1, 1, 1, 1, 
under  surface  of  the  infero-frontal  convolution;  4, 
under  surface  of  the  ascending  frontal,  and,  5,  of 
the  ascending  parietal  convolutions;  C,  central 
lobe,  or  island. 


FIG.  350.— BRAIN  OF  DOG,  SUPERIOR  SURFACE. 

(Colin.) 

1,  2,  3,  4,  the  four  primary  convolutions;  a,  centre  for  superior 
cervical  muscles ;  b,  for  adductors  and  extensors  of  anterior  ex- 
tremity ;  c,  for  flexors  and  rotators  of  anterior  extremity ;  d, 
motor  centre  for  posterior  extremity ;  /,  centre  for  facial  muscles. 


So,  also,  the  corpora  striata  in  all  vertebrates  are  covered  by  the  cere- 
bral hemispheres,  but  in  descending  the  animal  series  the  reduction  in 
the  size  of  the  cerebral  lobes  gives  a  relatively  greater  importance  to  the 
corpora  striata.  The  size  of  the  optic  and  olfactory  lobes  varies  in  dif- 
ferent groups  of  animals,  being  largest  in  those  in  which  the  special 
senses  associated  with  these  parts  of  the  brain  are  most  highly  developed. 


808  PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 

Further,  in  descending  the  vertebrate  series,  the  lateral  ventricles 
become  smaller  in  extent  and  of  simpler  form,  the  posterior  cornna 
being  absent  in  all  animals  below  the  quadrumana,  with  the  exception 
of  the  seal.  The  gray  matter  of  the  hemispheres  likewise  diminishes, 
until  in  fishes  the  gray  cortex  is  so  thin  as  to  be  almost  indistinguish- 
able to  the  naked  eye.  The  corpus  callosum  has  its  highest  develop- 
ment in  man,  and  in  the  lower  mammals  becomes  both  shorter  from 
before  backward  and  thinner,  and  gradually  becomes  inclined  upward 
and  backward.  In  the  marsupials  it  is  rudimentary,  and  in  no  vertebrate 
lower  than  mammals  is  there  any  trace  of  the  corpus  callosum,  it  being 
represented  in  birds,  reptiles,  amphibia,  and  fishes  merely  by  transverse 
commissural  fibres  crossing  at  the  base  of  the  cerebrum.  As  the  hemi- 
spheres become  reduced  in  importance  there  is  a  corresponding  simplifi- 
cation in  the  medulla-oblongata  and  a  diminution  of  the  cerebellum  and 
pons,  the  pons  being  absent  in  reptiles,  amphibia,  and  fishes. 

No  olivary  bodies  or  corpora  dentata  are  to  be  distinguished  in 
animals  lower  than  mammals,  the  anterior  and  posterior  prominences  and 
restiform  bodies  often  constituting  the  entire  mass  of  the  medulla 
oblongata. 

The  fourth  ventricle,  on  the  other  hand,  is  more  clearly  marked  in 
the  lower  animals  and  is  more  directly  continuous  with  the  central  canal 
and  spinal  cord. 

Like  the  cerebrum,  the  cerebellum  likewise  diminishes  in  passing 
from  the  highest  to  the  lowest  vertebrates.  In  birds  the  bulk  of  the 
cerebellum  is  composed  of  the  vermiform  process,  while  in  reptiles, 
amphibia,  and  fishes  this  median  portion  is  alone  present.  Like  the 
cerebrum,  the  cerebellum,  also,  becomes  progressively  simplified,  the 
laminae  or  convolutions  diminish  until  they  are  comparatively  few  in  the 
bird,  while  they  are  absent  in  reptiles,  amphibia,  and  fishes,  in  which  the 
surface  is  quite  smooth. 

In  the  frog  the  cerebellum  forms  a  simple,  smooth  band,  and  in  the 
lowest  fishes  is  so  reduced  in  size  as  to  no  longer  cover  the  medulla 
oblongata. 

In  many  carnivora  and  ruminants  the  cerebellum,  instead  of  being 
composed  of  broad,  smooth,  lateral  hemispheres  joined  by  the  vermiform 
processes,  is  very  uneven  on  its  surface,  and  apparently  consists  of  a 
cluster  of  a  number  of  lobules. 

The  internal  structure  of  the  cerebellum  likewise  becomes  simplified 
and  the  internal  laminae  of  gray  matter  disappear.  In  general,  it  would 
appear  that  the  more  complex  the  character  of  the  movements  of  which 
the  animal  is  capable  the  higher  will  be  the  plane  of  development  of  the 
cerebellum. 

Only  in  the  large  cetaceans  and  pachyderms  is  the  brain  absolutely 


FUNCTIONS   OF   THE   BRAIN.  809 

heavier  than  in  man ;  thus,  in  the  whale  its  weight  is  about  five  pounds, 
while  in  the  elephant  it  varies  from  eight  to  ten  pounds. 

Compared  with  the  weight  of  the  body,  the  brain  diminishes  in 
weight  in  the  following  order  : — 

In  mammals,  1  to  186;  in  birds,  1  to  212;  in  reptiles,  1  to  1321;  and 
in  fishes,  1  to  5668. 

In  mammals  the  relative  proportion  of  the  brain  to  the  bod.y  is 
smaller  in  the  larger  species.  Thus,  in  the  ox  it  is  as  1  to  860 ;  the 
elephant,  1  to  500 ;  the  horse,  1  to  400  ;  sheep,  1  to  350 ;  dog,  1  to  305 ; 
the  cat,  1  to  156;  the  rabbit,  1  to  140;  the  rat,  1  to  76;  field-mouse,  1  to 
31 ;  man,  1  to  36.  It  is  thus  seen  that  in  few  animals  is  the  brain 
heavier  compared  to  the  body  than  it  is  in  man,  though  in  a  few  singing- 
birds  it  may  amount  to  as  much  as  1  to  12. 

It  must  not  be  forgotten  that  the  estimates  of  the  weight  of  the 
brain  include  the  sensory  and  motor  ganglia  at  the  base  of  the  cerebrum, 
the  optic  thalami,  the  corpora  striati,  and  the  cerebellum,  and  in  the  lower 
mammals  these  portions  of  the  brain  constitute  by  far  the  greater  part ; 
hence  the  size  of  the  cerebral  lobes  as  an  index  of  the  power  of 
intelligence  is  not  disturbed  by  these  figures. 

To  recapitulate,  the  principal  difference  noticed  in  the  brain  in 
passing  from  the  highest  to  the  lowest  vertebrata  is  not  only  in  its 
relative  decrease  in  size  but  also  in  its  gradual  simplification  in  form  and 
structure,  more  especially  in  the  cerebral  hemispheres  and  cerebellum. 
These  organs,  indeed,  gradually  become  smaller  in  proportion  to  the 
sensory  and  motor  ganglia  at  the  base  of  the  cerebrum ;  or,  in  other 
words,  the  ganglia  exhibit  a  greater  proportionate  size  as  compared  with 
the  cerebral  hemispheres  and  cerebellum. 

In  the  highest  mammals  the  cerebral  hemispheres  completely  cover 
the  olfactory  lobes  in  front  and  the  corpora  quadrigemina  behind,  and 
in  man  even  overlap  the  cerebellum  ;  but  in  the  carnivora,  ruminants, 
and  lower  mammals  the  cerebral  hemispheres  no  longer  overlap,  but 
even  fail  to  cover  any  part  of  the  cerebellum,  while  in  the  ruminants 
the  anterior  part  of  the  hemispheres  is  so  diminished  as  to  permit 
the  projection  of  the  olfactory  lobes  beyond  them. 

In  rodents  the  cerebral  lobes  have  become  still  more  retracted 
and  now  a  portion  of  the  corpora  quadrigemina  becomes  visible. 
In  birds,  while  the  olfactory  lobes  are  covered,  the  optic  lobes  are 
exposed,  and  in  reptiles,  amphibia,  and  fishes  the  cerebral  hemispheres 
become  so  much  further  reduced  in  size  as  to  merely  cover  the  corpora 
striata  with  a  thin  layer  of  cerebral  substance. 

In  the  lowest  vertebrata  the  parts  of  the  encephalon  thus  appear  to 
be  arranged  in  a  double  symmetrical  row,  one  behind  the  other.  The 
most  anterior  in  this  row  are  the  ganglionic  masses  which  form  the 


810 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


olfactory  lobes;  behind  them  come  the  cerebral  lobes  covering  the 
corpora  striata,  and  the  third  and  usually  the  largest  mass,  correspond- 
ing to  the  optic  thalami  and  corpora  quadrigemina ;  behind  them  is  seen 
the  cerebellum  as  a  small  central  mass,  while  the  medulla  oblongata  is 
the  connecting  link  between  the  spinal  cord  below  and  the  basal  ganglia 
of  the  brain  above.  These  different  parts  of  the  brain  will  be  taken  up 
in  turn,  commencing  with  the  medulla  oblongata  as  the  cranial 
prolongation  of  the  spinal  cord. 

1.   MEDULLA  OBLONGATA. — The  medulla  oblongata,  like  the  spinal 
cord,  is  composed  of  two  symmetrical  halves,  each  capable  of  separation 


FIG.  351.— SECTION  OF  THK  DECUSSATION  OF  THE  PYRAMIDS.    (Landois.) 

/.La.,  anterior  median  fissure,  displaced  laterally  by  the  fibres  decussating  at  d ;  V,  anterior  column; 
C.a.,  anterior  cornu,  with  its  nerve-cells,  a,  b ;  c.c,  central  canal ;  S,  lateral  column ;  />.,  formatio  retic- 
ularis ;  ce,  neck,  and,  g,  head  of  the  posterior  cornu  ;  r.p.C.I.,  posterior  root  of  the  first  cervical  nerve ; 
M.C.,  first  indication  of  the  nucleus  of  the  funiculus  cuneatus;  n.q.,  nucleus  (clava)  of  the  funiculus  gra- 
cilis ;  HI,  funiculus  gracilis  ;  //2,  funiculus  cuneatua ;  s.l.p.,  posterior  median  fissure ;  x,  groups  of  gangli- 
onic  cells  in  the  base  of  the  posterior  cornu. 

by  the  naked  eye  into  three  different  divisions,  the  anterior  pyramids, 
the  olivary  and  restiform  bodies,  and  the  posterior  pyramid,  or  funiculus 
gracilis.  The  lower  end  of  the  medulla  oblongata,  at  the  point  of  exit 
of  the  roots  of  the  first  cervical  nerves,  is  characterized  by  a  deviation 
of  the  lateral  columns  (crossed  pyramidal  tract)  of  the  cord,  which,  up 
to  this  point  running  parallel  with  the  axis  of  the  cord,  here  turn  in 
through  the  gray  substance  of  the  anterior  horn  and  cross  to  the  oppo- 
site side  of  the  cord  in  the  anterior  white  commissure  to  join  the  direct 
pyramidal  tract.  The  lateral  columns  of  the  cord  consequently  form  a 
decussation  at  the  bottom  of  the  anterior  longitudinal  fissure  in  the 


FUNCTIONS   OF   THE  BKAIN.  811 

medulla,  this  point  of  crossing  being  termed  the  decussation  of  the 
pyramids  (Fig.  351). 

The  anterior  pyramids  are  thus  made  up  of  the  crossed  pyramidal 
tract  from  the  lateral  column  of  the  opposite  side  of  the  cord,  and  the 
direct  p3Tramidal  tract  from  the  anterior  column  of  the  same  side  of  the 
cord. 

Of  the  P3~ramidal  fibres  some  pass  through  the  pons  directly  to  the 
cerebral  cortex  in  a  manner  to  be  described  directly,  some  pass  to  the 
cerebellum,  and  some  join  fibres  coming  from  the  Olivary  body  to  form 
the  olivary  fasciculus. 

The  remainder  of  the  anterior  column,  the  antero-external  fibres,  lie 
under  the  anterior  pyramids  and  form  part  of  the  formatio  reticularis. 

In  the  neighborhood  of  the  first  cervical  nerve  and  the  point  of 
origin  of  the  first  root  of  the  hypoglossal  nerve,  laterally  from  the 
anterior  pyramids,  lie  the  remainder  of  the  lateral  columns  of  the  cord 
which  have  not  undergone  decussation,  the  direct  cerebellar  tract  passing 
backward  to  rejoin  the  restiform  body  and  go  to  the  cerebellum ;  the 
remaining  fibres,  passing  underneath  the  olivary  bodies  and  appearing 
in  the  floor  of  the  medulla,  form  the  fasciculus  teres  and  pass  to  the 
cerebrum. 

Farther  outward  from  the  anterior  pyramids  are  found  the  gray 
masses  of  the  olivary  bodies,  the  pj'ramidal  nucleus,  and  the  accessory 
olivary  nucleus,  through  which  passes  toward  the  middle  line  and  backward 
the  remainder  of  the  anterior  column.  The  gray  substance  of  the  olivary 
bodies  on  section  possesses  the  form  of  a  horseshoe,  whose  arch  is  thrown 
up  into  numerous  folds  and  whose  opening  is  directed  toward  the  centre 
of  the  medulla.  It  contains  numerous  small,  yellow,  pigmented  multi- 
polar  ganglion  cells,  and  embraces  like  a  capsule  a  tract  of  medullated 
nerve-fibres  which  enter  through  the  hylus  of  the  olivary  bodies  and 
spread  out  over  the  entire  inner  surface  of  the  gray  substance.  In  all 
probability  some  of  these  fibres  terminate  in  the  ganglion  cells  of  the 
olivary  bod}^.  The  remainder  pass  through  the  gray  substance  of  the 
olivary  bodjr  and  partly  unite  with  the  fibrous  columns  of  the  restiform 
bodies  and  partly  surround  the  exterior  surface  of  the  oliva^  bodies. 
The  gra}^  substance  of  the  pyramidal  nucleus  and  the  accessory  olivary 
nucleus  resembles  in  all  respects  that  of  the  olivary  bodies.  The  former 
lies  in  the  hylus  of  the  olivary  bodies  toward  the  posterior  central  line 
of  the  pyramidal  and  olivary  columns ;  the  latter,  in  the  form  of  a  thin, 
concave  plate  of  gray  matter,  lies  between  the  olivaty  hylus  and  the 
corpora  restiformes,  which,  by  a  collection  of  gray  matter  (Clarke's 
column),  form  an  unbroken  continuation  of  the  posterior  columns  of  the 
cord  to  the  cerebellum. 

The  restiform  bodies  form  the  posterior  division  of  the  medulla 


812  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

oblongata  and  appear  to  the  naked  eye  as  the  immediate  continuation  of 
the  posterior  white  columns  (postero-external  fibres)  of  the  spinal  cord. 
At  the  level  of  the  foramen  magnum  they  divide  and  expose  the  interior 
gray  substance  of  the  spinal  cord,  which,  previously  covered  by  the  pos- 
terior columns,  here  becomes  exposed  on  the  posterior  surface.  The  gray 
matter  at  this  point  also  becomes  flattened  out  through  the  opening  of  the 
central  canal  of  the  spinal  cord,  its  borders  being  flattened  out  laterally. 
The  posterior  pyramids  form  the  upward  continuation  of  the  postero- 
median  fibres  of  the  posterior  columns  of  the  cord. 

While  the  gray  substance  of  the  spinal  cord  forms  a  compact  mass 
traversed  only  by  the  narrow  central  canal  and  is  everywhere  surrounded 
by  a  sheath  of  white  substance,  in  the  medulla  it  becomes  exposed  and 
forms  a  flattened  layer,  and  is  divided  into  two  symmetrical  halves  lying 
on  each  side  of  the  median  line  and  bounded  only  by  a  slight  rim,  the 
last  trace  of  the  central  spinal  canal.  This  exposed  surface  of  gray 
matter  in  the  medulla  oblongata  has  the  form  of  an  elongated  rhomb, 
whose  longest  diagonal  coincides  with  the  median  line,  and  it  forms  the 
floor  of  the  fourth  ventricle,  communicating  above  with  the  aqueduct  of 
Sylvius  and  below  with  the  central  canal  of  the  spinal  cord,  the  lower 
pointed  end  of  this  surface  bearing  the  name  of  the  calamus  scriptorius. 
The  gray  substance  of  the  floor  of  the  fourth  ventricle  is  entirely  similar 
to  that  of  the  spinal  cord ;  it  contains  a  large  mass  of  multipolar  gan- 
glion cells,  of  which  a  few  form  distinct  roots  and  appear  to  be  in  direct 
communication  with  the  cranial  motor  nerves. 

The  ganglionic  origin  of  the  sensory  cranial  nerves  is  less  distinctly 
made  out.  It  is,  however,  clear  that  all  the  cranial  nerves,  from  the 
oculo-motor  to  the  hypoglossal,  originate  in  the  medulla  oblongata  and 
its  annexes.  Only  the  optic  and  olfactory  nerves  originate  within  the 
cerebrum.  The  gray  matter  of  the  floor  of  the  fourth  ventricle  forms  a 
direct  continuation  of  the  gray  matter  of  the  spinal  cord,  and  is  to  this 
extent  analogous  to  the  anterior  columns,  the  p3^ramids,  and  cerebellar 
fibres,  which  pass  without  interruption  from  the  spinal  cord  into  the 
medulla  oblongata. 

The  anterior  divisions  of  the  lateral  columns  of  the  spinal  cord 
likewise  pass  without  interruption  into  the  medulla  oblongata  and  force 
themselves  between  the  olivary  body  and  restiform  bod}'',  without,  how- 
ever, passing  farther  toward  the  median  line  (Fig.  352). 

From  the  raphe  originate  numerous  nervous  fibres,  or  so-called 
internal  transverse  fibres,  which  cross  the  longitudinal  fibres  of  the 
medulla  at  a  right  angle  and  split  up  into  a  large  number  of  smaller 
bundles,  the  net-work  so  formed  being  described  as  the  reticular  forma- 
tion of  the  medulla  oblongata.  This  net-work  incloses  in  its  spaces 
numerous  multipolar  ganglion  cells,  in  which  terminate,  in  all  probabilit}-, 


FUNCTIONS   OF   THE   BKAIN. 


813 


Sip 


certain  of  the  fibres  of  the  lateral  columns  of  the  cord,  and  so  enable  the 
medulla,  by  bringing  it  into  communication  with  impressions  coining 
from  below,  to  act  as  a  reflex  centre.  The  transverse  fibres  of  the 
medulla  are  to  be  regarded  as  commissural  fibres  connecting  the  two 
halves  of  the  medulla,  especially  the  olivary  bodies. 

Closely  allied  to  the  anterior  surface  of  the  olivary  columns  are  to 
be  found  the  gray  nuclei,  or  the  column  of  Goll  (Keil string),  from  which 
originate  the  arciform  fibres,  or  the  external  transverse  fibres  which 
surround  the  entire  external  surface  of  the  medulla  to  unite  with  the 
internal  transverse  fibres,  from  there 
to  pass  into  the  restiform  bodies,  and 
from  there  to  the  cerebellum. 

The  internal  interweaving  of 
the  centrifugal  and  centripetal 
fibres,  the  presence  of  numerous 
ganglionic  cells,  and,  to  a  certain 
extent,  the  evident  union  of  different 
classes  of  nerve-elements,  the  sym- 
metrical connection  b.y  transverse 
fibres  of  both  halves  of  the  medulla, 
nil  speak  in  the  clearest  way  as  to 
the  high  ph}'siological  importance  of 
this  portion  of  the  central  nervous 
system,  both  as  the  seat  of  reflex 
centres,  as  the  origin  of  numerous 
cranial  nerves,  and  as  the  paths  of 
communication  from  the  spinal  cord  FlG* 
to  the  brain. 

As  is  evident  from  the  anatom- 
ical description  of  the  medulla,  in 
many  respects  it  forms  the  most 
important  part  of  the  central  ner- 
vous System.  It  forms  the  ganglionic  n.e.i,  external  micleus~orth7fun^uius''cun7atu8TTo' 
,.  ,,  i  ,  nucleus  of  the  funiculus  gracilis  (or  clava)  •  771  funiculus 

termination     OI     a      large    number    Of      gracilis:  #2.  funiculus  cuneatus;  c.c.,  central  canal;  fa 

/o,i  /a,2  external  arciform  fibres. 

nbres;    most  ot   the  cranial  nerves 

find  in  it  their  origin,  and  in  it  the  most  diverse  systems  of  the  animal 
body  are  brought  into  nervous  connection.  For  the  ascending  motor 
and  sensory  nerves  of  the  spinal  cord  it  forms  not  only  the  means  of 
conduction,  but  is  the  seat  of  important  centres  of  co-ordination.  These 
paths,  and  the  most  important  centres,  are  represented  in  diagrammatic 
form  in  Figs.  353  and  354. 

It  has  been  seen  that  when  the  spinal  cord  is  divided  below  the  level 
of  the  medulla  oblongata  in  the  frog  it  remains  perfectly  motionless  and 


DECUSSATION 
(Landois.) 


OF    THE    PYRAMIDS. 


f.l.a.,  anterior,  s.l.p.,  posterior  median  fissures; 
n.XI,  nucleus  of  the  accessorius  vagus;  n.XII,  nucleus 
of  the  hypoglossal ;  d.a.,  the  so-called  superior  or  anterior 
decussation  of  the  pyramids;  py,  anterior  pyramid; 
n.ar.,  nucleus  arciformis;  ol,  median  parolivary  body  • 
o,  beginning  of  the  nucleus  of  the  olivary  body  n  I 


814 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


in  an  apparent  condition  of  almost  total  paralysis,  yet  after  the  shock  of 
the  operation  has  passed  off  a  number  of  highly  complex  reflex  motions 
may  be  evoked.  If,  however,  the  section  of  the  cord  be  made  at  the 
anterior  border  of  the  medulla  the  position  of  the  frog  after  the  shock  of 
the  operation  has  passed  off  is  more  nearly  normal,  and  allusion  has  been 


01. 


ff 


FIG.  353.—  DIAGRAM  OF  THE  CHIEF  TRACTS 
IN  THE  MEDULLA,  AFTER  ERB. 
(Ranney.) 

The  formatio  reticularis  is  represented  by  shading. 
01.,  olivary  body  ;  V  anterior,  S  lateral,  and  H  pos- 
terior spinal  funiculi  ;  «,  pyramido-anterior  tract  ;  d, 
pyramido-lateral  tract;  Py.,  pyramidal  tract;  b,  re- 
mainder of  anterior  column  ;  c,  remainder  of  the  lateral 
column  ;  e,  e,  cerebello-lateral  tract  ;  /,  funiculus  gra- 
cilis,  and,/',  nucleus  of  the  same;  g,  funiculus  cunea- 
tus,  and,  gt,  nucleus  of  the  same;  P.c.i.,  internal 
fasciculus  of  the  pedunc.  cerebelli  ;  P.c.e.,  external 
fasciculus  of  the  same  ;  Cq.F.,  tract  from  corp.  quadr. 
to  format,  retic.;  Cq.O.,  the  same  to  the  olivary  body; 
Thai.,  tract  from  the  thalamus  opticus. 


FIG.  354.— TRANSPARENT  LATERAL  VIEW 
OF  THE  MEDULLA,  SHOWING  THE 
RELATIVE  POSITIONS  OF  THE  MOST 
IMPORTANT  NUCLEI;  RIGHT  HALF 
OF  THE  MEDULLA,  SEEN  FROM  THE 
SURFACE  OF  SECTION;  THE  PARTS 
THAT  LIE  CLOSER  TO  THIS  SURFACE 
ARE  DEEPER  SHADED,  AFTER  ERB. 
(Ranney.) 

Py,  pyramidal  tract;  Py.  Kr,  decussation  of  pyramids; 
O,  olivary  body ;  O..s,  superior  olivary  body ;  V,  motor, 
Vt,  middle  sensory,  vn,  inferior  sensory  nucleus  of 
trigeminus  ;  VI,  nucleus  of  abdncens ;  G.  f,  genu  facialis  : 
VII,  nucleus  facialis  :  VIII,  posterior  median  acoustic 
nucleus ;  IX,  glosso-pharyngeal  nucleus  X,  nucleus  of 
vagus ;  XI,  accessorius  nucleus ;  XII,  hvpoglossal  nu- 
cleus; Kz,  nucleus  of  the  funiculus  gracilis;  RV.  tri- 
geminus roots  ;  those  of  the  R  VI,  abdueens,  and  R  VII, 


made  to  the  fact  that  in  the  mid-brain  is  seated  a  centre  which  inhibits 
reflex  action. 

When  the  cerebral  lobes  only  have  been  removed  in  the  frog,  volition 
is  apparently  the  only  function  of  the  animal  which  is  wanting,  and  in 
the  absence  of  stimuli  of  all  characters  the  animal  remains  absolutely 
inert.  If  such  a  frog  is  thrown  into  water  it  swims  ;  by  stimulating  its 


FUNCTIONS   OF   THE   BEAIN. 


815 


body  it  may  be  made  to  leap ;  when  placed  on  its  back  it  regains  its 
normal  attitude.  When  placed  on  an  inclined  plane  it  crawls  up  until  it 
gains  a  new  position,  and  if  such  an  experiment  be  made  by  placing  a 
frog  on  a  small  piece  of  board,  by  gradually  inclining  the  board  more 
and  more  the  frog  may  be  made  to  climb  up  the  board,  pass  over  to  the 
other  side,  and  the  piece  of  wood  may  be  turned  over  a  number  of  times, 
the  frog  always  moving  with  it  as  long  as  its  equilibrium  is  dis- 
turbed. Such  a  frog  will  likewise  be  apparently  sensible  to  light,  and  if 
made  to  jump  will  avoid  objects  casting  a  strong  shadow.  Such  move- 
ments as  above  described  are  evidently  carried  out  by  co-ordinating 
mechanisms  and  governed  by  definite  afferent  impulses  (Figs.  355  and 
356). 

It  is  evident,  from  the  existence  of  these  motions  in  the  frog 
deprived  of  its  cerebral  hemispheres,  that  the  mechanism  governing 
them  must  lie  in  parts  of  the  central  nervous  system  below  the  line  of 
section.  No  such  operations  can  be  effected  in  a  frog  in  which  the 
medulla  has  been  removed.  It  follows,  therefore,  that  in  the  medulla, 
or  perhaps  in  the  corpora  quadrigemina  and  optic  lobes,  are  found  the 
co-ordinating  centres  of  the  most  complex  muscular  movement. 


FIG.  3.55.— FROG  WITHOUT  ITS  CEREBRUM 
AVOIDING  AN  OBJECT  PLACED  IN 
ITS  PATH.  (Landois.) 


FIG.  356.— FROG  WITHOUT  ITS  CEREBRUM 
MOVING  ON  AN  INCLINED  BOARD, 
AFTER  GOLTZ.  (Landois.) 


In  the  mammal  or  bird  a  similar  state  of  affairs  is  present,  although, 
as  might  be  expected,  complicated  to  a  greater  degree  by  the  more 
severe  shock  of  the  operation. 

In  a  bird  or  a  mammal  in  which  the  medulla  remains  after  removal 
of  the  cerebral  lobes  the  attitude  may  become  perfectly  normal.  If 
placed  on  its  side  it  will  regain  its  feet.  If  a  bird  be  thrown  into  the 
air  it  will  fl}-  for  a  considerable  distance,  perhaps  avoiding  obstacles,  but 
its  movements  more  resemble  those  of  a  stupid,  sleep3T  animal  than  one 
in  full  possession  of  its  faculties.  A  mammal,  also,  so  operated  on  can 
stand,  run,  and  leap,  and  if  placed  on  its  back  can  regain  its  normal 
position,  but  if  left  alone  it  remains  absolutely  motionless.  If  food  is 
placed  in  the  mouth  of  the  animal  in  whom  ablation  of  the  cerebrum 
has  been  successfully  performed  the  animal  will  eat,  and  the  complicated 
motions  of  mastication  and  deglutition  will  be  accomplished  with  perfect 
regularity. 


816  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

In  the  case  of  mammals  it  ought,  perhaps  with  more  correctness, 
to  be  stated  that  these  highly  co-ordinate  movements  owe  their  perform- 
ance to  parts  above  the  medulla,  since  the  removal  of  the  optic  thalami, 
crura  cerebri,  corpora  quadrigemina,  cerebrum,  and  pons  varolii  is 
usually  followed  by  various  forced  movements,  or  the  animal  lies  partly 
on  its  side,  and,  although  various  complex  movements  may  be  produced,, 
they  are  much  more  limited  than  when  the  higher  parts  of  the  brain  are 
left  intact. 

The  medulla  oblongata  is  the  seat  of  a  large  number  of  centres 
governing  complex  co-ordinate  movements,  of  which  the  following  are- 
the  most  important : — 

(a)  The  Respiratory  Centre. — This  is  located  in  the  medulla  behind 
the  point  of  origin  of  the  pneumogastric  nerves  on  both  sides  of  the 
apex  of  the  calamus  scriptorius,  between  the  nuclei  of  the  vagus  and 
spinal   accessory  nerves.      This  centre  is  symmetrically  situated,  and 
may  be  separated  by  a  longitudinal  incision  without   interfering  with 
the  respiratory  movements.      Conditions  governing  the  actions  of  this 
centre  have  been  already  given  under  the  subject  of  respiration. 

(b)  The  Cardio-Inliibitory  Centre. — As  has  been  previously  stated r 
when  the  pneumogastric  nerve  is  stimulated  it  may  slow  or  arrest  the 
heart  in  diastole,  according  to  the  degree  of  stimulation.     The  inhibitory 
fibres  of  the  pneumogastric  reach  the  latter  nerve  through  the  spinal 
accessory  and  have  their  origin  in  the  medulla  oblongata.     The  conditions 
for  its  action  have  been  likewise  given. 

(c)  The   Vaso-Motor    Centre. — The  collection  of  nerve-cells  which 
govern  the  vaso-motor  nerves,  and  through  them  tlie  calibre  of  the  blood- 
vessels, is  located  in  the  floor  of  the  medulla  oblongata,  extending  from 
the  upper  part  of  the  floor  to  within  four  or  five  millimeters  of  the  col- 
umns of  the  cerebellum.     This  centre  is  also  a  double  one,  situated  sym- 
metrically on  each  half  of  the  medulla  and  each  part  corresponding  to  the 
upward  continuation  of  the  lateral  columns  of  the  spinal  cord.     Stimula- 
tion of  this  centre  causes  contraction  of  all  the  arteries  with  a  consequent 
increase  in  the  blood  pressure;  paralysis  causes  relaxation  and  dilatation 
of  the  blood-vessels  and  fall  of  blood  pressure.     Its  action  has  also  been 
described. 

(d)  Centre  for  Closure  of  the  Eyelids. — The  centre  for  the  closure 
of  the  eyelids  lies  close  to  the  calamus  scriptorius.    The  afferent  impulses 
reach  it  through  the  sensory  branches  of  the  fifth  cranial  nerve  from 
stimuli  applied  to  the  cornea,  conjunctiva,  and  skin  in  the  neighborhood 
of  the  eye  ;  reaching  the  centre  of  impulse,  are  transferred  to  the  special 
nerve,  through  which  the  afferent  impulses  reach  the  orbicularis  palpe- 
brarum. 

(e)  Centre  for  Sneezing. — The  location  of  this  centre  has  not  been 


FUNCTIONS   OF   THE   BRAIN.  817 

accurately  determined.  Stimuli  pass  through  the  internal  nasal  branches 
of  the  trigeminus  or  olfactory  nerves  and  efferent  fibres  are  found  in  the 
nerves  coming  to  the  muscles  of  expiration. 

(f)  The  Centre  for  Coughing. — This  centre  is  placed  a  little  above 
the  respiratory  centre.     The  afferent  fibres  pass  to  the  centre  through 
branches  of  the  pneumogastric,  the  efferent  in  the  nerves  of  expiration 
and  in  those  that  supply  the  muscles  that  close  the  glottis. 

(g)  Centre  for  the  Movements  of  Suckling  and  Mastication. — This 
centre  also  has  escaped  close  localization.     Afferent   paths   reach  the 
medulla   through   the   trigeminal   and   glosso-pharyngeal   nerves.     The 
efferent  fibres  in  the  case  of  suction  reach  the  lips  through  the  facial,  the 
tongue  through  the  hypoglossal,  and   the  muscles  which  depress  and 
elevate  the  lower  jaw  through  the  inferior  maxillary  division  of  the  fifth 
nerves.     The  same  nerves  are  concerned  in  the  movements  of  mastication, 
with  the  exception  that  when  the  food  passes  within  the  dental  arch  the 
hypoglossal  is  concerned  in  the  movements  of  the  tongue,  and  the  facial 
with  the  buccinator. 

(h)  The  Centre  for  the  Secretion  of  Saliva. — This  centre  lies  in  the 
floor  of  the  fourth  ventricle.  When  the  medulla  is  stimulated,  if  the 
chorda  t3rmpani  and  glosso-pha^ngeal  nerves  are  intact,  a  profuse  secre- 
tion of  saliva  is  the  result,  indicating  the  efferent  course  of  this  impulse. 
Afferent  impulses  reach  the  centre  through  the  ne.rves  of  taste. 

(i)  The  Centre  for  Deglutition. — This,  likewise,  is  located  in  the 
floor  of  the  fourth  ventricle.  The  afferent  paths  reach  the  centre  through 
the  second  and  third  branches  of  the  fifth  pair,  the  glosso-pharyngeal  and 
the  pneumogastric.  The  efferent  channels  are  found  in  the  motor 
branches  of  the  phaiyngeal  plexus. 

(&)  The  Centre  for  the  Dilatation  of  the  Pupil— This  centre,  like- 
wise, lies  in  the  medulla  oblongata,  the  efferent  fibres  passing  partly 
through  the  trigeminal  nerve  and  partly  in  the  lateral  columns  of  the 
spinal  cord,  as  far  down  as  the  cilio-spinal  region,  and  from  there  passing 
out  by  the  lowest  two  cervical  and  the  two  upper  dorsal  nerves  into  the 
cervical  sympathetic.  The  centre  is  normally  excited  in  a  reflex  manner 
by  diminishing  the  amount  of  light  entering  the  eye.  Its  action,  together 
with  that  of  the  centre  for  contracting  the  pupil,  will  be  referred  to 
subsequently. 

(/)  The  centre  for  vomiting  is  likewise  found  in  the  medulla.  Its 
functions  have  been  already  described. 

(in)  The  medulla  oblongata,  as  discovered  by  Bernard,  exerts  a 
certain  influence  on  the  glycogenic  function  of  the  liver.  When,  as 
already  described,  a  puncture  is  made  in  the  floor  of  the  fourth  ventricle 
in  the  neighborhood  of  the  origin  of  the  pneumogastric  nerve  temporary 
glycosuria  appears  within  an  hour  or  an  hour  and  a  half  after  the 

52 


818  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

operation.  The  method  by  which  this  influence  on  the  liberation  of 
sugar  by  the  liver  is  accomplished  has  been  described  under  the  heading 
of  Gtycogenesis. 

2.  THE  COURSE  OF  THE  FIBRES  OF  THE  MEDULLA  OBLONGATA. — We 
have  now  to  attempt  to  trace  the  paths  of  communication  of  the  different 
divisions  of  the  medulla  oblongata  with  the  cerebrum,  pons  varolii,  cor- 
pora quadrigemina,  and,  still  more  important  than  all,  the  formation  of 
the  hemispheres  of  the  cerebrum  and  their  means  of  communication  by 
the  cerebral  peduncles  with  the  mid-brain  and  its  ganglia  and  with  the 
cerebellum. 

In  tracing  up  the  fibres  from  the  medulla,  those  most  readily  followed 
are  the  continuations  of  the  restiform  bodies,  which  may  be  readily 
detected  to  pass  directly  into  the  cerebellum.  Their  termination  after 
reaching  the  cerebellum  is  only  partially  cleared  up,  and  before  attempt- 
ing its  explanation  we  must  first  consider  the  mode  of  construction  of 
the  cerebellum  itself. 

The  cerebellum  consists,  in  the  domestic  animals  and  man,  of  two 
flattened  hemispheres  connected  across  the  middle  line  by  the  middle 
lobe  or  vermiform  appendix,  which  is  the  fundamental  portion  of  the 
organ.  The  white  substance  of  the  cerebellum  exceeds  to  a  considerable 
degree  the  gray  matter.  The  latter  is  deposited  over  the  entire  surface 
of  the  two  hemispheres  of  the  cerebellum,  forming  the  gray  cortex  of  the 
cerebellum  ;  within  the  inner  white  medullary  substance  of  the  hemisphere 
is  a  collection  of  gra}r  matter  known  as  the  dentate  or  ciliary  body, 
which  in  its  general  appearance  somewhat  resembles  that  of  the  olivary 
bodies  found  in  the  medulla  oblongata,  and  which  here,  also,  has  the 
shape  of  a  horseshoe,  thrown  up  into  numerous  folds,  and  near  which  are 
also  found  associate  nuclei.  Although  it  is  clearly  established  that  the 
main  function  of  the  gray  matte;*  is  to  bring  the  nerve-fibres  and  nerve- 
cells  into  connection  with  each  other,  still,  as  yet,  no  direct  termination 
of  nerve-tubes  in  the  ganglion  cells  of  the  cerebellum  has  been  detected. 
Of  course,  this  does  not  imply  that  the  terminations  of  the  gray  cells  in 
the  cortex  of  the  cerebellum  with  nerve-cylinders  may  not  be  readily 
determined.  All  attempts,  however,  to  follow  up  these  nerve-fibres  has 
as  yet  resulted  in  almost  total  failure.  If,  however,  we  follow  the  resti- 
form bodies  (which  form  the  inferior  peduncles  of  the  cerebellum)  it  may 
be  seen  that  a  certain  amount  of  their  fibres  decussates  and  then  enters  into 
the  dentate  body,  forming  the  so-called  hitra-ciliary  fibres,  while  another 
passes  externally  and  forms  the  extra-ciliary  column. 

In  addition  to  its  communication  with  the  medulla,  the  cerebellum  is 
likewise  in  communication  with  the  corpora  quadrigemina  and  the  pons 
varolii.  The  fibres  passing  from  the  cerebellum  to  the  corpora  quadri- 
gemina and  crura  cerebri  (superior  cerebellar  peduncles)  originate  not 


FUNCTIONS    OF   THE   BRAIN.  819 

only  from  the  extra-ciliary  fibres  around  the  corpora  dentata,  decussating 
in  the  pons,  but  also  from  the  associate  nuclei,  while  the  fibres  from  the 
extra-ciliary  columns  alone  have  been  traced  into  connection  with  the 
pons.  It,  therefore,  is  evident  that  the  cerebellum  is  to  be  regarded  as 
a  complicated  collection  of  gray  ganglionic  masses  in  unbroken  connec- 
tion with  the  medulla  oblongata  and  pons  on  the  one  side  and  with  the 
cerebrum  on  the  other. 

The  pons  varolii  is  formed  by  a  collection  of  the  continuations  of 
the  reticular  formation  of  the  medulla,  the  pyramids  and  anterior  columns 
of  the  medulla,  together  with  the  fibres,  coming  directly  by  the  middle 
peduncle  from  the  cerebellum. 

Above  the  pons  the  two  collections  of  fibres  known  as  the  cerebral 
peduncles-  (crura  cerebri)  approach  each  other,  the  point  at  which  the 
union  is  accomplished  above  the  medulla  being  the  locality  in  which  the 
upper  end  of  the  fourth  ventricle  terminates  in  the  aqueduct  of  Sylvius. 

In  the  interior  of  each  cerebral  peduncle  is  found  a  mass  of  gray 
matter,  the  substantia  niger,  which  separates  the  fibres  of  each  cms  into 
two  layers,  the  upper  laj-er  forming  the  so-called  teymentum  cruris 
and  the  lower  the  basis  cruris.  The  upper  division  of  the  tegmentum 
contains  also  a  gray  nucleus  (nucleus  tegmentis). 

Although  these  two  divisions  of  the  crura  are  in  close  anatomical 
connection,  it  has  been  determined  with  a  considerable  degree  of  posi- 
tiveness  that  the  pyramidal  fibres  are  in  direct  communication  through 
the  basis  of  the  cerebral  peduncles  with  the  central  convolutions  of  the 
cerebral  hemisphere  on  the  same  side,  although  whether  a  direct  commu- 
nication, as  in  the  case  of  the  cerebellum,  of  these  fibres  with  the  gangli- 
onic cells  in  the  upper  surface  of  the  hemispheres  exists  or  not  has  not 
yet  been  determined.  Nevertheless,  it  appears  that  they  form  no  direct 
communication  with  the  other  gray  masses  of  the  hemispheres,  the 
lenticular  nucleus,  optic  thalamus  or  striated  body.  And  since  they 
undergo  degeneration  only  after  injury  of  the  central  convolutions,  it 
is  probable  that  they  are  in  direct  communication  with  the  cortex  of 
the  brain. 

Flechsig  claims  to  have  followed  them  in  an  unbroken  course  from 
the  pyramidal  columns  through  the  white  mass  between  the  lenticular 
nucleus  and  optic  thalamus,  the  so-called  internal  capsule,  direct  to  the 
gray  cortex  of  the  cerebral  convolutions.  The  course  of  these  fibres, 
together  with  the  other  important  cerebro-spinal  tracts  are  shown  in 
Fig.  357. 

The  cerebrum  is  divided  by  a  longitudinal  fissure  into  two  hemi- 
spheres in  man,  mammals,  and  birds,  and  its  external  surface  is  divided 
by  a  number  of  lesser  fissures  into  lobes  and  convolutions.  The  cere- 
brum contains  the  ganglia  of  the  brain,  the  optic  thalamus  or  corpus 


820 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


R 


Spinal  Cord 


FIG.  357.— A  DIAGRAM  DESIGNED  TO  ILLUSTRATE  THE  COURSE  OF  CERTAIN 
NERVE-TRACTS  WITHIN  THE  CEREBRUM,  CRUS,  PONS,  MEDULLA,  AND 
SPINAL  CORD.  MODIFIED  FROM  FLECHSIG.  (Ranney.) 

C.N.,  caudate  nucleus  ;  L.N.,  lenticular  nucleus  ;  O.T.,  optic  thalamus :  G.P.,  gray  matter  of  the  pons ; 
F.R.,  formatio  reticularis;  C.D.,  corpus  dentatum;  O,  olivary  body  ;  N.C.,  clavate  nucleus;  T.N.,  trian- 
gular nucleus:  C.Q.,  corpora  quadrigemina ;  I.C.,  upper  limit  of  the  capsular  fibres:  m,  m,  m,  motor 
centres  around  the  fissure  of  Rolando;  c.r.,  fibres  of  the  " corona  radiata."  1,  the  "pyramidal  tract," 
arising  from  the  motor  centres  of  the  cerebrum  and  terminating  in  the  cells  of  the  anterior  horns  of  the 
spinal  gray  substance  (13  and  14) ;  2,  3,  and  4,  fibres  connecting  the  cerebral  cortex,  the  caudate  nucleus, 
and  the  lenticular  nucleus  with  the  gray  matter  of  the  pons  after  decussation,  and  then  prolonged  as  0 
and  7  to  the  cerebellum ;  o,  fibres  of  the  superior  cerebellar  peduncle ;  6,  7,  8,  9,  and  10  show  by  their 
colors  the  tracts  with  which  they  are  associated,  as  well  as  their  origin  and  termination;  11  and  17,  the 
"direct  cerebellar  tract"  of  the  spinal  cord  (whose  probable  termination  is  not  correctly  shown  in  the 
cut,  as  it  probably  ends  in  the  vermiform  process) ;  12,  the  lemniscus  or  "fillet "  tract,  connecting  the 
olivary  body  with  the  optic  thalamus  and  the  corpora  quadrigemina:  13,  the  cells  of  the  cord  connected 
with  the  direct  pyramidal  tract ;  14,  the  cells  of  the  cord  connected  with  the  crowed  pi/ramidnl  tract;  15, 
fibres  of  the  column  of  Burdach,  terminating  superiorly  in  the  triangular  nucleus ;  16,  fibres  of  the 
column  of  Goll,  terminating  superiorly  in  the  clavate  nucleus ;  19,  fibres  of  the  cord  which  terminate  in 
the  so-called  "  reticular  formation  "  directly  ;  18,  fibres  of  the  ret.  form,  going  to  the  cerebellum. 


FUNCTIONS   OF   THE   BKAIN.  821 

striati,  the  caudate  and  lenticular  nuclei,  and  the  corpora  quadrigemina, 
being  connected  with  the  medulla  by  means  of  the  cerebral  peduncles, 
above  which  are  situated  the  corpora  quadrigemina. 

In  the  domestic  animals  the  anterior  pair  of  the  corpora  quadri- 
gemina are  composed  of  gray  matter,  while  the  posterior  are  white,  in 
direct  opposition  to  what  is  the  case  in  man.  In  herbivora  and  in  the 
hog  the  anterior  pair  are  the  larger,  while  in  carnivora  they  are  of  equal 
size,  or  the  posterior  may  be  somewhat  more  developed.  Between  the 
corpora  quadrigemina  and  the  optic  thalamus  lies  the  third  ventricle, 
while  under  the  corpora  quadrigemina  is  situated  the  aqueduct  of 
Sylvius,  connecting  the  third  and  fourth  ventricle. 

We  have  now  to  attempt  an  explanation  of  the  functions  of  these 
different  parts  of  the  brain. 

3.  THE  PONS  YAROLII. — We  have  seen  that  the  pons,  the  superior 
continuation  of  the  spinal  cord,  is  composed  of  two  sets  of  fibres.     The 
one,  the  transverse  fibres,  constituting  the  median  cerebellar  peduncles, 
serves  to  connect  the  two  lateral  hemispheres  of  the  cerebellum  and  exists 
only  in  animals  in  which  the  cerebellum  consists  of  two  lobes.    The  other 
part  of  the  pons  is  composed  of  a  mass  of  gray  substance  in  continuity 
with  that  of  the  medulla  and  traversed  in  an  antero-posterior  direction 
by  the  fibres  of  the  medulla,  passing  up  to  form  the  cerebral  peduncles. 

As  in  the  study  of  other  portions  of  the  nervous  system,  we  attempt 
here  to  determine  the  functions  of  the  different  parts  of  the  brain  by  the 
method  of  excitation  and  excision. 

When  the  pons  is  stimulated,  either  mechanically  or  by  an  electric 
current,  pain  and  muscular  spasms  are  produced,  evidently  by  the  mere 
implication  of  adjacent  motor  and  sensor}^  paths.  Where  section  of  the 
pons  is  performed  there  may  be  sensory,  motor,  or  vaso-motor  paralysis, 
together  with  forced  movements  when  the  middle  cerebellar  peduncles 
are  involved.  Thus,  if  there  be  an  injury  to  the  lower  half  of  one  side 
of  the  pons  there  will  be  both  sensory  and  motor  paralysis  of  the  face 
on  the  same  side  and  more  or  less  general  paralysis  of  the  opposite  side 
of  the  body ;  if  the  injury  be  to  the  upper  half  of  the  pons  the  facial 
paralysis  will  be  on  the  same  side  as  the  paralysis  of  the  body. 

The  pons,  like  the  spinal  cord  and  medulla,  also  acts  as  a  reflex 
centre ;  although  this  fact  is  not  capable  of  direct  demonstration,  its 
truth  is  rendered  probable  by  the  higher  degree  of  muscular  co-ordination 
preserved  by  an  animal  in  which  the  pons  has  been  retained  over  animals 
in  whom  the  section  has  been  carried  through  the  brain  below  this  point. 

4.  THE  CEREBRAL   PEDUNCLES. — The   cerebral   peduncles  form   the 
upward  prolongation  of  the  pons,  and  are  constituted  by  those  portions 
of  the  spinal  cord  which,  after  having  traversed  the  pons  and  medulla, 
pass  upward  through  the  optic  thalamus  and  corpora  striata  to  enter  the 


822  ,       PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

cerebral  hemispheres.  When  one  of  the  cerebral  peduncles  is  completely 
divided  it  produces  paralysis  of  voluntary  movement  on  the  opposite 
side  of  the  body,  with  a  diminution  of  the  sensibility  and  vaso-motor 
paralysis. 

Section  of  the  basis  of  both  cerebral  peduncles  totally  abolishes  all 
voluntary  movements,  although  reflexes  apparently  of  cerebral  origin 
still  persist. 

Section  of  the  tegmentum,  on  the  other  hand,  on  both  sides  entails 
the  loss  of  these  cerebral  reflexes,  but  allows  voluntary  motion  to  remain. 

Injury  to  one  cerebral  peduncle  causes  pain  and  convulsions  on  the 
opposite  side  of  the  body,  while  the  blood-vessels  contract.  As  the 
irritative  effects  pass  off  these  symptoms  give  place  to  paralysis. 

5.  THE  CORPORA  QUADRIGEMINA. — Destruction  of  the  corpora  quad- 
rigemina  on  one  side  causes  blindness,  which  may  be  either  on  the  side 
of  the  injury  or  on  the  opposite  side,  according  to  the  location  of  the 
mutilation.     Total  destruction  causes  absolute  blindness  in  both  eyes, 
with  the  absence  of  the  reflex  contraction  of  the  pupil  when  exposed  to 
the   light.     In   addition  to  blindness,  disturbance  of  equilibrium  and 
inco-ordination  of  movement  result.     When  stimulated  the  pupils  have 
been  noticed  to  dilate  either  on  the  same  side  or  the  opposite  side  of  the 
body ;  this  result  is  probably  produced  by  conduction  of  the  stimulus  to 
the  origin  of  the  S}Tmpathetic  nerve,  for  after  section  of  the  sympathetic 
dilatation  of  the  pupil  no  longer  takes  place.     Stimulation  of  the  right 
anterior  tubercle  causes  the  eyes  to  deviate  to  the  left,  while  if  a  vertical 
incision  is  made,  so  as  to  separate  the  right  and  left  corpora  quadri- 
gemina,  stimulation  of  one  side  only  causes  this  movement  to  take  place 
on  one  side. 

The  most  striking  result  of  injuries  to  the  corpora  quadrigemina 
are  the  so-called  forced  movements,  evidentty  due  to  peculiar  unilateral 
disturbances  of  equilibrium  causing  variations  from  the  symmetrical 
movements  of  the  two  sides  of  the  body.  These  movements  may  be  of 
various  kinds.  In  the  so-called  circus  movement,  instead  of  moving  in 
a  straight  line,  the  animal  runs  around  in  a  circle ;  rolling  movement, 
where  the  animal  rolls  on  its  long  axis,  and  the  index  movement,  when 
the  anterior  part  of  the  body  is  moved  around  the  posterior  part,  which 
remains  at  rest.  These  different  forms  of  movement  frequently  pass  into 
each  other,  and  they  may  be  produced  by  injury  either  of  the  corpus 
striatum,  optic  thalamus,  cerebral  peduncle,  pons,  middle  cerebellar 
peduncle,  and  certain  parts  of  the  medulla. 

6.  THE    FUNCTIONS    OF    THE    BASAL    GANGLIA. — (a)    Th,e    Corpus 
Striatum. — We  have  seen  that  the  corpus  striatum  consists  of  two  parts, 
the  intra-ventricular  portion  projecting  into  the  lateral  ventricle  to  form 
the  caudate  nucleus,  and  the  external  portions  the  lenticular  nucleus. 


FUNCTIONS   OF  THE  BRAIN.  823 

Lying  between  these  are  found  the  fibres  of  the  anterior  division  of  the 
internal  capsule,  which  seem  to  have  no  connection  with  these  ganglia. 

Electrical  stimulation  of  these  ganglia  causes  general  muscular  con- 
traction on  the  opposite  side  of  the  body.  Lesions  of  either  of  these 
ganglia,  provided  the  internal  capsule  be  not  injured,  do  not  appear  to 
cause  any  permanent  symptoms,  but  destruction  of  the  internal  capsule 
causes  paralysis  of  motion  or  sensibility  or  both  on  the  opposite  side  of 
the  body. 

External  to  the  lenticular  nucleus  is  the  external  capsule,  whose 
function  is  unknown,  as  is  also  the  case  as  regards  the  claustrum,  which 
is  located  externally  to  the  external  capsule. 

(6)  The  Optic  Thalamus. — Scarcely  anything  definite  is  known  as 
to  the  functions  of  this  organ,  since  we  have  been  compelled  to  abandon 
the  theory  supported  by  Carpenter  as  to  its  purely  sensory  nature. 
Injury  to  the  thalamus  of  one  side  sometimes  produces  partial  paralysis 
on  the  opposite  side  of  the  body,  and,  again,  sometimes  after  such  an 
injury  hemiansesthesia  of  the  opposite  side  of  the  body,  with  or  without 
disturbance  of  motion,  has  been  observed.  Frequently  the  thalamus  may 
be  irritated  without  producing  any  evidence  of  sensation  or  motipn. 
Since  the  posterior  portion  is  connected  with  the  origin  of  the  optic 
nerve  it  is  in  all  probabilit}7  concerned  in  the  sense  of  vision.  Together 
with  the  corpus  striatum,the  optic  thalamus  is  perhaps  mainly  concerned 
in  co-ordinate  and  complex  muscular  movements,  since  the  cerebrum 
may  be  removed  and  motion  still  be  normal,  provided  these  basal  ganglia 
are  left  intact;  when,  however,  they  are  disturbed  normal  progression 
and  co-ordinated  movements  are  then  rendered  impossible. 

The  principal  diflicult}r  in  determining  facts  in  regard  to  the  func- 
tions of  this  part  of  the  brain  is  that  they  do  not  admit  of  experimental 
investigation  without  the  most  extensive  injury  to  the  other  parts  of  the 
brain. 

7.  THE  FUNCTIONS  OF  THE  CEREBRAL  LOBES. — In  man  and  the  higher 
mammals  the  cerebral  lobes  represent  the  greatest  part  of  the  brain-sub- 
stance, and  usually  will  constitute  twelve-thirteenths  of  the  entire  weight 
of  the  brain.  The  cerebral  hemispheres  are  composed  of  an  internal 
white  substance,  representing  the  continuations  of  the  fibres  coming 
from  below  which  terminate  in  an  external  layer  of  gray  matter.  The 
external  matter,  the  cerebral  cortex,  is  folded  into  convolutions  sepa- 
rated from  each  other  by  fissures,  some  of  which  being  so  marked  as  to 
permit  of  the  division  of  the  cerebrum  into  adjacent  lobes.  From  the 
cells  of  the  cortex,  in  all  probability,  proceed  all  the  motor  fibres  which 
are  concerned  in  the  production  of  voluntary  movement,  and  to  them 
come  all  the  fibres  from  the  organs  of  special  and  general  sense  which 
enable  the  brain  to  appreciate  external  impressions.  Some  of  the  fibres 


824  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

terminating  in  the  cortex  traverse  the  basal  ganglia  ;  others,  constituting 
the  so-called  pyramidal  tracts,  proceed  from  the  motor  regions  of  the 
cerebrum  and  pass  through  the  white  matter  and  converge  in  the  internal 
capsule,  and  from  there  enter  the  crura  cerebri,  thence  to  the  pons,  and 
thence  to  the  opposite  side  of  the  medulla  oblongata. 

The  white  matter  of  the  cerebral  lobes  may,  therefore,  be  considered 
merely  as  the  continuation  of  the  paths  of  conduction  of  the  cord  and 
medulla  which  terminate  in  the  cells  of  the  gray  matter  of  the  convolutions. 

The  consideration  of  the  cerebral  lobes  resolves  itself,  therefore,  into 
the  study  of  the  functions  of  the  gray  matter  of  the  cortex.  While  the 
cerebrum  has  been  from  time  immemorial  looked  upon  as  the  seat  of  the 
will  and  intelligence,  and,  in  fact,  of  all  the  phj'sical  functions,  it  is  only 
since  1870  that  attempts  to  localize  the  different  functions  of  the  cortex 
have  been  attended  by  any  measurable  success. 

In  the  lower  animals,  when  the  cerebral  hemispheres  are  removed 
slice  by  slice,  the  animals  simply  become  more  and  more  dull  and  stupid, 
until  finally  they  lose  all  intelligence.  When  in  pigeons  both  cerebral 
hemispheres  are  removed  the  animals  apparently  appreciate  no  pain 
during  the  operation,  nor  are  any  movements  produced  by  operations  on 
the  cerebral  substance.  After  extirpation  of  the  cerebral  lobes  they 
pass  into  a  semi-comatose  or  stupid  condition,  and,  if  not  disturbed, 
remain  absolutely  motionless,  apparently  experiencing  no  sensation  of 
hunger,  and  will  die  of  starvation  in  the  midst  of  food  without  making 
any  effort  to  feed.  If  mechanically  disturbed,  provided  the  basal  ganglia 
are  intact,  they  are  capable  of  moving  in  a  perfectly  normal  manner, 
will,  to  a  certain  extent,  avoid  obstacles,  the  pupils  of  their  eyes  react 
to  light,  and  they  are  capable  of  reacting  to  violent  sudden  noises.  If 
food  is  placed  in  their  mouths  they  are  capable  of  swallowing  it,  and, 
in  fact,  they  preserve  the  powrer  of  completing  numerous  co-ordinated 
movements  which  depend  upon  reflex  stimuli,  indicating  that  the 
mechanisms  concerned  in  the  maintenance  of  equilibrium  are  located  in 
the  mid-brain,  probably  in  the  corpora  quadrigemina. 

If  a  single  cerebral  lobe  is  removed  in  the  lower  animals  no  effect 
other  than  the  apparent  dulling  of  intelligence  is  evident.  In  the  higher 
animals  after  such  a  mutilation  there  is  evident  a  certain  dulling  of 
sensibility  and  difficulty  in  movement  on  the  opposite  side  of  the  body, 
which,  however,  finally  in  the  majority  of  cases  gradually  disappear.  It 
is  concluded  from  these  experiments  that  the  cortex  is  the  chief  if  not 
the  exclusive  seat  of  intelligence. 

From  the  experiments  of  Fritsch  and  Hitzig  in  1870  dates  a  new 
era  in  our  knowledge  of  the  functions  of  the  cerebral  cortex.  They 
found  that  stimulation  by  means  of  electricity  of  certain  circumscribed 
regions  on  the  surface  of  the  cerebral  convolutions  was  followed  by 


FUNCTIONS   OF   THE   BRAIN.  825 

co-ordinated  movements  in  distinct  groups  of  muscles  of  the  opposite 
side  of  the  bod}^.  They  indicated  certain  areas  of  the  cerebral  cortex  as 
the  actual  centres  for  the  production  of  various  movements,  and  their 
experiments  have  been  confirmed  and  extended  by  a  large  number  of 
subsequent  observers.  These  points  are  termed  the  motor  centres  of 
the  cortex,  and  have  been  located  in  the  dog,  the  monkey,  the  cat,  sheep, 
and  the  rabbit,  but  are  absent  in  lower  animals,  such  as  the  frog  and  fish. 
They  are  all  found  in  the  anterior  part  of  the  parietal  lobe,  the  most 
important  being  shown  in  Fig.  358.  When  any  centre  which  has  been 
determined  to  govern  any  special  group  of  muscles  is  destroyed  or 
removed  the  corresponding  part  of  the  body  is  not  permanently  para- 
lyzed in  the  dog,  but  movements  which  are  produced  in  that  part  of  the 
body  become  irregular  and  variable,  and  after  a  time  the  disturbance  of 
movement  may  almost  completely  disappear. 

In  the  monkey  and  man,  on  the  other  hand,  destructive  lesions  of 
definite  motor  areas  of  the  cortex  cause  permanent  paralysis,  this 
difference  being,  perhaps,  explainable  as  due  to  the  higher  importance  of 
the  cortex  in  higher  species,  where  it  assumes  more  and  more  the 
functions  subserved  by  the  basal  ganglia  in  lower  animals. 

A  similar  series  of  experiments  has  led  to  the  localization  in  the 
cortex  of  certain  parts  which  are  in  close  relationship  with  the  organs 
of  sense,  for  we  know  that  sensory  impulses  from  the  opposite  side  of 
the  body  pass  upward  through  the  posterior  third  of  the  posterior  limb 
of  the  internal  capsule  to  pass,  in  all  probability,  to  the  cortex  of  the 
occipital  and  temporo-sphenoidal  lobes.  Excision  of  these  localities 
leads  to  disturbances  in  the  appreciation  of  sensations  coming  through 
the  sensory  organs.  Thus,  for  example,  in  the  dog  a  locality  has  been 
found  in  the  posterior  cerebral  lobe  (outer  convex  part  of  the  occipital 
lobe)  the  destruction  of  which  produces  blindness  in  the  opposite  eye  ;  or, 
if  both  corresponding  parts  are  removed,  total  blindness  results.  After 
extirpation  of  this  part  the  channels  which  connect  it  with  the  optic 
nerves  undergo  degeneration.  Centres  for  hearing  and  for  smelling  have 
also  been  located.  The  centre  for  hearing  in  the  dog  lies  in  the  second 
prima^  convolution,  while  in  man  and  the  monkey  it  has  been  located  in 
the  first  temporo-sphenoidal  convolution.  Such  disturbances  produced 
by  removal  of  parts  of  the  cortex  are,  like  the  motor  disturbances,  not 
permanent,  but  gradually  disappear,  and  dogs  rendered  deaf  or  blind  by 
excision  of  these  parts  of  the  cortex  again  learn  to  see  and  to  hear, — a  fact 
which  is  explained  Toy  the  substitution  of  function  in  some  corresponding 
part  of  the  .brain-cortex. 

8.  THE  FUNCTIONS  OP  THE  CEREBELLUM. — Experiments  as  to  the 
function  of  the  cerebellum  have  led  to  the  conclusion  that  it  is  the  great 
organ  for  the  co-ordination  of  muscular  movements, — a  fact  which  would 


826 


PHYSIOLOGY  OF   THE   DOMESTIC   ANIMALS. 


alone  be  rendered  probable  when  it  is  recognized  that  the  cerebellum  is 
in  direct  connection  not  only  with  all  the  columns  of  the  spinal  cord, 

i, 


F  ' 


FIG.  358.— UPPER  SURFACE  VIEW  OF  THE  CEREBRUM  OF  VARIOUS  ANIMALS. 

(Landois. ) 

I,  cerebrum  of  the  dog;  I,  u,  HI,  iv,  the  four  primary  convolutions;  s,  snlcus  cruciatus;  F,  Sylvian, 
fossa;  o,  olfactory  lobe;  1,  motor  area  for  the  muscles  of  the  neck  ;  2,  extensors  and  abductors  of  the  fore 
limb;  3,  flexors  and  rotators  of  the  fore  limb;  4,  the  muscles  of  the  hind  limb:  5,  the  facial  muscles; 
6,  lateral  switching  motion  of  the  tail ;  7,  retraction  and  abduction  of  the  fore  limb ;  8,  elevation  of  the 
shoulder  and  extension  of  the  fore  limb,  as  in  walking;  9,  9,  orbicularis  palpebrarum.  II,  aa,  retraction 
and  elevation  of  the  angle  of  the  mouth ;  b,  opening  of  the  mouth  and  movements  of  the  oral  centre ; 
cc,  platysma ;  d,  opening  of  the  eye ;  p,  optic  nerve ;  I,  t,  thermic  centre.  Ill,  cerebrum  of  rabbit,  from 
above ;  IV,  cerebrum  of  the  pigeon,  from  above :  V,  cerebrum  of  the  frog,  from  above ;  VI,  cerebrum  of 
the  carp,  from  above.  In  all  these  o  is  the  olfactory  lobe;  1,  cerebrum;  2,  optic  lobe;  3,  cerebellum; 
4,  medulla  oblongata. 

especially  with  the  posterior  columns,  whose  division  has  been  found  to 
lead  to  inco-ordination,  but  with  the  basal  ganglia  of  the  cerebrum,  which 
we  have  found  to  be  especially  concerned  in  this  function.  It  is 


FUNCTIONS   OF   THE   BKAIN.  827 

supposed  that  the  direct  cerebellar  paths  of  the  cord  conduct  sensoiy 
impressions  to  the  cerebellum,  and  thus  indicate  the  posture  of  the 
trunk  and  the  position  of  the  limbs,  while  the  motor  impulses  passing 
through  the  cord  may  be  influenced  by  fibres  passing  from  the 
cerebellum  through  the  restiform  body  to  the  lateral  columns.  Injuries 
of  the  cerebellum  produce  no  disturbance  of  the  psychical  function,  nor 
do  they  give  rise  to  pain.  When,  however,  the  cerebellum  is  gradually 
removed,  as  in  a  pigeon,  at  first  symptoms  of  weakness  and  slight 
disturbance  of  movement  are  evident ;  as  more  and  more  of  the 
cerebellum  is  removed  great  excitement  appears,  and  the  animal  now 
makes  violent  irregular  movements,  which,  while  not  similar  to  convul- 
sions, are  yet  free  from  all  apparent  purpose;  while  co-ordinated 
movements  are  impossible  vision  and  hearing,  nevertheless,  remain 
intact. 

Again,  section  of  the  middle  cerebellar  peduncle  on  one  side  almost 
always  gives  rise  to  forced  movements,  the  animal  revolving  rapidly  on 
its  own  longitudinal  axis,  and  this  disturbance  is  accompanied  by 
nystagmus,  or  oscillation  of  the  eyeballs. 

Injury  or  removal  of  the  lateral  lobe  produces  the  same  forced 
movement  as  section  of  the  middle  peduncle. 

In  mammals  the  dangers  are  so  great  in  operations  on  the 
cerebellum  that  but  few  successes  are  on  record.  In  operations  of 
extirpation  performed  on  mammals  which  have  proved  successful,  at 
first  the  symptoms  are  those  of  irritation  of  the  divided  peduncles,  and 
consist  in  clonic  contractions  of  the  muscles  of  the  fore  limb,  neck,  and 
back,  while  no  sensory  disturbances  are  perceptible.  When  recovery 
from  the  operation  is  complete  the  symptoms  dependent  upon  the 
loss  of  the  cerebellum  then  appear  and  consist  mainly  in  disturbances 
of  equilibrium,  and,  while  many  muscular  groups  apparently  maintain 
their  muscular  tone  intact,  the  power  of  associating  various  groups  of 
muscles  to  produce  complex  actions  is  lost.  When  the  injurj^  to  or 
extirpation  of  the  cerebellum  has  been  but  superficial  the  disturbances  of 
co-ordination  soon  pass  off,  while  if  the  injury  affects  the  lowest  third 
of  the  cerebellum  the  effects  are  permanent. 

We  may  now  return  to  the  subject  of  the  conduction  of  motor  and 
sensory  impulses  through  the  central  nervous  53' stem,  summarizing  the 
statements  which  have  been  made  during  the  consideration  of  the  func- 
tions of  the  spinal  cord,  medulla  oblongata,  and  brain  (Fig,  359). 

Sensory  impulses  originating  in  stimulation  of  the  peripheral  termi- 
nations of  afferent  or  sensory  nerves  pass  into  the  cord  through  the 
posterior  roots  of  the  spinal  nerves,  and  the  impulse  passes  either  to  the 
cerebrum  or  cerebellum  or  both.  After  entering  the  cord  the  fibres  of 
the  posterior  roots  diverge  and  carry  the  afferent  impulses  in  different 


828 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


directions :  part  of  the  fibres  communicate  with  the  direct  cerebellar 
tract  and  others  with  the  posterior  columns,  thus  furnishing  through 
the  restiform  body  a  direct  path  to  the  cerebellum.  Other  fibres  of 
these  roots  cross  the  middle  line  of  the  cord  a  little  above  where  they 


FIG.  359.— SCHEME  OF  THE  BRAIN.    (Landois.) 

C  C,  cortex  cerebri :  C  s,  corpus  striatum ;  N  1,  nucleus  lenticularis ;  T  o,  optic  thalamus ;  V,  corpora 
quadrigemina:  P,  pedunculus  cerebri;  H,  tegmentum,  and  p,  crusta;  1  1,  corona  radiata  of  the  corpus 
striatum :  22,  of  the  lenticular  nucleus ;  3  3,  of  the  optic  thalamus ;  4  4,  of  the  corpora  quadrigemina ;  5, 
direct  fibres  to  the  cortex  cerebri  (Flechsig) ;  6  6,  fibres  from  the  corpora  quadrigemina  to  the  tegmentum ; 
m,  further  course  of  these  fibres :  8  8,  fibres  from  the  corpus  striatum  and  lenticular  nucleus  to  the  crusta 
of  the  pedunculus  cerebri ;  M,  further  course  of  these :  8  S,  course  of  the  sensory  fibres ;  R,  transverse 
section  of  the  spinal  cord ;  v.W,  anterior,  and  h.W,  posterior  roots ;  a  a,  association  system  of  fibres ;  c  c, 
commissural  fibres  ;  II,  transverse  section  through  the  posterior  pair  of  the  corpora  quadrigemina  and  the 
pedunculi  cerebri  of  man  ;  p,  crusta  of  the  peduncle;  s,  substantia  niger;  v,  corpora  quadrigemina  with  a 
section  of  the  aqueduct ;  III,  the  same  of  the  dog ;  IV,  of  an  ape ;  V,  of  the  guinea-pig. 

enter,  and  some  pass  up  in  the  lateral  column  in  front  of  the  pyramidal 
tract,  others  into  the  posterior  column,  and  still  others  ascend  in  the 
gray  matter  on  the  opposite  side  of  the  cord.  In  the  medulla  the 


FUNCTIONS   OF   THE  BKAIN.  829 

sensory  impulses  travel  through  the  reticular  formation,  through  the 
posterior  half  of  the  pons,  and  enter  the  tegmentum  of  the  crura  cerebri, 
pass  under  the  corpora  quadrigemina  to  enter  the  posterior  third  of  the 
posterior  limb  of  the  internal  capsule,  and  thence  radiate  to  the  cortex 
of  the  occipital  and  temporo-sphenoidal  lobe.  The  path  of  the  sensory 
fibres,  therefore,  in  some  part  of  its  course  undergoes  decussation,  either 
in  the  cord,  the  medulla,  or  the  pons,  so  that  the  cortex  of  each  cerebral 
hemisphere  receives  sensory  impulses  which  originate  in  impressions 
made  on  the  opposite  side  of  the  body :  hence,  a  destructive  lesion  of  the 
cerebral  cortex,  internal  capsule  (posterior  third),  or  of  one-half  of  the 
cord  causes  anaesthesia  of  the  opposite  side  of  the  bod}- .  The  major  part 
of  the  crossing,  however,  occurs  in  the  posterior  commissure  of  the  cord. 
Voluntary  motor  impulses  originate  in  the  cells  of  the  cortex  in  the 
motor  areas  of  the  cerebrum,  pass  through  the  radiating  fibres  of  the  white 
matter  of  the  cerebral  hemispheres,  to  converge  into  the  internal  capsule, 
which  is  a  collection  of  white  nerve-fibres  tying  between  the  caudate 
nucleus  and  optic  thalamus  internally  and  the  lenticular  nucleus  external^. 
They  then  enter  the  basis  of  the  crura  cerebri,  occup}Ting  its  middle  third, 
the  fibres  for  the  face  being  next  the  middle  line  and  those  for  the  leg  most 
external,  the  fibres  for  the  arm  lying  between  the  two  ;  they  then  pass  to 
the  pons,  the  facial  fibres  here  undergoing  decussation  (becoming  con- 
nected with  the  nuclei  of  the  facial  and  hypoglossal  nerves),  the  others 
continuing  on  the  same  side  to  the  anterior  p3Tramids  of  the  medulla 
oblongata,  where  the  major  part  crosses  to  the  opposite  side  of  the  cord, 
where  they  descend  in  the  lateral  column  (the  crossed  pj-ramidal  tract) ; 
while  the  uncrossed  fibres  descend  in  the  anterior  columns  of  the  same 
side,  ultimately,  in  all  probabilit3r,  crossing  through  the  white  commissure. 
All  the  fibres  of  both  pj^ramidal  tracts  terminate  at  different  levels  in  the 
m ult i polar  cells  of  the  anterior  cornua  of  the  gray  matter  of  the  cord, 
and  from  each  of  these  cells  originates  a  single  unbranched  process  which, 
joining  with  similar  fibres,  passes  out  of  the  cord  in  the  anterior  roots  of 
the  spinal  nerves.  The  course  of  these  motor  and  sensory  fibres  is  like- 
wise shown  in  Figs.  360  and  361.  The  cerebellum  receives  through  its 
inferior  peduncle  the  afferent  fibres  derived  from  the  lateral  (direct  cere- 
bellar  tract)  and  posterior  columns  of  the  cord,  as  well  as  from  the  gray 
matter.  The  muscular  sense  is  supposed  to  be  conducted  by  means  of 
Clarke's  column,  together  with  the  direct  cerebellar  columns,  while  tactile 
sensations  pass  through  Burdach's  column.  While,  therefore,  the  sensa- 
tions of  pain  are  conducted  directly  to  the  cerebrum,  tactile  and  muscular 
sensations  first  reach  the  cerebellum  and  may  from  thence  be  conducted 
to  the  cerebrum  through  the  superior  peduncle  of  the  cerebellum,  passing 
into  the  posterior  part  of  the  corpora  quadrigemina  and  then,  perhaps, 
forming  connection  with  the  caudate  nucleus. 


830 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


I. 


FIG.  360. 


FIGS.  360  AND  361.— DIAGRAMS  OF  THE  COURSE  OF  THE  NERVE-FIBRES  IN  THE 
SUBSTANCE  OF  THE  BRAIN  AND  SPINAL,  CORD,  AFTER  AEBY.    (Ranney.) 

I,  view  of  a  transverse  section;  II,  profile  view;  III,  the  nuclei  of  the  medulla  (partly  after  Erb). 
The  crosses  of  color  corresponding  to  the  lines  upon  which  they  are  placed  designate  the  point  of  section  of 
each  tract  as  it  passes  through  different  levels  (the  crus  and  pons).  C  i,  internal  capsule,  with  radiating 
fibres  (in  yellow),  pyramidal  fibres  (red),  and  fibres  going  to  the  pons  (in  purple)  ;  P  C,  the  crnra  cerebri, 
with  the  pyramidal  fibres  and  th< 
substantia  niger,  the  fillet  tract  (i 
blue) ;  PC,  the  peduncles  of 


and  the  fibres  going  to  the  ganglia  of  the  pons  anteriorly,  and  posteriorly  the 
tract  (in  dotted  lines),  the  fibres  of  the  superior  peduncle'of  the  cerebellum  (in 
of  the  cerebellum,  showing  the  fibres  going  to  the  cerebrum,  the  pons,  and  the 


FUNCTIONS   OF   THE   BKAIN. 
II. 


831 


FIG.  361. 

medulla :  P,pons  varolii,  with  its  ganglia  on  either  side  (in  purple).  In  III,  the  nuclei  of  the  cranial 
nerve-roots  are  numbered  to  correspond  with  the  nerves.  Red  is  used  for  the  motor  nuclei,  and  blue  for 
the  sensory  nuclei.  The  trncfx  in  the  cord  are  designated  by  the  area  similarly  colored  in  the  cross-section 
of  the  cord  beneath,  c'.  column  of  Tiirck;  c,  crossed  pyramidal  column;  a,  anterior  horn;  a',  anterior 
root-zone :  e,  direct  cerebellar  column ;  b,  posterior  horn ;  b'?  column  of  Burdach ;  d,  column  of  Goll. 
Higher  up  are  seen  b",  the  inferior  peduncle  of  the  cerebellum:  df.  the  fillet  or  lemniscus  tract;  f,  the 
fibres  connecting  the  ganglia  of  the  pons  with  the  cerebrum  and  cerebellum  ;  b'",  the  fibres  of  the  superior 
cerebellar  peduncle;  h.  the  caudo-lenticular  and  thalamo-cortical  fibres ;  i,  the  commissural  fibres :  Th, 
optic  thalamus:  nc,  nucleus  caudatus:  nl,  nucleus  lenticularis:  gc.  central  convolutions. 
In  this  diagram  the  course  of  b"  seems  to  be  in  error  in  not  undergoing  a  decussation. 


832  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

VII.    THE   CKANIAL  NERVES. 

The  cranial  nerves,  twelve  in  number  on  each  side,  arise  from  differ- 
ent parts  of  the  brain  and  pass  through  foramina  in  the  base  of  the  skull, 
their  number  being  given  to  them  from  the  order  in  which  they  pass  out 
from  the  base  of  the  brain ;  other  names  are,  also,  given  them  from  the 
parts  to  which  they  are  distributed  or  from  their  functions. 

The  cranial  nerves  are  either  pure  sensory  nerves,  pure  motor  nerves, 
or  mixed  nerves.  The  pure  sensory  nerv*es  are  the  olfactory  (1),  optic 
(2),  and  acoustic  (8);  the  pure  motor  nerves  are  the  oculo-motor  (3),  the 
pathetic  (4),  and  the  abducens  (6);  the  trifucial  (5),  or  trigeminus,  is  a 
mixed  nerve,  arising  from  a  distinct  motor  and  a  distinct  sensory  root 
comparable  to  the  spinal  nerves.  Regarding  the  functions  of  the  other 
cranial  nerves  as  determined  by  the  functions  of  their  roots,  the  pneu- 
mogastric  and  glosso-pharyngeal  are  sensory  nerves  and  the  facial, 
spinal-accessory,  and  hypoglossal  nerves  are  motor.  The  trunks  of  these 
last  five  nerves,  however,  contain  both  afferent  and  efferent  fibres,  the 
pneumogastric  receiving  efferent  fibres  from  the  spinal-accessory  and  the 
glosso-pharyngeal  from  the  facial  and  motor  branch  of  the  trigeminus ; 
while  the  facial  receives  afferent  fibres  from  the  trigeminus,  pneumogas- 
tric, and  glosso-pharyngeal,  and  the  hypoglossal  sensory  fibres  from  the 
trigeminus,  vagus,  and  three  upper  cervical  nerves. 

The  functions  of  these  nerves,  although  already  considered  under 
different  subjects,  will  be  here  recapitulated. 

1.  THE  OLFACTORY  NERVE.     (See  Sense  of  Smell.) 

2.  THE  OPTIC  NERVE.     (See  Sense  of  Vision.) 

3.  THE  OCULO-MOTOR  NERVE. —  This  nerve  arises  from  the  oculo- 
motor nucleus  under  the  aqueduct  of  Sylvius,  the  fibres  of  origin  being 
traced  into  the  corpora  quadrigemina  and  through  the  cerebral  peduncle 
into  the  lenticular  nucleus.     It  contains  three  sets  of  fibres  which  are 
distributed  (1)  to  all  the  muscles  of  eyeball,  with  the  exception  of  the 
superior  oblique  and  external  rectus  muscles  and  the  levator  palpebrse 
muscles,  (2)  to  the  circular  muscles  of  the  pupil,  and  (3)  to  the  ciliary 
muscle.     Hence,  it  is  the  path  for  voluntary  motor  impulses  to  all  the 
muscles  of  the  eyeball,  with  the  exception  of  the  muscles  above  mentioned, 
it  is  the  efferent  nerve   for   the   reflex   contraction  of  the   pupil   from 
the  action  of  light  on  the  retina,  and  it  contains  the  voluntary  motor  fibres 
to  the  muscle  of  accommodation  (ciliary  muscle). 

4.  THE  PATHETIC  NERVE  (  Trochlearis). — The  fibres  of  the  fourth 
cranial  nerve  may  be  traced  back  from  their  apparent  origin  on  the  outer 
side  of  the  crus  cerebri  in  front  of  the  pons  varolii,  beneath  the  corpora 
quadrigemina,  to  the  valve  of  Yieussens  (behind  the  fourth  ventricle),  on 
the  upper  surface  of  which  it  is  connected  \>y  commissural  fibres  with  its 


CBANIAL   NERVES.  833 

fellow  from  the  opposite  side.  The  gray  nucleus  from  which  it  arises  is 
the  posterior  part  of  the  oculo-motor  nucleus  in  the  floor  of  the  aqueduct 
of  Sylvius ;  it  also  is  connected  with  a  gray  nucleus  in  the  part  of 
the  floor  of  the  fourth  ventricle  near  to  the  origin  of  the  fifth  nerve.  It 
is  a  purely  motor  nerve  and  is  distributed  to  the  superior  oblique  muscle 
of  the  eyeball. 

5.  THE  TEIFACIAL  NERVE  ( Trigeminus). —  This  is  a  mixed  nerve, 
arising,  like  the  spinal  nerves, .from  a  motor  and  sensory  root,  the  latter 
being  supplied  with  a  ganglion   (ganglion   of  Gasser).      The  anterior, 
smaller,  motor  root  arises  in  the  motor  trigeminal  nucleus  in  the  floor  of 
the  fourth  ventricle,  which  is  connected  with  the  cortical  motor  centre  on 
the  opposite  side  of  the  cerebrum ;   there  is  also  a  descending  motor 
root  from  the  corpora  quadrigemina.     The  larger  posterior  sensory  root 
is  connected  with  the  sensory  trigeminal  nucleus  at  the  level  of  the  pons 
with  the  gray  matter  of  the  posterior  horns  of  the  spinal  cord  as  far  as 
the  cervical  vertebra,  constituting  the  ascending  root,  and  with  the  cere- 
bellum through  the  crura  cerebelli.     This  extensive  origin  of  the  sensory 
fibres  explains  the  great  number  of  reflex  relations  of  this  nerve. 

After  passing  through  the  cranium  the  trifacial  nerve  divides  into 
three  divisions — the  ophthalmic,  superior  maxillary,  and  inferior  maxillary 
branches. 

The  ophthalmic  division,  which  receives  fibres  from  the  sympathetic 
nerve,  supplies  sensory  branches  to  the  conjunctiva,  lachrymal  gland, 
upper  eyelid,  brow,  and  root  of  nose,  trophic  fibres  to  the  eyeball,  and 
vaso-motor  fibres  to  the  dura  mater  and  lachn^mal  gland.  It  is  also  the 
afferent  nerve  for  the  reflex  stimulation  of  the  lachrymal  secretion. 

The  superior  maxillary  division  supplies  sensory  nerves  to  the  dura 
mater,  to  the  angle  of  the  eye,  skin  of  temple  and  cheek,  to  the  teeth  in 
the  upper  jaw,  gums,  periosteum,  the  lower  eyelid,  bridge  and  sides  of 
the  nose  and  upper  lip  as  far  as  the  angle  of  the  mouth,  nasal  chambers, 
hard  and  soft  palate.  B}^  receiving  motor  fibres  from  the  facial  (super- 
ficial petrosal  branch  to  Meckel's  ganglion)  it  gives  motor  nerves  to  the 
soft  palate  and  uvula,  and,  receiving  vaso-motor  fibres  from  the  cervical 
plexus,  it  is  the  vaso-motor  nerve  for  this  entire  region. 

The  inferior  maxillary  division  contains  all  the  motor  fibres  of  the 
fifth  nerve  and  supplies  motor  nerves  to  the  muscles  of  mastication,  the 
tensor  palati,  and  tensor  tympani  muscles.  It  also  contains  sensory  fibres 
which  are  distributed  to  the  mucous  membrane  of  the  cheek,  lower  lip, 
teeth,  external  auditory  canal,  and  tip  of  tongue,  the  lingual  branch  being, 
further,  the  special  nerve  of  taste.  This  division  also  contains  trophic 
and  vaso-motor  fibres. 

6.  THE  ABDUCENS  NERVE. — The  sixth  cranial  nerve  arises  from  the 
emenentia  teres  in  the  fourth  ventricle  in  front  of  and  partly  from  the 

53 


834  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

nucleus  of  the  facial  nerve,  its  nucleus  being  connected  with  the  nucleus 
of  the  third  nerve  on  the  opposite  side.  It  is  the  motor  nerve  of  the 
external  rectus  muscle  of  the  eye.  In  co-ordinate  movements  of  the  eyes 
its  action  is  involuntary.  It  receives  fibres  from  the  sympathetic  nerve 
in  the  neck. 

7.  THE  FACIAL  NERVE. — The  facial  nerve  consists  solely  of  efferent 
fibres,  and  arises  by  two  roots  from  the  floor  of  the  fourth  ventricle,  of 
which  the  smaller,  through  the  nerve  of  Wrisberg,  forms  a  connection 
with  the  auditory  nerve.     The  origin  of  the  facial,  the  facial  nucleus,  lies 
behind  the  origin  of  the  sixth  nerve  and  is  connected  with  the  cerebrum 
of  the  opposite  side.     The  facial  nerve  is  the  motor  nerve  of  the  muscles 
of  the  face,  and  hence  is  called  the  nerve  of  expression.     It  also  supplies 
motor   branches   to   the  stylo-hyoid,  posterior  belly   of   the   digastric, 
buccinator,  stapedius,  muscles  of  the  external  ear,  platysma,  and  levator 
palati.     It   is   the   secretory  nerve   of  the    parotid,   and    through    the 
chorda    tympani   of  the   submaxillary   gland.     It   also   contains   vaso- 
motor  fibres  for  the  tongue  and  side  of  the  face  and  vaso-dilator  fibres  for 
the  submaxillary  gland.     Through  its  anastomoses  with  the  trigeminu^ 
and  vagus  it  perhaps  contains  afferent  fibres. 

8.  THE  AUDITORY  NERVE. — (See  Sense  of  Hearing.) 

9.  THE   GLOSSO-PHARYNGEAL  NERVE. — This   nerve  arises  from  the 
glosso-pharyngeal  nucleus  deep  in  the  medulla  oblongata  near  the  olivary 
body,  and  is  connected  with  the  nucleus  of  the  vagus.     An  ascending 
root  from  the  spinal  cord  unites  with  it  and  serves  for  the  production  of 
spinal  reflexes.     It  is  supplied  to  the  palatine  and  pharyngeal  muscles, 
but  its  motor  function  to  these  muscles  is  not  absolutely  established ; 
possibly  its  motor  fibres  are  derived  from  the  facial.     It  is  the  nerve  of 
taste  for  the  back  of  the  tongue  and  pharynx,  as  well  as  being  the  nerve 
of  general  sensation  for  these  parts,  the  Eustachian  tube  and  tympanum. 

10.  THE  PNEUMOGASTRIC  NERVE. — The  vagus  nerve  has  a  common 
nucleus   with  the  ninth  and  eleventh  nerves  in  the  ala  cinerea  in  the 
lower  half  of  the  calamus  scriptorius.     It   contains   both  afferent  and 
efferent  fibres,  the  latter,  probably,  being  derived  from  the  spinal-acces- 
sory.    The  efferent  fibres  are  distributed  to  the  muscles  of  the  pharynx, 
larynx,  trachea,  bronchi,  oesophagus,  stomach,  and  intestines.     It  is  also 
the  inhibitory  nerve  of  the  heart,  and  contains  vaso-motor  fibres  for  the 
lungs  and  trophic  fibres  for  the  lungs  and  heart.     It  is  the  sensory  nerve 
for   the   external   ear,   pharynx,  oesophagus,   stomach,  and  respiratory 
passages.     It  contains  afferent  fibres,  which  may  augment   or   inhibit 
(laryngeal  nerve)  the  respiratory  centre,  augment  the  cardio-inhibitory 
centre,   inhibit   the   medullary   vaso-motor    centre    (depressor    nerve) ; 
through  it  afferent  impressions  may  pass  which  produce  the  salivary  or 
inhibit  the  pancreatic  secretions. 


SYMPATHETIC   NEKVOUS    SYSTEM.  835 

11.  THE    SPINAL-ACCESSORY    NERVE. — This    nerve    arises    by   two 
separate  roots,  one  from  the  accessory  nucleus  of  the  medulla,  which  is 
connected  with  the  nucleus  of  the  vagus,  the  other  between  the  anterior 
and  posterior  roots  of  the  spinal  nerves,  as  far  down  as  the  fifth  cervical 
nerve,  its  fibres  in  the  cord  having  been  traced  to  a  nucleus  on  the  outer 
side  of  the  anterior  cornua.     The  anterior  branch  passes  entirely  into 
the  vagus  and  gives  to  it  most  of  its  motor  fibres  and  all  the  cardio- 
inhibitory  fibres.     The  spinal-accessory  is  the  motor  nerve  to  the  sterno- 
mastoid  and  trapezius  muscles ;  it  receives  sensory  branches  from  the 
cervical  nerves. 

12.  THE  HYPOGLOSSAL  NERVE. — The  hypoglossal  nerve  arises  from 
two  large-celled  nuclei  in  the  calamus   scriptorius    and    one   adjoining 
small-celled  nucleus,  being  connected  both  with  the  olivary  body  and 
the  brain.     It  is  the  motor  nerve  for  the  muscles  of  the  tongue  and  most 
of  the  hyoid  muscles.     It  receives  afferent  fibres  from  the  fifth  and  tenth 
nerves  and  vaso-motor  fibres  from  the  sympathetic. 

VIII.    THE   SYMPATHETIC  NERVOUS   SYSTEM. 

The  great  sympathetic  nerve,  constituted  by  a  ganglionic  chain, 
composed  of  a  series  of  ganglia  connected  by  nerve-fibres,  is  located  on 
each  side  of  the  vertebral  column.  Three  different  forms  of  structure 
may  be  recognized  in  this  portion  of  the  nervous  system — the  ganglia, 
the  peripheral  branches,  and  the  connecting  filaments.  The  two  chains 
situated  on  each  side  of  the  median  line  are  connected  by  transverse 
fibres,  giving  off  numerous  branches,  which  anastomose  among  themselves 
and  form  plexuses  (Fig.  362). 

The  sympathetic  nerve  may  be  divided  into  three  divisions.  In  the 
cephalic  portion  are  found  the  ophthalmic,  the  spheno-palatine,  the  otic, 
the  submaxillary,  and  the  sublingual,  with  the  three  cervical  ganglia.  In 
the  thorax  and  abdomen  are  found  the  other  two  divisions,  which  like- 
wise consist  of  a  number  of  ganglia  united  together  by  anastomosing 
filaments. 

The  ganglia  consist  of  gray  substance  united  with  nerve-tubules. 

The  fibres  are  non-medullated  and  connect  the  ganglia.  Each  spinal 
nerve  forms  connections  with  adjacent  sympathetic  ganglia  by  means  of 
the  rami  communicantes,  which  are  formed  by  nerve-fibres  coming  from 
both  the  anterior  and  the  posterior  roots  of  the  spinal  nerves.  In  addi- 
tion to  the  non-medullated  fibres  entering  into  the  constitution  of  the  great 
sympathetic  nerve  are  also  fine  nerve-tubules,  which  in  their  structure 
are  analogous  to  those  of  the  cerebro-spinal  axis.  Such  filaments  are 
much  less  abundant  than  the  gray  or  non-medullated  fibres  of  Remak. 

The  functions  of  the  sympathetic  nervous  system  have  already  been 


836  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

given   somewhat  in  detail  in   previous  sections.     The  most  important 

function  which  it  fulfills  in  the  animal 
economy  is  in  the  regulation  of  the 
calibre  of  the  blood-vessels.  This  has 
already  been  described  under  the  subject 
of  the  Circulation. 

The  sympathetic  likewise  possesses  a 
number  of  independent  functions  either 
in  the  way  of  inhibiting  or  stimulating 
various  processes  which  ordinarily  are 
controlled  by  the  cerebro-spinal  nerves. 
As  examples  of  such  action  may  be  men- 
tioned the  automatic  ganglia  of  the  heart, 
the  mesenteric  plexuses  of  the  intestine, 
and  the  sympathetic  plexuses  of  the 
uterus,  Fallopian  tubes,  and  ureters.  Of 
course,  here,  also,  the  share  of  the  sym- 
pathetic in  regulating  the  calibre  of  the 
blood-vessels  occupies  an  important 
position. 

The  sympathetic  nerve,  also,  in  addi- 
tion to  such  functions  in  which  this  nerve 
may  be  regarded  as  an  efferent  nerve, 
carrying  impulses  from  the  central  ner- 
vous system,  likewise  acts  as  an  afferent 
nerve ;  as,  for  instance,  in  the  conduction 
of  sensory  impressions  from  the  abdominal 
viscera  through  the  splanchnic  nerves. 
It  has  further  been  claimed  that  the 
various  ganglia  of  the  sympathetic  may 
themselves  act  as  reflex  centres,  but  no 
clear  demonstration  of  this  statement  has 
ever  been  reached.  Its  strongest  advo- 
cate was  Claude  Bernard,  and  he  pointed 
to  the  submaxillary  ganglion  as  an  illus- 
tration of  such  an  independent  action  on 
the  part  of  the  sympathetic  ganglia, 
We  have  already  discussed  the  grounds 
for  doubting  the  correctness  of  this 
FIG.  362.—  SYMPATHETIC  NERVE  OP  statement. 

mmtL^s-.c,  Probably  the   main  function   of  the 

0'1  "  ganglia     of    the     sympathetic     nervous 

system    is    to    modify    impulses  -coming    from    the   central    nervous 


GENEKAL   AND   SPECIAL   SENSIBILITY.  837 

system,  through  the  cerebro-spinal  nerves,  so  as  to  inhibit  or  modify 
the  function  of  certain  organs.  As  an  illustration  of  this  may  be  men- 
tioned the  action  of  the  sympathetic  upon  the  pupil.  According  to 
Budge,  the  fibres  which  are  concerned  in  producing  dilatation  of  the 
pupil  arise  from  the  spinal  cord  and  run  from  the  upper  two  dorsal  and 
the  lowest  two  cervical  nerves  into  the  cervical  sympathetic,  which 
conveys  them  to  the  head.  The  influence  of  the  sympathetic  in 
governing  the  movements  of  the  iris  will  be  given  more  in  detail  in  the 
consideration  of  the  e}Te. 

Among  other  branches  arising  from  the  cervical  part  of  the  sym- 
pathetic are  found  motor  branches  going  partly  to  the  external  rectus 
muscle  of  the  eye.  vaso-motor  branches  to  the  ear,  the  side  of  the  face, 
the  conjunctiva,  the  iris,  the  choroid,  and  to  the  vessels  of  this  portion 
of  the  alimentary  and  respiratory  tract.  Secretory  and  vaso-motor  fibres 
are  distributed  to  the  salivary  glands  and  to  the  sweat-glands  of  the 
integument ;  while,  according  to  certain  authorities,  the  lachrymal  glands 
receive  sympathetic  secretory  fibres  from  this  portion  of  the  sympathetic. 

Of  the  thoracic  and  abdominal  sections  of  the  sympathetic  the  car- 
diac plexus,  which  receives  accelerator  fibres  for  the  heart,  occupies  the 
most  important  position.  The  influence  of  the  coeliac  plexus  of  the 
sympathetic  on  the  heart  has  already  been  given.  Of  the  abdominal 
sympathetic,  the  coeliac  and  mesenteric  plexuses  and  the  splanchnic 
nerves  are  the  most  important.  They  also  have  been  already  described. 

It  is  thus  seen  that  the  fibres  of  the  sympathetic  nervous  system 
act  as  conductors  of  both  afferent  and  efferent  impressions.  Impressions 
traveling  from  the  periphery  to  the  centre  through  the  sympathetic 
nerve  do  not  produce  an  impression  upon  the  sensorium.  In  other 
words,  the  brain  is  not  capable  of  taking  cognizance  of  afferent  im- 
pulses traveling  through  the  sympathetic.  Nor,  on  the  other  hand,  can 
voluntary  motor  impulses  pass  through  this  nerve. 

IX.    GENERAL   AND   SPECIAL   SENSIBILITY. 

Sensation,  or  general  sensibility,  is  that  function  of  the  brain  by 
which  it  perceives  or  becomes  conscious  of  impressions  which  are  made 
upon  the  surface  of  the  body  or  upon  the  nerves  running  from  the 
peripher}*  to  the  nerve-centres.  Ity  perception  is  meant  that  faculty  by 
which  sensations  are  referred  to  certain  external  causes.  It  is  important 
to  understand  that  all  sensations  take  place,  not  at  the  point  of  contact 
of  the  irritant  with  the  periphery,  but  in  the  brain  itself,  and  we  have 
evidence  of  this  in  the  fact  that  if  the  brain  be  in  a  state  of  torpor  no 
sensation  occurs.  Again,  if  a  ligature  be  passed  around  an  afferent  nerve 
at  some  point  between  its  origin  on  the  periphery  and  its  termination  in 
the  nerve-centre  no  sensation  occurs,  no  matter  how  severe  be  the 


838  PHYSIOLOGY   OF  THE   DOMESTIC   ANIMALS. 

stimulation  of  its  peripheral  ends ;  or,  if  the  nerve-trunk  be  divided,  the 
most  powerful  irritants  may  be  applied  to  the  peripheral  area  in  which 
that  nerve  is  distributed  without  calling  forth  sensation. 

When  an  impression  is  made  upon  a  sentient  surface,  that  impres- 
sion so  changes  the  molecular  equilibrium  in  the  terminal  filaments  as  to 
give  rise  to  afferent  impressions,  which  travel  along  the  nerve-trunk  to 
reach  the  centres  of  the  brain,  and  it  is  the  final  change  which  occurs 
within  the  nerve-cells  which  is  to  be  spoken  of  as  sensation,  and  it  is 
only  this  latter  change  of  which  the  brain  is  cognizant. 

Two  kinds  of  sensibility  may  be  recognized, — general  and  special 
sensibility.  Nerves  of  general  and  of  special  sense  are  concerned  in  the 
perception  of  these  two  kinds  of  sensation.  By  the  term  special  sensi- 
bility is  understood  that  sensation  which  arises  from  an  impression  of  a 
peculiar  kind  and  special  character,  which  is  capable  of  affecting  only 
one  kind  of  nerve  ;  or,  rather,  which,  when  applied  to  one  kind  of  nerve, 
will  invariably  produce  a  sensation  peculiar  to  that  nerve.  Thus,  for 
example,  a  stimulus  applied  to  the  terminal  filaments  of  the  nerve  of 
hearing  will  invariably  be  recognized  as  an  auditoiy  sensation  ;  so  a  stim- 
ulus of  the  optic  nerve,  whether  mechanical,  electrical,  or  chemical,  will 
be  recognized  as  a  visual  sensation. 

By  general  sensibility  is  meant  the  appreciation  of  sensations  arising 
from  impressions  of  a  general  character  applied  to  the  general  tegumen- 
tary  surface  of  the  body.  Under  this  head  are  to  be  included  the  tactile 
sense,  the  sense  of  heat  and  cold,  and  the  muscular  sense.  The  special 
sensations  are  the  sensations  of  smell,  taste,  sight,  and  audition. 

Certain  conditions  are  necessary  to  sensibility.  First,  there  must 
be  a  certain  degree  of  vascularity.  Unless  the  part  be  well  supplied  with 
blood  it  cannot  be  endowed  with  either  general  or  special  sensibility. 
An  illustration  of  this,  may  be  seen  on  tying  any  large  arterj^ ;  the  part  to 
which  it  is  supplied  becomes  almost  instantly  numb ;  the  blood  is  cut  off', 
the  vascularity  diminishes,  and  the  irritability  of  the  receptive  filaments 
of  the  nerve  becomes  depressed.  So,  also,  cold,  as  is  well  known, 
reduces  sensibility  by  diminishing  the  blood-supply  of  the  part. 

Secondly,  mere  vascularity  is  not,  however,  sufficient ;  there  must, 
likewise,  be  continuity  with  the  nerve-trunk.  Unless  the  afferent  fibres 
be  in  such  continuity  with  the  centre  no  sensibility,  either  general  or 
special,  may  take  place.  While,  finally,  the  centre  itself  must  be  in  a 
state  of  integrity  to  recognize  or  convert  into  perceptions  the 
impressions  brought  to  it  through  afferent  nerves. 

When  impressions  have  been  frequently  repeated  upon  nerves  of 
general  or  special  sensibility  the  sensations  to  which  they  ordinarily  ad- 
minister become  blunted.  An  illustration  of  this  may  readily  be  drawn 
from  the  nerves  of  special  sense.  Sights  or  sounds  constantly  present 


GENERAL  AND   SPECIAL   SENSIBILITY.  839 

to  the  eye  or  ear  after  a  while  fail  to  impress  them.  So,  also,  odors 
may  cease  to  be  recognized. 

This  point,  however,  must  not  be  misunderstood.  If  continued 
attention  be  directed  to  sensations,  instead  of  being  blunted  they  are 
exalted.  Of  this  we  have  numerous  examples  in  the  capability  of  the 
senses  to  attain  a  high  degree  of  acuteness  of  perception  from  education. 

When  an  impression  has  been  made  upon  a  nerve  of  special  sensi- 
bility, or  even  upon  one  of  general  sensibility,  that  impression  always 
remains  a  certain  length  of  time  after  the  irritating  cause  has  been 
removed ;  thus,  when  an  ignited  stick  is  rapidly  moved  before  the  eye 
the  impression  made  upon  the  retina  in  each  successive  position  of  the 
burning  point  remains  sufficiently  long  to  appear  continuous  with  that 
made  in  the  next  situation,  and  thus  the  appearance  of  a  line  of  light 
is  obtained.  So  in  the  case  of  the  ear;  it  is  well  recognized  that 
musical  tones  are  produced  by  a  regular  succession  of  vibrations.  When 
these  vibrations  succeed  each  other  more  frequently  than  sixteen  times 
in  a  second  they  give  rise  to  a  continuous  tone.  When  they  occur  less 
frequently  than  sixteen  times  in  a  second  there  is  produced  a  succession 
of  impressions,  each  one  terminating  before  the  other  begins.  No  nerve 
of  special  sense  can  take  upon  itself  the  function  of  any  other ;  thus  the 
auditory  nerve  is  incapable  of  transmitting  visual  impressions,  nor  can 
the  olfactory  nerve  serve  for  audition.  In  the  case  of  the  nerves  of 
general  sensibilit}^,  the  incapability  of  interchange  of  function  cannot 
be  so  positively  denied,  since  we  know  that  a  motor  nerve  may  so  unite 
with  a  sensory  nerve  as  to  conduct  afferent  impressions ;  or  in  the  case 
of  the  sense  of  taste,  which  is  one  of  the  lowest  of  the  special  senses, 
we  shall  find  that  there  other  than  the  special  nerves  of  taste  may, 
perhaps,  serve  for  conducting  gustatory  impressions. 

While  the  nerves  of  special  sense  are  especially  adapted  for  receiving 
certain  impressions,  they  may  yet  be  thrown  into  a  condition  of  irritability 
by  various  stimuli,  but  each  of  these  stimuli  will  produce  the  impression 
characteristic  of  the  nerve  over  which  it  passes. 

Sensations  have  been  divided  into  two  classes,  external  and  internal, 
or  objective  and  subjective.  External  impressions  are  those  which  arise 
from  impressions  made  upon  the  external  surface  of  the  body.  By 
internal  impressions  are  meant  those  which  arise  from  impressions  made 
upon  the  internal  recesses  of  the  body.  All  sensations,  however,  originate 
and  depend  upon  changes  taking  place  in  the  gray  matter  of  the  brain 
itself,  and,  as  a  consequence,  there  is  no  sensation  (which  in  general 
terms  is  produced  by  an  impression  made  upon  the  peripheral  termi- 
nation of  the  nerve)  which  may  not  to  a  certain  degree  be  produced 
by  an  impression  made  upon  the  nerve  in  its  course  or  at  the 
point  in  the  sensorium  where  the  nerve  terminates.  To  this  latter 


840  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

class  of  sensations  the  term  subjective  is  given  in  contra-distinction 
to  objective  sensations,  which  result  from  impressions  made  upon 
the  termination  of  the  nerve.  It  is  a  curious  fact  with  regard  to 
internal  or  subjective  sensations  that  those  which  arise  from  impressions 
made  upon  a  nerve  in  its  course  are  always  referred  to  the  peripheral 
termination  of  the  nerve  on  the  surface  of  the  body.  Thus,  if  the  ulnar 
nerve  is  compressed  at  the  elbow-joint  the  impression  is  not  felt  at 
the  point  of  stimulation,  but  at  the  extremity  of  the  fingers.  The  most 
common  cause  of  subjective  sensations  is  to  be  found  in  changes  of  the 
blood-supply  of  the  part;  thus,  for  example,  when  congestion  takes 
place  about  the  termination  of  the  optic  nerve  there  are  flashes  of  light 
about  the  eye;  if  about  the  auditory  nerve,  ringing  sounds  in  the  ear. 

By  the  term  sensory  organs  is  meant  those  parts  of  the  body  by 
which,  through  the  nerves  of  sense,  the  brain  becomes  cognizant  of  its 
surroundings. 

By  means  of  the  special  senses  the  preservation  of  both  the  indi- 
vidual and  of  the  species  is  rendered  possible.  By  means  of  the  special 
senses  animals  are  rendered  capable  of  seeking  and  recognizing  their 
food  and  are  enabled  to  avoid  danger,  and,  in  a  way  to  be  indicated 
directly,  are  led  to  the  accomplishment  of  the  act  of  reproduction. 

The  more  restricted  the  peripheral  portion  of  any  nerve  of  special 
sense  the  more  delicate  is  the  structure  of  that  terminal  organ.  In  the 
case  of  the  sensations  of  taste  and  of  smell  the  nerves  distribute  them- 
selves over  a  moist  mucous  membrane  which  has  other  functions  to  fulfill 
in  addition  to  acting  as  the  peripheral  terminations  of  nerves  of  special 
sense.  On  the  other  hand,  in  the  case  of  the  nerves  of  sight  and  hearing, 
the  terminations  are  found  in  structures  whose  sole  function  is  found  in 
ministering  to  these  special  sensations,  and  in  them  we  find  the  highest 
degree  of  complexity  of  the  end  apparatuses. 

It  is,  of  course,  not  possible  to  decide  whether  or  not  in  the  case  of 
the  lower  animals  impressions  made  upon  the  nerves  of  sense  affect  the 
brain  in  the  same  manner  as  in  man,  since  in  these  animals  the  expression 
of  sensations  is  greatly  restricted :  but  from  the  great  similarity  of  struc- 
ture of  the  organs  of  sense  in  man  and  in  the  higher  mammals  it  may 
be  concluded  that  impressions  are  appreciated  by  these  animals  in  the 
same  manner  as  in  man.  As  a  general  rule  it  may  be  stated  that  the 
senses  of  the  domestic  animals  are  quite  as  highly  developed  as  in  man, 
and  in  certain  instances  greatly  exceed  in  acuteness  the  corresponding 
sense  in  man.  Usually,  in  any  special  class  of  animals  we  find  one  of 
the  special  senses  developed  out  of  proportion  to  the  others.  Domesti- 
cation has  the  usual  result  of  reducing  the  acuteness  of  the  special 
senses,  since  the  principal  cause  for  their  exercise  in  the  protection  of 
the  animal  is  no  longer  present. 


SENSE   OF  SMELL.  841 


A.    THE   SENSE  OF  SMELL. 

By  the  sense  of  smell  animals  are  to  a  certain  extent  facilitated  in 
their  search  for  food,  in  the  avoidance  of  danger,  and  in  seeking  the 
opposite  sex. 

By  the  sense  of  smell  is  meant  the  sensation  that  is  created  when 
certain  substances  in  a  gaseous  form  are  inhaled  by  the  nostrils.  It  will  be 
shown  that  the  sense  of  smell  is  only  excited  under  certain  definite  condi- 
tions and  only  when  the  odorous  body  comes  directly  in  contact  with  the 
organs  of  sense.  Here,  as  in  the  case  of  taste,  the  sensation  is  locally 
excited,  probably  through  some  chemical  influence,  and  the  result  is  an 
entirely  specific  sensation.  It  is,  therefore,  unwarrantable  to  include 
the  sense  of  smell  among  the  other  senses,  since  it  is  quite  as  different 
from  the  sense  of  touch  or  of  taste  as  from  sight  or  hearing.  The  action 
of  the  organ  of  smell  is,  therefore,  due  to  a  special  nerve,  the  olfactory 
nerve,  the  first  cranial  pair,  which  differs  from  the  others  in  origin r 
position,  extension,  and  mode  of  distribution. 

Under  the  name  of  olfactory  nerves  are  usually  described  the  masses 
of  gray  matter  which  arise  from  the  anterior  portion  of  the  frontal  lober 
and  in  many  animals  exist  in  such  bulk  as  to  project  beyond  the  frontal 
lobes.  From  the  structure  of  these  masses,  as  well  as  from  comparative 
anatomy  and  from  their  developmental  history,  it  is  evident  that  these 
parts  are  not  to  be  regarded  as  identical  with  the  peripheral  branches  of 
other  nerves  of  sense,  or  the  cranial  nerves,  but  are  to  be  regarded  as 
distinct  parts  of  the  brain.  In  many  animals  the  olfactory  lobes  are 
hollow,  their  ventricles  communicating  with  the  other  ventricles  of  the 
brain.  As  olfactory  nerves  only  are  to  be  described  the  fibres  which 
originate  from  these  olfactory  bulbs  and  pass  through  the  cribriform 
plate  of  the  ethmoid  bone  to  be  distributed  to  the  olfactory  portion  of 
the  nasal  cavities. 

Fibres  from  the  olfactory  lobes  have  been  traced  in  three  bundles 
backward  into  the  cerebral  hemispheres,  and  the  centre  for  smell  in  the 
cortex  of  the  brain  has  been  located  in  the  tip  of  the  uncinate  gyrus  on 
the  inner  surface  of  the  cerebral  hemisphere.  Of  these  three  roots,  the 
inner  one  is  small,  the  middle  one  is  large  and  curves  inward  to 
the  anterior  commissure  around  the  head  of  the  caudate  nucleus  and 
decussates  through  the  anterior  commissure  to  the  extremity  of  the 
opposite  temporo-sphenoidal  lobe.  The  outer  root  passes  transversely 
into  the  pyriform  lobe  and  ends  in  the  anterior  extremity  of  the  optic 
thalamus. 

Microscopic  examination  of  the  olfactory  fibres,  by  which  are  meant 
the  fibres  passing  through  the  cribriform  plate,  shows  that  they  are  thin, 
transparent  fibres,  included  in  a  nucleated  connective-tissue  sheath. 


842 


PHYSIOLOGY  OF   THE   DOMESTIC   ANIMALS. 


Examination  of  the  structure  of  the  membrane  lining  the  nasal  cavities 
shows  marked  points  of  distinction  between  the  region  to  which  the 
olfactory  fibres  have  been  traced  and  other  portions  of  the  nasal  cham- 
bers. The  area  of  distribution  of  the  olfactory  nerve  is  termed  the 
regio  olfactoria,  and  in  the  main  embraces  the  upper  part  of  the  septum 
and  the  upper  part  of  the  middle  turbinated  bone.  The  remainder  of 
the  nasal  cavity  is  called  the  regio  respiratoria.  The  olfactory  region 
has  a  thicker  mucous  membrane  than  the  respiratory  part.  It  is  covered 
by  a  single  layer  of  cylindrical  epithelial  cells,  which  contain  yellow 
pigment  in  sufficiently  large  quantity  to  serve  even  by  the  naked  eye  to 
distinguish  this  part  of  the  nose  from  the  respiratory  passages.  The 
latter  division  of  the  nasal  cavit}^  is  covered  by  ciliated  epithelium  and 
contains  tubular  glands  and  serous,  acinous  glands.  In  the  olfactory 
region  are  found  between  the  ordinary  BB 

cylindrical     epithelium     cells     peculiar 


FIG.  363.— DIAGRAM  OF  THE  STRUCTURE 
OP  THE  OLFACTORY  REGION,  AFTER 
EXNER.  (Brucke.) 

C  C,  the  terminal  net-work  of  the  olfactory  nerve  in 
which  both  the  so-called  olfactory  cells  (A)  and  cylin- 
drical cells  are  imbedded. 


FIG.  364.— DIAGRAM  ILLUSTRATING  THE 
MODE  OF  CONNECTION  OF  THE  OL- 
FACTORY AND  CYLINDRICAL  CELLS 
WITH  THE  TERMINAL  NET-WORK  OF 
THE  OLFACTORY  NERVE.  (Brucke.) 

B  B,  cylindrical  epithelial  cells  ;  A,  olfactory  cell ; 
D,  protoplasmic  mesh-work  in  which  the  olfactory  nerve 
terminates. 


spindle-shaped  cells  with  a  large  nucleus,  containing  nucleoli,  and  sending 
up  between  the  cylindrical  cells  a  narrow  projection  which  in  various 
animals  terminates  in  delicate  projecting  filaments.  These  peculiar 
olfactory  cells  are  said  to  form  a  direct  communication  with  the  fibres 
of  the  olfactory  nerve. 

It  is  probable,  according  to  Exner,  that  these  cells  do  not 
directly  unite  with  the  olfactory  fibres,  but  through  the  mediation  of  a 
net-work  of  protoplasmic  prolongations  of  these  cells  lying  below  their 
bases.  Examination  has  further  shown  that  not  only  these  long  so-called 


SENSE   OF   SMELL.  843 

olfactory  cells  form  communication  with  this  net-work,  but,  also,  processes 
may  be  traced  into  it  from  the  so-called  cylindrical  cells,  and,  this  being 
the  fact,  it  would  seem  unwarrantable  now  to  draw  a  sharp  distinction 
between  the  functions  of  these  two  classes  of  cells  (Figs.  363  and  364). 

In  the  herbivora  the  convolutions  of  the  inferior  turbinated  plate 
are,  as  a  rule,  simpler  than  in  the  carnivora,  but  yet  more  complex  than 
in  man.  In  the  ruminants  and  solipedes  the  inferior  turbinated  bone 
divides  into  two  plates  which  are  rolled  around  each  other  in  opposite 
directions.  In  most  of  the  carnivora  it  is  also  similarly  convoluted,  but 
the  divisions  are  much  more  frequent  and  the  spaces  between  the 
different  leaves  narrow.  In  the  case  of  the  inferior  turbinated  bone  the 
higher  degree  of  complication  does  not  point,  as  in  the  case  of  the 
superior  turbinated  bones,  to  a  higher  degree  of  development  of  the 
sense  of  smell,  but  in  animals  where  this  condition  is  present  it  is  to  be 
regarded  as  a  means  of  mechanical  protection  against  the  entrance  of 
foreign  bodies  into  the  nose. 

The  different  cavities  in  connection  with  the  nasal  chambers,  such 
as  the  frontal,  sphenoidal,  and  maxillary  sinuses,  have  no  connection 
with  the  sense  of  smell,  but  are  to  be  regarded  simply  as  extensions  of 
the  respiratory  parts  of  the  nasal  chambers;  for  their  mucous  membrane 
is  identical  with  that  lining  this  portion  of  the  nose  and  contains  no 
terminal  filaments  of  the  olfactory  nerve.  This  also  applies  to  the  case 
of  the  ethmoidal  cells  ;  all  these  cavities,  therefore,  are  simply  concerned 
in  warming  the  inspired  air. 

Jacobson's  organ,  on  the  other  hand,  is  to  be  regarded  as  an  acces- 
sory organ  of  olfaction.  It  is  present  in  all  mammals,  and  consists  of 
two  narrow  tubes  protected  by  cartilage  and  placed  in  the  lower  and 
anterior  part  of  the  nasal  septum.  Each  tube  is  closed  behind,  but  an- 
terior^ opens  into  the  nasal  chamber  by  a  furrow,  the  naso-palatine 
canal.  The  wall  next  the  middle  line  is  connected  with  the  olfactory 
epithelium,  which  is  in  direct  communication  with  the  terminal  filaments 
of  the  olfactory  nerve.  The  outer  wall  is  covered  with  columnar,  ciliated 
epithelium. 

The  nose  in  mammals  is  generally  but  slightly  detached  from  the 
bones  of  the  face.  In  solipedes  and  ruminants  the  nares,  which  are  pos- 
sessed of  a  considerable  degree  of  mobility,  project  but  slightly,  while  in 
various  members  of  the  hog  tribe  the  nose  is  prolonged  anteriorly, 
forming  the  snout  or  muzzle.  In  the  elephant  and  in  the  tapir  this  pro- 
longation acquires  its  maximum  development.  In  the  cetaceans  and 
other  aquatic  mammals  in  which  the  olfactory  nerve  is  absent,  as  in 
the  dolphin,  or  where  it  is  only  faintly  developed,  the  nasal  chambers 
lose  all  significance  as  organs  of  olfaction  and  simply  fulfill  a  respiratory 
function. 


844  PHYSIOLOGY  OF  THE   DOMESTIC   ANIMALS. 

In  birds  the  sense  of  olfaction  is  less  strongly  developed  than  in 
mammals,  its  place  probably  being  taken  by  the  higher  degree  of  devel- 
opment of  the  sense  of  sight.  As  a  consequence  their  nasal  chambers 
are  simple  ;  at  the  most  three  turbinated  plates  (anterior,  middle,  and 
posterior)  are  present,  and  these  are  simple  in  form.  The  olfactory  nerve 
is  distributed  alone  to  the  posterior  turbinated  bone.  The  external 
nares  show  great  variations  in  shape,  while  the  posterior  nares  commu- 
nicate b}r  a  small,  slit-like  opening  with  the  aural  cavity.  The  olfactory 
lobes  are  most  highly  developed  in  birds  of  prey  and  in  palmipedes  who 
feed  on  living  fish. 

In  amphibia  the  nasal  chambers  are  even  less  complicated  than  is 
the  case  in  birds.  The  turbinated  plates  are  rudimentary  and  usually 
reduced  to  one  in  number.  In  reptiles  generally  the  nasal  chambers  are 
limited  in  extent  and  are  formed  of  two  canals  opening  externally,  and 
internally  communicating  with  the  mouth  by  two  canals  passing  through 
the  palatine  arch. 

In  the  fish  the  olfactory  apparatus  is  not  so  arranged  as  to  be  trav- 
ersed by  a  current  of  air.  In  them  the  olfactory  organ  consists  of  two 
small  cavities  terminating  in  a  cul-de-sac  and  opening  externally  by  two 
nostrils.  The  bottom  of  these  sacs  is  generally  thrown  up  into  folds, 
arranged  as  radii  from  a  central  point  to  which  fibres  coming  from  the 
olfactory  lobe  have  been  traced.  Water  carrying  odors  to  this  olfac- 
tory membrane  can  affect  it  but  slightly,  unless  we  can  conclude  that 
their  method  of  olfaction  differs  entirely  from  what  holds  in  air-breathing 
animals ;  for  we  find  that  if  in  the  latter  the  nasal  chambers  be  filled 
with  liquid  all  impression  on  the  sense  of  smell  is  impossible. 

In  the  invertebrates  no  organ  of  smell  can  be  recognized  in  the  ar- 
ticulates or  in  the  mollusks.  It  is,  nevertheless,  certain  that  in  some  of 
the  invertebrates,  and  particularly  in  insects,  the  sense  of  smell  is  highly 
developed.  It  has  been  supposed  that  here  the  antennae  or  tentacula  are 
the  seat  of  the  sense  of  smell. 

For  any  substance  to  be  odorous  it  must  possess  two  properties.  In 
the  first  place,  it  must  be  volatile — that  is,  be  capable  of  passing  into  the 
atmosphere;  and,  in  the  second  place,  it  must  to  a  certain  extent  be 
soluble  in  water,  that  it  may  pass  by  imbibition  into  the  fluid  which 
invariably  moistens  the  olfactory  membrane.  Odorous  substances  in- 
haled with  the  air  are  brought  into  contact  with  the  olfactory  mucous 
membrane  and  act  on  the  terminal  cells  of  the  olfactory  nerve  and  not 
directly  upon  the  nerve-fibres;  for  we  may  conclude  that  just  as  neither 
the  optic  nerve-fibres  are  affected  by  waves  of  light,  nor  the  auditory 
nerve-fibres  by  waves  of  sound,  the  fibres  of  the  olfactory  nerve  are 
equally  insensitive  to  odors.  Smell  consists,  therefore,  in  the  production 
of  some  change,  probably  of  a  chemical  nature,  in  the  terminal  apparatus 


SENSE  OF   SMELL.  845 

in  the  mucous  membrane  of  the  olfactory  portion  of  the  nose.  Changes 
there  excited  are  conducted  through  the  nerve-filaments  to  the  brain,  and 
only  then  become  recognized  as  the  sensation  of  smell. 

It  would  appear  that  the  sensation  of  smell  is  only  developed  on  the 
first  contact  of  the  odorous  particles  with  the  olfactory  nerve,  and,  as  a 
consequence,  in  order  to  obtain  an  exact  perception  of  delicate  odors  a 
number  of  rapid  inspirations  are  taken,  the  mouth  being  kept  closed. 
In  this  way  the  air  is  rarified  in  the  nasal  chambers  and  odorous  parti- 
cles stream  over  the  olfactory  region.  Consequently,  if  we  hold  our 
breath  the  sensation  of  smell  ceases,  even  if  we  are  in  an  atmosphere 
impregnated  with  odorous  substances.  It  is  further  stated  that  odorous 
substances  taken  into  the  mouth  and  then  expired  through  the  posterior 
nares  produce  no  sensation  of  smell,  possibly  from  the  fact  that  in  this 
direction  of  the  atmospheric  current  the  particles  are  not  brought  into 
contact  with  the  olfactory  region ;  while,  when  bodies  are  inhaled  with 
the  air  through  the  nostrils,  the  current  of  entering  air  is  broken  up  by 
striking  against  the  inferior  turbinated  bone,  and  part  of  the  current 
passes  directly  through  the  respiratory  passages  and  part  upward 
through  the  olfactory  region. 

The  reason  why  odorous  liquids  placed  in  the  nostrils  are  incapable 
of  affecting  the  sense  of  smell  is  perhaps  to  be  explained  by  the  action 
of  the  fluid  upon  the  olfactory  cells,  which  perhaps  possess  a  high  degree 
of  imbibition  and  are  paralyzed  when  brought  in  contact  with  large 
quantities  of  fluid.  Even  water  alone,  as  we  know,  will  temporarily 
arrest  the  sense  of  smell,  and  if  the  nostrils  be  filled  with  water  some 
time  will  elapse  after  the  removal  of  the  liquid  before  the  sense  of  smell 
is  regained. 

The  amount  of  substance  which  may  be  recognized  by  the  sense  of 
smell  is  extremely  small.  Valentin  has  calculated  that  ^ro.irov.iHro  of  a 
grain  of  musk  may  be  recognized  by  the  sense  of  smell.  Even  this  is, 
perhaps,  an  inside  estimate,  for  a  grain  of  musk  will  for  years  give 
its  characteristic  odor  to  the  atmosphere  of  a  room,  and  the  most  deli- 
cate balance  will  at  the  end  of  this  time  fail  to  recognize  any  reduction 
in  weight,  and  yet  we  are  compelled  to  suppose  that  the  odor  has  been 
given  to  the  atmosphere  through  the  volatilizing  of  the  particles  of  the 
musk. 

As  regards  the  sense  of  smell,  all  attempts  to  classify  the  impres- 
sions which  may  be  made  upon  it  entirely  fail.  The  only  distinction 
which  can  be  made  is  into  what  are  termed  pleasant  and  disagreeable 
odors,  and  yet,  of  course,  these  are  simply  relative  terms.  We  may  say 
that  a  substance  has  the  odor  of  turpentine  or  of  roses,  but  this,  of 
course,  gives  us  no  means  of  classifying  the  causes  of  the  sensations 
produced. 


846 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


The  intensity  of  the  sense  of  sinell  depends,  first,  upon  the  size  of 
the  olfactory  surface,  since  we  find  that  in  animals  in  which  the  sense 
of  smell  is  most  acute  the  turbinated  bones  of  the  olfactory  region  are 
most  complicated  ;  secondly,  on  the  concentration  of  the  odorous  sub- 
stance in  the  air;  and,  thirdly,  on  the  frequency  with  which  the  columns 
of  air  containing  the  odorous  particles  are  conducted  to  the  olfactory 
organs ;  hence  sniffing  tends  to  increase  the  intensity  of  odors. 

The  development  of  the  sense  of  smell  is  always  more  highly  marked 
in  animals  than  in  man  and  plays  an  important  part  in  their  organization. 
Game-dogs,  as  is  well  known,  will  recognize  the  odor  from  game-birds 
at  several  hundred  yards,  but  even  this  falls  below  the  acuteness  of  smell 
possessed  by  various  animals  which  are  able  to  scent  the  presence  of 
man  at  a  distance  of  a  mile  or  more. 

B.    THE  SENSE  OF  SIGHT. 

Vision  is  the  perception  of  the  sensation  caused  by  the  impression 
of  a  ray  of  light  upon  the  retina,  and  in  all  animals  depends  upon  the 
special  sensitiveness  of  the  optic  nerve-filaments  to  the  vibration  of 
luminous  rays.  Animals  may,  nevertheless,  be  sensible  of  light  without 
special  organs  of  vision,  and  may  even  be  capable  of  giving  evidence  of 
the  impression  of  such  light ;  thus,  the  hydra,  although  it  has  no  distinct 

organs  of  vision,  will  move  around 
from  side  to  side  of  the  vessel  in 
which  it  is  placed  until  it  has 
reached  that  on  which  the  sun  is 
shining  and  will  turn  itself  toward 
the  seat  of  light. 

In  its  simplest  form  the  visual 
apparatus  is  represented  by  a  col- 
lection of  pigment-cells  in  the 
outer  coverings  of  the  body  which 
are  in  connection  with  the  ter- 
mination of  afferent  nerves.  The 

FIG.  365.— HEAD  AND  COMPOUND  EYES  OF    ^io-mPTit  ah<inrh<a  tho  rnv«  nf  lio-hf 
THE  BEE.    (Carpenter.)  P'B111  rays          Hgni, 

The  ocelli  are  in  situ  on  the  one  side  (A)  and  displaced  on  the     and    in  that  function  SOme  DrOCCSS, 
other  (B) ;  A  A  A,  stemmata ;  B  B,  antennae. 

probably   of    a    chemical    nature, 

is  excited  and  the  sensitive  nerves  are  stimulated.  In  the  medusae, 
as  the  jelly-fish,  and  at  the  ends  of  the  rays  of  the  star-fish  and  other 
echinoderms  similar  collections  of  pigment  are  found,  but  as  the 
lens  is  wanting  no  distinct  image  can  be  formed,  and,  consequently, 
in  such  cases  the  distinction  between  light  and  darkness  is  all  that 
is  possible.  In  some  of  the  cephalopod  mollusks  two  simple  eyes, 
consisting  of  a  globular  lens  with  transparent  media  analogous  to  the 


SENSE   OF   SIGHT.  847 

cornea  of  higher  animals,  are  found  at  the  tips  of  the  tentacula.  Evi- 
dences of  a  choroid  and  of  a  nervous  net-work  representing  the  retina 
are  also  found.  Such  organs  are  termed  ocelli.  It  is,  therefore,  seen 
that  two  classes  of  visual  apparatus  may  be  recognized,  the  simple  and 
the  compound ;  the  former  consisting  simply  of  a  mass  of  pigment  in 
connection  with  the  nerve-fibres,  and  the  latter  of  a  cornea  and  of  other 
accessory  organs.  In  many  insects  and  in  some  crustaceans  both 
species  of  eyes  are  found.  The  simple  eyes  may  be  three  or  more  in 
number  and  are  most  usually  placed  on  the  summit  of  the  head.  In  the 
articulates,  such  as  insects  and  crustaceans,  are  found  eyes  of  a  special 
type  of  construction — what  may  be  termed  composite  eyes — consisting  of 
a  collection  of  a  considerable  number  of  diverging  radiating  tubes  or 
cones,  terminating  on  the  surface  in  the  shape  of  polygonal  opacities  and 
inclosing  in  their  interior  a  fluid  analogous  to  the  vitreous  body,  while 
their  deep  extremity  is  continuous  with  the  nerve-filament  and  their 


FIG.  366.— SECTION  OF  THE  EYE  OF  THE  COCKCHAFER  (Melolontha 

vulgaris).    ( Carpenter. ) 

A.  A,  facets  of  the  cornea;  B,  transparent  pyramids  surrounded  with  pigment;  C,  fibres  of  the  optic  nerve; 
D,  trunk  of  the  optic  nerve.    The  same  description  applies  to  B,  which  is  a  portion  of  the  eye  more  highly  magnified. 

interior  is  lined  with  pigment.  Each  one  of  these  two  eyes,  which  are 
frequently  but  a  few  millimeters  in  diameter,  often  incloses  from  ten  to 
twenty  thousand  of  these  little  tubes ;  while  the  inclosed  membrane, 
which  is  analogous  to  the  choroid,  is  impregnated  with  pigment  over  the 
greater  part  of  its  extent,  except  at  the  centre,  where  a  transparent 
opening  is  present  through  which  the  light  passes  (Fig.  865).  These  e}7es 
are  capable  of  forming  distinct  images,  but  each  of  the  diverging  cones, 
disposed  like  the  rays  of  a  segment  of  a  sphere  (Fig.  366),  is  only 
capable  of  transmitting  the  ray  of  light  which  coincides  with  its  long 
axis;  all  the  other  rays,  striking  more  or  less  obliquely  on  the  internal 
walls  lined,  with  pigment,  are  absorbed;  as  a  consequence,  in  such  an 
eye  the  image  is  formed  by  the  co-ordination  of  the  rays  coming  from 
corresponding  isolated  points  of  the  object.  While,  nevertheless,  objects 
may  be  clearly  appreciated  by  such  an  eye,  a  large  quantity  of  light 


848  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

must  be  lost  by  absorption  by  the  pigment,  and,  as  a  consequence, 
the  clearness  of  the  image  must  be  sacrificed.  The  field  of  vision  in 
such  an  e3Te  will,  of  course,  depend  upon  the  segment  of  the  sphere 
represented  by  the  termination  of  the  cones,  since,  although  the  eye  is 
convex,  no  movement  in  an  orbit  is  possible.  So,  again,  accommodation 
is  not  required  in  such  an  eye,  since  all  the  rays  of  light  appreciated  by 
each  cone  must  be  coincident  with  the  axis  of  each  cone.  Therefore, 
such  a  compound  eye  may  be  regarded  simply  as  a  combination  of  an 
immense  number  of  ocelli  compressed  together  and  taking  an  angular 
form,  in  insects  six-sided  and  in  crustaceans  four-sided.  The  color  of 
the  pigment  in  such  eyes  varies,  being  white,  yellow,  red,  green,  purple, 


FIG.  367.— DIAGRAM   OP  A  HORIZONTAL  SECTION  THROUGH  THE  HUMAN 

EYE.    (Yeo.) 

1,  cornea;  2,  sclerotic;  3,  choroid ;  4,  ciliary  processes  ;  5,  suspensory  ligament  of  lens;  6,  so-called 
posterior  chamber  between  the  iris  and  the  lens :  7,  iris  ;  8,  optic  nerve ;  8',  entrance  of  central  artery  of 
retina;  8",  central  depression  of  retina,  or  yellow  spot;  9,  anterior  limit  of  retina;  10,  hyaline  mem- 
brane; 11,  aqueous  chamber;  12,  crystalline  lens;  13,  vitreous  humor;  14,  circular  venous  sinus  which 
lies  around  the  cornea ;  a  a,  antero-posterior,  and  b  b,  transverse  axes  of  bulb. 

or  black.  Each  cornea,  or  the  termination  of  each  ocellus  or  tube,  is 
convex  on  one  side  and  convex  or  flat  on  the  other,  so  that,  to  a  certain 
extent,  it  takes  the  part  of  a  lens. 

Among  the  invertebrates  the  eyes  of  the  cuttle-fish  are  the  largest 
and  most  perfect,  resembling  the  eyes  of  higher  animals  in  possessing  a 
crystalline  lens  and  a  chamber  behind  filled  with  vitreous  humor. 

In  the  vertebrates  the  eye  is  formed  by  a  folding  in  of  the  external 
integument  to  form  a  lens  and  an  outgrowth  from  the  optic  vesicles  of 
the  brain  to  form  a  sentient  surface.  The  eyeball  in  vertebrates  consists 
of  an  external  white,  spherical  case,  or  sclerotic  coat,  which  serves  to 


SENSE   OF   SIGHT.  849 

protect  the  eye  from  external  injury,  and,  although  not  transparent,  is  to 
a  certain  extent  translucent.  Anteriorly  it  passes  into  the  cornea,  which, 
though  equally  thick,  is  absolutely  transparent.  The  latter  membrane 
rises  in  thickness  in  front  of  the  eye  like  a  watch-glass.  In  other  words, 
the  radius  of  curvature  of  the  cornea  is  that  of  a  smaller  circle  than  that 
of  the  body  of  the  eye.  The  shape  of  the  eye  is  preserved  by  two  fluids, 
the  aqueous  humor  filling  the  cavity  behind  the  cornea,  and  the  denser, 
jelly-like  vitreous  humor  occupying  the  larger  posterior  cavity  (Fig.  367). 

Between  these  two  chambers  is  a  diaphragm  the  size  of  whose  aper- 
ture is  capable  of  being  modified — the  iris.  Behind  the  iris  lies  the  cr}Ts- 
talline  lens  and  between  the  vitreous  humor  and  the  sclerotic  is  found 
the  choroid  membrane,  covered  with  dark  pigment-cells,  which  are 
arranged  like  a  mosaic  on  its  inner  surface.  Between  the  choroid  and 
the  vitreous  humor  is  found  the  retina,  which  is  the  transparent  expan- 
sion, in  a  number  of  layers,  of  the  terminal  filaments  of  the  optic  nerve. 

The  most  sensitive  part  of  its  surface  is  that  which  lies  in  contact 
with  the  black  pigment.  Externally,  in  most  vertebrates,  the  eyes  are 
protected  by  eyelids,  which  are,  however,  absent  in  fishes  ;  in  them,  the 
eyes  being  continually  bathed  in  fluid,  the  lachrymal  apparatus  is  like- 
wise absent.  Their  eyes  are,  as  a  rule,  but  slightly  mobile,  the  crystal- 
line lens  is  spherical,  the  cornea  almost  flat,  and  the  iris  but  slightly 
contractile.  In  most  fishes  the  eyes  are  placed  so  far  back  that  the  fields 
of  vision  are  distinct. 

In  reptiles  three  eyelids  are  often  found,  although  in  some,  as  in  the 
serpents,  they  are  entirely  wanting.  In  the  latter  case,  as  in  fishes,  the 
ocular  globe  is  then  covered  only  by  the  transparent  conjunctiva.  In 
many  reptiles  there  is  often  a  rudiment  of  the  lachrymal  apparatus.  The 
crystalline  lens  varies  greatly  in  form. 

In  birds  the  sense  of  sight  is  especially  developed.  Those  which  are 
in  the  custom  of  flying  at  great  heights  in  the  atmosphere  appear  to  be 
able  to  distinguish  with  the  greatest  exactness  small  bodies  on  the  sur- 
face of  the  earth.  In  birds,  at  the  centre  of  the  ocular  globe  and  pos- 
terior to  the  cr}'stalline  lens,  is  found  a  peculiar  projection  of  the 
choroid,  impregnated  with  the  choroid  pigment  and  covered  by  an  exten- 
sion of  the  retina,  which  is  termed  the  pectin.  It  is  not  known  in  what 
way  this  structure  serves  to  assist  vision.  Perhaps  it  contains  muscular 
fibres  which  act  upon  the  crystalline  lens  and  aid  in  accommodation. 

In  mammals  the  ocular  apparatus  takes  about  the  same  form  as  is 
seen  in  the  human  species,  there  scarcely  being  any  difference  except  in 
the  relative  volume  of  the  eyeball  and  the  pupillary  opening,  and  in  the 
fact  that  sometimes  the  shape  of  the  eyeball  is  elongated  rather  than 
spherical.  Animals  which  pass  the  greater  part  of  their  time  under 
ground  are  remarkable  for  the  smallness  of  their  eyeballs.  In  others 

54 


850 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


which  are  aquatic,  such  as  the  cetaceans,  the  crystalline  lens  is  almost  as 
spherical  as  in  the  fish,  and  in  them,  also,  the  difference  in  the  refrangi- 
bility  of  the  different  media  of  the  eye  is  much  less  than  in  animals  living 
in  the  air. 

In  many  mammals,  at  the  base  of  the  eye  is  found  a  collection  of 
brilliant  pigment-cells,  which  reflect  the  rays  of  light  falling  upon  the 
retina  and  so  give  to  these  eyes  when  seen  in  semi-darkness  a  peculiar, 
luminous  appearance.  This  tapetum  is  yellow  in  the  ox,  reddish  yellow 
in  the  cat,  and  blue  in  the  horse. 

In  mammals  the  eyes  are  placed  in  orbits  whose  direction  is  more 
or  less  inclined  toward  the  sides.  Only  in  man,  apes,  and  nocturnal 
birds  of  prey  are  the  orbits  so  arranged  that  vision  may  be  directed 
forward  simultaneously  on  the  two  sides. 

The  Iachr3rmal  apparatus  of  mammals  is  composed  of  a  single  or 
double  lachiymal  gland  placed  at  the  external  angle  of  the  orbit.  Gar- 
ni vora,  rodents,  pachyderms,  and 
some  ruminants  have  in  addition  in 
the  internal  angle  of  the  orbital  cav- 
ity the  so-called  gland  of  Harder, 


FIG.  368.— FORMATION  OF  AN  IMAGE  BY 
REFLECTION.    ( Ganot. ) 

The  rays  from  the  object  A  B  are  reflected  by  the 
mirror  N  M  so  as  to  make  their  angle  of  reflection  equal 
to  their  angle  of  incidence;  if  a  perpendicular,  A  D,  is 
let  fall  from  the  point,  A,  and  one,  B  C,  from  the 
point,  B,  and  the  reflected  rays  prolonged  until  they 
meet  these  perpendiculars,  the  image  is  apparently 
formed  behind  the  mirror  at  a  distance  equal  to  the 
actual  distance  of  the  object  in  front  of  the  mirror. 


FIG.  369.— DIAGRAM  ILLUSTRATING    RE- 
FRACTION OF  LIGHT.    (Ganot.) 

The  incident  ray,  S  O,  on  striking  the  surface,  n  in, 
is  bent  in  the  direction  OH.  SAO  being  the  angle  of 
incidence,  HOB  the  angle  of  refraction. 


which  furnishes  a  thick,  whitish  secretion,  which  often  accumulates  at 
the  corresponding  angle  of  the  eyelids.  Rudiments  of  this  gland  are 
also  found  in  solipedes.  The  tears  are  collected  by  the  lachrymal  points, 
which  conduct  them  through  the  lachrymal  duct  and  nasal  canal  to  the 
nasal  cavities..  In  certain  rodents,  the  hares  in  particular,  the  lachrymal 
canals  are  replaced  by  fissures  which  establish  communication  between 
the  conjnnctival  surface  and  the  nasal  fossae. 

In  the  study  of  the  appreciation  of  the  impression  of  a  ray  of  light 
upon  the  retina  and  the  formation  of  an  image  a  comprehension  of  the 
laws  of  light  is  essential.  The  eye  is  furnished  with  certain  mechanisms 
by  which  an  image  is  formed  somewhat  in  the  same  manner  as  in  a 
camera  obscura.  Such  mechanisms  are  what  are  termed  the  dioptric 
mechanisms  of  the  eye.  Rays  of  light  striking  the  'retina  give  rise  to 


SENSE   OF   SIGHT. 


851 


sensations,  and  we  shall,  therefore,  have  then  to  consider  the  mode  of 
production  of  the  visual  sensations. 

1.  The  Dioptric  Mechanisms  of  the  Eye. — When  rays  of  light 
proceed  from  a  luminous  body  they  always  pass  in  straight  lines,  form- 
ing in  their  divergence  a  cone,  the  apex  of  which  is  the  luminous  body 
and  the  base  such  a  plane  as  may  intercept  them.  So  long  as  the  medium 
is  of  uniform  density  rays  pass  in  straight  lines,  and  if  they  come  in 
contact  with  an  opaque,  polished  surface  they  will  be  reflected,  and  the 
angle  of  reflection  is  equal  to  the  angle  of  incidence  and  lies  in  the  same 
plane  (Fig.  368).  If  the  rays  fall  perpendicularly  to  this  opaque  surface 
they  will  be  reflected  in  the  same  straight  line  in  which  they  impinged. 
If  the  raj7s  fall  upon  a  translucent  surface  as  they  emerge  from  the 
opposite  side  they  will  be  found  to  be  bent  from  their  original  course 


FIG.  370.— DIAGRAM  ILLUSTRATING  REFRACTION.    (Landois.) 

If  Sj  D  represent  a  ray  of  light  passing  through  water,  when  it  emerges  at  D  into  the  atmosphere  it  will 
be  bent  away  from  the  perpendicular  G  D  and  lie  in  the  direction  S  D. 

through  the  medium,  and  though  they  pass  out  of  the  medium  in  a  line 
parallel  with  that  in  which  they  entered,  yet  they  are  not  coincident  with 
it  so  long  as  the  medium  is  bounded  by  parallel  surfaces  (Fig.  369).  If 
these  rays  pass  from  a  rarer  to  a  denser  medium  they  are  bent  toward 
the  perpendicular  at  the  point  of  incidence.  If  they  pass  from  a  denser 
to  a  rarer  medium  tliey  are  refracted  from  the  perpendicular  (Fig.  370). 
Thus,  when  an  oblique  luminous  ray  passes  through  a  piece  of  plate- 
glass  its  course  from  the  atmosphere  is  from  a  rarer  to  a  denser  medium, 
hence  it  is,  in  the  glass,  bent  toward  the  perpendicular;  but  in  passing 
out  it  passes  from  a  denser  to  a  rarer  medium,  hence  it  is  refracted  from 
f  the  perpendicular,  and  as  the  two  surfaces  are  parallel  the  amount  of 
refraction  toward  the  perpendicular  is  equal  to  the  amount  of  refrac- 
tion from  the  perpendicular  ;  therefore  the  course  of  the  emergent  ray  is 
parallel  to  the  course  of  the  entering  ray,  although  not  coincident  with  it. 


852 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


By  the  term  "  refractive  index  "  is  meant  the  number  which  shows 
how  many  times  the  sine  of  the  angle  of  incidence  (a  6,  in  Fig.  370, 
regarding  S  D  as  the  incident  ray)  is  greater  than  the  sine  of  the  angle 
of  refraction  (c  d),  it  being  always  assumed  that  in  comparing  the 
refractive  indices  of  two  media  the  incident  ray  passes  from  air  into  the 
medium.  On  passing  from  air  into  water  the  ray  is  so  refracted  that  the 
sine  of  the  angle  of  incidence  is  to  the  sine  of  the  angle  of  refraction  as 
4:3;  with  glass,  the  proportion  is  3  :  2. 


Fro.  371.— DIAGRAM  ILLUSTRATING  THE  COMPOSITION  OF  A  CONVEX  LENS  OF 
A  NUMBER  OF  PLANE  SURFACES.    (Ganot.) 

An  illustration,  first  suggested  by  Professor  Henry  Morton,  of  Hoboken, 
serves  greatly  to  simplify  the  conception  of  refraction.  It  has  been  stated  that  in 
passing  from  a  rarer  to  a  denser  medium  the  luminous  ray  is  bent  toward  the 
perpendicular.  If  a  line  of  men,  as  of  soldiers,  be  marching  obliquely  toward  the 
edge  of  a  plowed  field,  the  men  first  reaching  tbe  uneven  ground  will  experience 
difficulty  in  walking  over  the  rough  surface  and  their  end  of  the  line  will  move 
more  slowly  than  the  end  still  remaining  on  the  level  ground,  and,  as  a  conse- 
quence, the  entire  direction  of  the  line  of  men  will  be  changed.  On  the  other 


FIG.  372.— DIAGRAM  SHOWING  REFRACTION  BY  A  DOUBLE  CONVEX  LENS. 

(Ganot.) 

The  incident  ray,  L  B,  is  refracted  at  the  points  of  incidence.  B,  and  emergence,  D,  toward  the  axis, 
M  N  A,  which  it  cuts  at  F. 

hand,  as  they  reach  the  opposite  side  of  the  plowed  surface  the  end  of  the  line 
which  first  entered  will  be  the  first  to  emerge,  and,  as  a  consequence,  progress 
now  being  easier,  that  end  of  the  line  will  travel  faster  than  the  end  still  remain- 
ing on  the  plowed  ground,  and,  therefore,  the  line  of  men  will  now  be  bent  from 
ihe  perpendicular;  and  as  the  entire  line  emerges  the  line  of  progress  will  be 
parallel  with  the  original  line,  but  will  not  be  coincident  with  it. 


SENSE  OF  SIGHT.  853 

Refraction  takes  place  not  only  through  media  with  plane  surfaces, 
but  likewise  through  media  bounded  by  curved  surfaces,  for  the  circum- 
ference of  a  circle  may  be  supposed  to  be  made  up  of  a  number  of  infinitely 
small,  straight  lines :  this  is  indicated  in  the  case  of  a  lens  in  Fig.  371. 
Rays  of  light  passing  through  a  double  convex  lens  in  passing  in  are  bent 
toward  the  perpendicular  (Fig.  372).  Now,  if  the  rays  thus  acted  upon 
be  followed  they  will  be  found  to  meet  at  a  point  on  the  opposite  side 
of  the  lens,  called  the  focus,  at  which  light  and  heat  rays  will  converge. 
Rays  of  light  striking  the  centre  of  curvature  of  both  surfaces  of  the  lens 
will  pass  through  unchanged.  Such  a  line  is  called  the  chief  axis,  and 
the  centre  of  this  line  is  the  optical  centre  of  the  lens.  Rays  passing 
through  the  optical  centre  are  termed  principal  or  chief  rays.  Rays 
parallel  with  the  principal  axis  of  the  lens  are  refracted  so  that  they  are 
collected  on  the  opposite  side  of  the  lens  at  a  point  called  the  principal 
focus ;  the  distance  of  this  point  from  the  central  point  of  the  lens  is 
called  the  focal  distance.  On  the  other  hand,  it  is  evident  that  rays 
diverging  from  a  luminous  point  at  the  principal  focus  will  be  so  refracted 


FIG.  373.— DIAGRAM  ILLUSTRATING  ACTION  OF  A  DOUBLE  CONVEX  LENS  OF 
HIGH  CURVATURE  ON  DIVERGENT  RAYS.    (Ganot.) 

The  divergent  rays  from  the  luminous  point,  L.  are  brought  to  a  focus  at  I  behind  F,  the  principal  focus 
at  which  parallel  rays,  S  B,  converge. 

as  to  be  parallel  when  they  pass  from  the  lens.  Again,  ra}Ts  of  light  in  the 
principal  axis  and  from  a  point  beyond  the  principal  focus  will  converge 
to  a  point  on  the  opposite  side  of  the  lens  (Fig.  373). 

Four  cases  are  possible  :  First,  when  the  distance  of  the  light  from  the 
lens  is  equal  to  the  focal  distance  the  focus  will  lie  at  the  same  distance 
on  the  opposite  side  of  the  lens,  i.e.,  twice  the  focal  distance;  second, 
if  the  luminous  body  approach  to  the  lens,  or,  what  is  the  same  thing,  to 
the  focus,  then  the  focal  point  is  moved  farther  away ;  third,  if  the  light 
is  still  farther  from  the  lens  than  twice  the  focal  distance,  then  the  focal 
point  comes  correspondingly  nearer  to  the  lens ;  fourth,  if  the  rays 
proceed  from  a  point  on  the  chief  axis  within  the  focal  distance  they 
will  diverge  on  the  opposite  side  of  the  lens  and  not  again  come  to  a 
focus ;  whilej  on  the  other  hand,  converging  rays  passing  through  a  convex 
lens  will  have  their  focal  distances  at  a  nearer  point  than  that  at  which 
parallel  rays  are  collected.  These  facts  are  illustrated  in  the  following 
diagrams  (Fig.  374). 


854 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


in  ordinary  lenses  the  amount  of  refraction  at  the  centre  and  at  the 
circumference  is  not  equal.  Rays  passing  through  the  optical  centre,  as 
already  stated,  pass  directly  without  refraction,  while  those  which  pass 
near  the  centre  are  less  refracted  than  those  which  pass  near  the  circum- 


FIG.  374.— ACTION  OF  A  CONVEX  LENS  ON  LIGHT.    (Landois.) 

I.  m  m,  chief  axis  :  O,  optical  centre :  rays  (>i  n)  passing  through  this  centre  are  principal  rays,  and 
are  not  refracted.  II.  Parallel  rays  are  collected  at  a  focus,/,  /O  being  the  focal  distance.  III.  Rays 
diverging  from  a  point,  b,  on  the  chief  axis,  within  the  focal  distance,  pass  out  of  the  other  side  of  the 
lens  less  divergent,  but  do  not  come  to  a  focus.  IV.  Rays  from  a  source  of  light,  7,  beyond  the  principal 
focus,/,  again  converge  on  the  opposite  side  of  the  lens.  V.  Formation  of  an  inverted  image  by  a  convex 
lens. 

ference  ;  consequently,  the  amount  of  refraction  increases  as  the  circum- 
ference of  the  lens  is  approached.  This  is  known  as  spherical  aberration. 
If  a  screen  be  placed  in  the  focus  of  the  rays  passing  near  the  centre  of 


FIG.  375.— DIFFERENT  KINDS  OF  LENSES.     (Ganot.) 

A,  double  convex  ;  B,  plano-convex ;  C,  converging  concavo-convex ;  D,  double  concave :  E,  plano-concave ; 
F,  diverging  concavo-convex ;  C  and  F  are  also  called  meniscus  lenses. 

the  lens  the  resulting  image  will  be  bright  in  its  central  portion,  and  will 
have  surrounding  it  a  halo  which  becomes  fainter  and  fainter  as  we  pass 
from  the  centre  to  the  circumference  (Fig  376). 

Spherical  aberration  may  be  corrected  in  two  ways :  by  increasing 


SENSE  OF   SIGHT.  855 

the  density  of  the  lens  at  its  central  part,  in  order  that  it  may  act  more 
strongly  on  rays  of  light,  by  which  the  refracting  power  is  increased 
at  that  point ;  this  is  accomplished  in  the  ciystalline  lens  of  the  eye  in 
this  manner  since  it  is  less  dense  at  the  circumference  than  in  the  centre  : 
or,  spherical  aberration  may  be  diminished  by  placing  a  diaphragm 
between  the  object  of  which  the  image  is  to  be  formed  and  the  lens,  so  as 
to  cut  off  those  rays  which  pass  through  the  circumference  and  allow  the 
image  to  be  formed  only  by  the  central  rays.  This  method,  also,  is 
adopted  in  the  construction  of  the  eye,  where  the  movable  diaphragm  is 
represented  by  the  iris. 

Again,  another  point  is  to  be  mentioned :  white  light,  as  is  well 
known,  is  composed  of  seven  colors,  which  vary  in  their  different  degrees 
of  refrangibility — violet,  indigo,  blue,  green,  yellow,  orange,  and  red.  If 
a  beam  of  white  light  is  passed  through  a  triangular  prism  of  glass  it  is 


FIG.  376.— DIAGRAM  ILLUSTRATING  SPHERICAL  ABERRATION.    (Ganot.) 

The  rays  passing  through  the  edges  of  the  lens  have  a  shorter  focal  distance  than  those  passing  nearer  to 

the  centre. 

decomposed  into  its  constituent  ra}Ts,  the  violet  ra}^s  being  refracted 
most  strongly  and  the  red  the  least  (Fig.  377).  A  white  point  on  a  black 
ground  does  not  form  a  simple  image  on  the  retina,  but  many  colored  points 
appear  after  each  other.  If  the  eye  is  accommodated  so  as  to  focus  to  a 
sharp  image  the  violet  rays  are  refracted  most  strongly ;  the  other  colors 
will  form  concentric  diffusion  circles,  being  most  marked  in  the  case  of 
the  red  rays.  In  the  centre  of  all  the  colors  a  white  point  is  produced  by 
their  mixture,  while  around  it  are  placed  colored  circles.  Such  an  action, 
of  course,  produces  dimness  of  the  object,  and  is  known  as  chromatic 
aberration. 

This,  top,  may  be  corrected  in  two  ways :  either  by  making  use  of 
the  diaphragm  and  cutting  off  the  rays  passing  through  the  circumfer- 
ence of  the  lens ;  or  in  optical  instruments  by  the  use  of  two  kinds  of 
glass,  one  of  which  has  a  different  dispersing  power  from  the  other,  but 


856  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

equal  refracting  power.  Of  the  one  a  double  convex  lens  is  made,  of  the 
other  a  double  concave,  and  the  two  combined.  They  must  be  of  dif- 
ferent dispersive  power,  or  the  degree  of  concavity  which  would  correct 
the  chromatic  aberration  would  also  destroy  the  converging  power  of  the 
convex  lens.  In  crown  glass  and  flint  glass  we  have  such  media.  The 
flint  glass  has  greater  dispersive  power,  hence  the  degree  of  concavity 
necessary  to  correct  the  chromatic  aberration  will  be  attained  before  the 
degree  of  concavity  will  be  reached  which  would  destroy  the  converging 
power  of  the  convex  lens  of  crown  glass. 

In  the  different  refractive  media  of  the  eye  such  combinations  are 
to  a  certain  extent  represented,  and  serve,  together  with  the  action  of 
the  pupil  in  shutting  off  the  circumferential  rays,  to  correct  chromatic 
aberration. 

The  eye  as  an  optical  instrument  is  analogous  to  the  camera  obscura, 
and  forms,  in  a  manner  to  be  described  directly,  an  inverted  image  in 


FIG.  377.— DIAGRAM  ILLUSTRATING  THE  DECOMPOSITION,  IN  PASSING  THROUGH 
A  PRISM,  OF  WHITE  LIGHT  INTO  THE  SEVEN  COLORS  OF  THE  SPECTRUM. 
(Btclard.) 

r,  red  ;  o,  orange ;  j,  yellow ;  v,  green ;  b,  blue ;  i,  indigo  ;  vi,  violet. 

reduced  size  of  objects  before  it.  Instead  of  a  single  lens,  as  in  the 
camera,  the  eye  is  composed  of  a  number  of  different  refractive  media 
placed  behind  each  other — the  cornea,  the  aqueous  humor,  and  the  lens. 
The  field  of  projection,  or  the  point  on  which  the  image  is  focused,  is  the 
retina,  and  from  changes  which  have  recently  been  discovered  to  take 
place  in  the  retina  in  which  the  visual  purple  becomes  bleached  the 
analogy  to  the  process  of  photography  is  very  striking. 

As  is  well  known,  by  means  of  a  convex  lens  an  image  of  any  object 
may  be  formed  upon  a  screen ;  thus,  if  a  convex  lens  be  held  before  a 
window,  and  a  piece  of  paper  placed  behind  it  as  a  screen,  at  a  certain 


SENSE  OF   SIGHT.  857 

distance  behind  the  lens,  a  reversed  image  of  the  window  will  be  formed 
upon  it.  The  manner  in  which  this  image  is  formed  may  be  represented 
in  the  following  diagrams  (Figs.  378  and  319). 

In  these  figures  it  is  seen  that  rays  from  any  point  of  the  object,  which 
may  be  regarded  as  diverging  rays,  are  brought  to  a  point  behind  the 
lens.  If  the  figures  should  be  completed,  and  lines  drawn  from  each  indi- 
vidual point  of  the  objects  in  the  manner  represented  in  the  illustrations, it 
must  be  evident  in  tracing  each-  of  these  lines  that  a  small  inverted  image 


FIG.  378.— DIAGRAM  ILLUSTRATING  THE  FORMATION,  BY  A  DOUBLE  CONVEX 
LENS,  OF  A  SMALLER  INVERTED  IMAGE.    (Oanot.) 

must  be  formed  behind  the  lens.  If  a  screen  be  placed  at  this  point, 
which  corresponds  to  the  focal  length  of  the  lens,  it  is  evident  that  the 
image  will  be  distinctl}'  defined.  On  the  other  hand,  if  the  screen  be 
either  approached  or  removed  farther  from  the  lens  an  indistinct  image 
will  be  formed.  If  the  object  be  farther  removed  from  the  lens  the 
image  will  decrease  in  size,  and  to  have  a  distinct  image  the  screen  must 
be  approached  to  the  lens ;  and,  conversely,  if  the  object  be  approached 


FIG.  379.— DIAGRAM  ILLUSTRATING   THE   FORMATION  OF  AN  IMAGE  BY  A 
DOUBLE  CONVEX  LENS. 

to  the  lens  the  image  will  be  increased  in  size,  and  to  have  sharp  definition 
the  screen  must  be  moved  farther  from  the  lens. 

A  similar  process  occurs  within  the  eye,  although  the  refraction  of 
rays  of  light  is  much  more  complicated  than  in  the  simple  convex  lens, 
for  in  the  eye  the  ray  of  light  passes  through  several  media  and  is 
refracted  by  each.  Nevertheless,  in  the  eye,  a  small  inverted  image  is 
formed  on  the  retina,  as  may  be  readily  determined  by  removing  the  eye 
from  a  recentty  killed  animal,  and  if  the  sclerotic  be  removed  from  the 


858 


PHYSIOLOGY  OF   THE  DOMESTIC  ANIMALS. 


posterior  portion  of  the  eyeball  the  image  of  external  objects  in  a 
strong  light  may  be  seen  upon  the  retina  inverted  and  reduced  in  size 
(Figs.  380  and  381). 

The  principal  surfaces  by  which  rays  of  light  passing  through  the 
eye  are  refracted  are  the  cornea  and  the  anterior  and  posterior  surfaces 
of  the  lens.  Since  rays  of  light  passing  from  the  atmosphere  to  the 
cornea  pass  from  a  rarer  to  a  denser  medium,  the  rays  of  light  will  be 
bent  toward  the  perpendicular.  The  degree  of  refraction  at  this  point 
will  be  more  marked  than  in  passing  from  the  cornea  to  the  aqueous 
humor,  both  of  which  possess  the  same  refractive  power.  On  the 
other  hand,  the  refraction  will  be  still  greater  in  the  lens,  so  that  the 
rays  will  be  still  more  strongty  deflected  inward.  It  has  been  seen 
that  rays  of  light  passing  through  the  central  point  of  the  optical 
centre  of  a  convex  lens  do  not  undergo  refraction,  and  in  a  double 
convex  lens  of  equal  curvature  the  optical  centre  will  coincide  with  the 


FIG.  380.— FORMATION  OP  AN  IMAGE  IN  THK  EYE.     (Landois.) 

By  following  the  rays  from  the  object,  A  B,  it  may  be  seen  that  they  are  brought  to  a  focus  on  the  retina, 
where  a  small  inverted  image  is  formed. 

geometrical  centre.  In  such  a  compound  system  of  refracting  media 
as  in  the  eye  the  optical  centre  is  less  readily  determined.  It  has  been 
determined  that  in  the  eye  the  optical  centre  lies,  not  exactly  in  the 
centre  of  the  crystalline  lens,  but  between  that  point  and  the  posterior 
surface  of  the  lens ;  consequently,  the  rays  passing  through  this  point 
will  practically  undergo  no  refraction.  It  has  been  stated  that  a  screen 
may  be  so  arranged  in  relation  to  a  convex  lens  that  a  distinct  image  of 
the  object  will  fall  upon  it.  This  relation  is  attained  when  the  screen  is 
in  the  exact  focus  of  the  lens.  If  approached  to  the  lens  or  removed 
a  greater  distance  from  it  the  image  becomes  indistinct.  So,  also,  simi- 
lar blurring  or  indistinctness  is  produced  when  the  distance  between 
the  object  and  the  lens  is  altered. 

In  looking  at  a  distant  object  the  rays  of  light  may  be  regarded  as 
parallel,  and,  as  is  well  known,  are  focused  with  the  greatest  readiness 
upon  the  retina.  The  difference  between  the  action  of  the  eye  in 


SENSE  OF   SIGHT.  859 

forming  an  image  and  that  of  a  simple  lens  is  evident  in  the  fact  that 
with  the  normal  eye  an  object  may  be  seen  with  equal  distinctness 
whether  at  a  great  distance  or  closely  approached  to  the  eye.  This 
indicates  that  there  must  be  some  mechanism  in  the  eye  by  which  the 
focal  length  of  the  refracting  media  can  be  altered.  If  the  finger  be 
held  a  short  distance  before  the  eye,  the  other  being  closed,  it  may 
be  distinguished  with  the  greatest  distinctness.  If  the  finger  remain 
in  the  same  position,  and  the  eye  now  be  fixed  on  some  more  distant 
object,  the  finger  is  seen  indistinctly,  so  that  at  will  we  may  focus  our 
eyes  on  either  the  near  or  the  far  object  and  either  may  be  distinctly 
seen:  yet  when  the  eye  is  arranged  for  near  objects  far  objects  are  seen 
indistinctly,  and  the  reverse.  Such  an  adjustment  of  the  refracting 
powers  of  the  eye  is  termed  accommodation.  It  was  for  a  time  thought 
that  the  accommodation  of  the  e}'e  was  accomplished  by  approaching  or 
withdrawing  the  receiving  surface,  the  retina,  to  or  from  the  lens.  It 


FIG.  381.— DIAGRAM  ILLUSTRATING  THE  FORMATION  OF  AN  IMAGE  ON  THE 
RETINA.    (Yeo.) 

The  rays  from  the  point,  a,  passing  through  the  cornea,  lens,  etc.,  are  collected  in  the  retina  at  6.    Thosa 
from  a'  meet  at  b',  and  thus  the  lower  point  becomes  the  upper. 

has,  however,  been  shown  that  this  is  not  the  case,  and  that  accommo- 
dation is  accomplished  by  changes  in  the  curvature  of  the  cr3rstalline  lens. 
Referring  again  to  our  illustration  of  an  object,  a  convex  lens,  and  a 
screen,  as  has  been  stated,  if  we  determine  the  focal  length  of  the  lens 
or  the  point  at  which  a  distinct  image  will  be  formed  upon  the  screen  and 
then  approach  the  object  to  the  lens,  the  screen  not  being  removed  from 
its  position,  the  image  will  be  indistinct.  If,  now,  we  remove  the  object, 
the  screen  remaining  unmoved,  and  substitute  for  the  lens  originally 
used  one  of  a  greater  degree  of  curvature,  the  degree  of  refraction  will 
evidently  be  greater  and  the  focal  length  shorter,  so  that  the  rays  from 
the  object  in  the  near  position,  being  more  diverging,  may  be  brought  to 
a  focus  at  a  point  corresponding  to  that  of  the  less  diverging  rays  from 
the  farther-removed  object.  So,  again,  if  the  point  of  distinct  image  be 
determined  and  the  object  farther  removed,  the  screen  would  then  have 
to  be  approached  to  the  lens  in  order  to  obtain  a  distinct  image.  In  this 


860 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


case,  also,  a  distinct  image  might  be  formed  by  substituting  a  lens  of  a 
less  degree  of  curvature. 

In  the  eye  accommodation  is  accomplished  by  muscular  action  through 
which  the  shape  of  the  lens  is  changed.  When  the  eye  after  viewing  an 
object  at  a  distance  is  adjusted  to  form  a  sharp  image  of  a  nearer  object 
the  crystalline  lens  becomes  thicker  through  an  increase  of  the  curvature 
of  its  anterior  surface.  This  change  may  be  represented  in  the  following 
diagram,  after  Helmholtz  (Fig.  382). 

The  left  portion  of  the  figure  represents  the  eye  adjusted  for  distant 
objects,  while  the  right  half  is  accommodated  for  near  objects.  It  is  here 
seen  that  the  anterior  surface  is  increased  in  convexity,  moving  nearer 
the  cornea,  and  has  carried  the  iris  with  it.  It  is  well  known  that  the 
refraction  of  light  rays  caused  by  a  convex  lens  increases  with  its  increase 
of  curvature,  and  that  the  focal  length  of  one  lens  will  be  longer  than 


CS. 


asf 


FIG.  382.— SCHEME  OF  ACCOMMODATION  FOR  NEAR  AND  DISTANT  OBJECTS, 

AFTER  HELMHOLTZ.    (Landois.) 

The  right  side  of  the  figure  represents  the  condition  of  the  lens  during  accommodation  for  a  near 
object,  and  the  left  side  when  the  eye  is  at  rest.  The  letters  indicate  the  same  parts  on  both  sides ;  those 
on  the  right  side  are  marked  with  a  stroke.  A,  left,  B,  right  half  of  lens ;  C,  cornea ;  S,  sclerotic ;  C.S., 
canal  of  Schlemm ;  V.K.,  anterior  chamber ;  J,  iris ;  P,  margin  of  the  pupil ;  V,  anterior  surface,  H, 
posterior  surface  of  the  lens ;  R,  margin  of  the  lens ;  F. ',  margin  of  the  ciliary  processes ;  a  b,  space  be- 
tween the  two  former;  the  line  Z  Vindicates  the  thickness  of  the  lens  during  accommodation  for  a  near 
object ;  Z  Y,  the  thickness  of  the  lens  when  the  eye  is  passive. 

that  of  one  of  greater  curvature — in  other  words,  the  latter  will  produce 
a  greater  convergence  of  the  light-rays. 

A  similar  state  of  affairs  holds  in  the  adjustment  of  the  lens  in  the 
e3Te.  When  the  object  of  our  vision  is  closely  approached  to  the  eye 
the  lens  is  more  convex  than  when  the  distance  is  greater,  and  its  refract- 
ing power  is,  therefore,  increased  and  the  formation  of  an  image  on  the 
retina  rendered  possible.  Of  course,  with  every  variation  in  distance 
there  must  be  a  corresponding  variation  in  the  degree  of  curvature  of 
the  lens. 

The  mechanism  by  which  the  change  in  the  curvature  of  the  lens  is 
accomplished  is  the  ciliary  muscle.  The  capsule  of  the  lens  is  attached 
at  its  edge  to  the  zone  of  Zinn,  which  radiates  outward  and  keeps  the 
lens  in  a  state  of  constant  tension.  At  the  point  where  the  fibres  of  this 


SENSE   OF   SIGHT.  861 

ligament  are  attached  to  the  outer  membrane  are  also  attached  the  fibres 
of  the  ciliary  muscle.  When  the  eye  is  in  a  condition  of  rest,  and, 
therefore,  adjusted  for  distant  objects,  the  ciliary  muscle  is  relaxed  and 
the  zone  of  Zinn,  by  means  of  its  elastic  tension,  pulls  on  the  edges  of 
the  lens-capsule,  thereby  extending  the  lens  in  a  radial  direction  toward 
its  edge,  diminishing  its  thickness  and  flattening  its  curvature.  When 
we  want  to  focus  for  near  objects  the  zone  is  drawn  forward  and  inward 
by  the  contraction  of  the  ciliary  muscle.  Its  tension,  therefore,  decreases, 
and  the  lens,  by  means  of  its  elasticity,  bulges  forward  from  the  release 
of  the  tension  of  the  capsule  of  the  lens  and  so  increases  in  thickness, 
and  its  anterior  surface  becomes  more  curved.  It  is,  therefore,  evident 
why  a  strain  on  the  eyes  is  experienced  when  looking  at  near  objects, 
since  in  a  condition  of  rest  of  the  eye  the  muscle  is  relaxed  and  the  eye 
is  adjusted  for  parallel  rays  or  for  viewing  distant  objects;  but  when  near 
objects  are  closely  examined  a  prolonged  muscular  effort  is  required,  and 
this,  like  all  other  muscular  exertions,  results  in  fatigue. 


FIG.  383.— MYOPIC  EYE.    (Landois.) 

In  the  normal  eye  the  far  point  of  vision  may  be  placed  at  an  infinite 
distance,  for  in  the  normal  eye  the  degree  of  refraction  of  the  dioptric 
media  is  such  that  parallel  rays  of  light  are  brought  to  a  focus  on  the 
retina.  In  myopia,  or  near-sightedness,  parallel  rays  are  not  focused  on 
the  retina  in  a  condition  of  rest  of  the  ciliary  muscle,  but  cross  within 
the  vitreous  humor,  and  after  crossing  form  a  diffused  image  on  the 
retina.  The  focal  point  in  the  myopic  eye  for  parallel  rays  falls  in  front 
of  the  retina  (Fig.  383).  The  eyeball  is,  therefore,  too  long  as  compared 
with  the  focal  length  of  the  refracting  media.  The  near  point,  on  the 
other  hand,  or  the  nearest  point  at  which  objects  may  be  distinctly  seen, 
lies  abnormally  near,  and  the  range  of  accommodation  is  diminished. 

On  the  other  hand,  it  is  conceivable  that  the  refracting  media  of  the 
eye  may  be  such  that,  without  accommodation,  parallel  rays  of  light, 
instead  of  being  focused  on  the  retina,  as  in  the  emmetropic  or  normal 
eye,  or  in  front  of  the  retina,  as  in  the  myopic  eye,  will  come  to  a  focus 
behind  the  retina  (Fig.  384).  Such  a  defect  is  spoken  of  as  hypermetropia, 
and  is  due  to  the  fact  that  the  degree  of  refraction  of  the  media  of  the 


862  PHYSIOLOGY  OF  THE   DOMESTIC   ANIMALS. 

eye  is  not  sufficiently  great  to  bring  parallel  rays  of  light  to  a  focus  on 
tile  retina.  When  such  an  eye  is  at  rest  only  convergent  rays  are  capable 
of  forming  a  distinct  image  on  the  retina,  so  that,  therefore,  distinct 
images  can  only  be  formed  by  rendering  all  the  rays  of  light  which 
enter  the  eye  convergent;  and,  therefore,  such  an  individual  will  not  be 
able  to  see  distinctly  without  a  convex  lens  in  front  of  the  eye.  In  such 
an  eye  the  far  point  is  negative,  while  the  near  point  is  abnormally 
distant  and  the  range  of  accommodation  great.  In  the  hypermetropic 
eye,  consequently,  the  distance  between  the  retina  and  the  lens  is 
abnormally  short. 

When  the  eye  is  accommodated  for  near  objects  the  pupil  contracts ; 
when  in  accommodation  for  distant  objects  it  dilates.  So,  also,  when 
the  eye  is  exposed  to  a  bright  light  the  pupil  becomes  reduced  in  size, 
while,  on  the  other  hand,  it  dilates  when  the  light  becomes  reduced  in 
intensity. 

Changes  in  the  pupil  are  accomplished  by  the  action  of  the  muscular 
fibres  of  the  iris,  which  by  their  relaxation  and  contraction  increase  or 

diminish  the  size  of  the  pupil. 
The  iris,  therefore,  fulfills  the 
function  of  a  diaphragm  and 
serves  to  cut  off  the  circum- 
ferential rays  of  light,  which 
otherwise  would  lead  to  the 
production  of  spherical  aberra- 
tion. So,  also,  as  it  contracts 
FIG.  384,-HYPEKMETROPic  EYE.  (Landois.)  in  a  bright  light,  it  serves  to 

regulate  the  amount  of  rays  of 

light  entering  the  eye,  while,  further,  it  to  a  certain  extent  supports 
the  action  of  the  ciliary  muscle,  as  is  seen  in  the  changes  which  occur  in 
the  size  of  the  pupil  during  accommodation. 

The  iris  is  supplied  with  two  sets  of  muscular  fibres,  the  circular  or 
sphincter  fibres,  which  are  supplied  by  the  oculo-motor  nerve,  and  the 
radiating  fibres,  or  the  dilator  of  the  pupil,  supplied  chiefly  by  the  cervical 
sympathetic  and  the  trigeminus.  When  the  oculo-motor  nerve  is  divided 
the  pupil  dilates,  owing  to  the  contraction  of  the  dilator  fibres,  which 
still  preserve  their  integrity.  On  the  other  hand,  when  the  sympathetic 
is  divided  in  the  neck  the  pupil  contracts  through  the  antagonistic 
action  of  the  sphincter  fibres.  The  contractility  of  the  circular  fibres  is, 
nevertheless,  the  stronger,  for  if  both  nerves  be  stimulated  together 
contraction  of  the  pupil  will  take  place.  The  radial  muscular  fibres  are 
especially  developed  in  birds,  while  they  have  been  claimed  to  be  absent 
in  many  other  animals. 

Changes  in  the  size  of  the  pupil  fall  under  the  head  of  reflex  actions, 


SENSE   OF   SIGHT.  863 

since  they  cannot  be  produced  through  the  exercise  of  the  will.  When 
a  ray  of  light  falls  upon  the  retina  it  leads  to  contraction  of  the  pupil, 
In  which  the  optic  nerve  is  the  afferent  nerve,  the  oculo-motor  nerve  the 
efferent  nerve,  while  the  centre  lies  in  some  place  in  the  brain  below  the 
corpora  quadrigemina.  This  is  proven  by  the  fact  that  when  the  optic 
nerve  is  divided  intense  light  no  longer  produces  contraction  of  the  pupil, 
while,  also,  the  division  of  the  third  pair  renders  the  pupil  insensitive 
to  light,  and  stimulation  of  the  peripheral  portion  of  the  oculo-motor 
leads  to  contraction  of  the  pupil.  So,  also,  stimulation  of  the  floor  of 
the  aqueduct  of  Sylvius  will,  likewise,  if  the  oculo-motor  nerve  be  intact, 
lead  to  contraction  of  the  pupil. 

In  contradistinction  to  what  will  be  found  in  many  instances,  two 
symmetrically  disposed  centres  are  not  to  be  found  in  the  brain  for  gov- 
erning the  movements  of  the  pupil,  since  in  normal  conditions  a  stimulus 
applied  to  one  optic  nerve  will  lead  to  contraction  of  both  pupils,  while, 
also,  stimulation  of  the  centre  will  react  on  both  eyes. 

In  addition  to  the  oculo-motor  nerve,  the  iris  receives  nerve-fibres 
from  the  short  ciliary  nerves  coming  from  the  ophthalmic  ganglion, 
which  is  connected  by  its  root  with  the  third  nerve,  the  cervical  sympa- 
thetic nerve,  and  the  nasal  branch  of  the  ophthalmic  division  of  the  fifth 
nerve.  It  has  been  mentioned  that  section  of  the  cervical  sympathetic 
causes  contraction  of  the  pupil,  and  stimulation  of  the  cervical  sympa- 
thetic dilatation  of  the  pupil.  It  is  evident  that  these  effects  on  the 
pupil  are  directly  opposite  to  those  seen  in  the  blood-vessels  on  stimu- 
lation of  the  sympathetic  nerve. 

The  centre  for  the  dilatation  of  the  pupil  likewise  lies  in  the  front 
part  of  the  floor  of  the  aqueduct  of  Sylvius,  while  a  second  or  inferior 
centre,  the  so-called  cilio-spinal  centre,  lies  in  the  lower  cervical  portion 
of  the  cord  and  extends  downward  to  the  first  or  third  dorsal  vertebra. 
This  centre  may  be  reflexly  stimulated  by  irritation  of  various  sensory 
nerves,  when,  of  course,  dilatation  of  the  pupil  will  take  place.  It  is 
likewise  stimulated  by  the  blood  in  dyspnoea,  and  also  a  single  centre 
governs  the  movements  of  both  pupils,  for  if  one  retina  be  shaded  both 
pupils  will  dilate.  The  cilio-spinal  centre  is  in  connection  with  the  upper 
centre  for  the  dilator  of  the  pupil  through  fibres  passing  through  the 
lateral  columns  of  the  cord,  and  it,  together  with  the  inferior  centre, 
reacts  to  the  same  stimuli. 

When  the  83-111  pathetic  nerve  is  divided  in  the  neck  the  pupil  con- 
tracts. This  contraction  is  accompanied  by  a  great  increase  in  the  vascu- 
larity  of  the  iris  from  the  consequent  paralysis  of  the  walls  of  its 
blood-vessels.  This  at  one  time  was  supposed  to  be  sufficient  to  explain 
the  production  of  contraction  of  the  pupil  after  section  of  the  sym- 
pathetic. Various  other  conditions  which  lead  to  an  increased  blood 


864 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


supply  of  the  iris  will  influence  the  size  of  the  pupil.  Thus,  in  forced 
expiration,  by  which  the  return  of  the  blood  from  the  head  is  retarded, 
the  pupil  is  contracted.  So,  also,  when  the  intra-ocular  pressure  is  dimin- 
ished, as  by  puncture  of  the  anterior  chamber,  there  is  less  resistance  to 
the  flow  of  blood  to  the  blood-vessels  of  the  iris  and  the  pupil  is  imme- 
diately contracted.  On  the  other  hand,  strong  muscular  exertion,  which 
leads  to  the  blood  flowing  freely  into  the  contracting  muscles,  will  produce 
dilatation  of  the  pupil. 

The  size  of  the  pupil  may  be  modified  by  various  drugs.  Substances 
which  dilate  the  pupil  are  called  mydriatics  ;  those  which  lead  to  its  con- 
traction, myotics.  Of  the  former 
may  be  mentioned  atropine,  hom- 
atropine,  duboisine,  daturine,  and 
hyoscyamine.  They  act  chiefly 
by  paralysis  of  the  oculo-motor 
nerve,  while  also  acting  slightly 
upon  the  dilator  fibres,  for  after 
complete  paralysis  of  the  oculo- 
motor nerve  the  moderate  dila- 
tation thereby  produced  may  be 
intensified  by  the  administration 
of  atropine.  Atropine  appears  to 
act  mainly  by  a  local  mechanism, 
since  it-  produces  dilatation  of 
the  pupil  even  after  destruction 
of  the  ophthalmic  ganglion  and 
division  of  all  the  nerves  of  the 
eye  except  the  optic,  and  even, 
according  to  some  authorities, 
will  produce  dilatation  of  the 
pupil  in  an  excised  eye. 

Myotics,  of  which  physostig- 
mine  or  eserine  is  the  best  known, 
may  produce  contraction  of  the  pupil  either  by  stimulation  of  the 
oculo-motor  nerve  or  paralysis  of  the  sympathetic. 

2.  Visual  Sensations. — Our  considerations  of  the  action  of  the  organ 
of  vision  have  thus  far  dealt  simply  with  physical  processes.  The  rays 
of  light  entering  the  eye  have  been  traced  backward  through  the  trans- 
parent media  of  the  eye  until  they  resulted  in  the  formation  of  an  image. 
When  the  rays  reach  the  retina,  sensory  impulses  are  excited  and  are 
carried  through  the  optic  nerve  to  the  sensorium,  where  they  give  rise  to 
a  sensation. 

The  nature  of  the  changes  that  take  place  within  the  retina  does  not 


FIG.  385.— DlAGKAM  OF  THE    FORMATION    OP 

THE  RETINA.    (Yeo.) 

The  fibres  of  the  optic  nerve,  N,  pass  along  the  inner 
surface  of  the  retina,  R,  to  meet  the  ganglion  cells,  whence 
special  communications  pass  outward  to  the  layer  of  rods  and 
cones  in  the  pigment  layer,  p,  next  the  choroid,  c. 


SENSE   OF   SIGHT. 


865 


admit  of  as  close  analysis  as  the  physical  action  of  the  different  refract- 
ing media  of  the  eye.  It  is  known  that  it  is  only  the  layer  of  rods  and 
cones  of  the  retina  that  is  concerned  in  the  formation  of  the  image,  since 
rays  of  light  pass  through  the  anterior  layers  of  the  retina  without  giv- 
ing rise  to  any  sensations.  The  retina  is  a  highly  complicated  nervous 
apparatus,  which  may,  by  the  use  of  the  microscope,  be  divided  into 
eight  and  probably  ten  distinct  layers.  The 
innermost  layer — i.e.,  the  layer  in  contact 
with  the  vitreous  humor — consists  of  nerve- 
fibres  in  which  the  optic  nerve  terminates, 
radiating  from  the  entrance  of  the  optic 


WfS 


FIG.  386.— VERTICAL  SECTION  OF  HUMAN 
RETINA.     (Landois.) 

a,  rods  and  cones ;  b,  external,  j,  internal  limiting 
membranes;  c,  external,  and/,  internal  nuclear  layers; 
•e,  external,  and  g,  internal  granular  layers;  k,  blood- 
vessel and  nerve-cells ;  t,  nerve-fibres. 


FIG.  387.— LAYERS    OF   THE    RETINA. 

(Landois.) 

Pi,  hexagonal  pigment  cells;  Sf,  rods  and  cones; 
Le,  external  limiting  membrane;  auK,  external  nuclear 
layer;  iiugr,  external  granular  layer;  inK,  internal 
nuclear;  ingr,  internal  granular;  Gtjl,  ganglionic 
nerve-cells;  O.  fibres  of  optic  nerve ;  Li,  internal  limiting 
membrane :  Rk,  fibres  of  Miiller ;  K,  nuclei ;  Sg,  spaces 
for  the  nervous  elements. 


nerve  (Fig.  385).  At  this  point,  therefore,  the  retina  will  consist 
only  of  nerve-tubules.  At  one  spot  in  the  centre  of  the  retina  no  nerve- 
fibres  are  to  be  distinguished,  and  on  account  of  its  color  this  point  is 
termed  the  macula  lutea,  or  yellow  spot,  and  is  the  point  of  most  acute 
vision. 

The  layers  of  the  retina  have  been  described  as  follows  :  First,  and 

55 


866  PHYSIOLOGY   OF  THE   DOMESTIC  ANIMALS. 

most  internally,  exists  a  fine  limiting  membrane ;  second,  externally,  a 
layer  of  nerve-fibres  ;  third,  a  layer  of  nerve-cells  analogous  to  the  gan- 
glionic  cells  of  the  brain ;  fourth,  a  granular  layer  consisting  of  an  indis- 
tinct mass  of  fine  gray  granules  ;  fifth,  the  inner  granular  la}rer,  composed 
of  little  round  granules ;  sixth,  the  intermediate  granular  la}Ter,  in  which 
the  granular  mass  is  intermingled  with  small  fibres ;  seventh,  the  outer 
granular  layer,  analogous  to  the  inner  granular  layer ;  eighth,  a  second 
delicate  membranous  structure ;  and  ninth,  the  layer  of  rods  and  cones 
(Figs.  386  and  387). 

It  is  this  most  external  layer  of  the  retina  which  is  concerned  in  the 
reception  of  the  rays  of  light  and  the  formation  of  the  image.  It  con- 
sists of  small,  transparent  rods  packed  closely  together  at  right  angles  to 
the  surface  of  the  retina,  while  at  different  intervals  between  them  is  seen 
a  small  rod  expanded  at  the  end  so  as  to  form  a  conical  shape.  These 
cones  are  especially  abundant  in  the  yellow  spot,  where  there  is  a  slight 
depression  in  the  retina  and  where  no  rods  are  present.  To  reach  the 
layer  of  rods  and  cones,  the  rays  of  light  must  evidently  pass  through 
all  the  superimposed  la}*ers,  and  are  finally  stopped  at  the  choroid,  whichr 
with  its  pigment  layer,  may  be  regarded  as  forming  a  background  for  the 
retina. 

That  the  nerve-fibres  themselves  are  insensitive  to  light  may  be 
readity  determined  by  proving  that  the  point  of  entrance  of  the  optic 
nerve  is  entirely  insensitive  to  light.  If  one  eye  is  closed  and  the  other 
fixed  on  a  black  spot  on  a  white  sheet  of  paper  and  some  other  small 
body  be  gradually  moved  laterally  toward  the  outside  of  the  field  of 
vision,  at  a  certain  distance  the  moving  body  will  entirely  disappear  from 
sight,  while,  if  the  motion  be  continued,  it  will  again  come  into  the  field 
of  vision  ;  or  if  we  place  two  wafers  upon  a  board  at  a  distance  of  four 
or  five  inches  apart  and  stand  at  about  five  times  this  distance,  and 
closing  the  right  eye,  with  the  left  look  at  the  right-hand  wafer,  the  left- 
hand  wafer  will  disappear.  The  explanation  of  this  is  that  when  so  placed 
the  rays  of  light  from  the  left-hand  wafer  will  be  received  directly  on  the 
optic  nerve,  and  so  indicates  that  the  optic  fibres  themselves'  are  insen- 
sible to  light,  and  that  it  is  only  through  the  retinal  expansion  of  these 
fibres  that  sensations  of  vision  are  possible.  On  the  other  hand,  the 
macula  lutea  is  the  locality  of  most  distinct  vision.  When  we  fixedly 
regard  a  point  with  the  eye,  then  the  ra3Ts  of  light  from  that  point  pass 
through  the  middle  of  the  pupil  and  the  centre  of  the  lens  and  fall 
almost  on  the  centre  of  the  retina,  directly  on  the  yellow  spot.  The  for- 
mation of  the  macula  lutea  indicates  the  reason  of  its  especial  sensitive- 
ness to  light,  while  at  the  same  time  pointing  out  the  constituents  of  the 
retina  which  are  concerned  in  the  formation  of  the  image.  It  has  been 
mentioned  that  the  optic  fibres  surround  the  yellow  spot  without  passing 


SENSE   OF   SIGHT.  867 

over  it.  This  would  appear  to  indicate  such  an  adjustment  of  the  con- 
stituents of  the  retina  as  to  avoid  the  slightest  interference  with  rays 
striking  on  this  point,  since  we  have  seen  that  the  optic  nerve-fibres  are 
not  sensitive. 

Again,  in  the  yellow  spot  the  cones  of  the  retina  are  closely  packed 
together,  and  in  addition  numerous  ganglionic  cells  are  found,  while  the 
other  layers  of  the  retina  are  fainter  than  elsewhere.  The  yellow  color 
is  due  to  the  deposit  of  numerous  yellow  pigment  cells. 

If  it  be  admitted  in  the  first  place  that  the  optic  nerve-fibres  are  not 
sensitive  to  light,  and  in  the  second  place  that  the  layer  of  rods  and 
cones  represents  the  sentient  surface  for  light-waves,  a  connection  must 
evidently  exist  between  the  receiving  surface  and  the  nerve-fibres  to 
admit  of  the  impression  becoming  a  sensation  and  being  perceived  by 
the  brain.  Microscopical  examination  will  succeed  in  tracing  a  connec- 
tion by  means  of  fine  filaments  penetrating  all  the  layers  of  the  retina 
and  connecting  the  nerve-fibres  with  the  ganglionic  cells,  the  granular 
layers,  and  finally  with  the  rods  and  cones.  It  is  through  this  path  that 
the  irritation  caused  by  the  rays  of  light  and  received  in  the  meshes  of 
the  rods  and  cones  passes  to  the  optic  nerve-fibres,  and  thence  to  the 
brain,  there  creating  the  sensation  of  light. 

Like  other  nerves  of  special  sense,  the  fibres  of  the  optic  nerve, 
though  insensitive  to  light,  respond  to  other  irritants,  and  then  the  brain 
perceives  the  sensation  peculiar  to  that  special  nerve  and  recognizes 
that  an  irritant  has  acted  upon  the  nerve  of  vision,  and  a  flash  of  light 
is  the  result.  Thus,  in  cases  of  section  of  the  optic  nerve  a  flash  of 
light  is  experienced,  and  then  total  darkness  follows;  so,  also,  if  the 
optic  nerve  be  stimulated  by  electricity  a  sensation  of  light  is  the 
result.  All  the  nerves  of  special  sense  to  this  extent  agree  in  their 
nature,  and  the  optic  nerve  no  more  conve3^s  sound-waves  to  the  brain 
than  does  the  auditory  nerve  waves  of  light;  but  both  nerves  at  their 
terminations  are  supplied  with  special  forms  of  apparatus,  the  so-called 
special  sense  organs,  which  only  admit  of  being  excited  by  appropriate 
stimuli;  thus  the  terminal  fibres  of  the  optic  nerve  are  especially 
adapted  for  receiving  impressions  of  waves  of  light,  the  auditon^  nerve 
waves  of  sound,  the  difference  lying  in  the  different  impressions  made 
upon  different  special  centres  in  the  brain. 

As  to  the  mode  in  which  rays  of  light  call  into  action  the  specific 
functions  of  the  layer  of  rods  and  cones,  but  little  is  definitely  known. 
Recent  investigations  appear  to  point  to  a  chemical  decomposition  being 
concerned  in  this  process.  It  is  well-known  that  r&3'S  of  light  produce 
decomposition  in  many  substances,  which  are  then  spoken  of  as  sensitive 
to  light.  That  a  ray  of  light  shall  produce  such  decomposition,  it  must 
be  absorbed.  We  therefore,  perhaps,  see  the  explanation  of  the  invariable 


868  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

existence  of  pigment  cells  in  the  organ  of  vision.  It  has  been  mentioned 
that  the  first  indication  of  organs  of  vision  is  represented  by  an  accumu- 
lation of  pigment  cells,  and  we  never  find  the  presence  of  an  eye  which 
is  totally  free  from  such  pigment  matters. 

A  fact  which  at  first  seemed  to  show  exactly  how  this  process  was 
accomplished  was  the  discovery  in  the  retina  of  the  purplish-red  pigment, 
the  so-called  visual  purple,  or  rhodopsin,  which  is  so  extremely  sensitive 
to  light  that  by  proper  means  external  objects  may  actually  be  photo- 
graphed in  it  on  the  retina.  This  substance  may  be  extracted  from  the 
retina  by  means  of  a  2.5  per  cent,  solution  of  the  bile  acids,  especially  if 
the  eyes  have  been  kept  for  some  time  in  a  10  per  cent,  solution  of  com- 
mon salt.  Kiihne  stated  that  by  illuminating  the  retina  actual  pictures 
could  be  produced  on  the  retina,  and  that  they  gradually  disappeared. 
The  analogy  between  this  fact  and  the  action  on  the  sensitive  plate  in  the 
photographic  apparatus  is  very  striking,  and  the  further  behavior  of  the 
purple  pigment  of  the  retina  would  perhaps  show  that  it  is  concerned  in  the 
appreciation  of  light.  Thus,  if  a  rabbit  is  kept  in  the  dark  for  some  time 
and  then  killed,  and  its  retina  examined  by  a  monochromatic  light,  it  will 
be  found  to  be  of  a  brilliant  purple-red  color  with  the  single  exception  of 
the  macula  lutea;  on  the  other  hand,  exposure  to  light  will  result  in 
quickty  bleaching  it,  but  it  will,  however,  have  its  color  restored  if  the 
eye  be  again  placed  in  darkness. 

Unfortunately,  we  are  as  yet  entirely  unwarranted  in  forming  any 
such  conclusion  or  affirming  any  such  close  connection  between  this 
peculiar  substance  and  the  sensation  of  vision  by  the  fact  that  the  pigment 
is  confined  to  the  outer  segments  of  the  rods  and  is  absent  in  the  cones, 
which  we  have  found  to  be  the  most  sensitive  layer;  and  is,  in  fact,  absent 
in  the  macula  lutea,  which  we  have  found  to  be  the  most  sensitive  point 
of  the  retina.  Finally,  it  is  absent  in  pigeons,  hens,  and  bats,  although 
the  retina  of  the  latter  only  consists  of  cones,  while  it  is  found  in  both 
nocturnal  and  diurnal  animals.  Finally,  it  is  entirely  wanting  in  animals 
which  undoubtedly  see  very  distinctly,  and  may  be  entirely  removed 
from  the  eyes  of  certain  animals,  as  the  monkey,  by  prolonged  exposure 
to  strong  light,  when  the  retina  will  become  completely  bleached,  but 
will  still  apparently  be  perfectly  sensitive  to  light.  We  cannot,  there- 
fore, at  present  explain  visual  sensations  as  due  to  chemical  changes 
occurring  in  this  pigment.  The  discovery  of  the  retinal  pigment  is, 
nevertheless,  to  be  regarded  as  an  advance  in  the  elucidation  of  this  sub- 
ject, for  it  is  almost  impossible  to  conceive  that  it  is  not  in  some  way 
concerned  in  vision. 

It  has  been  stated  that  the  two  pupils  act  simultaneously,  and 
as  we  know  the  function  of  the  pupil  is  concerned  in  regulating  the 
entrance  of  rays  of  light  to  the  eye  and  that  vision  takes  place  simul- 


SENSE   OF   SIGHT.  869 

taneously  with  the  two  eyes,  the  question  arises,  Why  is  it  that  with 
two  retinae,  each  capable  of  receiving  a  distinct  image,  the  image  so 
formed  by  the  use  of  the  two  eyes  is  not  double  ?  The  explanation  of 
this  lies  not  so  much  in  the  anatomical  distribution  of  the  tunics  of 
the  eye  as  in  the  fact  that  when  rays  of  light  proceed  from  a  luminous 
body  and  fall  upon  the  retinae  they  fall  upon  parts  that  are  accustomed 
to  act  together.  Every  point  of  the  image  on  one  retina  falls  upon  a 
coincident  point  upon  the  other.  These  points  are  accustomed  to  act 
together  and  we  see  a  single  image.  The  eyes,  indeed,  receive  a  double 
impression,  and  this  may  be  illustrated  by  placing  two  small  bodies, 
as  the  lingers,  at  different  distances  from  the  e}Tes.  Directing  the  eyes 
to  the  nearer,  the  more  remote  will  appear  double,  or,  if  the  eye  be 
directed  to  the  more  remote,  the  nearer  will  appear  double.  This  is 
due  to  the  fact  that  the  images  of  the  object  upon  which  the  eye  is  not 
especialty  directed  do  not  fall  upon  coincident  parts  of  the  retina. 
The  same  thing  may  be  accomplished  by  throwing  the  two  parts  of  the 
retina  out  of  coincidence  with  each  other,  when,  almost  instantaneously, 
double  vision  will  occur.  If,  while  looking  at  a  single  object,  we  press 
to  one  side  the  globe  of  one  eye,  we  bring  two  parts  of  the  retina  to  act 
together  which  did  not  ordinarily  thus  coincide,  and  double  vision  ensues. 
Any  other  cause,  such  as  various  poisons,  disease,  or  fatigue,  which  will 
disturb  the  co-ordination  of  the  eyes  or  such  an  adjustment  of  the  posi- 
tion of  the  eyes  that  rays  of  light  do  not  fall  upon  corresponding  or 
coincident  parts,  will  result  in  double  vision. 

Again,  it  has  been  stated  that  the  image  formed  upon  the  retina  is 
an  inverted  one,  and  yet  it  is  a  matter  of  common  experience  that  every 
body  is  seen  in  the  field  of  vision  as  upright.  This  second  mental  rever- 
sion of  the  image  is  the  result  of  experience  acquired  in  the  exercise  of 
the  sense  of  sight.  It  is  not  to  be  understood  that  the  brain  takes  cog- 
nizance of  the  picture  upon  the  retina  and  that  vision  is  an  actual  trans- 
mission of  this  image  to  the  sensorium.  The  mind  does  not  look  upon 
the  picture  so  formed,  but  vision  is  a  mental  act  excited  by  an  impres- 
sion upon  the  optic  nerve  whose  neurility  is  excited.  There  need  be  no 
more  correspondence  between  the  change  in  the  brain  and  the  image  in 
the  eyes  than  between  the  signs  of  the  telegraph  operator  and  the  words 
of  the  written  message.  It  must  be  remembered  that  vision  consists  in 
the  change  developed  in  the  central  organ  as  a  consequence  of  changes 
in  the  optic  nerve.  Even  supposing  that  the  image  on  the  retina  is 
inverted,  what  difference  does  it  make?  Everything  is  inverted  and  the 
relative  position  of  things  is  unchanged.  All  objects  hold  the  same  rela- 
tion to  each  other  whether  the  image  be  inverted  or  erect ;  hence  the 
mind  is  not  conscious  of  any  inversion. 

Although  each  retina  receives  an  image  from  the  object  the  pictures 


870 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


are  not  precisely  the  same.  If  we  hold  up  any  object  and  look  at  it  first 
with  the  right  eye,  having  the  left  eye  closed,  and  then  with  the  left  eye, 
having  the  right  eye  closed,  it  will  be  readily  seen  that  the  picture  is  not 
precisely  the  same.  With  the  right  eye  we  see  the  right  side  of  the 
object,  and  with  the  left  eye  the  left  side.  When  these  two  pictures 
come  to  be  fused  in  the  brain  there  results  an  image  which  differs  from 
either  of  the  other  two  and  which  is  projected  into  space,  giving  the 
idea  of  one  solid  body  (Fig.  388). 

It  is  upon  this  principle  that  the  stereoscope  is  constructed.  The 
stereoscopic  picture  is  composed  of  two  images,  one  representing  the 
object  as  seen  by  the  right  eye,  and  another  representing  the  object 

as  seen  by  the  left.  When  these  two 
pictures  are  fused  the  resulting  picture 
is  formed,  which  is  a  compound  of  the 
two,  and  this  fusion  of  the  two  images 
gives  the  idea  of  solidity  of  the  object. 
When  the  e}^e  has  looked  at  an  ob- 
ject for  a  long  time,  especially  if  that 
object  be  luminous,  the  retina  becomes 
fatigued  and  no  longer  capable  of  re- 
ceiving impressions  from  it.  If  the 
object  be  small  only  a  small  portion  of 
the  retina  will  be  impressed.  If  we 
turn  away  from  the  object  and  fix  the 
eye  upon  a  white  wall  we  see  a  dark 
spot  upon  the  wall  corresponding  in 
size  with  the  object  upon  which  we 
have  been  looking.  Suppose  that  we 
fix  the  eye  upon  a  bright  red  wafer 
FIG'  ^u^RGvfswNLL7Sa™G  Bl"  strong^  illuminated,  and  look  at  it 

The  lines  from  the  object  indicate  that  the  rays   Steadily    With    OU1*    eVCS,    tllC    raVS     DrO- 
from  the  back  of  the  book  fall  on  coincident  points  of 

of^rilfon*' while  each  eye>  further>  has  a  special  field  ceeding  from  that  wafer  and  falling  upon 

one  point  of  the  retina  will  fatigue  that 

point  so  that  it  will  not  be  capable  of  receiving  rays  from  less  luminous 
objects,  and  when  we  turn  our  eye  to  the  wall  we  see  a  spot  on  the  wall 
like  the  wafer  in  size  but  of  a  different  color,  made  up  of  all  the  colors 
of  the  spectrum  except  red.  This  combination  constitutes  what  are 
termed  accidental  or  complementary  colors.  Again,  if  we  look  at 
a  white  object  for  a  long  time  and  then  look  at  the  wall  we  see  there  an 
object  of  the  size  of  the  original  one  of  a  black  color.  The  point  of  the 
retina  upon  which  the  image  fell  has  become  so  fatigued  that  it  cannot 
receive  an  impression  from  the  fainter  rays  reflected  from  the  wall,  while 
all  the  other  parts  of  the  retina  are  impressed  by  these  rays.  We,  there- 


SENSE   OF   SIGHT. 


871 


fore,  see  the  wall  with  a  dark  spot  upon  it.  These  accidental  colors  are 
produced  Ity  fatigue  of  the  retina,  and  consist  of  all  the  other  colors  of 
the  spectrum  except  that  of  the  luminous  object  at  which  we  have  been 
looking.  The  primary  colors,  so-called,  are  red,  yellow,  and  blue.  The 
intermediate  points  of  the  spectrum  are  made  up  by  combinations 
of  these  ;  thus,  violet  is  a  mixture  of  red  and  blue,  green  of  yellow  and 
blue,  and  orange  of  red  and  yellow.  Blue  is  thus  the  complement  of 
orange  and  yellow  of  violet. 


FIG.  389.— DIAGRAM  ILLUSTRATING  IRRADIATION.    (Stirling.) 

If  this  diagram  is  held  some  distance  from  the  eyes,  especially  if  not  exactly  focused,  the  white  dot  will 
appear  larger  than  the  black,  though  both  are  exactly  of  the  same  size. 

When  rays  of  light  from  a  strongl}r  luminous  body  fall  upon  the 
retina  they  are  not  confined  exactly  to  the  precise  points  upon  which 
they  impinge,  but  extend  themselves  to  a  greater  or  less  degree  around 
them.  Thus,  if  we  make  a  circular  white  spot  upon  a  black  ground,  and 
a  black  spot  of  corresponding  dimensions  upon  a  white  ground,  the 
former  will  appear  considerably  larger  than  the  latter,  apparently,  be- 
cause the  excitation  of  the  retina  by  the  luminous  impression  tends  to 
spread  itself  over  the  adjacent  unexcited  space  (Figs.  389,  390,  and  391). 

The    same  phenomena   are   seen  when 
the     experiment     is     performed    with 


FIG.  390.— DIAGRAM  ILLUSTRATING  IRRA- 
DIATION.    (Stirling.) 

The  two  white  squares  appear  the  larger,  and  they 
appear  to  run  into  each  other,  and  to  be  joined  by  a 
white  strip. 


FIG.  391.— DIAGRAM  ILLUSTRATING  IRRA- 
DIATION.    (Stirling.) 

The  white  strip,  which  is  of  equal  width  through- 
out, appears  wider  below,  between  the  black  squares, 
than  above. 


different  colored  bodies.  If  the  impressing  bod}',  though  small  in  size, 
illuminate  the  retina  strongly,  it  may  irradiate  its  impression  upon  the 
surrounding  part  of  the  retina  and  make  itself  appear  larger. 

In  our  perceptions  of  the  nature  of  external  objects  we  find  that 
the  sense  of  vision,  like  the  other  sensations,  is  not  infallible,  but  that 


872 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


various  errors  in  judgment  of  visual  sensations  frequently  occur.  Some 
of  these  admit  of  explanation,  others  do  not.  The  most  striking  example 
of  such  an  error  in  perception,  and  one  which  is  the  most  readily 
explained,  is  as  follows  : — 

If  a  series  of  parallel  vertical  black  lines,  two  millimeters  in  diameter, 
are  drawn  on  white  paper,  with  equal  white  areas  between  them,  and  then 
intently  regarded  in  a  good  light,  in  a  short  time  the  lines  will  assume 
the  shape  seen  in  Fig.  392  at  A.  They  appear  of  this  shape  because  of 


a 


FIG.  392.— DIAGRAM  ILLUSTRATING  BERG- 
MANN'S  EXPERIMENT.    (Stirling.) 


FIG.  393.— ZOLLNER'S  LINES.    (Stirling.) 


the  manner  in  which  the  images  of  the  lines  fall  on  the  cones  in  the 
yellow  spot,  as  shown  in  B. 

If  a  series  of  oblique  lines  are  drawn  perfectly  parallel  to  each  otherT 
and  then  they  are  crossed  in  different  directions  by  a  number  of  short 
parallel  oblique  lines,  although  the  long  oblique  lines  are  perfectly 
parallel,  the  short  oblique  lines  cause  them  to  appear  to  slope  inward  or 
outward,  according  to  the  direction  of  the  oblique  lines  (Fig.  393). 

In  the  figure  8  and  the  capital  letter  S  the  upper  half  to  most  per- 
sons appears  of  about  the  same  size  as  the  lower  half.  If,  however,  the 
page  on  which  they  occur  be  inverted  it  will  be  seen  that  the  lower  part 


ssssssss 


88888888 


FIG.  394.— DIAGRAM  ILLUSTRATING  AN  IMPERFECTION  OF  VISUAL  JUDGMENT. 

(Stirling.) 

is  considerably  the*  larger  (Fig.  394)  ;  or  if  the  centre  of  Fig.  395  be 
fixed  at  about  three  or  four  centimeters  from  the  eye,  by  indirect  vision 
the  broad  black  and  white  peripheral  areas  will  appear  as  small  and  the 
lines  bounding  them  as  straight  as  the  smaller  central  areas. 

If  a  disk  similar  to  that  seen  in  Fig.  396  is  rotated  the  disk  appears 
to  be  covered  with  circles,  which,  arising  in  the  centre,  gradually  become 
larger  and  disappear  at  the  peripheiy.  If,  after  looking  at  such  a  revolv- 
ing disk  for  some  moments,  it  be  attempted  to  read  a  printed  page,  or  to 
look  at  a  person's  face,  the  letters  appear  to  move  toward  the  centre, 
while  the  person's  face  appears  to  become  smaller  and  recede.  If  the 
disk  be  rotated  in  the  opposite  direction  the  opposite  results  are  obtained. 


SENSE   OF   SIGHT.  873 

Movements  of  the  Eye. — The  position  of  the  eyeball  in  the  orbit 


FIG.  395.— DIAGRAM  ILLUSTRATING  IMPERFECT  PERCEPTION  OF  SIZE.    (Stirling.) 

corresponds  to  a  ball-and-socket  joint,  and   each  eyeball  is  capable  of 
moving  around  an  immovable  centre  of  rotation,  which  has  been  found  to  be 


FIG.  396.— DIAGRAM  ILLUSTRATING  RADIAL  MOVEMENT.    (Stirling.) 

placed  a  short  distance  behind  the  centre  of  the  e}^e.     The  movements  of 
the  eye  are  accomplished  b}^  six  muscles — four  straight  and  two  oblique. 


874 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


The  recti,  or  straight  muscles,  all  take  origin  about  the  optic  foramen  and 
radiate  outward,  being  inserted  in  the  globe  of  the  eye  on  either  side, 
tibove  and  below,  constituting  thus  the  external  and  internal  straight 
muscles  and  the  superior  and  inferior  straight  muscles.  Of  the  oblique 
muscles,  the  superior  alone  arises  from  the  optic  foramen  and  runs 
forward  over  the  superior  and  inner  part  of  the  orbit  through  a  pulley 
in  the  depression  just  within  the  inner  extremity  of  the  superior  orbital 
margin,  then  outward  and  backward  beneath  the  superior  straight  muscle, 


til 

FIG.  397.— SCHEME  OF  THE  ACTION  OF  THE  OCULAR  MUSCLES.    (Landois.) 

and  is  inserted  in  the  eyeball  midway  between  the  latter  and  the  external 
straight  muscle,  the  cornea,  and  the  optic  nerve.  The  inferior  oblique 
muscle  arises  from  the  anterior  portion  of  the  edge  of  the  orbit,  and  runs 
by  its  tendon  to  be  inserted  beneath  that  of  the  external  rectus  muscle. 
The  function  of  the  superior  oblique  muscle  is  to  roll  the  eye  downward 
and  inward,  that  of  the  inferior  oblique  muscle  upward  and  inward, 
although  this  may  be  accomplished  by  the  different  recti  muscles  acting 
simultaneously.  The  above  diagram  indicates  the  action  of  the  ocular 
muscles  (Pig.  397). 


SENSE   OF   HEAKING.  875 

The  oculo-motor  nerve  supplies  all  of  the  muscles  of  the  eye  with 
the  exception  of  the  external  recttis  and  the  superior  oblique.  The  ex- 
ternal rectus  muscle  is  supplied  by  the  abducens,  or  sixth  pair,  while  the 
superior  oblique  is  supplied  by  the  patheticus  or  fourth  pair. 

C.      THE   SENSE   OF   HEAEING. 

The  sense  of  hearing  or  audition  may  be  defined  as  that  sense  by 
which  the  mind  takes  cognizance  of  the  undulations  of  the  elastic 
medium  which  give  rise  to  the  sensation  of  sound.  The  mind  recog- 
nizes not  the  body  producing  the  soimd,  but  the  impression  made  by  its 
vibrations  upon  the  sensorium.  Sound,  then,  does  not  take  place  in  the 
ear,  but  in  the  brain.  When  we  speak  of  a  resounding  string  or  a 
sonorous  bell  we  make  a  mistake ;  the  string  and  the  bell  simply 
vibrate.  These  vibrations  give  rise  to  undulations  in  the  elastic  ether, 
which  undulations  are  transmitted  in  various  directions,  and  finally 
through  the  auditory  passages  impress  the  auditory  nerve  and  give  rise 
to  sound.  The  physiological  aspects  of  the  question  are  here  alone 
regarded.  Regarding  sound  as  the  recognition  of  the  impressions 
made  by  vibrating  sonorous  bodies  on  the  auditory  nerve,  if  every  one 
were  deaf  there  would,  of  course,  be  no  sound;  but,  on  the  other  hand, 
we  say  that  no  sound  may  be  produced  in  a  vacuum,  although  we  know 
that  sonorous  vibrations  still  take  place ;  hence  we  are  also  permitted  in 
a  physical  sense  to  give  the  above  explanation  of  the  word  sound. 

The  simplest  form  of  the  organ  of  hearing  is  a  sac  filled  with  fluid, 
in  which  the  ends  of  the  auditory  nerve  terminate.  In  all  groups  of 
animals  the  essential  part  of  the  organ  of  hearing  consists  in  a  certain 
special  form  of  termination  of  the  nerve,  which  is  alone  capable  of 
receiving  auditory  impressions  and  of  transmitting  them  to  the  central 
ganglia  of  the  brain.  The  more  highly  complicated  forms  of  auditory 
apparatus  simply  depend  upon  modifications  which  assist  in  the  trans- 
mission of  sound  to  this  part. 

In  all  the  invertebrates  the  organ  of  hearing  is  restricted  to  such  a 
simple  sacular  form,  in  some  instances  containing  otoliths,or  small,  hard 
granules,  and  the  vibrations  of  the  sonorous  body  are  communicated  to 
the  nerve  of  hearing  spread  over  this  sac.  In  such  animals  it  is  prob- 
able that  while  a  nerve  of  hearing  is  present  only  simple  sounds  and 
noises  can  be  recognized,  while  no  difference  in  pitch  or  intensity  can  be 
distinguished.  Such  a  simple  form  of  apparatus,  consisting  simply  of 
liquid  contained  in  a  sac,  is  found  in  mollusks. 

In  crustaceans  there  is  a  rudimentary  organ  of  hearing  present, 
placed  on  each  side  of  the  base  of  the  anterior  antennae.  It  likewise 
consists  simply  of  a  membranous  sac  filled  with  fluid,  and  on  which 
ramify  the  fibres  of  the  nerve  of  hearing. 


876  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS.  • 

Many  insects  are  apparently  free  from  any  evidences  of  anything 
resembling  an  organ  of  hearing,  yet  it  is  clear  that  these  animals  are 
sensible  of  external  sounds.  It  is  possible  that  in  these  animals,  as  in 
certain  radiates  and  many  mollusks,  the  vibrations  of  sound  are  not 
appreciated  as  sound,  but,  perhaps,  as  some  modification  of  the  sense  of 
touch. 

In  fishes  there  is  no  external  ear,  no  tympanic  cavity,  and  no 
cochlea.  The  ear  is  reduced  to  the  membranous  part  of  the  vestibule 
and  the  semicircular  canals,  the  latter  varying  from  two  to  three  in 
number,  while  the  vestibule  and  semicircular  canals  represent  a  closed 
cavity,  since  there  is  neither  oval  nor  round  window,  no  tympanic 
cavity,  nor  auditory  ossicles.  Sometimes,  as  in  cartilaginous  fishes,  the 
membranous  internal  ear  is  lodged  in  the  cartilaginous  substance  of  the 
bones  of  the  head,  while  in  osseous  fishes  it  is  sometimes  in  part  within 
the  bones  of  the  cranium,  and  part  free  in  the  cephalic  cavity,  resting 
against  the  brain.  The  internal  ear  is  in  all  cases  supplied  with  terminal 
fibres  of  the  auditory  nerve,  and  is  filled  with  a  liquid  in  which  are 
found  various  calcareous  concretions  of  greater  or  less  volume. 

In  reptiles  there  is  no  external  ear,  neither  a  pinna  nor  an  external 
auditory  canal,  the  tympanic  membrane  being  flush  with  the  head  and 
lying  directly  below  the  skin,  although  in  some  instances  a  drum  mem- 
brane is  absent.  When  present,  as  is  the  case  in  the  majority  of  instances, 
it  communicates  generally  b}^  a  large  opening — the  Eustachian  tube — 
with  the  pharynx.  The  auditory  ossicles  are  usually  reduced  to  two  in 
number.  When  the  tympanic  membrane  is  absent,  the  ossicles,  attached 
at  one  side  to  the  oval  window,  are  fastened  on  the  other  directly  against 
the  external  integument. 

In  lizards,  crocodiles,  and  serpents  the  internal  ear  is  composed  of 
the  vestibule,  semicircular  canals,  and  cochlea.  In  them,  consequently, 
the  internal  ear  communicates  with  the  cavity  of  the  tympanum  by  the 
oval  window  and  by  the  round  window.  The  cochlea  in  them  is  not  con- 
voluted, but  almost  straight. 

In  the  batrachians  no  cochlea  is  present,  and,  as  a  consequence,  no- 
round  window,  the  internal  ear  being  reduced  to  the  vestibule  and  the 
semicircular  canals,  the  only  communication  with  the  tympanum  being 
by  the  oval  window. 

In  birds  the  apparatus  of  hearing  is  almost  as  complete  as  in  mam- 
mals, with  the  single  exception  of  the  external  auditory  pinna,  which  is 
absent.  The  external  auditory  canal  is  formed  by  a  bony  canal  travers- 
ing the  temporal  bone,  and  the  t3-mpanic  cavity,  separated  from  this 
canal  by  the  tympanic  membrane,  is  well  developed.  It  communicates 
with  bony  cavities  in  the  interior  of  almost  all  the  cranial  bones,  and  by 
the  intermediation  of  the  Eustachian  tube  with  the  pharynx.  The 


SENSE   OF   HEARING.  877 

internal  ear  is  formed  of  the  vestibule,  semicircular  canals,  and  cochlea ; 
the  latter,  being  but  little  developed,  is  not  convoluted  in  a  spiral  form, 
but,  resembling  that  of  lizards  and  serpents,  consists  of  an  almost  straight 
osseous  tube  canal  terminating  in  a  cul-de-sac. 

In  mammals  the  ear,  for  the  convenience  of  study,  ma}^  be  divided 
into  three  parts — the  external,  the  middle,  and  the  internal  ear.  Of  these 
three  the  internal  ear  is  the  essential,  and  the  others  are  simply  for  the 
purpose  of  receiving  or  modifying  impressions  from  the  sounding  body. 

In  the  external  ear  we  include  the  auricle,  or  pinna,  and  the  external 
auditory  meatus,  bounded  internally  b}-  the  membrane  of  the  tympanum ; 
in  the  middle  ear,  the  tympanum,  or  drum  of  the  ear,  with  its  contained 
ossicles ;  and  in  the  internal  ear,  that  portion  situated  in  the  petrous  por- 
tion of  the  temporal  bone,  consisting  of  the  semicircular  canals,  the 
vestibule,  and  the  cochlea  (Fig.  398). 


FIG.  398.— SCHEME  OF  THE  ORGAN  OF  HEARING.    (Landois.) 

AG,  external  auditory  meatus  ;  T,  tympanic  membrane ;  K,  malleus  with  its  head  (h),  short  process 
(Kf ),  and  handle  (m) ;  a,  incus  with  its  short  process  (x)  and  long  process:  the  latter  is  united  to  the 
stapes  (s)  by  means  of  the  Sylvian  ossicle  (z) ;  P,  middle  ear;  o,  fenestra  ovalis;  r,  fenestra  rotunda;  x, 
beginning  of  the  lamina  spiralis  of  the  cochlea ;  pt,  itsscala  tympani;  vt,  its  scala  vestibuli ;  V,  vestibule; 
S,  saccule ;  U,  utricle ;  H,  semicircular  canals ;  TE,  Eustachian  tube.  The  long  arrow  indicates  the 
line  of  traction  of  the  tensor  tympani ;  the  short,  curved  one,  that  of  the  stapedius. 

In  different  groups  of  mammals  a  marked  difference  is  found  in  the 
form  and  size  of  the  auricle,  or  pinna.  This,  in  the  majority  of  cases,  is 
a  trumpet-shaped  dilatation  of  the  external  auditory  canal  formed  for  the 
purpose  of  receiving  the  undulations  communicated  to  the  atmosphere, 
collecting  them,  and  transmitting  them  inward  to  the  middle  ear.  This 
portion  of  the  external  auditory  canal  owes  its  shape  to  the  cartilages 
present  in  it,  which  in  some  instances,  as  in  the  horse,  the  ass,  the  goat, 
and  the  rabbit,  are  erect  and  straight ;  while  in  other  cases  the  cartilages 
are  more  delicate  and  soft,  folding  on  themselves  so  that  the  auricles  lie 


878 


PHYSIOLOGY  OF   THE   DOMESTIC   ANIMALS. 


in  contact  with  the  side  of  the  head,  although  they  may  by  the  influence 
of  various  muscles  be  drawn  into  a  more  or  less  erect  position.  Such  is 
the  case  in  the  elephant  and  in  the  do^.  In  most  mammals  the  auricle 


FIG.  399.— DIAGRAM  OP  THE  EXTERNAL,  SURFACE  OP  THE  LEFT  TYMPANIC 
MEMBRANE.    (Hetuen.) 

a,  head  of  the  malleus ;  b,  incus ;  e,  joint  between  malleus  and  incus ;  between  c  and  d  is  the  flaccid 
portion  of  the  membrane;  ax,  axis  of  rotation  of  ossicles.  The  deeply  shaded  central  portion  is  called 
the  "umbo." 

is  much  more  mo'bile  than  in  man,  and  may  be  directed  toward  the  source 
of  sound  by  the  contraction  of  voluntary  muscles  and  thus  be  enabled  to 
accomplish  more  successfully  its  functions. 


FIG.  400.— TYMPANIC  MEMBRANE  AND  AUDITORY  OSSICLES  SEEN  FROM  THE 
TYMPANIC  CAVITY.    (Landois.) 

M,  manubrium,  or  handle  of  the  malleus ;  T,  insertion  of  the  tensor  tympani ;  h  head,  1  F  long  proc- 
ess, of  the  malleus;  a,  incus  with  the  short  (K)  and  the  long  (1)  processes;  S,  plate  of  the  stapes;  Ax, 
Ax  is  the  common  axis  of  rotation  of  the  auditory  ossicles  ;  S,  the  pinion-wheel  arrangement  between  the 
malleus  and  incus. 

The  external  auditory  meatus  is  a  canal,  partly  cartilaginous  and 
partly  bony,  which  varies  in  length  according  to  the  species.  Thus, 
while  it  is  five  or  six  centimeters  long  in  ruminants,  it  is  very  short  in 


SENSE   OF   HEAKING.  879 

carnivora.  It  is  bounded  internal!}-  by  the  tympanic  membrane  and  its 
function  is  to  conduct  to  the  middle  ear  the  undulations  collected  bv 
the  auricle.  In  the  external  auditor}'  canal  are  found  the  ceruminous 
glands  secreting  the  wax,  which  is  principally  intended  for  lubricating 
purposes,  and  thus  facilitates  the  transmission  of  sound,  while,  also,  by 
its  extremely  bitter  taste  it  perhaps  prevents  the  entrance  of  insects. 

The  tympanic  membrane  forms  the  boundary  between  the  external 
auditory  canal  and  the  middle  ear.  This  membrane  consists  of  three 
distinct  layers,  the  outer,  the  external  integument,  the  middle  or  fibrous 
Ia3'er,  and  the  inner  or  mucous  la}*er,  continuous  with  mucous  membrane 
lining  the  middle  ear.  This  membrane  is  an  elastic,  almost  unyielding, 

Ax 


Fro.  401.— LEFT  TYMPANUM  AND  AUDITORY  OSSICLES.    (Landois.) 

A.G.,  external  meatus ;  M,  membrana  tympani,  which  is  attached  to  the  handle  of  the  malleus,  n, 
and  near  it  the  short  process,  p :  h,  head  of  the  malleus ;  a,  incus ;  K.  its  short  process,  with  its  ligament; 
1,  long  process :  s,  Sylvian  ossicle :  S,  stapes :  A  x,  A  x,  the  axis  of  rotation  of  the  ossicles,  shown  in  per- 
spective :  t,  line  of  traction  of  the  tensor  tympani.  The  other  arrows  show  the  movements  of  the  ossicles 
when  the  tensor  contracts. 

membrane,  elliptical  in  form,  and  is  placed  obliquely  in  the  floor  of  the 
external  meatus  at  an  angle  of  about  40°,  being  directed  from  above 
downward  and  inward.  This  oblique  position  enables  a  larger  surface 
to  be  presented  to  the  undulations  conducted  from  the  external  auditory 
canal  than  if  it  were  placed  vertically.  This  membrane  is  not  entirely 
flat,  but  at  its  centre  is  drawn  slightly  inward  where  the  handle  of  the 
malleus  is  attached  to  it,  while  the  short  process  of  the  malleus  causes 
a  slight  bulging  of  the  membrane  near  its  upper  margin  (Figs.  399  and 
400). 

The  middle  ear,  or  the  drum  of  the  ear  or  the  tympanum,  is  bounded 
by  the  tympanic  membrane  on  the  exterior,  and  on  the  interior  by  the 


880 


PHYSIOLOGY  OF   THE   DOMESTIC   ANIMALS. 


labyrinth.  It  connects  interiorly  with  the  fauces  by  the  Eustachian  tube, 
and  posteriorly  with  the  mastoid  cells  of  the  mastoid  portion  of  the  tem- 
poral bone.  In  some  animals  these  mastoid  cells  are  greatly  developed 
and  so  form  an  important  augmentation  of  the  tympanic  cavity,  while  the 
Eustachian  tube,  which  is  short  and  straight  in  the  case  of  most  rumi- 
nants, is  very  much  dilated  in  the  horse  where  it  forms  what  may  be 
termed  guttural  pouches  (Fig.  401). 


FIG.  402.— I.  THE  MECHANICS  OF  THE  AUDITORY  OSSICLES,  AFTER  HELM- 
HOLTZ.    II.  SECTION  OF  THE  MIDDLE  EAR,  AFTER  HEUSEN.    (Munk.) 

I.  rt.  malleus ;  h,  incus :  am,  long  process  of  incus ;  s,  stapes ;  the  arrows  show  the  direction  of  mo- 
tion. II.  G,  external  auditory  canal ;  M.t.,  membrana  tympani ;  C,  tympanum ;  H,  malleus ;  L.S., 
superior  ligamant ;  S,  stapes. 

Stretching  across  the  middle  ear  from  one  side  to  the  other  is  the 
chain  of  bones,  each  named  from  its  resemblance  to  some  instrument  ; 
thus,  the  malleus,  so-called  from  its  resemblance  to  a  hammer,  is  attached 
to  the  membranum  of  the  tympanum  by  its  handle  (Fig.  402).  The  second 

bone,  from  its  resemblance  to  an  anvil,  is 
called  the  incus,  and  is  attached  on  the 
one  side  to  the  malleus  and  on  the  other 
to  the  stapes  or  stirrup-bone,  which  is 
connected  by  its  base  to  the  membrane 
of  the  fenestra  ovalis,  which  opens  into 
the  internal  ear.  All  these  ossicles  are 

/upper,  h  horizontal,  and  s  posterior  semi-        rnnvaKIp  nn   Pnoh     nthpr    Vint     tliPir  VIQVA    r»r» 
circular  canals  of  the  left  side.    The  cochlea  is        niOVaDlC  OU  CaCll    OtDer,   Dtlt    tliey  HaVC    UO 

lateral    connection    with     any    structure. 

Sometimes  at  the  end  of  the  incus  is  found  a  separate  bone  known  as  the 
os  orbiculare.  In  the  inner  boundary  of  the  middle  ear  is  placed,  in 
addition  to  the  oval  window,  a  second,  also  communicating  with  the 
vestibule,  and  called  the  fenestra  rotunda,  or  round  window. 

The  internal  ear,  or  labyrinth,  is  composed  of  bone,  and  consists  of 


FIG.  403.— EXTERNAL,  APPEARANCE 
OF  THE  LABYRINTH  AND  FE- 
NESTRA OVALIS.  (Landois.) 


SENSE   OF   HEARING. 


881 


the  vestibule,  and,  communicating  with  this,  three  semicircular  canals  and 
the  cochlea  (Figs.  403  and  404).  Lining  the  internal  ear  and  forming  a 
complete  cast  of  the  vestibule  and  semicircular  canals  is  the  so-called 
membranous  labyrinth,  while  between  the  walls  of  the  membranous 


\ » 


FIG.  404.— SCHEME  OF  THE  AUDITORY  APPARATUS.    (Beaunis.) 

A,  external  ear;  B,  middle  ear;  C,  internal  ear;  1,  auricle:  2,  external  auditory  canal:  3,  tympanic 
cavity;  4,  tympanic  membrane:  5,  Eustachian  tube;  6,  mastoid  cells;  7,  malleus;  8,  incus;  9,  stapes; 
10,  round  window;  11,  oval  window;  12,  vestibule;  13,  cochlea;  14,  scala  tympani;  15,  scala  vestibuli; 
16,  semicircular  canal. 

labyrinth  and  the  semicircular  canals  and  vestibule  is  a  fluid  called  the 
perilymph,  which  is  also  contained  in  the  cochlea.  Within  the  mem- 
branous labyrinth  is  a  similar  fluid  termed  the  endolymph.  In  .the 
interior  of  the  membranous  lab}^rinth  are 
often  found  little  particles  consisting 
almost  entirely  of  carbonate  of  lime, 
called  otoliths,  or  ear-stones  (Fig.  405). 
Sometimes  these  are  attached  to  the  walls 
of  the  membranous  labyrinth,  and  some- 
times they  are  found  tying  loosely  and 
are  intended  to  increase  the  intensity  of 
the  sounds. 

The  cochlea  consists  of  a  spiral 
canal  making  two  and  one-half  revo- 
lutions about  a  central  axis.  It  is  divided 
by  a  spiral  lamina,  partly  membranous  and  partly  bony,  into  two 
divisions  known  as  scalae,  of  which  one  is  above  the  other.  The  superior 
at  its  inferior  extremity  terminates  in  the  vestibule  and  is  known  as  the 

56 


FIG.  405.— A,  OTOLITHS  FROM  THE 
HORSE  ;  B,  EPITHELIUM  WITH 
AUDITORY  HAIRS  FROM  THE 
CRISTA  ACOUSTICA  OF  THE 
BABBIT.  ( Munk. ) 


882 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


scala  vestibuli,  while  the  other,  or  inferior,  terminates  in  the  round 
window  and  is  called  the  scala  tympani.  On  these  laminae  spirales  fire 
distributed  portions  of  the  auditory  nerve,  which  takes  origin  from  the 
floor  of  the  fourth  ventricle  and  runs  into  the  petrous  portion  of  the 
temporal  bone  through  the  meatus  auditorius  internus  and  divides  into 
two  divisions,  one  going  to  the  cochlea  and  the  other  to  the  vestibule 
near  to  the  end  of  the  semicircular  canals.  It  loses  itself  upon  the  walls 
of  the  vestibule  and  the  walls  of  the  ampullae,  or  membranous  dilatations 
at  the  commencement  of  the  three  semicircular  canals  (Fig.  406). 

The  cochlear  nerve  is  distributed  to  the  scalae  of  the  cochlea,  where 
its  terminal  fibres  form  connection  with  Corti's  organ,  which  is  placed 


FIG.  406.— SCHEME  OF  THE  LABYRINTH  AND  TERMINATION  OF  THE  AUDITORY 
NERVE.    (Landois.) 

I.  Transverse  section  of  a  turn  of  the  cochlea.  II.  A.  ampulla  of  a  semicircular  canal :  a  p.  auditory 
cells,  p,  provided  with  a  fine  hair;  T,  otoliths.  III.  Scheme  of  the  human  labyrinth.  IV.  Scheme  of 
a  bird's  labyrinth.  V.  Scheme  of  a  fish's  labyrinth. 

in  the  ductus  cochlearis,  a  small,  triangular  chamber,  cut  off  from  the 
scala  vestibuli  by  the  membrane  of  Reissner  (Fig.  401). 

Corti's  organ  is  placed  on  the  membranous  portion  of  the  lamina 
spiralis,  and  consists  of  an  apparatus  composed  of  the  so-called  Corti's 
arches,  each  of  which  consists  of  two  Corti's  rods.  Every  two  rods 
unite  to  form  an  arch,  so  that  there  are  always  two  or  three  inner  rods 
and  two  outer  rods.  Toward  the  apex  of  the  cochlea  the  rods  become 
longer  and  the  span  of  the  arches  increases.  The  terminal  organs  of 
the  cochlear  nerve  are  the  <rylindrical  hair-cells  described  by  Corti,  of 
which  there  are  two  rows,  the  row  of  inner  cells  resting  on  a  layer  of 
small,  granular  cells,  and  the  outer  cells  distributed  in  three  or  four  rows 
resting  on  a  basement  membrane.  Between  the  outer  cells  there  are 


SENSE   OF   HEARING. 


883 


other  cellular  structures  to  be  noticed,  which  are,  perhaps,  to  be  regarded 
as  special  cells  (Fig.  408). 

Waves  of  sound  falling  upon  the  auditory  nerve  produce  no  sound, 
but  only  when  the  terminal  organs  are  stimulated. 

The  Function  of  Hearing. — To  be  enabled  to  understand  the  use  of 
the  different  portions  of  this  complicated  organ  it  will  be  necessary  to 
refer  to  some  of  the  more  important  laws  governing  the  propagation  of 
sound.  Sound,  as  before  stated,  is  the  result  of  the  vibrations  of  elastic 
bodies,  which  result  in  the  production  of  alternate  condensation  and 
rarefaction  of  the  surrounding  medium.  As  a  consequence,  sound-waves 


FIG.  407.— SCHEME  OF  THE  DTJCTTTS  COCHLEARIS  AND  THE  ORGAN  OF  CORTI. 

(Landois.) 

N,  cochl ear  nerve ;  K  inner  and  P  outer  hair-cells ;  n,  nerve-fibrils  terminating  in  P:  a,  a,  supporting 
cells :  d,  cells  in  the  sulcus  spiralis ;  z,  inner  rod  of  Corti :  Mb.  Corti,  membrane  of  Corti,  or  the  niem- 
brana  tectoria ;  o,  the  membrana  reticularis ;  H,  G,  cells  filling  up  the  space  near  the  outer  wall. 

are  produced,  in  which  the  particles  vibrate  longitudinally,  or  in  the 
direction  of  the  propagation  of  the  sound,  forming  so-called  waves  of 
condensation  and  rarefaction,  occurring  in  concentric  circles  around  the 
sounding  body. 

Like  rays  of  light,  sound-waves  may  be  reflected  when  they  impinge 
upon  an  opaque  solid,  and  the  same  rules  as  to  the  angle  of  incidence 
and  reflection  prevails.  It  is  this  throwing  back  of  sound  from  a  resisting 
medium  that  constitutes  the  echo. 

When  transmitted  through  the  atmosphere  these  waves  of  sound 
are  collected  by  the  auricle,  and  from  the  auricle  they  are  transmitted 
through  the  external  auditory  meatus  to  the  membrana  tympani,  which 
is  thus  thrown  into  vibration.  Thus,  they  are  communicated  to  the 


884 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


chain  of  bones  and  reach  the  membrane  of  the  fenestra  ovalis.  From 
that  point  they  are  communicated  to  the  peritymph,  thence  to  the 
membranous  labyrinth,  thence  to  the  endolymph,  and  finally  to  the 
otoliths,  which  serve  to  increase  the  vibratory  impression  upon  the 
nerve  of  hearing.  This  transmission  of  sound  from  the  exterior  and  its 
recognition  in  the  centre  plainly  involves  important  considerations  with 
regard  to  the  propagation  of  sounds. 

Sounds  are  transmitted  in  three  ways :  first,  by  reciprocation;  second, 
by  sympathetic  vibration;  and,  third,  by  conduction.  As  regards  vibra- 
tions by  reciprocation,  if  two  strings  of  equal  tension,  length,  and 


St 


FIG.  408.— I.  SECTION  THROUGH  THE  UNCOILED  COCHLEA.  II.  SECTION 
THROUGH  THE  TERMINAL  NERVE-APPARATUS  OF  THE  COCHLEA,  AFTER 
HEUSEN.  (Munk.) 

I.  F.  r.,  Fenestra  rotunda;  H,  the  helicotrema ;  St..,  the  stapes.  II.  z,  Huschke's  process;  bt, basilar 
membrane;  e,  Corti's  arch;  g,  supporting  cells ;  h,  cylindrical  cells;  i,  Deiter's  hair-cells;  c,  membrana 
teetoria;  n,  nerve-fibres;  nt,  non-medullated  nerve-fibres. 

density  be  stretched  side  by  side  each  one  is  capable  of  producing  the 
same  musical  tone  when  thrown  into  vibration.  Now,  when  one  of  these 
strings  is  thrown  into  vibration  the  other  will  fall  into  vibration  by 
reciprocation,  although  it  be  not  itself  touched.  The  same  thing  will 
occur  when  the  same  musical  note  is  sounded  on  another  instrument,  as 
the  tuning-fork,  if  in  sufficient  proximity.  If  one  of  the  strings  be 
stretched  tighter  than  the  other  a  higher  musical  note  will  be  produced. 
If  this  string  be  thrown  into  vibration  near  one  of  lower  note  the  latter 
will  be  divided  into  equal  divisions,  which  are  likewise  thrown  into  vibra- 
tions of  reciprocation,  and  increased  sound  will  result.  If,  however, 


SENSE  OF  HEAEING.  885 

a  string  of  less  tension  be  thrown  into  vibration  near  one  of  higher 
tension  there  will  be  no  response,  for  no  membrane  or  string  can  recip- 
rocate a  note  lower  than  its  own  fundamental  note.  By  the  term  funda- 
mental note  we  mean  the  lowest  note  which  any  string  or  membrane  can 
produce.  If  a  higher  note  be  sounded  alongside  of  a  string  of  low 
tension  the  latter,  as  before  stated,  will  divide  itself,  and  the  divisions 
will  be  separated  by  points  of  rest,  called  nodal  points,  while  the 
intermediate  parts  of  the  string  in  vibration  are  termed  loops. 

These  remarks  are  true  not  only  of  strings,  but  also  of  membranes. 
If  some  sand  be  sprinkled  on  a  membrane  stretched  across  a  drum-head, 
so  as  to  be  capable  of  a  musical  tone,  and  then  another  note  of  precisely 
the  same  pitch  be  struck  near  it,  the  sand  will  begin  to  dance  on  the  sur- 
face of  the  drum-head,  thrown  into  vibrations  of  reciprocation,  and  will 
accumulate  on  the  lines  of  rest — the  nodal  lines ;  but  if  we  sound  near 
it  a  note  higher  than  that  of  the  membrane  stretched  across  the  drum, 
then  the  membrane,  instead  of  vibrating  across  its  whole  surface,  will 
divide  itself,  and  the  sand  will  collect  in  dark  lines  on  the  nodal  points 
as  before.  If  we  sound  near  the  membrane  a  note  lower  than  its 
fundamental  note,  it  will  not  respond. 

A  column  of  air  may  be  thrown  into  vibrations  of  reciprocation  by 
sounding  a  note  in  proximity  to  it. 

Sounds  are  also  propagated  by  resonance.  If  an  instrument  capable 
of  producing  a  musical  note  while  vibrating  be  placed  in  contact  with  a 
medium  whose  molecules  are  capable  of  being  thrown  into  vibration,  the 
second  substance  will  vibrate  and  increase  the  intensity  of  the  original 
sound,  even  if  the  medium  with  which  we  place  the  sounding  instrument 
in  contact  is  not  itself  capable  of  producing  musical  tones.  Thus,  when 
we  strike  a  tuning-fork  under  ordinary  circumstances  in  the  air  the  sound 
is  but  faintly  heard,  while  if  we  place  the  fork  in  contact  with  a  piece 
of  wood,  the  sound  is  greatly  increased  in  intensity.  The  woody  fibres 
are  thrown  into  vibrations  which  reciprocate  the  original  sound. 

Sound  is  also  propagated  by  conduction,  and  this  occurs  when  an}' 
sonorous  body  during  its  vibrations  is  brought  in  contact  with  any 
medium  capable  of  being  thrown  into  vibration.  A  familiar  example  of 
this  is  found  in  the  fact  that  while  the  tuning-fork  held  in  the  air  is  but 
indistinctly  heard,  if  placed  in  contact  with  the  bones  of  the  head  it  is 
heard  distinctly.  In  this  case  the  sound  is  conducted  from  the  tuning- 
fork  to  the  nerve  of  hearing  through  the  bones  of  the  head.  All  media 
do  not  conduct  sounds  with  the  same  degree  of  rapidity.  Solids  conduct 
better  than  fluids,  fluids  better  than  gases,  while  in  a  vacuum  no  sound 
whatever  can  be  conducted. 

That  a  sound  may  be  appreciated,  it  is  evident  that  it  must  be  con- 
ducted to  the  terminal  filaments  of  the  auditory  nerve  in  the  labyrinth, 


886  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

and  the  first  process,  therefore,  to  be  considered  in  the  study  of  the 
function  of  hearing  is  the  means  by  which  sound-waves  reach  the  laby- 
rinth, and  then  the  way  in  which  they  excite  the  nerve  of  hearing. 

It  has  been  seen  that  every  sonorous  body  is  in  a  state  of  vibration 
and  that  it  transmits  these  vibrations  to  the  surrounding  atmosphere, 
resulting  in  waves  of  condensation  and  rarefaction  traveling  in  radii  from 
the  locality  in  which  the  sonorous  body  is  located. 

It  has  been  further  stated  that  sound-waves  may  be  conducted  through 
any  elastic  medium,  but  in  the  appreciation  of  sound  by  the  ear  evidently 
the  greatest  importance  is  to  be  placed  on  the  conduction  of  sound- 
waves through  the  air,  since  the  conduction  of  sounds  through  solids 
can  but  infrequently  be  of  any  importance.  It  has  been  stated  that 
sound-waves  can  be  conducted  through  the  bones  of  the  head,  and 
although  this  must  be  exceptional  in  the  case  of  man,  yet  in  fishes,  where 
no  external  ear,  auditory  canal,  or  ear-bones  are  present,  it  plays  an 
important  part.  So,  in  this  case,  the  sound-waves  of  the  water  are 
directly  transferred  to  the  labyrinth. 

We  have  now  to  trace  the  path  of  the  sound-waves  from  the  sonorous 
body,  through  the  external  ear  and  auditory  canal,  through  the  tympa- 
num to  their  termination  in  the  labyrinth,  with  the  operation  of  the 
different  apparatuses  by  which  this  transfer  is  facilitated. 

The  external  ear  evidently  fulfills  the  part  of  an  ear-trumpet,  and 
the  great  improvement  in  hearing  produced  by  artificial  addition  to  the 
auricle  serves  to  emphasize  this  point.  The  external  ear  is  evidently  of 
a  certain  amount  of  assistance  in  recognizing  the  direction  of  sound, 
but,  as  is  well  known,  we  are  liable  in  this  respect  to  make  errors  of 
judgment.  The  origin  of  sound-waves  is  determined  simply  b}r  the  fact 
that  the  sound  is  heard  most  distinctly  when  the  auditory  canal  is  in  the 
line  of  propagation  of  the  sound-waves,  and,  therefore,  in  order  to 
determine  the  direction  of  a  sound  we  turn  the  head  from  one  side  to  the 
other  until  the  sound  appears  to  be  the  loudest.  In  the  lower  animals 
this  is,  to  a  certain  extent,  facilitated  by  the  exceptional  degree  of  mobility 
possessed  by  the  auricle,  where  we  must  assume  that  the  recognition  of 
the  direction  of  a  sound  is  a  matter  of  greater  importance  and  accom- 
plished with  a  greater  degree  of  facility  and  perhaps  exactness. 

Having  reached  the  auricle,  sound-waves  enter  through  the  external 
auditory  canal  and  strike  against  the  tympanic  membrane.  It  has  been 
stated  that  if  a  tightly  stretched  membrane  be  set  into  vibration  it  will 
produce  a  sound,  the  lowest  note  being  termed  the  fundamental  tone; 
and,  further,  that  if  a  sound  which  corresponds  with  the  fundamental 
tone  of  such  a  membrane  be  sounded  in  its  proximity  the  membrane  will 
be  set  in  vibration  by  sympath}^.  It  is  evident,  if  such  a  fact  were  ap- 
plicable to  the  tympanic  membrane,  the  greatest  confusion  would  result 


SENSE   OF   HEARING.  887 

in  the  perception  of  sounds.  Sounds  which  coincide  with  the  funda- 
mental tone  of  the  tympanic  membrane  would  so  predominate  as  to 
drown  or  confuse  all  other  sounds.  The  tympanic  membrane,  however, 
is  free  from  this  disadvantage,  while  it  possesses  in  the  highest  degree 
the  power  of  being  set  in  motion  by  an  immense  range  of  vibrations. 
Thus,  sounds  may  be  recognized  that  are  dependent  upon  thirty-two 
vibrations  a  second  up  to  such  an  extremely  high  pitch  as  sounds  with 
thirty-eight  thousand  vibrations  a  second  will  produce.  This  property 
of  the  tympanic  membrane  by  which  it  appreciates  such  a  wide  range  of 
sounds,  while  being  free  from  any  fundamental  tone  itself,  is  due  to  two 
factors — in  the  first  place,  the  funnel-shaped  form  of  the  membrane,  and, 
in  the  second  place,  its  being  damped  by  the  chain  of  ear-ossicles.  If  a 
sheet  of  india-rubber  be  stretched  over  a  wide  tube  and  be  pressed  by  a 
rod  in  the  centre  perpendicularly  inward  it  will  form  a  funnel-shaped 
surface  curved  from  within  outward.  It  is  evident  that  in  such  a  mem- 
brane the  tension  will  vary  at  different  parts,  increasing  toward  the  cen- 
tre. Such  a  membrane,  like  the  tympanic  membrane,  will  have  no  funda- 
mental tone,  since  its  tension  is  not  equal,  while  the  tympanic  membrane 
will  also  have  in  principle  the  same  form,  since  it  radiates  from  the  cen- 
tre, within  outward,  in  a  convex  form.  The  tympanic  membrane,  there- 
fore, is  not  very  extensible,  but  its  tension  is  just  sufficient  to  draw  it 
slightly  inward  from  the  centre  without  it  being  able  to  produce  any 
audible  fundamental  tone. 

On  the  other  hand,  great  resistance  is  offered  to  the  vibrations  of  the 
tympanic  membrane  by  its  union  with  the  auditory  ossicles,  which  not 
only  deprive  the  membrane  of  every  trace  of  a  fundamental  tone,  so  that 
it  can  accommodate  itself  equally  well  to  vibrations  of  every  degree  of 
rapidit}r,  but  by  loading  the  membrane  entirely  prevent  the  occurrence 
of  after-vibrations ;  so  that,  therefore,  in  this  respect  the  ear-bones  act 
like  the  dampers  of  the  pianoforte,  which  fall  upon  the  wire  after  every 
note  has  been  struck. 

Another  point  is  worthy  of  attention  in  this  connection.  Since  the 
tympanic  membrane  possesses  the  shape  of  a  funnel,  the  point  of  greatest 
vibration  must  be  situated  somewhere  between  the  apex  and  the  edge,  but 
the  force  of  all  vibrations  passes  from  the  sides  toward  the  centre  and  at 
this  point  vibrations  of  the  greatest  intensity  are  produced.  Moreover,  the 
tension  of  the  tympanic  membrane  may  be  altered  by  muscular  action  in 
a  way  to  be  directly  described.  The  t3rmpanic  membrane  is  in  direct 
contact  with  the  chain  of  ear-bones,  and  this  serves  to  transfer  the  vibra- 
tions of  the  tympanic  membrane  to  the  perilymph  of  the  Iab3'rinth,  and, 
likewise,  by  their  points  of  attachment  to  different  muscles,  serve  to  vary 
the  tension  of  the  membrana  tympani  and  at  the  same  time  the  pressure 
on  the  lymph  of  the  labyrinth. 


888  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

The  ear-ossicles  form  a  jointed  chain  of  bones  connecting  the  mem- 
brane with  the  oval  window.  As  is  well  known,  solids  are  capable  of 
conducting  sound-waves  by  being  thrown  into  molecular  vibration,  and 
the  rapidity  of  such  conduction  is  greater  on  account  of  the  greater 
elasticity  and  density  than  in  the  atmosphere.  From  the  very  fact  of 
the  greater  rapidity  of  the  conduction  through  solids  the  wave  length 
will  be  longer,  but  the  conduction  of  sound  through  the  ear-ossicles  is 
entirely  distinct  from  such  molecular  vibrations.  In  the  transmission 
of  sound-waves  from  the  tympanic  membrane  to  the  labyrinth  the  chain 
of  bones  vibrates  as  a  whole.  The  average  wave  length  of  medium 
tones  in  the  ear  varies  from  one-half  to  one  meter,  while  in  solid  bodies 
it  is  still  greater.  The  ear-bones  are  by  no  means  immovably  fixed. 
From  their  small  mass  they  are  extremely  light,  so  that  an  impulse  acting 
on  one  end  will  set  the  whole  chain  of  bones  in  motion.  Consequently, 
when  waves  of  sound  strike  against  the  t}rmpanic  membrane  the  vibra- 
tions are  transmitted  directly  to  the  ear-bones,  and  the}'  vibrate  in  a 
transverse  direction  and  carry  the  vibrations  to  the  oval  window  by 
vibrating  in  mass  and  not  through  molecular  vibration. 

The  mode  of  movement  of  the  ear-ossicles  has  been  a  subject  of 
considerable  study.  As  is  known,  the  handle  of  the  malleus  is  attached 
to  the  tympanic  membrane  through  its  entire  length,  while  its  head  pro- 
jects above  the  edge  of  the  membrane  into  the  tympanic  cavity.  Besides 
this,  the  malleus  is  fixed  by  ligaments  in  such  a  way  that  motion  is  only 
possible  in  a  to-and-fro  vibration  around  the  so-called  axis  of  rotation, 
which  lies  in  a  plane  almost  parallel  to  the  tympanic  membrane  and  passes 
through  the  neck  of  the  malleus.  When  the  handle  of  the  malleus  is 
drawn  inward  its  head  will,  of  course,  move  in  the  opposite  direction,  and 
as  the  handle  of  the  hammer  is  set  in  vibration  the  anvil  will  also  be  set 
in  motion  through  its  articulation  with  the  head  of  the  hammer.  The 
incus  is  only  loosely  connected  by  a  ligament  passing  through  its  short 
process  to  the  posterior  wall  of  the  tympanic  cavity  in  front  of  the  open- 
ings of  the  mastoid  cells,  while  its  mode  of  articulation  with  the  malleus 
has  been  compared  by  Helmholtz  to  the  action  of  cog-wheels ;  so  that 
when  the  handle  of  the  malleus  moves  inward  to  the  tympanic  cavity  the 
incus  and  its  long  process,  which  is  parallel  with  the  handle  of  the  malleus, 
also  passes  inward,  from  the  fact  that  the  head  of  the  malleus  pulls  the 
articulating  surface  of  the  incus  outward.  Therefore,  the  handle  of  the 
malleus  and  the  long  process  of  the  incus  vibrate  in  the  same  direction. 
As  the  long  process  of  the  incus  moves  inward  it  gives  an  impression  to 
the  stirrup-bone,  with  which  it  articulates  almost  at  right  angles.  If, 
however,  as  by  a  great  condensation  of  air  in  the  tympanum,  the  tym- 
panic membrane  is  moved  outward  it,  of  course,  draws  the  handle  of  the 
malleus  with  it,  and,  as  a  consequence,  the  hammer-head  is  forced  inward, 


SENSE   OF   HEAKING. 


889 


and  the  tendency  would  be  to  drag  the  stapes  from  the  oval  window. 
This  is,  however,  prevented  by  the  loose  articulation  of  the  malleus  and 
incus,  which  separate  to  a  certain  extent  and  thus  prevent  dragging  on 
the  stapes  (Fig.  409). 

Hence,  the  system  of  ear-ossicles  forms  an  angular  lever,  which 
moves  around  a  common  axis  in  a  plane  vertical  to  the  plane  of  the 
membrana  tympani,  one  arm  of  the  lever  on  which  the  power  of  the 
vibrations  act  being  the  hammer-handle,  the  other,  the  hammer-head  with 


FIG.  409.— MOVEMENTS  OF  THE  MALLEUS  AND  INCUS.    (Beaunis.) 

M,  malleus ;  E,  incus ;  A,  short  process  of  the  incus ;  R,  long  process  of  the  incus ;  P,  handle  of  the 
malleus ;  A  B,  axis  of  movement  of  the  ossicles. 

the  handle,  serving  to  set  the  entire  fluid  of  the  labyrinth  into  vibration. 
The  vibrations  of  the  ear-ossicles  are,  therefore,  transverse,  although  not 
analogous  to  the  transverse  vibrations  occurring  in  a  stretched  cord, 
since  the  ear-ossicles  do  not  vibrate  on  account  of  their  elasticity,  but 
resemble  a  system  of  movable  levers.  As  the  long  process  of  the  incus 
is  only  one-third  the  length  of  the  handle  of  the  malleus,  of  course  the 
excursions  of  the  former,  and  with  it  the  stapes,  will  be  less  than  that  of 
the  tip  of  the  malleus,  while,  on  the  other  hand,  the  force  of  the  vibration 
in  the  former  will  be  increased ;  so  that  the  stapes  is  forced  inward  by 


890  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

a  more  powerful  but  less  extensive  vibration.  So  much  for  the  mode  of 
conduction  of  sound  through  the  ossicles. 

By  contraction  of  the  muscular  fibres  in  connection  with  the  ear- 
ossicles  the  position  and  tension  of  the  tympanic  membrane,  as  well  as 
the  pressure  on  the  lymph  of  the  labyrinth,  may  be  altered.  Two 
muscles  are  found  in  connection  with  the  ear-ossicles,  the  tensor  tympani 
and  the  stapedius  muscle.  The  tensor  tympani  lies  in  the  osseous 
groove  above  the  Eustachian  tube,  and  has  its  tendon  inserted  into  the 
malleus  immediate!}7  above  the  axis.  When  this  muscle  contracts  the 
handle  of  the  malleus  is  pulled  inward  and  the  tympanic  membrane 
tightened.  As  a  consequence,  the  stapes  is  likewise  pressed  inward. 
On  the  other  hand,  when  this  muscle  relaxes  the  elasticity  of  the  axial 
ligament  and  of  the  tympanic  membrane  itself  causes  the  membrane  to 
again  assume  its  condition  of  equilibrium.  By  the  increased  tension  of 
the  tympanic  membrane  a  greater  resistance  is  offered  to  the  sympathetic 
vibrations  when  the  sound-waves  are  very  intense,  since  it  has  been  found 
that  stretched  membranes  are  less  susceptible  to  sympathetic  vibrations 
than  are  relaxed  membranes  ;  and  increase  of  the  tension  of  the  t}^mpanic 
membrane  by  contraction  of  this  muscle,  therefore,  serves  to  protect  the 
auditory  apparatus  by  preventing  intense  vibrations  reaching  the  nerve 
terminations. 

The  stapedius  muscle  arises  within  the  pyramidal  eminence,  and  is 
inserted  into  the  head  of  the  stapes.  When  it  contracts  it  draws  upon 
the  head  of  the  stapes  and  causes  the  bone  to  assume  an  oblique  position, 
the  posterior  end  of  the  plate  being  pressed  deeply  inward  into  the 
fenestra  ovalis,  while  the  anterior  edge  of  the  plate  is  displaced  outward. 
The  stapes  is  thus  firmly  fixed  and  the  annular  ligament  surrounding 
the  fenestra  ovalis  becomes  more  tense.  The  function  of  this  muscle  is 
likewise  directed  to  preventing  the  communication  of  too  intense  an 
impulse  from  the  incus  to  the  stapes.  The  stapedius  muscle  is  supplied 
by  the  facial  nerve  and  the  tensor  tympani  by  a  branch  of  the  trigeminus 
which  passes  from  the  otic  ganglion. 

The  chain  of  bones  lies  within  the  tympanic  cavity,  and  it  is 
evident  that  the  vibration  of  the  tympanic  membrane  will  greatly  vary 
according  as  the  air  in  the  tympanic  cavity  is  in  a  greater  or  less  degree 
of  condensation.  If  this  space  were  entirely  shut  off  from  the  atmos- 
phere the  air  in  it  would  evidently  soon  be  absorbed,  or,  at  any  rate, 
undergo  change  in  its  composition,  and  probably  be  replaced  by  fluid 
secretions,  since  we  know  that  the  middle  ear  is  lined  by  a  secreting 
mucous  membrane.  By  means  of  the  Eustachian  tube  the  ventilation 
of  the  middle  ear  is  rendered  possible.  Through  it  secretions  are  con- 
ducted out,  and  by  it  the  equilibrium  of  pressure  between  the  air  in  the 
tympanum  and  the  atmosphere  is  rendered  possible.  As  soon  as  the 


SENSE   OF   HEARING.  891 

pressure  of  the  atmosphere  is  greater  than  that  within  the  tympanum 
the  membrane  of  the  tympanum  would  be  pressed  inward.  On  the 
other  hand,  if  the  pressure  within  the  tympanum  be  greater  than  that  of 
the  atmosphere  the  membrane  would  be  pressed  outward,  and  in  both 
cases  the  movements  of  the  tympanic  membrane  would  be  restricted  and 
sound  to  such  an  extent  interfered  with.  The  equilibrium  is  maintained 
through  the  opening  of  the  Eustachian  tube  in  the  act  of  swallowing, — 
an  act  which  is  performed  not  only  during  eating,  but  also  at  frequent 
intervals  to  carry  away  the  secreted  saliva,  At  other  times  the  Eusta- 
chian tube  is  closed,  and  by  this  means  the  conduction  of  sound-waves 
downward  into  the  pharynx  or  the  conduction  upward  of  sound-waves 
from  the  voice  is  rendered  impossible. 

The  sound-waves  are  thus  conducted  from  the  tympanic  membrane 
to  the  chain  of  ossicles,  and  thence  by  the  vibration  of  the  stapes  to  the 
oval  window.  The  membrane  of  the  fenestra  ovalis  is,  as  a  consequence, 
set  into  transverse  vibration,  and  these  vibrations  are  directly  communi- 
cated to  the  fluid  of  the  labyrinth.  The  lymph,  like  other  fluids,  is  incom- 
pressible, and  if,  therefore,  the  membrane  of  the  oval  window  be  pressed 
inward  there  must  be  a  corresponding  exit  at  some  other  point  of  the 
apparatus.  This  counter-opening  is  found  in  the  round  window,  and  as 
soon,  therefore,  as  the  stapes  vibrates  inward  the  membrane  of  the  circu- 
lar window  vibrates  outward,  and  the  pressure  upon  the  fluid  of.  the 
labyrinth  is  thus  relieved  while  being  set  into  vibrations  corresponding 
with  those  of  the  stapes. 

From  the  oval  window  the  wave  travels  into  the  vestibule  and  from 
there  into  the  cochlea,  and  we  must  assume  that  it  there  throws  the 
membranous  apparatus  with  its  organ  of  Corti  into  vibration.  The  ves- 
tibule is,  however,  divided  by  the  two  membranous  sacs  which  it  contains 
into  two  portions,  each  containing  fluid,  the  one  in  connection  with  the 
oval  window  and  the  other  with  the  round  window ;  so  that,  therefore, 
we  cannot  imagine  that  the  fluid  in  the  vestibule  is  directly  driven  by 
the  vibrations  of  the  stirrup-bone  to  the  round  window,  for  the  scala 
vestibuli  of  the  cochlea,  which  is  in  connection  with  the  oval  window, 
is  shut  off  from  the  scala  tympani  by  the  membrane,  and  ai^  wave,  there- 
fore, started  by  the  vibrations  of  the  stapes  will  pass  rapidly  up  the 
scala  vestibuli,  while  it  will  also  transfer  its  vibrations  to  the  membran- 
ous partition  and  thus  throw  the  fluid  of  the  scala  tympani  likewise  into 
vibration. 

In  the  cochlea  the  vibrations  of  the  peritymph  throw  into  vibration 
the  fibres  of  the  basilar  membrane  and  the  organ  of  Corti,  consisting  of 
the  rods  and  the  inner  and  outer  hair-cells,  which  may  be  regarded  as  a 
series  of  stretched  strings,  a  portion  of  which  may  be  thrown  into  sym- 
pathetic vibration  independently  of  the  whole. 


892  PHYSIOLOGY   OF   THE   DOMESTIC  ANIMALS. 

The  vibrations  communicated  to  these  structures  in  some  way  give 
rise  to  nervous  impulses  passing  into  the  terminal  filaments  of  the 
auditory  nerve.  As  to  the  way  in  which  this  is  accomplished  but  little 
is  known.  The  temptation  is  strong  to  find  the  receiving  apparatus 
in  the  organ  of  Corti,  which  is  composed  of  a  long  series  of  rods 
varying  regularly  in  length  and  in  the  span  of  their  arches.  The 
analogy  between  these  structures  and,  for  example,  the  strings  of  the 
piano  is  very  striking.  As  is  well  known,  a  musical  tone  sounded 
in  front  of  an  open  piano  will  set  into  vibration  the  corresponding 
string  of  this  instrument.  The  temptation  is  almost  irresistible  to 
suppose  that  a  similar  mechanism  is  concerned  in  the  perception  of 
different  sounds.  If  we  could  imagine  that  certain  definite  parts 
of  the  organ  of  Corti  were  thrown  into  vibration  only  by  appropri- 
ate sounds  the  complex  process  of  the  perception  of  different  musical 
intervals  would  be  greatly  simplified,  but  the  more  the  subject  is 
examined  into  the  greater  are  the  difficulties  surrounding  such  an 
explanation. 

In  the  first  place,  the  terminal  filaments  of  the  auditory  nerve  have 
been  traced  to  the  inner  and  outer  hair  cells,  and  it  must,  therefore,  be  in 
this  locality  and  not  in  the  rods  of  Corti  that  the  sensory  impulses 
commence. 

.  In  the  second  place,  the  rods  of  Corti  are  entirely  absent  in  birds, 
who,  without  doubt,  are  capable  of  appreciating  musical  sounds;  while, 
again,  the  variation  in  length  of  the  rods  of  Corti  would  be  insufficient  to 
explain  the  great  scope  which  the  ear  possesses  in  the  recognition  of  the 
pitch  of  sounds. 

On  the  other  hand,  the  basilar  membrane  is  tense  in  a  radial 
direction  and  loose  longitudinally,  and,  therefore,  as  Helmholtz  has 
suggested,  may  be  compared  to  a  series  of  strings  of  varying  tension 
and  length. 

If  this  basilar  membrane  be  looked  upon  as  the  receptive  organ  we 
must  then  assume  that  each  vibration  travels  up  the  scala  tympani, 
throws  into  sympathetic  vibration  a  small  part  of  the  basilar  membrane, 
which  transfers  the  vibration  to  the  sensory  structures  above  it. 

In  support  of  this  view  it  may  be  mentioned  that  the  radial  dimen- 
sions of  the  basilar  membrane  offer  a  wider  field  of  difference  than 
we  find  in  the  length  of  Corti's  rods.  The  whole  subject  is,  however,  in 
the  highest  degree  obscure,  and  all  that  we  can  say  is  that  the  organ  of 
Corti,  composed  of  the  basilar  membrane,  the  rods,  and  hair-cells,  is  in 
some  way  concerned  in  the  reception  of  sound-waves;  the  manner  is, 
however,  entirely  unknown.  After  all,  it  must  not  be  forgotten  that  the 
perception  of  sound  takes  place  not  in  the  ear  but  in  the  brain,  and  that 
sound-waves,  received  in  whatever  way  by  the  terminal  filaments  of  the 


SENSE  OF  TASTE.  893 

auditory  nerve,  must  be  conducted  to  the  brain  to  be  recognized  as 
sounds,  and  that  the  analysis  of  sounds  take  place  not  in  the  ear, 
although,  perhaps,  we  may  have  there  a  special  organ  set  aside  for  the 
observation  of  certain  sounds,  but  in  the  brain. 

D.  THE   SENSE  OF  TASTE. 

The  sense  of  taste  is  generally  described  as  the  facultj^  by  which 
the  flavors  of  different  sapid  substances  is  distinguished.  It  will  be 
shown  direct^  that  the  sense  of  taste  is  much  more  limited  than  this,  as 
many  substances  which  are  said  to  be  appreciated  through  the  sense  of 
taste  are  only  effective  through  exciting  the  sense  of  smell.  The  sense 
of  taste  even  in  this  restricted  sense  is  more  highly  developed  in  man 
than  in  other  animals,  for  it  is  not  the  sense  of  taste  but  the  sense  of 
smell  which  guides  animals  in  their  choice  of  food,  for  that  choice 
precedes  the  prehension  of  food. 

Even  in  man  and  the  higher  mammals  there  is  a  considerable 
difference  of  opinion  as  to  what  regions  of  the  mouth  are  endowed  with 
the  sense  of  taste,  and  this  difficulty  of  location  becomes  even  more 
marked  as  we  descend  the  animal  series.  In  animals  where  a  tongue  is 
present  it  is  probable  that  that  organ  partakes,  with  the  upper  part  of 
the  digestive  tract,  in  the  property  of  presiding  over  the  sensation  of 
taste,  but  in  many  animals  the  tongue  is  absent  or  is  so  horny  as  to  pre- 
clude this  possibility.  In  invertebrates,  where  no  analogue  of  a  tongue 
exists,  if  the  sense  of  taste  is  present,  as  it  would  seem  without  doubt 
to  be,  as  in  insects,  its  seat  must  be  in  the  parts  about  the  mouth,  such 
as  the  proboscis,  suckers,  etc.  In  fishes  the  tongue  is  rudimentary  and 
in  many  it  is  covered  with  horny  scales  or  even  rudimentary  teeth,  and  if 
the  sense  of  taste  is  present  in  this  group  of  animals  it  is  either 
confined  to  the  upper  part  of  the  digestive  passages  or  perhaps  to  the 
olfactory  cavities. 

In  reptiles  a  thick,  fleshy  tongue  is  often  present,  but  it  is  more  fre- 
quently slender,  sometimes  bifid  and  protractile,  and  is  to  be  regarded, 
as  already  indicated,  as  an  organ  for  the  prehension  of  food. 

In  birds  the  sense  of  taste  must  be  very  obtuse,  since  they  swallow 
their  food  without  comminution,  and  the  tongue  is  usually  hard  or  semi- 
cartilaginous,  especially  at  the  point.  This  particularly  obtains  in  her- 
bivorous birds,  while  in  birds  of  prey,  where  the  tongue  is  fleshy,  it  may 
perhaps  be  supposed  that  the  sense  of  taste  is  present. 

In  mammals  the  sense  of  taste  may,  to  a  certain  extent,  be  definitely 
localized  in  the  tongue,  and  special  sense  organs  have  been  detected 
which  apparently  preside  over  this  function.  The  so-called  taste  bulbs 
are  found  on  the  lateral  surface  of  the  circumvallate  papillae  and  upon 
the  external  side  of  the  depression  which  surrounds  the  central  eminence 


894 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


(Fig.  410).  They  are  also  found  to  a  less  extent  on  the  fungiform  papillae, 
the  papillae  of  the  soft  palate  and  uvula,  and  even  on  the  posterior  surface 
of  the  epiglottis  and  on  the  inner  side  of  the  arytenoid  cartilages,  and  on 
the  vocal  cords.  These  latter  localities  would  seem  to  throw  doubt  upon 
the  connection  between  these  structures  and  their  connection  with  the 
sense  of  taste,  but  the  fact  that  after  section  of  the  glosso-pharyngeal 
nerve  these  taste  bulbs  degenerate,  and  that  direct  communication  can 
be  traced  between  this  nerve  and  these  cells,  would  seem  to  place  their 
position  as  the  terminal  organs  of  the  special  nerve  of  taste  beyond  doubt. 
These  taste  bulbs  are  barrel-shaped  and  consist  of  series  of  nucleated 
external,  almost  cylindrical  protecting  cells,  arranged  so  as  to  leave  an 
opening, — the  so-called  gustatory  pore.  Lying  in  the  axis  of  such  a 
structure  are  found  from  one  to  ten  gustatory  cells,  some  provided  with 


FIG.  410.— STRUCTURE  OF  THE  GUSTATORY  ORGANS.    (Landois.) 

I.  Transverse  section  of  a  circumvallate  papilla:  W,  the  papilla;  v,  v,  the  wall  in  section;  R,  R,  the 
circular  slit  of  fossa;  K,  K,  the  taste  bulbs  in  position:  N,  N,  the  nerves.  II.  Isolated  taste  bulbs:  D. 
supporting  or  protective  cells ;  K,  under  end ;  E,  free  end,  open,  with  the  projecting  apices  of  the  taste 
cells.  III.  Isolated  protective  cell,  d,  with  a  taste  cell,  e. 

delicate  processes  at  their  free  extremities,  while  their  lower,  fixed  ends 
become  continuous  with  the  non-medullated  terminations  of  the  nerve  of 
taste  (Figs.  411,  412,  and  413). 

The  tongue  of  mammals  in  its  general  characteristics  resembles  that 
of  man,  and  similar  papillae  are  found  on  it.  In  the  different  domestic 
animals,  especially  in  the  herbivora,  the  sense  of  taste  must  differ  from 
that  in  the  carnivora,  although  we  have  every  da}'  evidences  of  its  exist- 
ence, and  we  know  that  in  the  herbivora  likewise  decided  preference  for 
different  substances  are  manifest,  which  evidently  must  be  dependent  upon 
differing  degrees  of  excitation  of  the  sense  of  taste,  although  the  expla- 
nation of  that  fact  is  yet  entirely  beyond  us.  Thus,  as  to  why  a  horse 
should  prefer  oats  to  hay,  or  the  latter  to  straw,  must  evidently  be  ex- 
plained by  some  difference  in  impression  of  the  substances  on  the  nerve 
of  taste  and  not  a  mere  matter  of  instinct. 


SENSE   OF   TASTE. 


895 


Only  four  different  varieties  of  taste  can  be  distinguished.  Sub- 
stances may  be  either  bitter,  sweet,  acid,  or  saline.  Substances  to 
which  we  attribute  the  property  of  flavor  owe  that  characteristic  more 
to  their  implication  of  the  sense  of  smell  than  of  taste.  Thus,  we  speak 
of  tasting  wines,  onions,  asafeticla,  and  so  on,  while,  as  is  well  known, 
their  flavor  is  due  to  the  excitement  of  the  sense  of  smell,  and  not  to  a 
specific  stimulation  of  the  nerve  of  taste  ;  this  may  be  readily  proven  by 
the  disappearance  of  their  characteristic  flavors  when  smell,  by  closure 
of  the  nostrils  or  by  catarrh,  is  rendered  impossible. 

That  substances  may  be  tasted  it  is  necessary,  in  the  first  place, 


FIG.  411.— STRUCTURE  OF  THE  GUSTATORY  ORGANS.    (Munk.) 

A,  perpendicular  section  through  the  taste  organs  of  a  rabbit's  tongue;  g,  taste  furrows.    B,  isolated 
protective  (a)  and  (b  c)  taste  cells. 

that  they  should  be  dissolved  in  the  fluids  of  the  mouth,  while  the 
intensity  of  the  sensation  will  depend  upon  the  size  of  the  surface  acted 
upon  and  upon  the  concentration  of  the  solution.  It  has  been  found 
that  the  following  series  of  substances  cease  to  be  distinguished  in  the 
order  here  stated,  as  the}'  are  gradually  diluted  :  syrup,  sugar,  common 
salt,  aloes,  quinine,  and  sulphuric  acid.  Thus,  quinine  may  be  diluted 
twenty  times  more  than  salt  and  still  be  distinguished. 

The  time  elapsing  between  the  contact  of  the  substance  with  the 
tongue  and  its  appreciation  by  the  taste  also  varies  with  different 
substances.  Saline  substances  are  tasted  most  rapidly,  perhaps,  from 
their  more  rapid  diffusion. 


896  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

The  galvanic  current  is  likewise  capable  of  producing  the  sensation 
of  taste,  which  varies  according  to  the  direction  of  the  current.  Thus, 
a  bitter  metallic  taste  is  developed  when  the  anode,  and  an  acid  taste 
when  the  cathode,  is  placed  on  the  tongue.  In  this  instance  it  is 
doubtful  whether  the  sensation  of  taste  is  due  to  a  direct  stimulation  of 
the  taste  bulbs  or  to  electrolytic  changes  occurring  through  the  action 
of  the  galvanic  current. 

All  the  localities  in  which  the  taste  bulbs  have  been  detected  are 
probably  possessed  of  the  sense  of  taste,  although  certain  regions,  as 
the  entrance  to  the  larynx  and  the  hard  palate,  do  not  admit  of  experi- 
mental demonstration  as  regards  this  point.  Without  doubt  the  root  of 
the  tongue  and  its  tip  and  margins  are  gustatory,  while  it  is  probable 
that  the  under  surface  of  the  tongue  possesses  no  power  of  taste. 

The  nerves  which  preside  over  the  sense  of  taste  are  certain  fibres 
of  the  lingual  and  the  glosso-pharyngeal.  After  the  lingual  nerve  is 
divided  the  sense  of  taste  disappears  from  the  tip  of  the  tongue.  When 
the  glosso-pharyngeal  is  divided  the  sense  of  taste  is  lost  in  the  posterior 


FIG.  412.— TASTE  FURROW  IN  MAYER'S     FIG.  413.— SECTION  or  MAYER'S  ORGAN  IN  THE 
ORGAN  IN  THE  HOG.    (Csokor.)  HORSE.    (Csokor.) 

part  of  the  dorsum  of  the  tongue.  Contrary  to  our  experience  with  the 
other  nerves  of  special  sense,  stimulation  of  the  trunks  of  these  nerves 
does  not  give  rise  to  the  sense  of  taste,  probably  owing  to  the  fact  that 
both  of  these  nerves  are  mixed  nerves,  and  contain  other  afferent  fibres 
as  well  as  those  of  the  sense  of  taste. 

Certain  substances  seem  to  possess  the  power  of  antagonizing  the 
impressions  which  others  ordinarily  make  on  the  terminal  filaments  of 
the  nerves  of  taste ;  thus  the  taste  of  bitter  and  sour  substances  may  to 
a  certain  extent  be  corrected  by  the  admixture  of  sugar,  even  without 
any  chemical  change  occurring  in  the  mixture.  Such  a  result  is  only  to 
be  explained  as  some  kind  of  interference  of  the  sensations;  on  the  other 
hand,  substances  having  a  sweet  taste  do  not  possess  the  power  of  modi- 
fying saline  tastes. 

Any  explanation  as  to  why  certain  substances  possess  one  peculiar 
taste  and  others  another  is  in  our  present  state  of  knowledge  impossible, 
with  the  single  exception  of  the  characteristic  taste  of  acids  and  alkalies, 
where  we  find  the  characteristic  taste  associated  with  certain  definite 
chemical  characteristics. 


SENSE  OF  TOUCH.  897 

The  acuteness  of  the  sense  of  taste  admits  of  education,  but  is  by  no 
means  as  delicate  as  the  sense  of  smell ;  thus,  a  solution  of  one  part  of 
sulphuric  acid  to  one  thousand  of  water  gives  its  characteristic  taste 
when  only  one  drop,  which  may  be  said  to  contain  about  s^oo  Par^  °f  a 
gramme,  is  placed  upon  the  tongue. 

E.    THE  SENSE  OF  TOUCH. 

When  any  portion  of  the  external  integument  is  brought  in  contact 
with  a  foreign  body  we  appreciate  what  is  termed  the  sensation  of  touch, 
and  we  are,  therefore,  warranted  in  regarding  the  skin  as  a  sensory  organ, 
inclosing  our  entire  body  and  adapted  to  render  everjT  part  of  the  body 
sensible  to  external  impressions.  These  may  be  of  the  most  manifold 
kind,  and  excite  peculiar  sensations  dependent  upon  the  nature  of  the 
contact.  To  a  limited  extent  this  power  of  tactile  sensibility  possessed 
by  the  integument  belongs  likewise  to  the  internal  mucous  surfaces  of 
the  body,  but  only  for  a  short  distance  from  their  respective  orifices. 

Tactile  sensations,  as  we  shall  find  directl}T,  vary  among  themselves, 
and  give  us  means  of  determining  the  physical  characters  of  the  body 
producing  the  contact  and  the  locality  at  which  the  contact  takes 
place.  When  such  a  tactile  sensation  is  increased  in  intensity  it  may  be 
converted  into  a  painful  sensation.  If,  for  example,  as  in  the  illustra- 
tion given  b}T  Weber,  the  edge  of  a  knife  is  placed  on  the  skin  we  feel 
the  edge  by  means  of  the  sense  of  touch,  a  sensation  is  perceived  which 
is  referred  to  the  object  which  has  caused  it.  If,  however,  the  skin  is 
cut  by  the  knife  pain  is  felt,  a  feeling  which  is  no  longer  referred  to  the 
cutting  knife,  but  which  we  feel  within  ourselves,  and  which  indicates  to 
us  the  fact  of  a  change  of  condition  in  our  own  body.  By  the  sensation 
of  pain  we  are  neither  able  to  recognize  the  object  which  causes  it  nor  its 
nature.  Thus,  if  a  body  is  placed  within  the  month  we  are  able  to 
recognize  its  general  characters  and  to  a  certain  extent  its  shape, 
whether  it  be  solid  or  liquid,  hot  or  cold;  but  if  the  body  be  swallowed 
tactile  sensation  disappears  as  soon  as  the  body  reaches  the  oesophagus, 
and  then,  if  any  sensation  be  excited,  it  can  only  be  a  painful  sensation. 
The  sensation  caused  by  a  too  hot  liquid  cannot  be  distinguished  from  a 
corroding  acid  liquid,  or  from  the  passage  of  an  irregular  hard  body 
through  the  oesophagus. 

The  sense  of  touch  is  the  simplest  and  is  the  only  universal  sense, 
and  exists  in  all  members  of  the  animal  kingdom.  In  the  articulata, 
whether  covered  by  horny  (insects)  or  by  calcareous  (crustaceans)  cover- 
ings, the  sensation  of  touch  is  possessed  by  all  parts  of  the  body  in 
common,  while  it  is  especially  developed  in  the  antennae  which  project 
from  the  sides  of  the  head. 

In  mollusks  and  zoophytes  sensibility  is  much  more  obtuse,  but  is 

57 


898  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

likewise  distributed  over  the  entire  surface  of  the  body,  and  here,  also,  is 
perhaps  more  highly  developed  in  the  tentacles  or  pseudopods  which  are 
so  often  found. 

In  fishes  projecting  organs  at  the  side  of  the  buccal  opening  receive 
terminations  of  afferent  nerves,  and  these,  together  with  the  fins,  may  be 
regarded  as  especially  developed  tactile  organs,  although  here,  also,  the 
entire  body  surface  possesses  general  sensibility. 

In  reptiles  no  special  tactile  organ  is  present,  unless  the  tongue,  in 
certain  instances,  may  fulfill  this  function. 

In  birds  the  tactile  sensibility  of  the  skin  must  be  to  a  certain  ex- 
tent interfered  with  by  the  thick  coating  of  feathers  and  the  sensibility 
of  the  feet  by  the  dense  scales  which  usually  cover  these  parts.  In  birds 
in  general  it  is  the  beak  which  possesses  tactile  sensibility  in  the  highest 
degree. 

In  mammals  the  greatest  variation  exists  in  the  specialization  of 
certain  parts  of  the  body  for  the  appreciation  of  tactile  sensations.  In 
monkeys,  although  four  hands  may  be  said  to  be  present,  they  are  not  to 
be  regarded  as  sensitive  organs  as  are  the  hands  of  man;  since,  in  the 
first  place,  their  fingers  do  not  possess  the  power  of  separate  movement 
and  their  thumb  is  much  shorter  and  incapable  of  being  brought  into 
apposition  with  the  fingers ;  while  the  palm  of  the  hand,  which  frequently 
serves  as  a  means  of  progression,  is  covered  with  calloused  epithelium. 
In  certain  monkeys  with  prehensile  tails  this  organ  is  doubtless  possessed 
of  tactile  power  in  the  highest  degree. 

In  solipedes,  ruminants,  and  carnivora,  in  whom  the  extremities  of 
the  limbs  terminate  in  a  single  or  double  hoof,  in  claws,  or  calloused 
skin,  in  these  localities  the  sense  of  touch  must  be  very  imperfect.  But 
these  parts  of  the  animal  body  must  be  capable,  nevertheless,  of  giving 
distinct  notions  as  regards  resistance,  solidity,  and  consistence,  since 
these  horny  parts  rest  on  a  highly  developed  papilkuy  layer  of  the  derm. 
In  solipedes  and  ruminants,  especially  in  the  former,  the  lips  possess  a 
considerable  degree  of  mobility,  and  are,  as  has  been  shown,  the  princi- 
pal organs  of  prehension  and  are  highly  endowed  with  tactile  sensibility. 
In  carnivora  the  termination  of  the  soft  parts  about  the  anterior  nares  is 
extremely  sensitive  and  is  employed  by  them  as  a  tactile  organ,  while  it 
is  only  a  step  farther  to  the  hog  or  the  elephant,  where  the  prolongation 
of  this  part  of  the  body  acquires  extreme  perfection  as  an  organ  of 
tactile  sensibility.  In  certain  animals  the  long  hairs  growing  from  the 
upper  lip,  as  in  the  cat  and  the  rat  and  the  seal,  are  to  be  regarded  as 
tactile  organs,  since  they  conduct  tactile  impressions  to  the  sensory 
nerves.  Probably,  also,  the  spines  of  the  porcupine  fulfill  the  same 
function. 

Like  the  more  specific  sensations,  the  sensations  of  touch  require  for 


SENSE   OF   TOUCH.  899 

their  production  terminal  organs  which  are  found  in  the  epidermis  of  the 
skin  and  surrounding  the  underlying  nerve  structures.  The  manner  in 
which  the  terminal  filaments  of  the  sensory  nerves  are  distributed  to 
the  skin  varies. 

Five  general  different  modes  of  distribution  have  been  recognized. 
The  touch  corpuscles  of  Wagner  and  Meissner  lie  in  the  papillae  of  the 
true  skin  and  are  most  numerous  in  the  palm  of  the  hand  and  the  sole 
of  the  foot,  and  especially  on  the  fingers  and  toes.  They  are  oval 
or  elliptical  bodies  covered  by  layers  of  connective  tissue  arranged 
transversely  and  containing  within  a  granular  mass  with  longitudinally 
striped  nuclei.  Each  of  these  corpuscles  is  surrounded  in  a  special 
manner  b}^  a  medullated  nerve-fibre  which  loses  its  nryelin  and  divides 
into  a  number  of  fibrils  within  the  corpuscle. 

Pacini's  corpuscles  are  oval  bodies  likewise  found  in  the  subcu- 
taneous tissue  of  the  skin  of  the  fingers  and  toes  and  of  various  other 
localities.  They  consist  of  numerous  layers  of  nucleated  connective 
tissue  separated  from  each  other  by  fluid  and  lying  one  within  the  other, 
like  the  coats  of  an  onion.  Into  the  axis  of  each  passes  a  medullated 
nerve-fibre  whose  sheath  of  Schwann  becomes  united  with  the  capsule. 
In  the  interior  or  central  core  of  the  corpuscle  each  nerve-fibril 
terminates  in  a  small,  hair-shaped  enlargement. 

Grouse's  corpuscles  are  elongated  or  rounded  bodies  found  in  the 
deeper  layers  of  the  conjunctiva,  the  floor  of  the  mouth,  and  various 
other  mucous  surfaces.  The  sheath  of  Henle  communicates  with  the 
nucleated  capsule,  while  the  non-medullated  fibre  is  continued  into  the 
internal  core. 

Merckel's  tactile  corpuscles  occur  in  the  beak  and  tongue  of  the 
duck  and  goose,  in  the  tactile  hairs  or  feelers,  and  also  in  the  epidermis 
of  man  and  other  mammals.  They  are  composed  of  a  capsule 
containing  two  or  three  or  more  granular  nucleated  cells  piled  one 
on  another  in  a  vertical  row.  Each  corpuscle  receives  at  one  side 
a  medullated  nerve-fibre  which  terminates  either  in  the  cells  themselves 
or  in  the  transparent  protoplasmic  substance  between  the  cells.  In 
addition  to  these  special  terminal  organs  of  the  afferent  nerves  in 
many  localities  their  axis  cylinder  splits  up  into  fibrils  to  form  a 
nervous  net-work  which  is  to  be  regarded  as  an  organ  of  sensation. 

Nerve-trunks  are  supposed  to  contain  fibres  which  are  especially 
concerned  in  conducting  painful  impressions  and  tactile  impressions. 
Sensations  of  temperature  fall  under  the  second  head.  As  already 
indicated,  the  -first  of  these  modes  of  sensation  may  be  converted  into 
the  second. 

Thus,  when  a  body  is  brought  in  contact  with  the  skin  we  may  form 
a  conception  of  the  weight  of  the  bod}" — that  is,  the  amount  of  pressure 


900 


PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 


which  it  exerts  upon  the  skin — and  to  a  certain  extent  its  temperature. 
If  the  degree  of  pressure  be  greatly  increased,  the  sensation  of  pressure 
gives  place  to  one  of  pain,  and  so,  also,  for  extremely  hot  or  extremely 
cold  bodies.  On  the  other  hand,  impressions  which  are  not  localized  on 
the  terminal  organs,  as,  for  example,  the  passage  of  the  electric  current 
through  the  skin,  are  not  capable  of  being  regarded  as  tactile  sensations. 
In  other  words,  we  are  unable  to  distinguish  one  such  mode  of  stimula- 
tion, except  within  narrow  limits,  from  another.  Thus,  for  example,  the 
sensation  of  mechanically  pricking  the  skin  is  probably  identical  with 
that  produced  by  the  passage  of  the  current.  Again,  the  contact  of  a  fluid 
with  the  skin  will  cause  a  tactile  sensation,  since  it  is  in  contact  with  the 
nerve  terminations,  and  if  that  fluid  be  an  acid  and  pass  below  the  terminal 
organs  and  implicate  the  nerve-fibres  a  sensation  of  pain  will  be  caused ; 
so  that  stimulus  which  when  applied  only  to  the  nerve  terminations  may 
cause  a  tactile  impression,  when  applied  to  the  nerve-trunk  results  in  a 
painful  sensation. 

The  intensity  of  the  sensation  produced  by  pressure  depends  almost 
as  much  upon  the  rapidity  of  the  application  of  the  pressure  as  upon  the 
degree  of  the  pressure.  If  the  increase  be  gradual,  more  pressure  may 
be  applied  with  scarcely  a  perceptible  sensation  ;  while,  on  the  other 
hand,  the  rapid  application  of  a  less  pressure  may  cause  a  much  more 
intense  sensation.  All  parts  of  the  skin  are  not  equally  susceptible  to 
pressure  for  the  simple  reason  that  all  parts  are  not  equally  supplied 
with  tactile  corpuscles.  In  man  the  most  sensitive  localities  are  on  the 
palmar  surface  of  the  fingers,  on  the  forehead,  and  on  the  flexor  surfaces 
of  the  limbs  as  contrasted  with  the  extensor  surfaces. 

If  two  points  of  the  skin  are  subjected  to  pressure  the  sensation 
becomes  fused  when  the  two  points  are  sufficiently  close.  When  an  im- 
pression is  made  upon  any  part  of  the  body,  not  only  the  character  but 
the  locality  are  appreciated.  This  power,  however,  of  localizing  pressure 
sensations  varies  in  different  localities. 

The  following  table  from  Weber  gives  the  minimum  distances  at 
which  simultaneous  stimulation  of  two  points  may  be  recognized  as  two 
distinct  sensations : — 

Tip  of  tongue,       .... 

Palm  of  last  phalanx  of  finger,    . 

Palm  of  second  phalanx  of  finger, 

Tip  of  nose,  . 

White  part  of  lips, 

Back  of  second  phalanx  of  finger, 

Skin  over  malar  bone, 

Back  of  hand, 

Forearm, 

Sternum, 

Back,     . 


1.1  millimeter. 

22 

4.4 

6.6 

8.8 

11.1 

15.4 

29.8 

39.6 

44. 
66. 

BOOK   III. 


THE  REPRODUCTIVE  FUNCTIONS. 


(901) 


SECTION    I. 

THE  REPRODUCTIVE  PROCESSES. 

ALL  of  the  functions  of  the  animal  body  economy  which  have  as  yet 
been  considered  have  dealt  solely  with  the  preservation  of  the  individual. 
Through  the  exercise  of  the  reproductive  function  is  accomplished  the 
preservation  of  the  species.  The  duration  of  the  life  of  any  single 
animal  is  a  limited  one,  and  if,  therefore,  each  species  did  not  possess 
the  power  of  reproducing  itself  in  a  new  and  similar  individual  the 
species  would  eventually  die  out. 

The  mechanism  by  which  reproduction  is  accomplished  greatty 
differs  in  different  groups  of  the  animal  kingdom.  In  all  vertebrates  it 
is  accomplished  by  the  union  of  two  individuals  of  opposite  sexes,  male 
and  female.  In  a  large  number  of  the  invertebrate  animals  the  two 
sexes,  or  at  least  the  two  sexual  organs,  are  found  united  in  the  same 
individual,  and  the  different  acts  of  generation  are  thus  accomplished  in 
the  body  of  the  same  animal;  while  the  mode  of  reproduction  offers 
a  strong  analogy  to  that  of  the  vegetables,  which,  likewise,  contain 
within  the  same  floral  envelope  the  organs  of  the  two  sexes.  In  other 
animals  still  more  imperfect  a  mode  of  generation  may  be  observed 
which  is  analogous  to  that  of  cryptogamous  plants.  Here  no  organs  of 
generation  can  be  detected,  and  reproduction  is  accomplished  by  sep- 
aration of  parts  of  the  parent  body  which  possess  the  power  of 
development  and  growth.  Sometimes  the  germ  detaches  itself  from 
the  individual  in  the  form  of  a  vesicle,  which  passes  through  all  the 
phases  of  development.  Such  a  mode  of  reproduction  is  spoken  of  as 
generation  by  spores.  At  other  times  a  bud  may  be  noticed  to  form 
from  within  or  without  the  animal,  which,  after  having  acquired  a  more 
or  less  complete  development,  separates  itself  from  the  parent,  and  after 
the  separation  continues  to  grow  and  develop  into  a  new  animal.  Such 
a  mode  of  reproduction  is  spoken  of  as  gemmiparous  generation. 
Finally,  the  new  organism  may  develop  from  the  parent  organism  by  a 
simple  process  of  detachment  of  a  part  of  the  parent,  after  the  separa- 
tion the  detached  portion  forming  a  new  animal,  while  the  parent 
replaces  the  part  which  was  lost.  Such  a  mode  of  reproduction  is 
spoken  of  as  generation  by  fission. 

In  all  animals  provided  with  organs  of  generation,  whether  borne 
by  different  individuals  or  united  in  the  same  individual,  generation  is 

(903) 


904  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

invariably  accomplished  by  the  formation  of  an  egg  by  the  female  and 
of  a  fecundating  liquid  by  the  male,  which,  coming  in  contact  with  the 
egg  developed  by  the  female  organism,  gives  to  the  latter  its  power  of 
independent  growth  and  development.  Sometimes  the  fluid  formed  by 
the  male  conies  in  contact  with  the  egg  of  the  female  after  it  has  passed 
from  the  body  of  the  female,  as  is  the  case  in  fishes,  while  at  other 
times  the  male  fecundates  the  egg  before  its  exit  and  while  it  is  still 
within  the  body  of  the  female,  where  it  undergoes  a  certain  part  of  its 
developmental  changes,  as  in  the  bird.  Finally,  the  egg  fecundated  by 
the  male  may  be  retained  within  the  cavity  of  the  female  until  it  has 
undergone  the  first  phases  of  its  development. 

Although  numerous  differences  may  be  met  with  in  different  mem- 
bers of  the  animal  kingdom,  these  fundamental  facts  are  always  observed  : 
on  the  one  side  the  production  of  an  egg,  and  on  the  other  the  production 
of  a  fecundating  fluid. 

In  all  the  vertebrates,  whether  mammals,  birds,  reptiles,  or  fishes, 
generation  is  accomplished  by  the  union  of  the  two  sexes,  the  sexual 
organs  being  found  in  different  individuals. 

In  mammals  the  process  of  fecundation  takes  place  within  the 
interior  of  the  sexual  organs  of  the  female,  and  copulation  is,  therefore, 
essential.  In  most  reptiles  a  similar  process  takes  place,  although  in 
some  fecundation  is  external  •"  that  is  to  say,  the  male  extrudes  the 
seminal  fluid  upon  the  eggs  as  they  leave  the  body  of  the  female.  This 
latter  process  is  also  that  which  holds  in  fishes.  In  the  fishes  the  eggs, 
covered,  as  in  the  case  of  the  batrachians,  with  a  soft  membrane,  are 
usually  deposited  along  the  banks  or  at  the  bottoms  of  rivers  or  ponds, 
while  the  male  deposits  at  variable  intervals  the  fecundating  liquid.  As 
a  consequence  of  the  exposure  to  so  many  different  causes  of  destruction 
a  large  number  of  eggs  escape  fecundation,  but  the  immense  number  de- 
posited b}'  the  fishes  serves,  however,  to  prevent  the  ultimate  extinction 
of  the  species.  As  many  as  a  million  eggs  have  been  said  to  be  extruded 
at  one  time  from  the  body  of  the  female  of  various  fishes. 

The  ovaries  of  the  female  fish  are  two  voluminous  glands,  which 
almost  fill  the  abdominal  cavit}^  of  the  fish  at  the  time  of  spawning.  In 
most  of  the  bony  fishes  the  oviducts  are  continuous  with  the  ovaries  and 
form  the  extrusory  canal.  In  many  of  the  cartilaginous  fishes  the 
abdominal  extremity  of  the  duct  is  free,  as  is  the  case  in  mammals, 
reptiles,  and  birds.  The  oviducts  open  into  the  cloaca. 

The  testicles  form  in  the  male  two  voluminous  glands,  opening  by 
means  of  the  spermatic  canals  either  into  the  cloaca,  or  by  a  special 
opening  in  the  neighborhood  of  the  anus.  In  certain  of  the 'cartilaginous 
fishes  fecundation  occurs  within  the  body  of  the  female,  and  there  is, 
therefore,  true  copulation  analogous  to  that  in  birds.  In  these  fishes  the 


REPRODUCTIVE  FUNCTIONS.  905 

eggs  are  covered  by  a  horn}-  envelope.  In  others  the  fecundated  eggs 
remain  in  the  interior  of  the  oviducts  and  there  develop,  and  the  animal 
bears  its  young. 

In  reptiles,  as  in  birds,  the  product  of  generation  comes  from  the 
female  organs  in  the  state  of  an.  egg,  while  in  most  cases  fecundation 
precedes,  as  in  the  birds,  the  escape  of  the  egg,  and  the  egg  at  the  time 
of  its  exit  is  contained  within  a  solid  envelope,  although,  as  a  rule,  less 
resistant  than  that  surrounding  the  egg  of  the  bird. 

Various  batrachians  extrude  their  eggs  before  fecundation  and  the 
male  fecundates  them  while  clinging  to  the  body  of  the  female  at  the 
moment  of  their  exit.  In  cases  where  copulation  takes  place  the  exit  of 
the  eggs  occurs  at  a  considerable  interval  after  their  detachment  from  the 
ovary,  and  the  egg  retained  in  the  oviduct  develops  and  is  not  expelled 
until  just  at  the  point  at  which  the  young  is  able  to  carry  on  a  separate 
existence;  while  in  some  instances,  as  in  some  serpents,  incubation  is 
terminated  and  the  eggs  are  ruptured  within  the  body  of  the  female,  and 
the  living  young  are  expelled  from  the  body  of  the  mother.  Reptiles,  as 
a  rule,  do  not  incubate  their  eggs  themselves  after  extrusion,  but  the}^  de- 
posit them  in  the  sand  or  in  the  water,  as  in  the  case  of  the  amphibious 
reptiles,  where  the  external  heat  is  sufficient  to  accomplish  their 
incubation. 

Females  of  the  class  of  reptiles  have  two  ovaries  and  two  oviducts, 
which  open  separately  into  the  cloaca,  the  oviducts,  as  in  birds  and 
mammals,  not  being  continuous  with  the  ovary,  but  being  free  in  the 
abdominal  cavity,  and  possessing  trumpet-shaped  extremities  analogous 
to  the  fimbriated  extremities  of  the  Fallopian  tubes  in  mammals. 

The  male  organs  of  generation  differ  in  different  species.  In  the 
batrachians  there  are  no  organs  of  copulation.  The  spermatic  canals  open 
into  the  cloaca,  and  fecundation  occurs,  as  in  the  birds,  by  the  application 
of  the  ani,  when  fecundation  precedes  the  expulsion  of  the  eggs.  In  other 
groups  of  reptiles  a  penis  is  present,  into  which  the  spermatic  canals 
open. 

Of  all  the  reptiles  batrachians  are  the  most  productive.  Turtles 
extrude  four  to  five  eggs,  serpents  ten  to  twenty,  and  frogs  many  hun- 
dreds. After  escaping  from  the  egg  batrachians  are  not,  as  a  rule,  fully 
developed,  but  during  the  first  two  weeks  undergo  a  true  metamorphosis, 
first  existing  in  the  form  of  tadpoles,  deprived  of  limbs,  but  having  a 
tail  and  breathing  by  branchia  situated  at  the  side  of  the  neck.  Grad- 
ually limbs  develop  and  the  tail  as  well  as  the  gills  disappear,  and  the 
animal  then  breathes  by  lungs. 

In  birds  the  product  of  generation  leaves  the  sexual  organs  of  the 
female  while  still  within  the  egg,  and  such  animals  are,  therefore,  termed 
oviparous,  although  it  must  not  be  forgotten  that  man  and  other  animals 


906  PHYSIOLOGY  OF  THE  DOMESTIC   ANIMALS. 

are  also  in  the  strict  sense  of  the  word  oviparous  animals,  only  in  them 
the  egg  does  not  leave  the  body  of  the  female  until  completely  developed. 

In  mammals  the  fecundated  egg  passes  through  the  Fallopian  tube 
and  becomes  arrested  in  the  uterus  and  is  there  fixed,  and  there  under- 
goes what  may  be  termed  an  internal  incubation,  while  at  the  same  time 
vascular  connections  between  the  egg  and  the  body  of  the  mother  are 
established.  In  birds,  likewise,  the  fecundated  egg  passes  through  the 
oviduct  and  there  becomes  coated  with  an  albuminous  layer,  around 
which  is  finally  deposited  a  la}^er  of  calcareous  matter  which  hardens 
before  the  egg  is  extruded.  It,  therefore,  contains  within  itself  the 
materials  necessary  for  the  development  of  the  embryo,  and  is,  as  a  con- 
sequence, more  voluminous  than  that  of  the  mammal.  The  eggs  of  birds 
are  finally  developed  by  external  incubation. 

Birds,  like  reptiles,  are,  as  a  rule,  possessed  of  no  external  male 
organs  of  copulation.  The  testicles  are  placed  near  the  kidneys,  and  the 
spermatic  canals  open  at  the  inferior  extremity  of  the  digestive  tract  at 
the  cloaca,  and  it  is  by  the  application  of  the  anus  of  the  male  to  the 
cloaca  of  the  female  that  fecundation  is  accomplished.  In  certain  birds, 
as  the  ostrich,  duck,  and  goose,  a  rudimentary  penis  is,  nevertheless, 
present. 

The  fundamental  part  of  the  egg,  or  the  yelk,  is  formed  in  the  ovary 
of  the  female.  When  the  yelk  has.  attained  its  full  development  the 
ovarian  capsule  breaks  and  the  yelk,  inclosed  by  the  vitelline  membrane, 
passes  into  the  oviduct.  There  it  meets  with  the  seminal  fluid  and  becomes 
enveloped  by  a  layer  of  albuminous  matter,  while  the  yelk  undergoes  a 
rotatory  movement  and  the  chalazae,  or  albuminous  ligaments,  found 
in  the  white  of  the  egg  are  formed.  About  six  hours  after  the  exit  from 
the  ovary,  and  when  the  egg  has  reached  the  lower  third  of  the  oviduct, 
the  albuminous  layer,  or  the  white  of  the  egg,  becomes  enveloped  by  a 
membrane,  at  first  transparent,  and  which  finally  doubles  itself  into  two 
folds.  The  fold  adhering  to  the  albumen  remains  in  the  state  of  a  mem- 
brane, while  calcareous  matters  are  deposited  in  the  more  external 
membrane  so  as  to  form  the  egg-shell.  The  formation  of  the  shell  is 
much  slower  than  that  of  the  albumen,  and  it  is  only  after  about  twent}7- 
four  hours  that  the  complete  egg  is  expelled  from  the  inferior  part  of  the 
oviduct  into  the  cloaca  and  thence  to  the  exterior,  the  small  point  of  the 
egg  being  first  extruded. 

If  examined  while  still  within  the  oviduct,  or  immediately  after  its 
extrusion,  it  may  be  readily  determined  that  characteristic  changes  have 
occurred  within  the  germinal  vesicle,  and  these  progress  until  the  embryo 
is  completely  developed,  its  life  being  sustained  during  the  period  of 
incubation  by  the  albuminous  matters  stored  up  in  the  egg,  while  respi- 
ration takes  place  through  the  pores  of  the  shell  membrane.  In  the  case 


BEPKODUCTIVE  FUNCTIONS.  907 

of  birds,  in  contradistinction  to  what  holds  in  mammals,  segmentation 
is  partial,  while  the  remainder  of  the  yelk  contained  within  the  umbilical 
vesicle,  and  consequently  communicating  with  the  intestine  of  the  bird, 
serves  for  its  nutrition ;  as  a  consequence  the  umbilical  vesicle  persists 
during  the  entire  period  of  incubation  and  even  up  to  the  time  when  the 
bird  issues  from  the  shell. 

The  heat  necessary  for  the  development  of  the  embiyo  within  the 
egg  is,  as  a  rule,  supplied  by  the  body  of  the  mother,  but,  as  is  well 
known,  eggs  may  be  artificially  incubated,  it  only  being  necessary 
to  place  them  at  a  constant  temperature  of  from  35°  to  40°  C.,  turning 
them  each  day. 

In  mammals  the  female  nourishes  its  young  for  a  variable  period 
after  birth  through  the  secretion  formed  by  the  mammary  glands. 

In  mammals  the  different  acts  of  generation  closely  correspond  with 
similar  processes  in  man,  the  principal  differences  lying  in  the  number 
of  the  young,  the  duration  of  gestation,  the  frequency  of  the  acts  of 
reproduction,  and  certain  anatomical  peculiarities  relative  to  the  mode 
of  adherence  of  the  foetus  or  foetuses  to  the  uterine  cavity.  Among 
mammals  some  bear  but  one  young  at  a  time.  These  are  the  cow,  mare, 
ass,  stag,  elephant,  and  monkey  ;  the  bear,  the  roebuck,  the  castor,  the 
marmot,  and  the  guinea-pig  three  to  four;  the  lion,  the  tiger,  and  the 
leopard  four  to  five  ;  the  dog,  the  fox,  the  wolf,  and  the  cat  five  to  six  ; 
the  rabbit  and  the  water-rat  six  to  eight ;  the  pig  and  the  rat  as  many 
as  fifteen. 

The  duration  of  gestation  is  three  weeks  in  the  guinea-pig,  four 
weeks  in  the  rabbit  and  hare,  five  weeks  in  the  rat  and  marmot,  six 
weeks  in  the  ferret,  eight  weeks  in  the  cat,  nine  weeks  in  the  dog  and  fox, 
ten  weeks  in  the  sloth,  fourteen  weeks  in  the  lion,  seventeen  weeks  in  the 
castor  and  sow,  twenty-one  weeks  in  the  sheep,  twenty-two  weeks  in  the 
goat,  twenty-four  weeks  in  the  roebuck,  thirty  weeks  in  the  bear,  thirty- 
six  weeks  in  the  stag,  forty-one  weeks  in  the  cow,  forty-three  weeks  in 
the  mare,  the  ass,  and  the  zebra,  forty-five  weeks  in  the  camel,  and  one 
hundred  weeks  in  the  elephant. 

The  number  of  young  borne  by  mammals  is  capable  of  being  modi- 
fied under  different  conditions.  Animals  which  in  a  state  of  nature, 
copulate  but  once  in  a  year,  when  reduced  to  a  state  of  domestication 
enter  anew  into  heat  and  may  copulate  a  short  time  after  the  previous 
birth  ;  this  is,  without  doubt,  due  to  the  more  abundant  nourishment  sup- 
plied to  such  animals  in  a  state  of  domestication.  The  mare  may  pass 
into  heat  ten  or  twelve  days  after  the  birth,  the  cow  after  twenty  days. 

The  number  of  young  borne  by  mammals  is  principally  subordinate 
to  the  duration  of  gestation.  Small  mammals,  which  carry  their  young 
but  a  short  time,  as  a  rule  bear  more  frequently  than  those  in  which 


908  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

gestation  is  of  longer  duration.     Thus,  the  water-rat  or  guinea-pig  may 
bear  five  or  six  times  a  year. 

In  most  mammals  the  uterus  is  not  constituted  by  a  single  cavity, 
as  in  the  human  female,  but  is  prolonged  more  or  less  on  each  side,  con- 
stituting what  are  termed  the  horns  of  the  uterus.  Sometimes,  as  in  car- 
nivora,  the  division  of  the  uterus  is  prolonged  up  to  the  vaginal  orifice 
of  the  uterus.  This  division  of  the  uterus  into  two  horns,  or  two  pouches, 
more  or  less  distinct,  does  not  occasion  any  difference  in  the  mode  of 
connection  of  the  eggs  with  the  uterine  mucous  membrane.  In  the 
carnivora  and  in  rodents  the  mucous  membrane,  as  in  the  human  species, 
adheres  to  the  body  of  the  organ  and  separation  is  extremely  difficult. 
In  solipedes  and  the  pachyderms  the  uterine  mucous  membrane  is  but 
slightly  adherent  to  the  subjacent  tissue  and  may  even  be  thrown  into 
folds. 

In  horned  ruminants,  as  the  cow,  the  mode  of  union  of  the  egg 
with  the  uterine  mucous  membrane  presents  a  remarkable  peculiarity. 
The  foetal  placenta  occurs  in  isolated  cotyledons,  the  cotyledons  being 
formed,  as  in  the  human  species,  of  vascular  loops  implanted  in  the 
mucous  membrane  of  the  uterus,  being  designated  under  the  name  of  the 
uterine  cot}7ledons.  These  uterine  cotjdedons  exist  in  the  female  even 
before  pregnancy  and  persist  after  the  separation  of  the  foetus  and  its 
multiple  placenta. 

When  the  young  of  a  mammal  is  born  the  membranes  of  the  egg  and 
the  umbilical  cord  frequently  rupture  spontaneously.  In  other  cases  the 
female  breaks  the  membranes  and  the  cord  with  her  teeth.  Most  car- 
nivorous animals  devour  the  after-birth.  In  the  horned  ruminants  the 
adhesion  of  the  cotyledons  of  the  foetal  placenta  with  the  uterine  coty- 
ledons is  so  close  that  frequently  several  days  elapse  after  the  birth  of 
the  foetus  before  the  placenta  becomes  detached.  In  such  animals  the 
expulsion  of  the  placenta  cannot  be  facilitated  by  drawing  on  the  umbili- 
cal cord  without  great  risk  of  hemorrhage  from  rupture  of  the  uterine 
vessels. 

When  the  animal  is  multiparous  the  membranes  and  placenta  of  each 
are  expelled  with  the  young  to  which  they  belong.  In  certain  species  of 
mammals  the  young  are  but  slightly  developed  and  are  incapable  of 
making  use  of  their  limbs.  Many  such  animals,  as  the  marsupials, 
remain  permanently  attached  to  the  breasts  of  the  mother  while  carried 
in  pouches  formed  by  a  fold  of  the  integument  of  the  abdomen. 

1.  THE  REPRODUCTIVE  TISSUES  OF  THE  FEMALE. — As  already  stated, 
reproduction  is  dependent  upon  the  union  of  the  ovum  contributed  by 
the  female  with  the  spermatozoa  formed  by  the  sexual  organs  of  the 
male.  These  reproductive  tissues  in  mammals  now  deserve  somewhat 
further  attention.  Nothing  need  be  added  to  the  morphological  descrip- 


KEPEODUCTIVE   FUNCTIONS.  909 

tion  of  the  ovum,  which  has  already  been  fully  considered.  Some  points 
in  the  development  of  the  ovum  and  its  attendant  phenomena  neverthe- 
less deserve  consideration. 

The  ova  are  developed  in  the  matrix  of  the  ovar}*.  The  latter  con- 
sists of  a  connective-tissue  frame-work  supplied  with  blood-vessels, 
nerves,  and  lymphatics,  whose  surface  is  covered  with  a  layer  of  columnar 
epithelium — the  remains  of  the  germinal  epithelium.  The  most  super- 
ficial layer  of  the  ovary  is  called  the  tunica  albuginea  and  contains  no 
ova;  but  if  section  be  made  of  the  ovar}^,  throughout  its  entire  sub- 
stance will  be  found  small  follicles  varying  from  one-hundredth  to  one- 
thirtieth  of  an  inch  in  size.  In  each  of  these  Graafian  follicles  will  be 
found  an  ovum  in  different  stages  of  development.  Immediately  after 


FIG.  414.— SECTION  OF  ATS  OVARY.    (Landois.) 

e,  germ  epithelium;  1,  large-sized  follic'es :  2  2,  smaller  sized  follicles;  o,  ovum  within  a  Graafian  follicle; 
v  v,  blood-vessels  of  the  stroma ;  y,  cells  of  the  membrana  granulosa. 

birth  the  ovary  contains  immense  numbers  of  ova — in  the  human  female 
infant  from  fort}T  thousand  to  sevent3r  thousand.  The  ova  develop  from 
the  layer  of  germinal  epithelium  which  originally  completely  surrounded 
the  ovary.  At  different  intervals  on  the  surface  depressions  form,  which 
serve  to  carry  in  a  la}^er  of  germinal  epithelium  to  form  the  so  called 
ovarian  tubes.  These  tubules  gradually  become  deeper  and  deeper,  and 
contain  within  their  interior  large,  single,  spherical  cells,  with  a  nucleus 
and  a  nucleolus,  in  addition  to  the  small,  columnar  cells  lining  the  tube. 
As  the  tubules  extend  into  the  ovary  the  growth  of  the  stroma  of  the 
ovary  serves  to  constrict  the  orifices  of  the  tubules,  and  finally  their 
openings  become  completely  obliterated,  and  the  tubule,  which  originally 
began  as  a  pocket-shaped  depression  on  the  surface  of  the  ovary,  now 


910  PHYSIOLOGY   OF   THE   DOMESTIC   ANIMALS. 

exists  as  a  closed,  more  or  less  circular  follicle,  completely  separated  by 
the  ovarian  stroma  from  the  surface  (Fig.  414). 

Each  compartment,  or  Graafian  follicle,  so  formed  usually  contains 
one,  or  at  the  most  two,  ova,  which  develop  from  the  large  cells 
(primordial  cells)  already  referred  to. 

The  lining  of  the  tubule,  which  it  must  not  be  forgotten  was  derived 
from  the  exterior  covering  membrane  of  the  ovary,  is  spoken  of  as  the 
membrana  granulosa,  and  at  one  point  its  cells  become  elevated  to  form 
a  projection,  the  proligerous  disk,  by  which  the  ovum  is  connected  with 
the  membrana  granulosa.  The  follicles  are  at  first  only  .03  millimeter 
in  diameter,  but  they  gradually  become  larger,  especially  at  the  time  of 
puberty.  The  entire  cavity  of  the  Graafian  follicle  is  occupied  by  a  fluid, 
the  so-called  liquor  folliculari,  which  gradually  accumulates  during  the 
growth  of  the  Graafian  follicle.  Each  Graafian  follicle  is,  therefore,  com- 
posed of  an  external  tunic  which  is  highly  vascular  in  character.  Within 
this  is  the  granular  layer  rising  at  one  point  to  form  the  proligerous 
disk,  in  contact  with  which  is  the  ovum,  while  the  remainder  of  the  fol- 
licle is  occupied  with  fluid.  As  the  follicles  increase  in  size  they 
become  depressed  toward  the  centre  of  the  ovary,  but  when  about  to 
burst  again  rise  to  the  surface,  until,  finally,  the  walls  of  the  Graafian 
follicle  will  lie  directly  below  the  germinal  epithelium  on  the  surface  of 
the  ovary.  Its  diameter  is  now  from  one  millimeter  to  1.5  millimeters. 
The  rupture  of  the  first  Graafian  follicle  corresponds  with  the  occurrence 
of  puberty  or  of  fertilit3r  and  indicates  the  period  at  which  the  female 
organism  first  becomes  capable  of  the  functions  of  generation.  The 
smaller  the  mammal  the  earlier  does  this  capability  for  procreation 
appear.  In  the  smaller  mammals,  such  as  the  rabbit,  the  guinea-pig,  and 
the  rat,  as  well  as  in  birds,  it  appears  within  the  first  year ;  in  larger 
animals,  as  the  cat  and  the  dog,  in  the  second  year,  while  in  the  largest 
mammals,  as  the  horse,  cattle,  and  the  lion,  in  three  years  ;  in  the  llama, 
in  four  years ;  in  the  camel,  in  five  years  ;  in  the  human  female,  about 
the  fourteenth  year,  and  in  the  elephant,  between  the  twentieth  and  the 
thirtieth  year. 

Puberty  in  the  human  female  is  recognized  by  the  first  occurrence 
of  menstruation,  which  consists  in  the  escape  of  blood  from  the  external 
genitals.  In  warm  climates  menstruation  first  sets  in  between  the  ages 
of  eleven  and  twelve  }Tears ;  in  cold  climates  between  the  ages  of  four- 
teen and  sixteen  years.  The  duration  of  each  single  menstrual  period 
varies,  as  a  rule,  from  three  to  five  days,  although  it  may  last  as  long  as 
eight,  or  only  one  or  two  days.  Toward  the  age  of  forty  or  fifty 
years  in  the  human  female  the  procreative  faculty  disappears  and  with 
it  the  menses  cease.  Such  a  period  is  spoken  of  as  the  climacteric  or 
menopause. 


KEPKODUCTIYE   FUNCTIONS.  911 

At  the  occurrence  of  puberty  various  changes  take  place  which  mark 
the  appearance  of  reproductiveness.  As  such  may  be  mentioned  in- 
creased vascularity  and  development  of  the  external  and  internal  gener- 
ative organs,  the  characteristic  changes  which  now  commence  in  the 
pelvis,  the  development  of  the  mamma?,  and  the  growth  of  hair  on  the 
pubes  and  in  the  axilla.  Menstruation  recurs,  usually,  at  intervals  of 
twent3T-eight  days,  and  each  menstrual  period  corresponds  with  the  ripen- 
ing and  rupture  of  a  Graafian  follicle.  During  menstruation  from  one 
hundred  to  two  hundred  grammes  of  blood  escape.  This  blood  has  lost 
its  power  of  coagulation,  probably  through  mixture  with  the  alkaline 
secretions  of  the  uterus  and  vagina.  The  source  of  the  hemorrhage  is 
the  mucous  membrane  lining  the  uterus.  The  ciliated  epithelium  of  the 
uterus  becomes  swollen,  congested,  and  soft,  and  almost  entirely  shed. 
A  similar  congestion  likewise  occurs  in  the  ovaries  and  Fallopian  tubes, 
the  congestion  of  the  ovary  leading  to  a  greater  transudation  of  fluid 
into  the  Graafian  follicle  and  consequent  rupture,  while  the  great  conges- 
tion and  engorgement  of  the  blood-vessels  of  the  uterus  lead  to  the 
rupture  of  the  finer  capillaries  and  the  consequent  escape  of  blood. 

In  addition  to  the  congestion  of  the  internal  genital  organs,  the 
external  genital  organs  also  become  more  strongly  congested  and 
swollen. 

Phenomena  analogous  to  the  process  of  menstruation  in  the  human 
female  occur  in  all  females  of  the  class  of  mammals,  in  the  domestic  animals 
the  condition  being  spoken  of  as  heat,  and  its  first  occurrence  marks  not 
only  the  first  appearance  of  the  power  of  procreation  but  also  the  times 
at  which  copulation  with  the  male  will  be  permitted.  In  all  of  the 
domestic  animals  the  occurrence  of  heat  coincides  with  the  rupture  of 
one  or  more  Graafian  follicles  and  the  escape  of  one  or  more  ova  from 
the  ovar}~,  together  with  the  increased  vascularity  of  the  genitals.  The 
external  signs  of  heat  are  the  following :  Slight  swelling  and  reddening 
of  the  vagina  and  vulva,  more  or  less  flow  of  mucous,  reddish  discharge 
from  the  genitals,  characterized  by  a  peculiar  odor,  which  especially  seems 
to  possess  the  power  of  attracting  the  male,  frequent  urination,  often 
slight  swelling  of  the  mammary  gland  with  alteration  in  the  characters 
of  the  milk ;  the  disposition  of  the  animal  becomes  restless,  it  seeks  the 
male  of  the  same  species,  frequently  gives  vent  to  various  cries,  and 
sometimes  refuses  to  eat.  The  characteristics  of  heat  vary  somewhat 
in  different  animals.  In  the  mare  urination  is  frequent,  the  vulva  is  the 
seat  of  spasmodic  discharge,  and  the  clitoris  becomes  erect.  The  mare 
whinnies  and  seeks  the  male.  Occasionally  a  small  amount  of  blood 
escapes  from  the  external  genitals.  The  cow  becomes  very  restless,  con- 
tinually bellows,  and  attempts  to  mount  other  animals  even  of  the  same 
sex.  In  sheep  the  appearances  of  heat  are  less  characteristic,  and  are 


912  PHYSIOLOGY  OF   THE   DOMESTIC  ANIMALS. 

evidenced  simply  by  greater  uneasiness,  leaving  the  flock  and  seeking  the 
ram,  and  will  only  then  permit  the  act  of  copulation.  The  same  remarks 
also  appty  to  the  goat.  The  sow  at  this  time  appears  to  grunt  more  than 
usual,  is  more  irritable  and  more  vivacious,  is  restless,  may  bite,  and 
shows  loss  of  appetite.  Heat  reaches  its  maximum  in  twelve  to  sixteen 
hours.  In  the  bitch  there  occurs  a  great  hypersemia  of  the  genital  parts 
and  an  abundant  exudation  of  bloody  mucus.  The  vulva  is  congested 
and  swollen,  and  the  animal  is  much  more  lively  and  vivacious  than  usual 
and  playful,  especially  with  dogs  which  are  attracted  from  a  great  dis- 
tance by  the  peculiar  odor  of  the  discharge. 

In  all  the  domestic  animals  the  phenomena  of  heat  have  a  longer  or 
shorter  duration.  In  the  mare  they  last  from  two  to  three  days ;  in  the 
cow,  from  fifteen  to  thirty  hours  ;  in  the  sow,  from  one  to  three  days  ;  in 
the  sheep,  from  two  to  three  da}-s  ;  in  the  goat,  from  two  to  three  days, 
and  in  the  bitch,  from  nine  to  fourteen  days. 

If  conception  occurs  the  phenomena  of  heat  only  make  their  reap- 
pearance after  delivery.  In  the  cow  this  occurs  in  three  to  four  weeks 
after  delivery,  and  recurs  every  three  weeks  if  impregnation  does  not 
occur.  In  the  mare  heat  may  appear  from  five  to  nine  weeks  after 
delivery,  and,  if  impregnation  does  not  occur,  every  nine  days  afterward. 
So  long  as  the  sow  is  suckling  phenomena  of  heat  do  not  appear,  but 
after  the  removal  of  the  young  heat  comes  on  about  the  third  day,  and, 
if  impregnation  does  not  occur,  recurs  every  nine  or  twelve  days.  In 
the  sheep,  after  delivery,  heat  occurs  in  from  three  to  four  weeks ;  when 
suckling  only  two  to  four  months  later,  and  recurs  at  intervals  of  from 
seventeen  to  twenty-five  days.  The  mare  is  in  heat  usually  in  the  spring 
and  again  in  the  autumn;  the  goat  in  the  autumn;  the  sheep  in  the 
autumn  and  spring,  while  the  other  animals  are  in  heat  at  intervals 
throughout  the  entire  year  at  the  intervals  already  mentioned  (Strebel). 

The  occurrence  of  menstruation  and  heat  coincides  with  the  ripening 
of  an  ovum.  In  the  human  female,  as  in  the  mare  and  cow,  one  ovum  or, 
at  the  most,  two  ripen  at  one  time ;  in  the  goat,  from  one  to  four,  while 
in  the  dog  and  cat  as  man}^  as  ten  ova  may  mature  together. 

Through  an  increase  of  the  blood  pressure  in  the  vessels  of  the 
ovary  blood  transudes  into  the  interior  of  the  Graafian  follicle,  and  thus, 
by  increasing  the  pressure,  causes  a  rupture  of  the  wall  at  its  thinnest 
point,  and  the  ovule,  together  with  the  proligerous  disk  and  the  follicular 
fluid,  escape  into  the  abdominal  cavity.  The  ovary  lies  free  in  the 
abdominal  cavity  in  a  fold  of  the  peritoneum.  As  the  ovule  escapes  from 
the  ovary  the  Fallopian  tube,  and  its  fimbriated  extremity,  is  found,  from 
its  state  of  congestion,  in  a  condition  of  erection,  and  in  all  probability 
the  fimbriated  extremity  becomes  closely  applied  to  the  ovary.  As  a  con- 
sequence, the  ova  escaping  from  the  ovary  fall  within  the  mouth  of  the 


REPRODUCTIVE   FUNCTIONS.  913 

ovarian  tube  and  are  carried  toward  the  uterus  by  means  of  the  cilia 
lining  the  Fallopian  tube.  Frequently  such  a  close  contact  does  not 
occur,  since  numerous  cases  of  failure  of  the  ova  to  enter  the  Fallopian 
tube  are  recorded,  and,  as  a  consequence,  abdominal  pregnancy  may 
take  place.  Still,  there  is  no  doubt  that  the  congestion  of  the  Fallo- 
pian tubes  must  result  in  their  erection,  as  may  be  accomplished  arti- 
iicially  by  injection  of  their  blood-vessels.  It  is  probable  that  the  cur- 
rents set  up  by  the  continued  motion  of  the  cilia  in  the  Fallopian  tubes 
are  the  main  cause  in  leading  to  the  entrance  of  the  ova  into  the  Fallo- 
pian tubes. 

After  the  ovum  has  entered  the  Fallopian  tube  from  one  to  three 
days  is  required  for  its  passage  to  the  uterus.  Here,  if  not  already 
impregnated,  it  may  meet  with  spermatozoa,  or  ma}^  undergo  fatty  degener- 
ation, although  certain  changes,  as  already  detailed,  may  occur  in  the  ovum 
even  when  unimpregnated. 

As  the  Graafian  follicle  bursts  it  discharges  its  contents  and  col- 
lapses, while  in  its  interior  remains  the  residue  of  the  granular  membrane 
and  a  small  quantity  of  blood,  which  rapidly  coagulates.  The  vascular 
walls  of  the  follicle  swell  up,  and  connective-tissue  proliferation  gradually 
leads  to  the  filling  up  of  the  follicle,  whose  contents  finally  undergo  fatty 
degeneration,  and  from  the  yellow  appearance  thus  produced  the  name 
corpus  luteum  has  been  applied  to  this  spot.  If  pregnancy  has  not 
occurred  the  fatty  matter  is  rapidly  absorbed,  the  blood  breaks  up  into 
hsematin  and  other  derivatives,  while  the  entire  mass  gradually  shrivels, 
and  by  the  end  of  four  weeks  has  almost  disappeared.  Such  a  corpus 
luteum  is  spoken  of  as  a  false  corpus  luteum.  If  impregnation  has  taken 
place  this  corpus  luteum  instead  of  disappearing  increases  in  size,  so  that 
at  the  end  of  three  or  four  months  its  walls  are  thicker  and  its  color 
deeper,  and  at  the  termination  of  gestation  it  may  be  as  large  as  six  or 
ten  millimeters  in  diameter,  and  may  remain  for  a  long  time  afterward. 
Such  a  form  is  spoken  of  as  a  true  corpus  luteum.  It  is,  however,  prob- 
able that  too  much  importance  has  been  laid  upon  the  distinction  between 
these  two  forms. 

2.  THE  REPRODUCTIVE  TISSUES  OF  THE  MALE. — The  secretion  of  the  male 
genital  organs  is  known  as  the  seminal  fluid,  or  sperm,  and  it  is  formed 
by  the  secreting  tubules  of  the  testicles.  It  consists  of  a  whitish-yellow, 
sticky  fluid  of  high  specific  gravity  and  of  neutral  or  alkaline  reaction. 
In  the  seminal  fluid  of  the  horse  are  found  18  per  cent,  of  solids,  in  that 
of  the  bull  17.6  per  cent.,  while  in  that  of  man  there  is  only  10  per  cent, 
of  solids,  of  which  4  per  cent,  consists  of  inorganic  salts,  especially  of 
calcium  and  magnesium  phosphate.  When  exposed  to  the  air  it  becomes 
more  fluid,  and  when  water  is  added  to  it,  it  becomes  gelatinous.  The 
seminal  fluid  as  discharged  from  the  urethra  is  mixed  with  the  secretions 

58 


914 


PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 


of  the  glands  of  the  vas  deferens,  of  Cowper's  glands,  of  the  prostate 
gland,  and  of  the  vesiculae  seminales.  It  contains  water,  varying  from 
80  per  cent,  to  90  per  cent,  in  different  animals,  serum-albumen, alkali  albu- 
men, nuclein,  lecithin,  cholesterin,  fats,  salts,  especially  the  phosphates 
of  the  alkaline  earths,  with  sulphates,  carbonates,  and  chlorides,  and 
a  peculiar  odorous  principle  the  nature  of  .which  is  unknown. 

When  examined  with  the  microscope  it  is  found  that  the  seminal 
fluid  may  be  divided  into  a  plasma  and  formed  elements.  The  constit- 
uents already  mentioned  constitute  the  plasma  of  the  semen  and  the 
formed  elements  are  the  so-called  spermatozoa,  and  it  is  the  latter  which 
are  the  active  elements  of  the  secretion  in  the  function  of  reproduction. 


k 

m 

mm 


FIG.  415.— SPERMATOZOA.    (Landois.) 

1,  human  (X  600),  the  head  seen  from  the  side ;  2,  on  edge ;  7c,  head ;  m,  middle  piece ;  /,  tail ;  e,  ter- 
minal filament.  3,  mouse.  4,  bothriroephalus  latus.  5,  deer.  6,  mole.  7,  green  woodpecker.  8,  black 
•wan.  9,  from  a  cross  between  a  goldfinch  (m)  and  canary  (/).  10,  cobitis. 

Each  spermatozoon  consists  of  a  flattened  or  pear-shaped  head,  fol- 
lowed by  a  rod-shaped  middle  piece  with  a  long,  tail-like  prolongation,  or 
cilium.  When  examined  shortly  after  extrusion  from  the  testicle,  the 
cilium  is  found  to  be  in  rapid  vibration,  and  by  this  motion  the  entire 
spermatozoon  is  propelled  forward  at  the  rate  of  about  half  a  millimeter 
in  a  second.  The  movement  of  the  spermatozoon  is  identical  with  that 
of  other  forms  of  ciliated  movement  and  is  affected  in  the  same  way  by 
the  same  reagents.  At  first  the  movements  are  active,  and,  under  favor- 
able circumstances,  they  come  to  rest  only  after  two  or  three  days.  The 
spermatozoa  of  different  animals  differ  in  shape  and  size,  as  is  shown  in 


REPKODUCTIYE  FUNCTIONS. 


915 


the  accompanying  diagram  (Fig.  415).  In  man  the  spermatozoa  are  about 
.05  millimeter  in  length,  the  head  being  oval  with  a  thickened  posterior 
border,  and  their  shape  is,  therefore,  somewhat  analogous  to  that  of  a  pear. 
The  spermatozoa  are  developed  from  the  nucleated  protoplasmic 
cells  which  line  the  seminal  tubules  of  the  testicle.  These  tubules  are 
lined  by  several  layers  of  more  or  less  cubical  cells.  The  outer  cells, 
next  the  basement  membrane,  often  show  a  large  nucleus  in  process  of 
subdivision.  Internal  to  these  are  several  layers  of  inner  cells  with 
nuclei,  often  dividing  so  that  they  form  a  progeny  of  cells  internal  to 
those  toward  the  lumen  of  the  tube.  From  these  cells  so  formed  by  sub- 
division and  which  are  termed  spermatoblasts  the  spermatozoa  are 
formed.  These  spermatic  cells  are  spindle-shaped  and  form  nucleated 
protoplasmic  prolongations  which  project  into  the  lumen  of  the  tube  and 
break  up  at  their  free  ends  into  flat,  round,  or  oval  lobules.  During  the 


a 


FIG.  416  —SEMI-DIAGRAMMATIC  SPERMATOGENESIS.    (Landois.) 

I.  Transverse  section  of  a  seminal  tubule;  a,  membrane;  b,  protoplasmic  inner  lining;  c,  Spermato- 
blast ;  x,  seminal  ceils.  //.  Unripe  Spermatoblast ;  /,  rounded  cleavage  lobules ;  p,  seminal  cells.  ///. 
Spermatoblast,  with  a  fre*  spermatozoon,  t.  IV.  Spermatoblast,  with  ripe  spermatozoa,  k,  not  yet 
detached ;  r,  tail ;  n,  wall  of  the  seminal  tubule ;  h,  its  protoplasmic  layer. 

process  of  development  of  these  spermatoblasts  each  lobule  lengthens 
into  a  tail  or  cilium-like  prolongation,  while  the  deeper  part  still  in 
connection  with  the  walls  of  the  tube  will  ultimately  form  the  head  and 
middle  portion  of  the  spermatozoon :  so  that  in  this  stage  of  its  develop- 
ment the  sperm  is  composed  of  an  enlarged  cylindrical  cell  terminating 
in  cilium-like  prolongations.  When  the  development  is  complete  the 
head  becomes  detached  and  the  remainder  of  the  Spermatoblast  under- 
goes fatty  degeneration,  although  a,  small  amount  of  the  protoplasm  may 
remain  temporarily  attached  to  the  head  of  the  spermatozoon  (Fig.  416). 
Between  the  spermatoblasts  lining  the  lumen  of  the  seminal  tubules 
are  found  numerous  round  cells  possessed  of  amosboid  movement,  the  so- 
called  seminal  cells,  which  are  probably  concerned  in  the  formation  of 
the  fluid  parts  of  the  semen. 


916  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

As  in  the  maturity  of  the  ova,  so  the  formation  and  maturity  of  the 
spermatozoa  indicate  the  occurrence  of  puberty.  In  the  human  male  this 
takes  place  about  the  age  of  fifteen  or  sixteen  years,  and  in  other  mammals 
it  occurs  a  short  time  later  than  the  occurrence  of  fertility  in  the  female  of 
the  same  species.  The  appearance  of  puberty  in  the  male  is  also  attended 
with  certain  characteristic  signs.  The  larynx  undergoes  a  rapid  increase 
in  size,  and,  as  a  consequence,  the  voice  becomes  deeper,  while  hair 
makes  its  appearance  on  the  pubes,  in  the  axillae,  and  on  the  face.  The 
sebaceous  glands  become  larger  and  more  active.  In  the  male  of  the 
domestic  animals  the  appearance  of  procreativeness  is  recognized  by  the 
occurrence  of  the  capability  of  erection  of  the  penis  and  the  birth  of 
sexual  desires.  In  the  domestic  animals  in  a  state  of  nature  sexual  ex- 
citement occurs  in  the  male  only  at  definite  periods  of  the  year,  but  in 
domestication  this  makes  its  appearance  whenever  a  mature  male  is  in 
the  neighborhood  of  a  female  of  the  same  species  when  in  heat. 

IMPREGNATION. — Only  those  mammalian  ova  become  developed  into 
embryos  which  are  fecundated  through  contact  with  the  male  spermatic 
element,  and  that  this  may  be  accomplished  the  introduction  of  the 
seminal  fluid  within  the  internal  genital  organs  of  the  female  is  essential. 
That  this  process,  which  is  termed  coition,  may  be  accomplished  the 
erection  of  the  male  genital  organ,  the  penis,  is  essential  in  order  to 
permit  its  penetration  within  the  vagina  of  the  female. 

The  penis  is  composed  of  the  two  cylindrical  corpora  cavernosa  with 
the  corpus  spongiosum,  perforated  by  the  urethra,  lying  between  and 
below  them,  these  three  bodies  being  held  together  by  fibrous  and  mus- 
cular sheaths.  The  corpora  cavernosa,  and  to  a  less  extent  the  corpus 
spongiosum,  are  composed  of  erectile  tissue,  which  consists  of  a  tendinous 
connective-tissue  sheath  containing  thickly  woven  elastic  tissue  and 
smooth  muscular  fibres,  forming  thus  a  fibrous  envelope ;  while  the  in- 
terior is  composed  of  numerous  fibrous  interlacing  trabeculae,  the  spaces 
being  in  communication  with  the  veins,  and  'are  thus  to  be  regarded  as 
venous  sinuses.  At  the  outer  part  of  the  corpus  spongiosum  some  of 
the  small  arteries  terminate  directly  in  the  outer  venous  sinuses,  while 
some,  however,  terminate  in  capillaries  which  ultimately  reach  the  venous 
sinuses,  to  be  collected  again  in  the  venous  radicals  which  converge  to 
form  the  dorsal  vein  of  the  penis. 

Erection  is  accomplished  by  the  overfilling  of  these  venous  sinuses, 
while  the  engorgement  so  produced  by  compressing  the  outgoing  venous 
trunk  serves  to  prevent  the  escape  of  blood  from  these  parts.  The 
overfilling  of  the  blood-vessels  of  the  penis  results  in  a  three-  or  four- 
fold increase  in  its  volume,  while,  at  the  same  time,  a  higher  tempera- 
ture, pulsatile  movement,  an  increased  consistence,  and  erection  of  the 
organ  results.  The  first  phenomenon  in  the  production,  of  erection  is  to 


KEPRODUCTIVE  FUNCTIONS.  917 

be  found  in  the  dilatation  of  the  minute  arteries  through  the  action  of 
the  nervi  erigentes.  These  nerves  are  to  be  regarded  as  containing  vaso- 
dilator fibres  which  are  in  connection  with  a  centre  in  the  spinal  cord, 
controlled  to  a  certain  extent  by  the  medulla  oblongata,  and  also  capa- 
ble of  being  reflexly  excited  by  impressions  made  upon  the  terminal 
filaments  of  the  sensory  nerves  of  the  penis.  The  centre  in  the  lumbar 
portion  of  the  cord  is  also  capable  of  being  controlled  by  various  other 
afferent  impulses,  especially  by  the  psychical  activity  of  the  cerebrum. 
When,  through  any  impression  on  the  centre  for  erection,  the  blood-ves- 
sels dilate  through  the  action  of  the  nervi  erigentes,  the  completion  of 
the  act  of  erection  is  accomplished  by  the  action  of  several  transversely 
striated  muscles.  The  ischio-cavernosus  muscle  arises  from  the  coccyx, 
and  by  its  tendinous  union  with  its  fellow  from  the  opposite  side  sur- 
rounds the  root  of  the  penis,  and  by  its  contraction  compresses  the  penis 
so  as,  to  a  certain  extent,  to  prevent  the  flow  of  blood  from  the  organ. 
This  muscular  action  was  at  one  time  supposed  to  be  the  main  factor  in 
the  accomplishment  of  erection,  but  that  this  is  not  the  case  is  proven 
by  the  fact  that  the  dorsal  vein,  lying  in  the  groove  between  the  two 
corpora  cavernosa,  is  protected  from  compression,  and  the  congestion  of 
the  organ  is  by  no  means  due  to  the  complete  arrest  of  the  venous  circu- 
lation. Otherwise,  in  certain  pathological  conditions  where  erection  is 
continuous,  gangrene  would  result.  The  deep  transverse  muscle  of  the 
perineum  also  serves  to  facilitate  erection  by  compressing  the  deep  veins 
of  the  penis  as  they  come  from  the  corpora  eavernosa  between  its  con- 
tracted horizontal  fibres;  while,  finally,  the  bulbo-eavernosus  muscle  com- 
presses the  bulb  of  the  urethra  and  so  assists  in  the  erection  of  the 
urethral  corpus  spongiosum.  That  erection  is  dependent  upon  the  nerv- 
ous system  is  proven  by  the  fact  that  section  of  the  nerves  of  the  penis 
will  prevent  erection,  as  has  been  experimentally  proven  in  the  case  of 
the  stallion. 

In  the  bull,  in  the  process  of  erection,  the  S-shaped  curve  disappears 
and  the  erected  organ,  protruding  from  the  sheath,  may  acquire  a  length 
of  a  meter  or  more,  while  the  increase  in  diameter,  owing  to  the  great 
development  of  the  fibrous  sheath  of  the  organ,  is  less  than  in  other 
mammals. 

The  erection  of  the  penis  has  simply  for  its  object  the  giving  such 
an  increase  to  the  rigidity  of  the  organ  as  to  permit  of  its  introduction 
within  the  genital  organs  of  the  female. 

The  contact  of  the  sensitive  glans  with  the  rugae  of  the  vagina 
inaugurates, a  reflex  process  which  terminates  in  the  discharge  of  the 
seminal  fluid  through  the  urethra. 

In  this  process,  which  is  termed  ejaculation,  two  different  factors 
are  concerned.  In  the  first  place,  the  passage  of  the  seminal  fluid  to  the 


918  PHYSIOLOGY  OF  THE  DOMESTIC  ANIMALS. 

vesiculse  seminales  is  caused  by  the  newly  secreted  fluid  forcing  on, 
through  the  influence  of  the  ciliated  epithelium  and  the  peristaltic  action 
of  the  vas  deferens,  the  fluid  already  formed  in  front  of  it ;  so  that,  there- 
fore, the  seminal  fluid,  being  continuously  formed  by  the  secreting  surface 
of  the  testicle,  is  gradually  pushed  onward,  even  in  the  intervals  of  sexual 
excitement,  to  the  vesiculse  seminales,  where  it  collects.  Ejaculation  is, 
however,  due  to  strong  peristaltic  contraction  of  the  vasa  deferentia  and 
the  vesiculse  seminales,  due  to  the  reflex  stimulation  of  the  centre  in  the 
spinal  cord,  which  co-ordinates  the  muscular  phenomena  of  ejaculation. 
The  mechanical  stimulation  of  the  sensitive  integument  of  the  glans, 
through  action  on  this  centre,  leads  to  rhythmical  contraction  of  the 
bulbo-cavernosus  muscles  and  to  strong  peristalsis  of  the  vasa  deferentia 
and  the  vesiculse  seminales,  which  discharge  their  contents  into  the 
urethra.  At  the  same  time  the  ischio-cavernosus  and  the  deep  transverse 
muscle  of  the  perineum  contract,  although  the  former  has  no  effect  on 
the  act  of  ejaculation,  and  through  their  rhythmical  contraction  the 
seminal  fluid  is  projected  from  the  extremity  of  the  urethra.  The  degree 
of  stimulation  of  the  glans  which  is  required  to  start  this  mechanism 
varies  very  considerably  in  different  animals.  In  all,  the  role  fulfilled  by 
the  male  is  an  active  process,  the  female  being  passive,  although  a  condi- 
tion somewhat  similar  to  that  of  ejaculation  also  exists  in  the  female.  It 
has  been  found  that  at  the  moment  of  ejaculation  a  reflex  movement  sets 
in  in  the  Fallopian  tubes  and  uterus  resulting  in  the  discharge  of  a  cer- 
tain amount  of  uterine  mucus  into  the  vagina.  This  is  followed  by  a 
rhythmical  contraction  of  the  sphincter  cunni,  which  is  the  analogue  of 
the  bulbo-cavernosus  and  of  the  ischio-cavernosus  and  of  the  deep  trans- 
verse muscle  of  the  perineum,  while,  at  the  same  time,  the  uterus  is 
erected  by  the  contraction  of  its  muscular  fibres  and  round  ligaments, 
at  the  same  time  descending  toward  the  vagina.  In  the  case  of  the  bull, 
ejaculation  occurs  almost  immediately  after  the  introduction  of  the  male 
organ  within  the  vagina  of  the  female,  and  the  to-and-fro  movement 
characteristic  of  the  process  in  other  animals  is  here  absent.  This  is 
probably  to  be  explained  by  the  peculiar  shape  of  the  penis  of  the  bull. 
In  the  first  place,  as  has  been  stated,  the  organ  increases  but  slightly  in 
its  diameter,  and,  as  a  consequence,  any  friction  of  the  body  with  the 
capacious  vagina  of  the  female  would  be  at  best  at  a  minimum.  In  the 
second  place,  the  glans  penis  of  the  bull  is  extremely  pointed,  and  it  has 
been  supposed  that  the  glans  directly  enters  the  open  mouth  of  the  uterus, 
and  that  the  irritation  thus  produced  is  sufficient  to  start  the  process  of 
ejaculation.  This  view  is  to  a  certain  extent  supported  by  the  fact  that 
examination  of  the  female  ruminant  immediately  after  the  act  of  copula- 
tion will  disclose  the  presence  of  spermatozoa  within  the  uterine  cavity. 
This  has  frequently  been  determined  to  be  the  case  in  sheep,  where  the 


EEPEODUCTIVE  FUNCTIONS.  919 

process  is  similar.  In  the  case  of  the  horse  the  process  is  more  pro- 
longed. Here  the  glans,  instead  of  being  pointed,  as  in  the  case  of  the 
bull,  possesses  a  considerably  larger  diameter  than  other  portions  of  the 
organ,  and  it  is  found  that  complete  erection  of  this  portion  of  the  penis 
does  not  take  place  until  after  the  introduction  of  the  organ  within  the 
vagina  of  the  female.  The  penis  completely  fills  the  vagina  of  the  mare, 
and  more  or  less  prolonged  friction  between  its  surface  and  that  of  the 
penis  is  necessary  before  the  act  of  ejaculation  is  accomplished. 

In  the  dog,  on  the  other  hand,  the  process  differs  from  what  has 
been  described  in  either  of  the  other  groups  of  mammals.  After  the 
introduction  of  the  penis  within  the  vagina  of  the  female  spasmodic  con- 
traction of  the  sphincter  cunni  muscle  sets  in,  and,  as  a  consequence,  the 
withdrawal  of  the  male  organ  from  the  body  of  the  female  is,  on  account 
of  its  peculiar  shape,  rendered  impossible  until  almost  complete  relaxa- 
tion has  taken  place.  In  the  dog  the  process -of  relaxation  is  slower  than 
in  other  animals,  and  may  not  be  completed  until  within  half  an  hour  or 
even  so  long  as  two  hours  after  the  act  of  ejaculation.  In  these  animals, 
therefore,  after  the  act  of  coition  is  accomplished,  the  penis  becomes  in- 
verted on  itself,  until,  instead  of  projecting  anteriorly,  it  is  drawn  back- 
ward between  the  hind  legs  of  the  animals  through  the  attempts  of  the 
male  to  leave  the  body  of  the  female,  and  the  two  posterior  surfaces  are 
kept  in  contact  by  the  imprisonment  of  the  male  organ. 

Ejaculation  is  accompanied  by  the  contraction  of  various  other 
muscles.  The  cremaster  muscle  elevates  the  testicle  within  the  scrotum, 
and  the  walls  of  the  urethra  contract  in  its  various  portions,  serving  to 
compress  the  prostate  and  Cowper's  glands  and  so  cause  the  extrusion 
of  their  contents.  In  the  stallion  the  act  of  ejaculation  is  accompanied 
by  a  rhythmical  contraction  of  the  muscles  inserted  into  the  tail.  By 
every  contraction  of  the  ejaculator  urinse  muscles  the  muscles  passing 
from  around  the  anus  to  the  tail  are  compressed,  and,  as  a  consequence, 
the  rhythmical  motion  of  the  ejaculator  seminae  is  communicated  to  the 
tail,  and,  therefore,  by  its  movement  affords  an  index  to  the  completion 
of  the  act  of  ejaculation.  After  the  act  of  copulation  is  completed  the 
male  organ  is  withdrawn  and  erection  gradually  disappears,  while  there 
may  be  an  escape  of  seminal  fluid  from  the  genital  organs  of  the  female. 
This  is  especially  observable  in  the  case  of  the  mare,  where  it  has  become 
the  custom  immediately  after  the  completion  of  the  act  of  copulation  to 
either  load  the  back  of  the  mare  or  to  make  her  move  rapidly,  so  as  to 
prevent  to  a  certain  extent  this  loss. 

A  single  spermatozoon  is,  in  all  probability,  sufficient  to  fertilize  an 
ovum,  and  this  is  accomplished  by  the  entrance  of  the  spermatozoon  into 
the  ovum  by  a  boring  movement  through  the  vitelline  membrane,  either 
through  the  porous  canals  or  the  micropyle. 


920  PHYSIOLOGY  OF   THE  DOMESTIC   ANIMALS. 

The  locality  in  which  fertilization  takes  place  may  be  either  the 
ovary,  as  is  shown  by  the  occurrence  of  abdomidal  pregnancy,  the  Fal- 
lopian tube,  or  the  cavity  of  the  uterus  itself.  The  manner  in  which  the 
spermatozoa  obtain  access  to  the  ovum  is  not  capable  of  clear  demon- 
stration. In  the  case  of  the  ruminants,  as  has  been  seen,  there  are  reasons 
for  believing  that  the  spermatozoa  are  deposited  directly  within  the 
cavity  of  the  uterus.  In  other  animals,  where  in  all  probability  this  does 
not  take  place,  the  entrance  of  the  spermatozoa  into  the  uterus  may  be 
accomplished  by  the  suction  which  results  from  the  relaxation  of  the 
uterus  as  this  condition  of  erection  and  engorgement  passes  off,  and  it  is 
a  matter  of  common  experience  that  the  introduction  of  semen  even 
within  the  vestibule  of  the  vagina  is  frequently  sufficient  to  produce  fer- 
tilization. It  is  probable  that  the  vibration  of  the  cilia  is  concerned  in 
causing  their  movement  to  meet  the  ova.  It  must  not  be  forgotten,  how- 
ever, that  within  the  uterus,  and  especially  within  the  Fallopian  tubes,  the 
motion  of  the  ciliated  epithelium  is  normally  in  the  opposite  direction 
to  that  in  which  the  spermatozoa  must  move  to  reach  the  ovary,  so  that 
while  this  ciliary  motion  would  facilitate  the  descent  of  the  ovum,  it  must 
offer  an  obstacle  to  the  ascent  of  the  spermatozoa. 

Nothing  absolutely  definite  is  known  as  to  the  manner  in  which 
the  bringing  together  of  the  male  and  female  spermatic  elements  is 
accomplished.  It  is  only  clearly  known  that  the  spermatozoa  in  some 
way  possess  the  power  of  rapidly  ascending  through  the  internal  sexual 
organs  of  the  female.  Spermatozoa  have  been  found  within  the  uterine 
cavity  of  the  dog  a  quarter  of  an  hour  after  the  act  of  copulation,  and  in 
the  Fallopian  tube,  even  at  its  abdominal  end,  within  one  or  two  hours. 

The  spermatozoa  retain  their  power  of  fertilizing  the  ovum,  as  indi- 
cated by  the  persistence  of  their  power  of  movement,  for  as  long  as  eight 
days  while  within  the  body  of  the  female, — a  period  which  is  abundant  to 
permit  the  ripening  and  discharge  of  an  ovum  and  its  contact  with  the 
spermatozoa.  Even  if  copulation  takes  place  in  the  intervals  between 
the  maturing  of  the  ova,  fertilization  may,  nevertheless,  take  place. 

As  a  rule,  fertilization  of  ova  is  only  possible  from  the  contact  with 
spermatozoa  from  the  same  species ;  }ret  in  certain  instances  fertilization 
may  take  place  between  different  species  of  the  same  genus  of  animals, 
as,  for  example,  between  the  horse  and  the  ass,  between  the  dog  and  the 
wolf,  between  the  dog  and  the  fox,  between  the  lion  and  the  tiger,  and 
between  the  rabbit  and  the  hare.  The  results  of  such  impregnation  are 
spoken  of  as  hybrids,  and  possess  characteristics  midway  between  the 
two  species.  The  products  of  such  impregnation  are,  as  a  rule,  barren 
from  arrested  development  of  their  genital  organs  (testicle  and  ovary). 

The  impregnated  ovum,  whatever  be  the  locality  in  which  impreg- 
nation takes  place,  is  borne  to  the  interior  of  the  uterus,  there  to 


KEPEODUCTIVE  FUNCTIONS.  921 

undergo  the  changes  which,  starting  in  the  clevage  of  the  blastodermic 
membrane,  as  already  described,  terminate  in  the  development  of  the 
embryo.  When  such  a  fecundated  ovum  reaches  the  uterus  it  inaugu- 
rates certain  changes  in  the  mucous  membrane  of  that  organ.  It  has 
been  noticed  that  the  maturity  and  escape  of  the  OArum  is  accompanied 
by  congestion  and  swelling  of  the  uterine  mucous  membrane  with  the 
ultimate  solution  and  discharge  of  the  mucous  surface.  When  the  im- 
pregnated ovum  reaches  the  uterus  it  becomes  covered  by  a  membrane 
which  was  first  described  by  William  Hunter  as  the  membrana  decidua, 
because  it  was  removed  at  birth.  Three  different  divisions  of  this  mem- 
brane may  be  recognized.  The  decidua  vera  is  the  thickened,  highly 
vascular,  and  softened  mucous  membrane  of  the  uterus.  As  the  ovum 
reaches  the  uterine  cavity  it  becomes  fixed  (conception)  in  a  fold  of  the 
uterine  decidua  or  decidua  vera,  which  grows  up  in  the  form  of  folds, 
entirely  surrounding  the  ovum.  These  folds  finally  meet  over  the  back 
of  the  ovum  and  so  form  the  decidua  reflexa.  The  part  of  the  decidua  vera 
behind  the  ovum,  i.e.,  between  the  ovum  and  the  uterine  wall,  is  spoken 
of  as  the  decidua  serotina,  in  which  locality  the  placenta  is  ultimately 
formed.  The  ovum,  covered  with  villous  processes,  is  thus  entirety  sur- 
rounded by  the  decidua,  and,  gradually  increasing  in  size,  remains  within 
the  cavity  of  the  uterus  until  mature. 

For  the  consideration  of  the  development  of  the  different  tissues  and 
organs  of  the  embryo,  the  reader  is  referred  to  text-books  on  Anatomy  or 
Embryology. 


to 


0 


INDEX. 


Abdominal  muscles,  action  of,  in  expira- 
tion, 579 

Abducens  nerve,  833,  875 
Aberration^  chromatic,  855 

spherical,  854 

Abomasum,  structure  of,  320 
Absorption,  453 

by  the  lymphatics,  456 

by  the  skin,  656 

coefficient  of,  59 

of  fat,  456 

of  gases,  58 

of  tissues  for  colors,  68 
Accelerator  nerves  of  the  heart,  551 
Accessory  foods,  160 

muscles  of  inspiration,  578 
Accommodation,  mechanism  of,  859 
Acid  albumen,  98 

of  gastric  juice,  349 
Adamkiewicz's  test  for  proteids,  92 
Adhesion,  40 

Adipose  tissue,  formation  of,  120,  664 
Age,  signs  of,  in  domestic  animals,  262 

the  determination  of,  by  the  teeth,  255 
Air-vesicles,  571 
Ajutage,  influence  of,  518 
Albumen,  alkali,  101 

destruction  of,  in  starvation,  676 

factor  of,  673 

of  milk,  estimation  of,  634 
Albumens,  92 
Albuminates,  derived,  98 
Albuminoids,  104 

collagenous,  105 
Albuminous  bodies,  85 
classes  of,  92 
decomposition  of,  109 
general  characteristics  of,  88 

food-constituents,  fate  of,  660 
Alcoholic  fermentation,  147 
Alimentary  rations,  195 
Alkali  albumen,  101 

albuminate,  101 
Alkaline  phosphates,  130 
Amandin,  94 
Amble,  the,  746 
Ammonium  carbonate,  136 
Amoeba,  13 

digestive  processes  in,  204 
Amoeboid  contractility,  14 

movements,  14,  75 
Amphiarthroses,  729 
Amphibia,  brain  of,  804 

olfaction  in,  844 


Amyloid  substance,  102,  115 

Amylolytic  ferment,  112 

Amy  loses,  112 

Amylum,  113 

Analysis  of  milk,  631 

Anelectrotonus,  780 

Animal  cells,  chemical  processes  in,  142 

foods,  188 

composition  of,  184 

heat,  693 

influence  of  nervous  system  on,  697 
of  different  animals,  696 

locomotion,  731 
Animals  and  plants,  distinctions  between,  5 

diet  of,  193 
Anode,  777 

Anterior  pyramids,  structure  of,  811 
Antipeptone,  409 
Aortic  valves,  action  of,  514 
Arabin,  120 
Arabinose,  120 
Area  opaca,  21 

pellucida,  21 

Arterial  blood,  characteristics  of,  597 
gases  of,  592 

tension,  526 

tonus,  557 
Arteries,  blood  pressure  in,  528 

circulation  in,  523 

elastic  tissue  of,  525 

influence  of  the  nervous  system  on,  552 

muscular  coat  of,  525 

physical  structure  of,  524 
Arterioles,  circulation  in,  538 
Articulata,  nervous  system  of,  767 
Articulations,  classification  of,  729 
Arthrodia,  730 
Asphyxia,  604 
Ass,  larynx  of,  760 
Aster,  17 

Atropine,  action  of,  on  heart,  543 
Audition,  875 

Auditory  apparatus  of  birds,  876 
of  fishes,  876 
of  reptiles,  876 

canals,  880 

nerve,  834 
Augmentation,  785 
Auricle,  877 
Auricles,  contraction  of,  503 

muscular  fibres  of,  501 
Auriculo-ventricular  valves,  action  of,  510 
Automatism,  765,  784 

of  protoplasm,  14 

(923) 


924 


INDEX. 


Ball-and-socket  joint,  730 
Barley -bran,  171 

composition  of,  170 

straw,  171 
Basal  ganglia  of  the  brain,  development  of, 

807 

functions  of,  822 
Basis  cruris,  819 
Beef-tea,  composition  of,  190 
Beet  residue,  182 
Beets,  174 
Bile,  382 

acid,  preparation  of,  385 

acids,  384 

chemical  characteristics  of,  383 

coloring  matters  of,  387 
test  for,  388 

composition  of,  383 

crystallized  preparation  of,  385 

inorganic  constituents  of,  390 

physiological  action  of,  393 

salts,  test  for,  385 

secretion  of,  391 
Biliary  fistulae.  394 
Bilirubin,  388 
Biliverdin,  389 
Birds,  auditory  apparatus  of,  876 

brain  of,  804 

digestive  apparatus  of,  211 

gastric  digestion  in,  379 

nervous  system  of,  770 

olfaction  in,  844 

organs  of  circulation  in,  497 

production  of  sound  in,  759 

reproduction  in,  905 

respiratory  apparatus  of,  568 

vision  in,  849 

Biuret  reaction  of  proteids,  91 
Blastema,  16 
Blastoderm,  20 

changes  in  form  in  impregnation,  22 

section  of,  21 

segmentation  of,  22 
Blastodermic  vesicle,  25 
Blastopore,  25 
Blood,  469 

absorption  of  carbon  dioxide,  595 
of  gases,  592 

circulation  of,  491 

coagulation,  483 

composition  of,  471 

corpuscles,  27 
red,  471,  474 
white,  479 

crystals,  475 

current,  velocity  of,  530 

gases  of,  490,  592 

plasma,  483 

plates,  483 

pressure,  525 

experiment,  526 

in  arteries,  528 

in  different  mammals,  530 


Blood  pressure  in  the  capillaries,  538 

quantity  of,  470 

respiratory  changes  in,  591 

serum,  489,  595 

tension  of  gases  in,  596 
Bone-corpuscles,  29 
Bone,  development  of,  35 
Bones  of  the  ear,  880 

heart,  509 
Bran,  barley,  171 

Branching  tubes,  flow  of  liquids  in,  521 
Brain,  development  of,  803 

functions  of,  803 

of  mammals,  809 

size  of,  in  different  animals,  808 

weight  of,  in  different  animals,  809 
Bread,  composition  of,  165 
Brewers'  grains,  179 
British  gum,  116 
Bronchi,  structure  of,  570 
Brunner's  glands,  416 
Buckwheat,  171 
Buckwheat-meal,  172 
Buckwheat-straw,  172 
Budding,  16 
Bulbs  and  roots,  174 
Burdach,  column  of,  787,  797 
Butter,  617 

estimation  of,  633 
Buttermilk,  188 
Butyric  acid,  122 
Butyrin,  122 

Csecal  fistulae,  428 
Cfficum,  221 

functions  of,  423 

secretion  of,  428 

structure    f,  426 
Calcium  carbonate,  130 

fluoride,  136 

phosphate,  133 

sulphate,  136 
Cane-sugar,  119 

gastric  digestion  of,  354 
Canter,  751 
Capillaries,  blood  pressure  in,  538 

circulation  in,  536 

development  of,  34 

of  the  lung,  571 

structure  of,  536 
Capillarity,  40 

Capillary  phenomena,  explanation  of,  40 
Carbohydrate  food-constituents,  fate  of,  666 
Carbohydrates,  112 

action  of  pancreatic  juice  on,  406 

as  sources  of  fat,  666 

construction  of,  85 

gastric  digestion  of,  354 

influence  of,  on  nutrition,  683 
Carbonate  of  ammonium,  136 

of  calcium,  130 

of  magnesium,  130 

of  potassium,  129 


INDEX. 


925 


Carbonate  of  sodium,  129 

Carbon  dioxide,  absorption  of,  by  blood,  595 

Cardiac  contraction,  phases  of,  508 

ganglia,  541 
Cardiograph,  506 
Cardio-inhibitory  centre,  551,  816 
Carnivora,  characteristics  of,  196 
urine  of,  637 

dentition  of,  254 

digestive  power  of,  436 

faeces  of,  446 

foods  of,.  160 

gastric  digestion  in,  360 

mastication  in,  239 

prehension  of  food  in,  235 

stomach  of,  215 
Cartilage,  fibrillar,  35 

fibro-,  35 

forms  of,  29 

hyaline,  35 

structure  of,  35 
Casein,  102,  614 

estimation  of,  634 

gluten,  94,  95 

mode  of  formation  of,  627 
Caserns,  vegetable,  94 
Cat-fat,  123 
Cathode,  777 

Cattle,  normal  foods  for,  690 
Cell-constituents,  inorganic,  123 

nitrogenous  organic,  88 

non-nitrogenous,  112 
Gel],  contents  of,  12 

variation  in,  29 

definition  of,  13 

doctrine,  15 

formation,  endogenous,  17 
free,  16 

membrane,  13 

nucleolus  of,  13 

nucleus,  13 

pigment,  motions  in,  75,  76 

polar,  18 

typical,  12 
Cells,  11 

chemical  constituents  of,  85 

chemical  processes  in,  136 

ciliated  epithelial,  77 

development  of  force  in,  147 

difference  in  size  of,  27 

endogenous  formation  of,  16 

epiblastic,  25 

form  of,  27 

general  properties  of,  12 

hypoblastic,  25 

inorganic  constituents  of,  86 

mechanical  movement  in,  70 

modification  in  the  form  of,  26 

of  spinal  cord,  27 

origin  of,  14 

physical  process  in,  37 

protoplasmic,  movements  in  contents  of, 
73 


Cells,  reproduction  of,  16 

water  of,  86 
Cellular  chemistry,  85 

physics,  37 
Cellulose,  114 

digestion  of,  429 
Cement,  structure  of,  246 
Centre,  cardio-inhibitory,  551,  816 

cilio-spinal,  795 

for  closure  of  the  eyelids,  816 

for  coughing,  817 

for  deglutition,  817 

for  dilatation  of  the  pupil,  817 

for  glycogenesis,  817 

for  inhibition  of  reflex  action,  793 

for  micturition,  649 

for  respiration,  816 

for  secretion  of  saliva,  817 

for  sneezing,  816 

for  suckling  and  mastication,  817 

for  vomiting,  817 

of  gravity  of  animals   731 
Cereals,  163 

Cerebellar  peduncle,  results  of  section  o£ 
827 

tract,  797 
Cerebellum,  functions  of,  825 

structure  of,  818 
Cerebral  convolutions,  804 

cortex,  functions  of,  824 

hemispheres,  809 

lobes,  804 

functions  of,  823 

peduncles,  functions  of,  821 
Cerebrin,  775 
Cerebrum,  structure  of,  823 

functions  of,  824 

Chameleon,  movements  of  pigment-cells,  75 
Cheeks,  action  of,  in  mastication,  264 
Cheese,  188 
Chemical  constituents  of  cells,  85 

phenomena  in  respiration,  587 

processes  in  animal  cells,  142 
in  cells,  136 
in  vegetable  cells,  137 
Chloride  of  magnesium,  136 

of  potassium,  128,  129 

of  sodium,  128 

Chlorophyll,  functions  of,  136,  137 
Cholesterm,  389 
Cholic  acid,  387 
Chondrin,  107 
Chondrogen,  107 

Chorda  tympani,  influence  on  salivary  se- 
cretion, 298 

Choroid  membrane,  849 
Chromatic  aberration,  855 
Chyle,  459 

composition  of,  461 

movement  of,  462 
Chyle-vessels,  457 
Chyme,  characteristics  of,  419 
Cicatricula,  20 


926 


INDEX. 


Ciliary  movement,  77 

influence  of  acids  on,  80 
alkalies  on,  81 
anaesthetics  on,  81 
imbibition  on,  80 
mechanical  force  of,  78 
protoplasmic  nature  of,  81 
temperature  on,  80 

nerves,  863 

Ciliated  epithelial  cells,  77 
Cilio-spinal  centre,  795 
Circulation,  hydraulic  principles  of,  516 

estimation  of  duration  of,  531 

in  arteries,  523 

in  fishes,  494 

influence  of  nervous  system  on,  540 
of  the  respiration  on,  605 

in  mammals,  497 

in  the  capillaries,  536 

in  the  veins,  539 

of  lymph,  467 

of  the  blood,  491 

organs  of,  491 

rapidity  of,  531 
Clarke's  column,  799 
Cleavage  of  ovum,  15,  19 
Clover,  composition  of,  187 
Coagulated  proteids,  102 
Coagulation  of  blood,  483 

of  milk,  614 
Cochlea,  877 
Cochlear  nerve,  882 
Co-efficient  of  absorption  of  gases,  59 

of  elasticity,  66 
Cohesion,  38 

of  tissues,  62 

Cold,  action  of  on  heart,  548 
Collagen,  106 

Collagenous  albuminoids,  105 
Colloids,  osmosis  of,  52 
Colon,  functions  of,  429 
Colostrum,  609 

changes  in,  620 

corpuscles,  610 

Comparative  physiology,  definition  of,  1 
Complemental  volume  of  air,  573 
Conduction  in  the  spinal  cord,  795 
Conglutin,  94 
Connective-tissue  constituents,  104 

tissues,  34 

Constituents  of  food,  fate  of,  664 
Contents  of  cells,  12 
Contractile  tissues,  701 
Contractility  of  protoplasm,  14,  70 
Convolutions  of  the  brain,  804 
Co-ordination,  785 
Copper,  136 
Cornea,  849 
Corpora  bigemina,  807 

quadrigemina,  807 
functions  of,  822 

striata,  807 
Corpuscles  of  bone,  29 


Corpus  luteum,  913 

Corpus  striatum,  functions  of,  822 

Cortex  of  the  brain,  functions  of,  524 

Corti's  organ,  882 

Cotton-seed  cake,  183 

Coughing,  605 

centre  for,  817 
Cranial  nerves,  832 

origin  of,  812 
Cream,  617 

composition  of,  618 
Crop,  functions  of,  380 
Crura  cerebri,  818 

functions  of,  821 
Crying,  "605 
Crystallin,  97 
Crystalline  lens,  849 
Cutaneous  absorption,  656 

functions,  651 

respiration,  656 
Cyclosis,  73 
Cytoblasts,  16 

Decomposition  of  the  albuminous  bodies, 

109 

Decussation  of  pyramids,  810 
Defecation,  451 
Deglutition,  307 

centre  for,  817 
Dental  formula,  252 
Dentine,  structure  of,  246 
Dentition  in  domestic  animals,  263 

in  herbivora,  258 
Depressor  nerve,  556 
Derived  albuminates,  98 
Development  of  bone,  35 

of  tissue,  explanation  of,  15 

of  tissues  and  organs,  31 
Dextrin,  116 

test  for,  116 
Dextrose,  117 

Diabetes,  production  of,  672 
Diabetic  centre,  671,  817 
Dialysis,  53 
Diapedesis,  539 
Diarthroses,  729 
Diarthrosis  rotatoria,  730 
Diastatic  ferment  of  the  liver,  671 
Diaster,  17 

Dicrotic  wave,  explanation  of,  536 
Diet  of  animals,  193 

Diffusion,  application  of  to  respiration,  596 
Diffusion  of  gases,  56 

in  the  animal  organism,  60 

in  the  lungs,  592 

through  porous  partitions,  58 

of  liquids,  49 

Digastric  muscle,  functions  of  in  mastica- 
tion, 242 

Digestibility  of  food-stuffs,  432 
Digestion,  203 

gastric,  337 

m  the  mouth,  268 


INDEX. 


927 


Digestion  in  the  small  intestine,  382 
Digestive  apparatus,  characteristics  of,  203 

co-efficient,  435 

Dionaea  muscipula,  movements  of,  72 
Dioptric  mechanisms  of  the  eye,  851 
Distillery  mash,  180 
*    Diuretics,  mode  of  action  of,  647 
Division  of  nucleus,  17 
Dog,  dentition  in,  260 

fat,  123 

larynx  of,  761 

urine  of,  640 
Dogs,  diet  of,  362 
Double  refraction,  6'8 
Drinking,  mechanism  of,  236 
Dry  fodder,  162 

composition  of,  184 
Duodenal  follicles,  416 
Dyspnoea,  603 

Ear-ossicles,  880 

movements  of,  888 
Ear,  structure  of,  877 
Egg-albumen,  93 
Egg  of  hen,  formation  of,  20,  21 
Egg-osmometer,  55 
Eggs,  composition  of,  190 
Egg-yelk,  structure  of,  20 
Elasticity,  co-efficient  of,  66 

of  tissues,  65 
Elastic  tissues,  35 

tubes,  flow  of  liquids  through,  522 
Elastin,  108 

Electrical  phenomena  of  tissues,  70 
in  muscle,  721 
in  nerves,  779 

Electricity,  influence  of,  on  nerves,  777 
Electrotonus,  780 
Elementary  organisms,  11 
Enamel,  structure  of,  245 
Enarthrosis,  730 
Encephalin,  775 
Endogenous  cell-formation,  16 
Endolymph,  881 
Endothelia,  33 
Ensilage,  177 
Enzymes,  111 
Epiblast,  23 
Epiblastic  cells,  25 

spheres,  24 
Epithelial  cells,  28 
Epitheliums,  structure  of,  33 
Erection,  mechanism  of,  916 
Esparcet,  176 
Eustachian  tube,  880,  890 
Expiration,  mechanism  of,  578 
Expired  air,  constituents  of,  588 
temperature  of,  588 
watery  vapor  of,  588 
Extensibility  of  tissues,  66 
External  intercostal  muscles,  action  of,  in 

inspiration,  577 
Eyeball,  muscles  of,  874 


Eye,  development  of,  848 

formation  of  image  in,  857 

refraction  in,  858 
Eyes,  composite,  847 

structure  of,  848 

Facial  nerve,  834 

Faeces,  composition  of,  445 

Fat,  absorption  of,  456 

feeding  with,  682 
Fat-ferment,  112 
Fat  of  milk,  production  of,  626 

influence  of,  on  nitrogenous  waste,  677 
on  nutrition,  680 

metabolism  of,  673 

sources  of,  665 
Fats,  120 

action  of  pancreatic  juice  on,  406 

composition  of,  123 

detection  of,  121 

factor  of,  673 

of  milk,  617 

Fattening  animals,  foods  of,  687 
Fatty  acids,  construction  of,  85 

constituents  of  food,  fate  of,  664 

tissue,  formation  of,  664 
Feeding,  nutritive  processes  in,  680 

proper  intervals  between,  689 

witn    carbohydrates,    nutritive     pro- 
cesses in,  683 

with  meat,  nutritive  processes  in,  680 
Fenestra  ovalis,  880 

rotunda,  880 
Ferment,  amylolytic,  112 

diastatic,  112 

fat,  112 

fibrin,  487 

inversive,  112 

milk-curdling,  112 

of  the  liver,  112,  671 

proteolytic,  112 
Fermentation,  alcoholic,  147 

of  -lactic  acid,  147 

in  small  intestine,  418 

putrefactive,  147 
Fermentations,  145 
Ferments,  110 

of  the  pancreatic  juice,  403,  404 

soluble,  110 

Fertilization  of  ovum,  result  of,  15 
Fibrillar  cartilage,  35 
Fibrin,  98,  488 

ferment,  487 

formation  of,  485 

gluten,  95 

vegetable,  95 
Fibrinogen,  97,  487 
Fibrinoplastin,  487 
Fibro-cartilage,  35 
Fibrous  tissue,  35 
Filtration,  48 

in  the  kidneys,  644 
Fishes,  auditory  apparatus  of,  876 


928 


INDEX. 


Fishes,  brain  of,  804 

circulation  in,  494 

digestive  apparatus  of,  210 

eyes  of,  849 

nervous  system  of,  770 

olfactory  apparatus  in,  844 

reproduction  in,  904 

respiratory  apparatus  of,  566 
Fistula,  gastric,  342 

pancreatic,  398 

parotid,  275 

submaxillary,  279 
Flexibility  of  tissues,  67 
Flustra,  digestive  apparatus  of,  205 
Fodders,  amounts  of  salts  in,  679 

changes  in,  176 

composition  of,  184 

dry,  162 

green,  162' 

influence  of  chopping  on,  688 

nutritive  proportions  in,  685 
Food,  action  of  gastric  juice  on,  351 

carbohydrate,  fate  of,  666 

constituents,  albuminous,  fate  of,  660 

for   cattle,  horses,  sheep,   and   swine, 
690 

prehension  of,  226 

products,  composition  of,  184 

required  by  the  herbivora  under  dif- 
ferent conditions,  684 

stuffs,  digestibility  of,  432 
Foods,  157 

animal,  188 

inorganic,  191 

nutritive  values  of,  685 

of  animals,  158 

of  carnivora,  160 

of  herbivora,  160 

vegetable,  161 
Force,  consumption  of,  in  cells,  147 

development  of,  in  cells,  147 
Formatio  reticularis,  811 
Form  of  cells,  modification  in,  26 
Frog,  heart  of,  502 
Frohde's  test  for  proteids,  92 
Fructivora,  characteristics  of,  197 
Functions,  animal,  8 

definition  of,  8 

nutritive,  155 

of  relation,  definition  of,  8 

reproductive,  8,  901 

specialization  of,  15,  32 

vegetative,  definition  of,  8 
Funiculus  cuneatus,  797 

gracilis,  810 

Gaits  of  the  horse,  739 
Gall-bladder,  382 
Gallop,  749 
Ganglia  of  the  heart,  541 

sporadic,  782 
Ganglion-cell,  27 
Ganglionic  cells,  structure  of,  772 


Gaseous  diffusion,  56 

in  the  animal  organism,  60 
through  porous  partitions,  58 
Gases,  absorption  of,  58 

of  blood,  490 
Gastric  digestion,  337 
in  birds,  379 
in  carnivora,  360 
in  omnivora,  363 
in  the  horse,  368 
in  ruminants,  374 
fistula,  342 

glands,  changes  of,  in  digestion,  357 
juice,  acid  of,  349 

action  of,  on  food,  351 

artificial,  341 

chemistry  of,  342 

influence  of  nervous  system   on, 

360 

mechanism  of  secretion  of,  360 
secretion  of,  356 
movements,  340 
Gelatin,  106 

vegetable,  96 
Gelatinous  tissue,  35 
Gemmation,  16 
Gemmiparous  generation,  903 
General  physiology,  definition  of,  1 
Generation  by  fission,  903 

by  spores,  903 

Germinal  disk  of  hen's  egg,  23 
spot,  15 
vesicle,  15 
Gestation,  duration  of  in  different  animals, 

907 

Ginglymous  joint,  730 
Gizzard,  functions  of,  381 
Glands,  mammary,  structure  of,  624 
of  stomach,  tubular,  356 
structure  of,  36 
Glandular  tissue,  34 
Gliadin,  96 
Globulins,  96 

vegetable,  97 

Glomerulus,  functions  of,  642 
Glosso-pharyngeal  nerve,  834 
Glottis,  movements  of,  762 

in  respiration,  579 
Glucoses,  117 

tests  for,  118 
Glucosides,  117 
Gluten,  95 
casein,  95 
fibrin,  95 
Glycerin,  122 
Glyceryl,  121 
Glycin,  387 
Glycochol,  387,  664 
Glycocholate  of  sodium,  384 
Glycocholic  acid,  386 
Glycogen,  116 

characteristics  of,  668 

influence  of  the  nervous  system  on,  671 


INDEX. 


929 


Glycogen,  origin  of,  669 

preparation  of,  668 

relation  of,  to  diet,  669 
Glycogenic  centre,  817 
Glycogenesis,  667 
Goat  and  sheep,  urine  of,  640 

prehension  of  food  in,  235 
Goll,  column  of,  787,  797 
Graafian  follicles,  909 
Graham's  law  of  the  diffusion  of  gases,  58 
Grains  and  fruits,  composition  of,  184 
Granivora,  characteristics  of,  197 
Granulose,  114 
Grape-sugar,  117 
Grasses,  175 
Green  fodder,  162 

composition  of,  184 
Growth  of  protoplasm,  14 
Gustatory  cells,  894 

nerves,  896 

Haemoglobin,  475,  593 

reduced,  594 

spectrum  of,  594 
Harder's  gland,  850 
Hauling,  mechanism  of,  755 
Hay,  composition  of,  187 
Hearing,  function  of,  883 

sense  of,  875 
Heart,  accelerator  nerves  of,  551 

action  of,  499 
heat  on,  547 

changes  of  shape  in  contraction,  505 

inhibitory  nerves  of,  549 

intrinsic  nervous  system  of,  540 

movements  of,  502 

in  mammals,  503,  504 

of  frog,  502 

of  mammals,  498 

of  ox,  509 

sounds  of,  514 

structure  of,  500 

tetanus,  547 

work  of,  532 
Heat,  action  of,  on  heart,  547 

animal,  693 

centres,  698 

modes  of  loss  of,  696 

sources  of,  694,  696 

symptoms  of,  in  animals,  911 
Hemipeptone,  409 
Hen's  egg,  structure  of,  20 
Herbivora,  characteristics  of,  197 
urine  of,  637 

digestive  power  of,  436 

faeces  of,  446 

food  required  by,  684 

foods  of,  160 
Hiccough,  604 
Hippunc  acid,  663 
Hog,  composition  of  bile  of,  384 

larynx  of,  761 

structure  of  stomach  of,  363 


Hogs,  food  required  in  fattening,  688 

normal  foods  for,  690 
Holoblastic  ovum,  19 
Homocerebrin,  775 
Horse,  dentition  of,  253 

fat,  123 

gaits  of,  739 

gastric  digestion  in,  368 
juice  of,  370 

glottis  of,  760 

mechanics  of  the  limbs  of,  739 

normal  foods  for,  690 

power,  755 

prehension  of  food  in,  234 

respiratory  movements  of,  582 

tongue  of,  233 

urine  of,  638 

Human  physiology,  definition  of,  1 
Hunger,  692 
Hyaline  cartilage,  35 
Hydra,  digestive  processes  in,  205 
Hydrates,  formation    of,  from  anhydrates, 

146 

Hydraulic  principles  of  the  circulation,  516 
Hydrocarbons,  120 

construction  of,  85 
Hydrochloric  acid,  135 
Hypermetropia,  861 
Hypoblast,  24 

division  of,  25 
Hypoblastic  cells,  25 

spheres,  24 
Hypoglossal  nerve,  835 

Imbibition,  44 

influence  on  ciliary  movements,  80 

on  protoplasmic  motion,  82 
Impregnation,  916 
Incus,  880 
Indican,  412 
Indol,  411 
Infusoria,  ciliated  movement  in,  77 

digestive  processes  in,  204 
Inhibition,  785 

Inhibitory  nerves  of  the  heart,  549 
Inorganic  cell-constituents,  123 

constituents  of  cells,  86 

foods,  191 
Inosite,  118 
Insects,  digestive  apparatus  of,  207 

eyes  of,  847 

Inspiration,  mechanism  of,  574 
Intensity  of  sound,  758 
Intercellular  tissues,  34 
Intercostal  muscles,  action  of,  in  inspira- 
tion, 577 

nerves,  influence  of  on  respiration,  599 
Intestinal  digestion,  382 

in  different  animals,  419 

fistula,  416 

juice,  416 

action  of  on  food -stuffs,  418 
characteristics  of,  417 


930 


INDEX. 


Intestinal  reaction,  421 
Intestines,  characteristics  of,  217 

fermentation  in,  418 

large,  digestion  in,  423 

movements  of,  448 

muscular  structure  of,  448 
Inulin,  116 

Inversive  ferment,  112,  418 
Invert-sugar,  119,  418 
Iris,  849 

muscular  fibres  of,  862 
Iron,  136 
Irradiation,  871 
Irritability,  muscular,  709 

of  muscle,  influence  of  temperature  on, 
719 

of  nerves,  776 

Jacobson's  organ,  843 
Jaws,  movements  of,  241 
Joints,  formation  of,  729 

gliding,  730 
inged,  730 
rotatory,  730 
Jumping,  mechanism  of,  in  man,  738 

Karyokinesis,  17 

Kathelectrotonus,  780 

Keratin,  109 

Kicking,  753 

Kidney,  structure  of,  640 

Kidneys  and  skin,  correlation  of,  645 

Kreatin,  formation  of,  66J 

Labyrinth  of  the  ear,  880 

Lachrymal  apparatus  of  mammals,  850 

duct,  850 

secretion,  658 
Lacteals,  457 

Lactic  acid  fermentation,  147 
Lactose,  120 
Laevulose,  118 
Lardacein,  102 
Large  intestine,  digestion  in,  423 

structure  of,  430 

Larvae,  digestive  apparatus  of,  206 
Laryngeal  muscles,  action  of,  762 
Larynx,  nerves  of,  764 

of  birds,  760 

Latent  period  in  muscular  contraction,  713 
Laughing,  605 
Lecithin,  481 
Legumin,  94 
Leguminous  plants,  173 
Lens,  action  of,  853 
Lenses,  formation  of  images  by,  857 
Leucin,  410 

Levatores  costarum,  action  of  in  inspira- 
tion, 577 

Lever  motion  of  muscles,  725 
Levers,  724 

Lieberkuhn's  glands,  416 
Light,  reflection  of,  851 


Lignin,  115 

Lips,  action  of,  in  mastication,  264 

Liquids,  cohesion  of,  39 

diffusion  of,  49 

flow  of,  through  elastic  tubes,  522 
rigid  tubes,  518 

surface  tension  of,  39 
Liver  ferment,  112,  671 

glycogenic  function  of,  667 
Lobes  of  the  brain,  804 
Localization  of  the  functions  in  the  cortex 

825 

Locomotion,  animal,  731 
Lungs,  diffusion  of  gases  in,  592 
Lying  down  and  rising  up,  mechanism  of, 

754 
Lymph,  463 

circulation  of,  467 
Lymphatics,  absorption  of,  456 

Macula  lutea,  865 
Magnesium-ammonium  phosphate,  136 

carbonate,  130 

chloride,  136 

phosphate,  134 
Malleus,  880 
Maltose,  120 
Mammalian  heart,  498 

ovum,  changes  in,  from  impregnation, 

segmentation  of,  19 
Mammals,  brain  of,  809 

circulation  in,  497 

digestive  apparatus  of,  213 

movements  of  the  heart  in,  503 

ocular  apparatus  in,  849 

process  of  fecundation  in,  904 

reproduction  in,  906 
Mammary  glands,  histological  changes  in, 

628 

innervation  of,  629 
structure  of,  624 

secretion,  609 
Manganese,  136 
Manometer,  526 
Manyplies,  functions  of,  377 

structure  of,  319 
Marey's  tambour,  581 
Margaric  acid,  122 
Margarin,  122 

Masseter  muscle,  action  of,  243 
Mastication,  338 

centre  for,  817 

duration  of,  266 

influence  of  saliva  on,  267 
Meal,  buckwheat,  172 
Meat,  188 

composition  of,  189 

nutritive  processes    of   feeding  with, 

680 

Mechanical  movement  in  cells,  70 
Meconium,  composition  of,  445 
Medulla  oblongata,  810,  816 


INDEX. 


931 


Medulla  oblongata,  course  of  fibres  of,  818 

functions  of,  814 
Membrane  of  cells,  13 

vitelline,  15 
Mesencephalon,  803 
Mesoblast,  23,  25 
Meta-albumen,  103 
Micturition,  centre  for,  649 

mechanism  of,  648 
Milk,  188 

cistern,  624 
coagulation,  614 
curdling  ferment,  112r  347 
action  of,  615 
of  pancreatic  juice,  411 
gases  of,  619 
gastric  digestion  of,  354 
globules,  610 

influence  of  albuminoids  on,  622 
diet  on  quantity  of,  622 
fat  on,  623 
water  on,  622 

inorganic  constituents  of,  619 
inspection  and  analysis,  631 
of  different  animals,  composition   of, 

613 
physical  and  chemical  properties  of, 

610 

quantity  of,  620 
reaction  of,  611 
secretion  of,  609,  624 

influence   of  nervous  system  on, 

629 

skimmed,  619 
solids,  estimation  of,  633 
sugar,  120,  616 

estimation  of,  634 
origin  of,  627 
uterine,  610 

variation  in  the  quantity  and  compo- 
sition of,  619 

Millon's  reaction  for  proteids,  91 
Mimosa  pudica,  71 
Mitral  valves,  509 
Mollusks,  digestive  apparatus  of,  209 

nervous  system  of,  767 
Motion  from  imbibition  in  cells,  70 
Motor  centres  of  the  cortex,  825 

impulses  in  spinal  cord,  path  of,  801 
Motory  impulses,  paths  of,  829 
Mouth,  digestion  in,  268 
Movement,  ciliary,  77 
physiology  of,  701 

protoplasmic,  general  conditions  of,  82 
Movements,  amoeboid,  75 

from  imbibition  in  cells,  70 

of  cell  contents,  70 
in  cells,  70 

in  protoplasmic  contents  of  cells,  73 
of  intestines,  448 
of  stomach,  340 
of  the  heart,  502 
Mucedin,  96 


Mucoid  tissue,  35 
Mulberry  mass,  15,  19 
Muscarine,  546 
Muscin,  104 

characteristics  of,  105 
preparation  of,  105 
Muscle,  accessory,  578 
analysis  of,  709 
chemical  composition  of,  704 

processes  in,  708 
coagulation  of,  705 
current,  722 
curve,  713 

electrical  phenomena  in,  721 
ferment,  706 
gases  of,  708 

microscopic    changes  of,   in    contrac- 
tion, 719 
plasma,  705 
serum,  707 
stapedius,  890 
tensor  tympani,  890 
Muscles,  classification  of,  722 
intercostal,  action  of,  577 
of  the  eye,  874 
structure  of,  36,  701 
Muscular  contraction,  81,  710,  714 
chemical  changes  in,  719 
heat  production  in,  720 
phenomena  of,  710 
wave  of,  718 
work  of,  721 

contractility,  applications  of,  722 
corpuscles,  703 
fibres,  isolated,  28 
of  heart,  500 
striped,  701 
structure  of,  701 
unstriped,  703 
irritability,  709 
preparation,  711 
sound,  716 
stimuli,  710 
tissue,  34 

Myelencephalon,  803 
Myo-albumose,  707 
Myoglobulin,  707 
Myograph,  712 
Myopic  eye,  861 
Myosin,  97,  99,  704 

ferment,  706 
Myosinogen,  706,  707 
Myriapods,  digestive  apparatus  of,  206 

Negative  impulse,  508 

variation  of  nerve-current,  780 
Nerve,  abducens,  833 

auditory,  834 

centres,  general  physiology  of,  78} 
of  spinal  cord,  789 

corpuscles,  structure  of,  772 

current,  779 

depressor,.  556 


£32 


INDEX. 


Nerve,  facial,  834 

fibres,  physical  properties  of,  775 

structure  of,  30 
Lypoglossal,  835 
oculo-motor,  832 
olfactory,  832' 
optic,  832 
pathetic,  832 
pneumogastric,  834 
gpinal  accessory,  835 
stimuli,  776 

tissue,  development  of,  34 
trifacial,  833 
trigeminal,  833 
trunk,  structure  of,  772 
Nerves,  acceleratory,  551 
afferent,  772 
centrifugal,  772 
centripetal,  772 
degeneration  of,  778 
efferent,  772 

electrical  phenomena  in,  779 
functional,  distinctions  between,  772 
influence  of  constant  current  on,  777, 

780 

inhibitory,  549 
intercostal,  599 
laryngeal,  influence  of,  in  respiration, 

601 

of  taste,  896 
phrenic,  599 

pneumogastric,  influence  of  in  respira- 
tion, 600 

vaso-constrictor,  558 
vaso-dilator,  558 
vaso-motor,  554 
Nervous  influence  on  protoplasmic  motion, 

76 

irritability,  776 

system,  conduction  of  motor  and  sen- 
sory impulses  through,  827 
influence  of,  on  arteries,  552 
on  bodily  temperature,  697 
on  circulation,  540 
on  micturition,  649 
on  renal  secretion,  645 
on  respiration,  598 
secretion  of  milk,  629 
of  articnlata,  767 
of  birds,  770      . 
of  fishes,  770 
of  mollusks,  767 
of  reptiles,  770 
of  star-fish,  766 
of  the  heart,  540 
^of  vertebrates,  769 
'organs  of,  36 
physiology  of, '765 
scheme  of,  766 
•      structure  of,  770' 
sympathetic,  835 

tissues,  chemical  and  physical  charac- 
teristics of,  774 


Neurokeratin,  775 
Nicotine,  action  of,  on  heart,  546 
Nitrogen,  excretion  of,  672 
Nitrogenous  matter,  metabolism  of,  673 

organic  cell-constituents,  88 

tissue,  constituents  of,  85 
Nceud  vital,  600 

Non-nitrogenous  organic   cell -constituents, 
112 

tissue,  constituents  of,  85 
Nostrils,  movements  of,  in  respiration,  579 
Nuclein,  482 
Nucleolus  of  cells,  13 
Nucleus,  deviation  in  form  of,  27 

division  of,  17 

of  cells,  13 

of  Pander,  21 
Nutrition,  659 

of  nerves,  influence  of  spinal  cord  on, 
778    : 

of  protoplasm,  14 

statistics  of,  672 
Nutritive  functions,  155 

processes  in  feeding,  680 

proportion  in  foods,  684 

proportions,  195 

salts,  192 

substances,  159 

Oats,  composition  of,  167; 
CSsophageal  canal,  320 

functions  of,  376 
Ocelli,  847 
Ocular  apparatus  in  mammals,  849 

muscles,  875 
Oculo-motor  nerve,  832,  875 

action  of,  on  pupil,  862 
Odorous  substances,  properties  of,  844 
'Oleic  acid,  122 
Olein,  122 
Olfactory  cells,  842 

lobes,  807,  841 

nerve,  832,  841 

distribution  of,  842 
Olivary  bodies,  811 
Omasum,  structure  of,  319 
Omnivora*,  characteristics  of,  198 

digestive  power  of,  436 

gastric  digestion  in,  363 
Optical  characteristics  of  tissues,  68 
Optic  lobes,  807 

nerve,  832 

nerve-fibres,  867 

thalamus,  functions  of,  823 
Organic  acids,  construction  of,  85 

nitrogenous  cell-constituents,  88 
Organisms,  elementary,  11 
Organized  and  unorganized  bodies,  distinc- 
tions between,  2 

bodies,  structure  of,  11 

body,  definition  of,  2 
Organs  and  tissues,  development  of,  31  , 

classification  of,  36  ; 


INDEX. 


933 


Organs,  composition  of,  36 

of  circulation,  491 

of  respiration,  562 
Origin  of  cells,  14 
Osmosis,  51 

causes  of,  55 

explanation  of,  54 

illustrations  of,  56 

rapidity  of,  52 
Osmotic  equivalent,  52 
Osteoblaste,  36    ; 
Otoliths,  881 
Ova,  909 
Ovary,  909 
Ovum,  15 

changes  of  fertilization  in,  18 

cleavage  of,  15,  19 

fertilization  of,  15 

holoblastic,  19 

meroblastic,  19 

of  animals,  classes  of,  19 

of  mammals,  18 

of  rahrbit,  size  of,  25 

size  of,  15 
Ox,  dentition  in,  258 

fat,  123 

heart  of,  509 

prehension'  of  food  in,  234 

tongue  of,  233 

urine  of,  639 

Oxen,  food  required  in  fattening,  687 
Oxygen,  absorption  of,  by  haemoglobin,  594 
by  the  blood,  592 

influence  of  protoplasmic  movements, 

83 
Oxy haemoglobin,  476 

spectrum  of,  594 

Pacing,  747 
Palmitic  acid,  122 
Palmitin,  122 
Pancreas,  anatomy  of,  639 

histological  changes  of,   in  digestion, 

413 

of  the  bird,  398 
of  the  cat,  398 
of  the  dog,  397 
Pancreatic  ferments,  403 
isolation  of,  404 
fistulaa,  398 

juice,  action  of,  on  carbohydrates,  406 
on  fats,  406 
on  food-stuffs,  405 
on  proteids,  408 
artificial,  405 

chemical  composition  of,  402 
milk-curdling  ferment  of,  411 
secretion  of,  412 
secretion,  396 

influence  of  nervous  system  on, 

415 

Pander,  nucleus  of,  21 
Papillary  muscles,  510 


Para-albumen,  103 
Paraglobulin,  97,  487 
Paramyosinogen,  706 
Parapeptone,  99 
Parotid  fistula,  275 

gland,  nervous  supply  of,  303 

saliva,  composition  of,  278 

secretion,  274 
Pathetic  nerve,  832,  875 
Pathology,  definition  of,  1 
Peas,  composition  of,  173 
Penis,  structure  of,  916 
Pepsin,  112 

preparation  and  characteristics  of,  346 
Pepsinogen,  358 
Peptone,  absorption  of,  454 

characters  of,  353 
Peptones,  103 
Perichondrium,  36 
Peristalsis  of  the  intestines,  448 
Perspiration,  652 
Phosphate  of  alkalies,  130 

of  calcium,  133 

of  magnesium,  134 

of  magnesium  and  ammonium,  136 

of  potassium,  130 

of  sodium,  130 
Phrenic  nerves,  influence  of,  in  respiration, 

599 
Physical  process  in  cells,  37 

properties  of  proteids,  89 

of  tissues,  61 
Physiology,  definition  of,  1 

of  inpvement,  701 
Pig,  dentition  in,  261 

fat,  123 

prehension  of  food  in,  235 

urine  of,  640 

Pigment-cells,  motions  in  chameleon,  75 
Pinna,  877 
Pitch  of  sounds,  758 
Placenta  of  ruminants,  908 
Plants  and  animals,  distinction  between,  5 

reproduction  in,  903 

respiration  in,  562 
Plasma  of  blood,  483 
Plasmine,  486 
Pneumogastric,  direct  stimulation  of,  550 

influence  of  section  of,  551 

reflex  action  of,  550 

nerve,  834 

action  of,  on  heart,  549 
of  frog,  545 

nerves,  influence  of,  in  respiration,  600 
Polar  cell,  18 
Pons  varolii,  functions  of,  821 

structure  of,  819 
Potassium  carbonate,  129 

chlorides,  128 

phosphates,  130 

sulphate,  135 
Prehension  of  food,  226 

of  liquids,  236 


934 


INDEX. 


Prehension  of  solids,  226 

Processes,  reproductive,  903 

Pronucleus,  female,  18 

Prosencephalon,  803 

Protagon,  775 

Protamceba  primitiva,  13 

Proteids,  action  of  pancreatic  juice  on,  408 

Adamkiewicz's  test  for,  92 

biuret  reaction  of,  91 

chemical  properties  of,  90 

coagulated,  102 

coagulation  of,  90 

composition  of,  88 

Frohde's  test  for,  92 

general  characteristics  of,  88 

Millon's  reaction  for,  91 

origin  of,  88 

physical  properties  of,  89 

fechultz's  test  for,  92 

tests  for,  90 

xantho-proteic  reaction  of,  91 
Proteolytic  ferment,  112 
Protoplasm,  11 

automatism  of,  14 

characteristics  of,  73 

contractility  of,  14 

nutrition  of,  14 

properties  of,  14,  73 

reproduction  of,  14 

respiration  of,  14 

Protoplasmic  contents  of  cells,  movements 
in,  73 

growth,  14 

movement,  70 

general  conditions  of,  82 
influence  of  degree  of  imbibition 

on,  82 
chemical  and  physical  agents 

on,  84 

nervous  system  on,  76 
oxygen  on,  83 
temperature  on,  82 

nature  of  ciliary  movements,  81 
Psalter,  functions  of,.  377 

structure  of,  319 
Pseudo-fibrin,  101 
Pseudopodia,  14 
Ptyalin,  112,  273 
Pulmonary  capillaries,  571 

infundibula,  570 

valves,  action  of,  514 
Pulse,  533 

and  blood  pressure,  causes  of  modifica- 
tions in,  560 

of  different  animals,  548 

wave,  production  of,  534 

rate  of  movement  of,  533 
Pupil,   centre   for  the   dilatation   of,    817, 
863 

changes  of  in  accommodation,  862 

influence  of  drugs  on,  864 

nerve  supply  of,  862 
Putrefactive  fermentation,  147 


Pyloric  glands,  356 

Pyramidal  tract  of  spinal  cord,  797 

Quality  of  sounds,  758 

Rabbit  ovum,  size  of,  25 
Rack,  the,  747 
Rations,  alimentary,  195 
Rearing,  751 

Red  blood-corpuscles,  474 
Reduced  haemoglobin,  594 
Reflection  of  light,  851 
Reflex  action,  782 

laws  of,  791 

inhibitory  centre,  793 

nutritive  action,  794 

secretory  action,  793 

vaso-motor  action,  793 
Refraction,  double,  68 

of  light,  851 

of  tissues,  68 
Refractive  index,  852 
Regio  olfactoria  of  the  nose,  842 

respiratoria,  842 
Relation,  functions  of,  8 
Remak's  division,  17 
Renal  secretion,  635 

mechanism  of,  640 
Rennet,  112 

action  of,  on  milk,  615 
Reproduction,  903 

of  cells,  16 

of  protoplasm,  14 
Reproductive  functions,  8,  901 

processes,  903 

tissues  of  the  female,  908 

of  the  male,  913 
Reptiles,  auditory  apparatus  of,  876 

brain  of,  804 

digestive  apparatus  of,  210 

nervous  system  of,  770 

organs  of  circulation  in,  496 

reproduction  in,  904 

respiratory  apparatus  of,  568 

vision  in,  849 

Residual  volume  of  air,  574 
Resistance  to  traction,  63 
Resonance,  885 
Respiration,  561 

changes  of  the  air  in,  588 

chemical  phenomena  in,  587 

cutaneous,  656 

influence  of,  on  circulation,  605 

mechanical  processes  of,  574 

nervous  mechanism  of,  598 

of  protoplasm,  14 

organs  of,  562 

rhythm,  579 

Respirations,  numbers  of,  in  different  ani- 
mals, 581 
Respiratory  centre,  816 

action  of  blood  on,  602 
location  of,  600 


INDEX. 


935 


Respiratory  changes  in  the  blood,  591 

curve,  581 

movements,  modified,  604 

organs  of  birds,  568 
of  fishes,  566 
of  reptiles,  568 
types  of,  563 

volumes  of  air,  585 
Restiform  bodies,  811 
Reticulum,  functions  of,  376 

structure  of,  318 
Retina,  functions  of,  867 

structure  of,  865 
Retinal  purple,  868 
Rheoscopic  frog,  722 
Rhodopsm,  868 
Rhythm  of  respiration,  579. 
Ribs,  movements  of,  in  respiration,  575 
Rigid  tubes,  flow  of  liquids  through,  518 
Rigor  mortis,  704 
Rising  up  and  lying  down,  mechanism  of, 

754 

Roots  and  bulbs,  composition  of,  184 
Rotatory  joint,  730 
Rumen,  functions  of,  374 
Ruminants,  convolutions  of  the  brain  of, 
805 

dentition  of,  258 

gastric  digestion  in,  374 

larynx  of,  761 

respiratory  movements  of,  582 
Rumination,  316  w 

changes  of  food  in,  323 

influence  of  nervous  system  on,  330 

structure  of,  317 
Ru :m-ing  in  quadrupeds,  749 

mechanism  of,  m  men,  738 
Rtr.OLl 
K/e  residue,  181 

SacHiarates,  119 

Saccharose,  119 

Saliva,  centre  for  secretion  of,  817 

chemical  composition  of,  271 

course  of,  270 

physiological  uses  of,  287 

quantity  of,  286 

Salivary  glands,  experiments  on,  295 
histological  changes  in,  305 

secretion,  268 

characteristics  of,  284 
mechanism  of,  293 
Salts,  absorption  of,  454 

amount  of,  in  fodders,  679 

influence  of,  on  nutrition,  678 

nutritive,  192 
Saponification,  121 
Sarkin,  663 
Scalene  muscles, '  action  of,  in  inspiration, 

577 

Schleiden's  cell  doctrine,  15 
Schultze's  test  for  reaction  of  proteids,  92 
Schwann's  cell  doctrine,  15 


Sclerotic,  849 

Sebaceous  secretion  of  the  skin,  655 

Secretion  of  bile,  391 

of  gastric  juice,  356 

of  milk,  609 

of  sweat,  652 

of  tears,  658 

of  the  skin,  sebaceous,  655 

parotid,  274 

salivary,  268 

sublingual,  283 

submaxillary,  279 
Secretory  phenomena,  793 
Section  of  spinal  cord,  results  of,  800 
Segmentation  of  mammalian  ovum,  19 
Semicircular  canals,  877 
Semilunar  valves,  action  of,  513 
Seminal  fluid,  913 
Sensation,  837 
Sensations,  tactile,  897 

visual,  864 
Sense  of  hearing,  875 

of  sight,  846 

of  smell,  841 

of  taste,  893 

of  touch,  897 
Sensibility,  conditions  of,  838 

general  and  special,  837 
Sensitive  plant,  71 

motions  of,  71 

Sensory  impulses,  paths  of,  801,  827 
Serum-albumen,  92 

of  blood,  489 

Setchenow's  inhibitory  centre,  793 
Sheep  and  goat,  urine  of,  640 
Sheep,  dentition  of,  259 

fat,  123 

food  required  in  fattening,  687 

normal  foods  for,  690 

prehension  of  food  in,  235 
Shell-membrane  of  egg,  formation  of,  22 
Sighing,  604 
Sight,  sense  of,  846 
Silicon,  136 
Sinus  venosus,  503 
Sitting,  mechanism  of,  in  man,  733 
Skin  as  a  heat  regulator,  651 

as  an  excretory  organ,  651 

functions  of,  651 

sebaceous,  secretion  of,  655 
Smell,  intensity  of,  846 

sense  of,  841 
Sneezing,  605 

centre  for,  816 
Soaps,  121 
Sobbing,  605 
Socket-and-ball  joint,  730 
Sodium  carbonate,  129 

chloride,  128 

phosphate  of,  130 

sulphate,  135 
Solids,  prehension  of,  226 
Solipedes,  gastric  digestion  in,  368 


:93B 


INDEX. 


Soluble  ferments,  110 
Solution,  43 

Sound,  reflection  of,  883 
Sounds,  conduction  of,  884 
of  the  heart,  514 
pitch  of,  884 
reciprocation  of,  884 
sympathetic  vibration  of,  884 
transmission  of,  884 
variations  in,  758 
Special  physiology,  definition  of,  1 
Specialization  of  function,  15,  32 
Specific  gravity  of  tissues,  62 
Spectra  of  haemoglobin,  477 
Spermaceti,  122 
Spermatic  cells,  915 
Spermatoblasts,  915 
Spermatozoa,  28,  914 
development  of,  915 
motion  of,  77     • 
Spherical  aberration,  854 
Sphygmograph,  536    < 
Spinal  accessory  nerve,  835 

cord  as  a  collection  of  nerve-centres, 

789 

course  of  fibres  in,  789,  797 
functions 'of,  786 
histology  of,  789 
influence    of    on  renal  secretion, 

645 

reflex  action  of,  790 
section  of  antero-lateral  columns 

of,  801 

experiments  on,  800 
longitudinal  section  of,  80.1 
section  of,  800 
structure  of,  786 
'tracts  of,  796 
roots,  course  of  fibres  in,  798   - 

influence  of,  on  nervous  nutrition, 
|   778...    .  ,v.; 
Splanchnic  nerves,  influence  of,  on   renal 

seerefcmn,  645 

Spleen,  influence  of  on  pancreas,  409 
Stability  of  animal  bodies,  731 
Stable  equilibrium,  731 
Standing  in  quadrupeds,  733 

mechanism  of,  in  man,  732 
Stapedius  muscle,  890 
Stapes,  880 

Starch,  changes  of,  through  saliva,  289 
Starches,  112 

gastric  digestion  of,  354 
test  for,  114 

Star- fish,  nervous  system  of,  766 
Starvation,  loss  of  weight  in  different  tis- 
sues, 676 

tissue  changes  in,  674 
Stearic  acid,  122 
Stearin,  122 
Stereoscope,  870 
Stimuli  of  nerves,  776 
Stomach,  accumulation  of  food  in,  338 


Stomach,  changes  of  food  in,  341 

characteristics  of,  215 

of  hog,  216 

structure  of,  363 

of  horse,  215 

of  ruminant,  capacity  of,  339 

structure  of,  356 
Straw,  barley,  171 

buckwheat,  172 

composition  of,  178 
Stroma  of  blood-corpuscles,  474 
Structure  of  organized  bodies,  11 
Sublingual  secretion,  283 
Submaxillary  saliva,  composition  of,  280 

fistula,  279 

secretion,  279 
Succus  entericus,  416 
Suckling  and  mastication,  centre  for,  817 
Sugar,  -absorption  of,  454 

fate  of,  670 
,':.:  -milk,  120, 

of  milk,  616 
Sulphate  of  calcium,  136 

of  potassium,  135 

of  sodium.,  135 

Supplemental  volume  of  air,  573 
Sweat,  composition  of,  652 

influence  of  nervous  system  on,  654 

quantity  of,  653 

secretion,  652 

of,  654 

Swimming  in  the  horse,  755 
Swine,  normal  foods  for,  690 
Sympathetic  nerve,  835 

action  of,  on  pupil,  862 

influence  of,  on  temperature,  697 
Synarthroses,  729 
Syntonin,  99 
Syrinx  of  birds,  760 

Tactile  sensations,  897 
Taste  bulbs,  893 

nerves  of,  896 

sense  of,  893 
Taurin,  387 

Taurocholate  of  sodium,  384 
Taurocholic  acid,  386 
Tears,  composition  of,  658 
Teeth,  ;action  of,  in  mastication,  245 

compound,  structure  of,  246 

structure  of,  245 
Tegmentum  cruris,  819 
Temperature  influence  on  ciliary  motion,  80 
on  nerve  irritability,  776 
on  protoplasmic  movement,  82 

of  different  domestic  animals,  696 
Temporal  muscle,  action  of,  243 
Tensor  tympani  muscle,  890 
Tetanus,  715 
Thirst,  92 

Thoracic  duct,  chyle  of,  460 
Thorax,  571 
Tidal  volume  of  air,  573 


INDEX. 


937 


Timbre  of  sounds,  758 
Timothy,  composition  of,  187 
Tissue  changes  in  starvation,  674: 

elastic,  35 

fibrous,  35 

gelatinous,  35 

glandular,  34 

mucoid,  35 

muscular,  34 

nerve,  development  of,  34 

nitrogenous  constituents  of,  85 

non-nitrogenous  constituents  of,  85 
Tissues,  absorption  of,  for  colors,  68 

and  organs,  development  of,  31 

classification  of,  33 

cohesion  of,  62 

connective,  34 

contractile,  701 

development  of,  15 

elasticity  of,  65 

electrical  phenomena  of,  70 

extensibility  of,  66,  67 

flexibility  of,  67 

intercellular,  34 

optical  characteristics  of,  68 

physical  properties,  61 

refraction  of,  68 

reproductive,  of  the  female,  908 

resistance  of,  to  flexion,  64 
to  pressure,  63 
to  torsion,  64 
to  traction,  63 

specific  gravity  of,  62 
Vongue,  action  of,  in  mastication,  264 

of  horse,  233 

of  ox,  233 

,Torricelli's  theorem,  517 
Touch  corpuscles,  899 

sense  of,  897 

Trachea,  structure  of,  569 
Tradescantia  virginica,  73 
Transudation,  48 
Tread,  20 

Trifacial  nerve,  833 
Tricuspid  valve,  509 
Trigeminal  nerve,  833 
Trochlearis,  832 
Trot,  748 
Trypsin,  409 

Tubular  glands  of  stomach,  356 
Tympanic  membrane,  879 
Tympanum,  877,  879 
Tyrosin,  410 

Unformed  ferments,  111 
Unorganized  and  organized  bodies,  distinc- 
tions between,  22 
Unstable  equilibrium,  731 
Urea,  excretion  of,  in  starvation,  676 

formation  of,  661,  662 
Uric  acid,  663 

source  of,  662 
Urinary  secretion,  mechanism  of,  640 


Urinary  tubules,  functions  of,  643,  '646 
Urination,  mechanism  of,  648 
Urine,  composition  of,  636 

of  carnivora,  637 

of  dog,  640 

of  herbivora,  637 

of  horse,  638 

of  ox,  639 

of  pig,  640 

of  sheep  and  goat,  640 

physical  and  chemical  properties   of, 

635     ' 
Uterus,  908 

Vagus  nerve  of  frog,  545 

wave,  549 

Vallisneria,  movements  in,  74 
Valves  of  the  heart,  action  of,  508 
Vaso-constrictor  nerves,  558 

dilator  nerves,  558 

motor  centre,  555 
centres,  794 
nerves,  554 
Vegetable  albumens,  93 

caseins,  94 

cells,  chemical  processes  in,  137 

fibrin,  95 

foods,  161 

gelatin,  96 

globulins,  97 

physiology,  definition  of,  10 
Vegetative  functions,  definition  of,  8 
Veins,  blood  pressure  in,  539 

circulation  in,  539 

velocity  of  circulation  in,  540 
Velocity  of  the  blood,  530 
Vena  contracta,  518 
Venous  absorption,  453 

blood,  gases  of,  592 

sinus,  503 

Ventricle,  fourth,  of  the  brain,  812 
Ventricles,  capacity  of,  532 

movements  of,  503 

muscular  fibres  of,  502 
Ventriculus,  functions  of,  3'80 
Venus'  fly-trap,  motions  of,  72 
Vernix  caseosa,  655 
Vertebrates,  digestive  apparatus  of,  209 

nervous  system  of,  769 
Vesicle,  blastodermic,  25 

germinal,  15 

modifications  of  free  fertilization 

in,  18 

Vestibule  of  the  ear,  877 
Villi,  structure  and  functions  of,  456 
Vision,  sense  of,  846 
Visual  apparatus,  structure  of,  846 

imperfection,  872 

purple,  868 

sensations,  864 

Vital  capacity,  volume  of,  586 
Vitellin,  97 
Vitelline  membrane,  15 


938 


INDEX. 


Vitreous  humor,  849 

Vocal  cords,  757 

muscles  of,  762 

Voice,  757 

production  of,  758 

Vomiting,  centre  for,  817 
mechanism  of,  330 
nervous  mechanism  of,  334 

Walking  backward  in  the  horse,  754 
mechanism  of,  in  the  horse,  744 
in  man,  737 

Water,  124,  191 
in  cells,  86 

White  blood-corpuscles,  479 


Wool-producing  animals,  food  required  by, 

688 
Worms,  digestive  apparatus  of,  205 

Xanthin,  663 

Xantho-proteic  reaction  of  proteids,  91 

Yawning,  604 

Yelk  of  egg,  structure  of,  20 

Yellow  spot  of  the  retina,  865 

Zona  pellucida,  15 

radiata,  15 
Zymogen,  409 


MARCH,    1890. 


CATALOGUE 


OF  THE 


MEDICAL  PUBLICATIONS 

OF 

F.   J°L.    ID  AVIS, 

Medical    F>tibli«tier    arid    Bookseller, 

1231  FILBERT  STREET,  PHILADELPHIA,  U.S.A. 


BRANCH    OFFICES: 


45  East  Twelfth  St.,  New  York.  U.S.A. 
24  Lakeside  Bui/ding,  214-220  S.  Clark  St., 
Cor.  Adams,  Chicago,  III.,  U.S.A. 


1  Kimball  House,  Wall  St.,  Atlanta,  Ga.,  U.S.A. 
427  Sutter  St.,  San  Francisco,  CaL,  U.S.A. 
139-143  Oxford  St.,  London,  W.,  England. 


NOXICK. 

In  addition  to  our  own  Publications,  we  keep  constantly  on  hand 
a  large  stock  of  MEDICAL,  DENTAL,  PHARMACEUTICAL,  AND  VETERINARY 
BOOKS.  Complete  Catalogue  (64  pages)  furnished  free  on  application. 

We  give  prompt  and  careful  attention  to  ever}-  inquiry,  as  well 
as  to  every  order. 

ALL  NEW  BOOKS  RECEIVED  AS  SOON  AS  PUBLISHED. 

REMITTANCES  SHOULD  BE  MADE  BY  EXPRESS  MONEY-ORDER,  POST- 
OFFICE  MONEY-ORDER,  REGISTERED  LETTER,  OR  DRAFT  ON  NEW  YORK 
CITY,  PHILADELPHIA,  BOSTON,  OR  CHICAGO. 

We  do  not  hold  ourselves  responsible  for  books  sent  by  mail ;  to 
insure  safe  arrival  of  books  sent  to  distant  parts,  the  package  should  be 
registered.  Charges  for  registering  (at  purphaser's  expense),  ten  cents 
for  each  four  pounds  or  less. 


NEW  BOOKS  IN  PRESS  AND  IN  PREPARATION. 


BACTERIOLOGICAL  DIAGNOSIS— TABULAR  AIDS  FOR  USE  IN 
PRACTICAL  WORK.  By  JAMES  EISENBERG,  Ph.D.,  M.D.,  Vienna.  Trans- 
lated and  augmented,  with  the  permission  of  the  author,  from  the  Second  German 
Edition,  by  NOEVAL  II.  PIEKCE,  M.D.,  Surgeon  to  the  Out-Door  Department  of 
Michael  Reese  Hospital;  Assistant  to  Surgical  Clinic  College  of  Physicians  and  Sur- 
geons, Chicago,  111.  In  one  Octavo  volume.  IN  PKESS. 

LECTURES  ON  ARTISTIC  ANATOMY  AND  THE  SCIENCES  USE- 
FUL TO  THE  ARTIST.  A  series  delivered  at  the  Art  Institute,  Chicago,  by 
S.  V.  CLEVENGER,  M.D.,  Consulting  Physician  Reese  and  Alexian  Hospitals ;  Member 
numerous  American  Scientific  and  Medical  Societies ;  Author  of  "  Spinal  Concussion," 
"Comparative  Physiology  and  Psychology,"  etc.  Illustrated  with  Seventeen  (17) 
fine  fall-page  Lithographic  Plates.  In  one  handsome  Quarto  volume.  IN  PRESS. 

TWELVE  LECTURES  ON  THE  STRUCTURE  OF  THE  CENTRAL 
NERVOUS  SYSTEM.  For  Physicians  and  Students.  By  Dr.  LUDWIG 
EDINGER,  Frankfort-on-the-Main.  Second  Revised  Edition,  with  133  Illustrations. 
Translated  by  WILLIS  HALL  VITTUM,  M.D.,  St.  Paul,  Minn.  Edited  by  C.  EUGENE 
RIGGS,  A.M.,  M.D.,  Professor  of  Mental  and  Nervous  Diseases,  University  of  Minne- 
sota; Member  of  the  American  Neurological  Association.  In  one  Octavo  volume. 
IN  PRESS. 

THE  PRINCIPLES  OF  SURGERY.  For  Students  and  Practitioners.  By  N. 
SENN,  M.D.,  Ph.D.,  Attending  Surgeon  Milwaukee  Hospital ;  Profeasor  of  Principles 
of  Surgery  in  Rush  Medical  College,  Chicago,  111.,  etc.  In  one  Octavo  volume. 
Illustrated.  IN  PREPARATION. 

DISEASES  OF  THE  HEART,  LUNGS,  AND  KIDNEYS.  By  N.  S. 
DAVIS,  JR.,  A.M.,  M.D.,  Professor  of  Principles  and  Practice  of  Medicine  in  the 
Chicago  Medical  College,  Chicago,  111.,  etc.  In  one  neat  12mo  volume.  No.  5  in  ihe 
"  Physicians'  and  Students'  Ready-Reference  Series."  IN  PREPARATION. 

CHILDBED:  ITS  MANAGEMENT :  DISEASES  AND  THEIR  TREAT- 
MENT. By  WALTER  P.  MANTON,  M.D.,  Visiting  Physician  to  the  Detroit 
Woman's  Hospital;  Consulting  Gynaecologist  to  the  Eastern  Michigan  Asylum; 
President  of  the  Detroit  Gynaecological  Society ;  Fellow  of  the  American  Society  of 
Obstetricians  and  Gynaecologists,  and  of  the  British  Gynaecological  Society  ;  Member 
of  the  Michigan  State  Medical  Society,  etc.  In  one  neat  12mo  volume.  No.  6  in 
the  "  Physicians'  and  Students'  Ready-Reference  Series."  IN  PREPARATION. 

Arrangements  are  being  made  for  volumes  upon  the  "Eye,"  ''Nose  and 
Throat,"  "Gynaecology,"  "Medical  Microscopy,"  "Physiology,"  etc., 

to  follow  the  above,  at  intervals,  in  the  "Physicians'  and  Students'  Ready-Reference 
Series." 

The  Physicians'  and  Students'  Ready-Reference  Series 

Includes -publications  of  great  value  to  students  during  their  attendance  at  college,  and 
to  the  busy  physician  in  his  daily  practice.  While  they  in  no  way  attempt  to  supplant 
the  various  ^ext-Books,  it  cannot  he,  doubted  that  they  are  necessary  to  the  often  overworked 
student  when  examination  time  is  approaching,  previous  to  which,  for  weeks,  but  little 
time  can  be  gained  from  the  lectures  in  which  to  make  careful  and  thorough  preparation 
for  the  examination-room. 

Complete  synopses  of  the  several  important  branches,  and  valuable  monographs  on 
various  important  subjects,  are  furnished  in  the  publications  of  this  series  in  such  form 
and  arrangement  by  competent  writers  as  to  render  them  of  special  practical  value  to  the 
busy  student  and  also  to  the  physician  in  active  practice.  The  volumes  are  neat  and  con- 
venient in  size  and  shape,  and  appropriately  illustrated  with  many  fine  wood-engravings. 

See  Pages  3,  2O,  21,  and  27  for  those  now  published,  and  the 
upper  part  of  this  page  for  those  in  preparation. 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


JUST  PUBLISHED—  A  NEW  AND  VALUABLE  WORK  ON 

PRACTICAL  ELECTRICITY 

MEDICINE  AND  SURGERY. 


G.  A.  LIEBIG,  Jr.,  Ph.D., 


Assistant  in  Electricity,  Johns  Hopkins    University;    Lecturer  on    Medical   Electricity,  College  of  Phy- 

sicians and  Surgeons,  Baltimore;    Member  of  the  American  Institute 

of  Electrical  Engineers,  etc., 

-AND- 

GEORGE  H.  ROHE,  M.D., 

Processor  of  Obstetrics  and  Hygiene,  College  of  Physicians  and  Surgeons,  Baltimore;  Visiting  Physician 

to  Bay  View  and  City  Hospitals;    Director  of  the  Maryland  Maternite;  Associate 

Editor  "Annual  of  the  Universal    Medical  Sciences,"  etc. 

PROFUSELY  ILLUSTRATED  BY  WOOD-ENGRAVINGS  AND   ORIGINAL   DIAGRAMS,  AND  PUBLISHED  IN  ONE 

HANDSOME  ROYAL  OCTAVO  VOLUME  OF  ABOUT  400  PAGES,  BOUND  IN  EXTRA  CLOTH. 
NET  PRICE,  UNITED  STATES  and  CANADA,  $2.00,  Post-paid;  GREAT  BRITAIN,  8s.  6d.  ;  FRANCE,  12  fr.  40. 


The  part  on  Physical  Electricity,  written  by  Dr.  Liebig,  one  of  the  recognized 
authorities  on  the  science  in  the  United  States,  treats  fully  such  topics  of  interest  as 
Storage  Batteries,  Dynamos,  the  Electric  Light,  and  the  Principles  and  Practice  of 
Kif-ftrieal  Measurement  in  their  relations  to  Medical  Practice. 

Professor  Rohe,  who  writes  on  Electro-Therapeutics,  discusses  at  length  the  recent 
developments  of  Electricity  in  the  treatment  of  stricture,  enlarged  prostate,  uterine 
tibroids,  pelvic  cellulitis,  and  other  diseases  of  the  male  and  female  genito-urinary  organs. 

The  applications  of  Electricity  in  dermatology,  as  well  as  in  the  diseases  oi  the 
nervous  system,  are  also  fully  considered. 

THE  SECOND  VOLUME  IN  THE  PHYSICIANS'  AND  STUDENTS' 
READY  REFERENCE  SERIES. 


OF 

Materia  Mediea, ptiarmaeij,  and  Therapeutics 

By  CUTHBERT  BOWEN,  M.D.,  B.A., 

Editor  of  "  Notes  on  Practice." 


EXTRACT  FROM  THE  PREFACE.—"  While  this  is  essentially  a  STUDENT'S  MANUAL,  a  large 
amount  of  matter  has  been  incorporated  which,  it  is  hoped,  will  render  it  auseful  reference-book  to  the  YOUNG 
GRADUATE  who  is  just  entering  on  his  professional  career,  and  more  particularly  the  individual  whose  sphere 
of  work  demands  a  more  practical  acquaintance  with  pharmaceutical  processes  than  is  required  of  the  ordi- 
nary city  practitioner.  Great  care  has  been  taken  throughout  the  book  to  familiarize  the  student  with  the 
best  methods  of  administering  the  various  drugs  he  will  be  called  upon  to  use,  and  with  this  object  a  large 
number  of  standard  prescriptions  have  been  selected  from  the  works  of  the  most  eminent  authorities,  which 
he  can  either  adopt,  with  modifications  to  suit  particular  cases,  or  use  as  models  on  which  to  construct  his  own 
formulae."  


This  excellent  manual  comprises  in  its  366  small 
octavo  pages  about  as  much  sound  and  valuable  in- 
Jorinatioii  on  the  subjects  indicated  in  its  title  as 
could  well  be  crowded  into  the  compass.  The  book 
is  exhaustively  and  correctly  indexed,  and  of  a  con- 
venient form.  The  paper,  press-work,  and  binding 
are  excellent,  and  the  typography  (long  primer  and 
brevier  i  is  highly  to  be  commended,  as  opposed  to 
the  nonpareil  and  agate  usually  used  incompendsof 
this  sort,  and  which  are  destructive  to  vision  and 
temper  alike. — Sf.  Louis  Med.  and  Surg.  Jour.  , 

In  going  through  it,  we  have  been  favorably  im- 
pressed by  the  plain  and  practical  suggestions  in 
regard  to  prescription  writing,  and  the  metric  sys- 
tem, and  the  other  things  which  must  be  known  in 
order  to  write  good  and  accurate  prescriptions. — 
Medical  and  Surgical  Reporter. 

Many  works  claim  more  in  their  title-pages  than 
can  be  verified  further  on,  but  the  only  adverse 


criticism  we  can  make  on  this  volume  is  that  it  does 
not  claim  enough. — Southern  California  Prac- 
titioner. 

The  book  is  one  of  the  very  best  of  its  class. — 
Columbus  Medical  Journal. 

This  is  a  very  condensed  and  valuable  resume 
of  the  drugs  recognized  by  the  United  States  Phar- 
macopoeia, and  all  the  officinal  and  important 
preparations. — Southern  Medical  Record. 

Dr.  Bo  wen's  work  is  a  very  valuable  one  indeed, 
and  will  be  found  "to  fill  a  want"  beyond  a  doubt. 
— Cincinnati  Medical  News. 

It  is  short  and  concise  in  its  treatment  of  the 
subjects,  yet  it  gives  sufficient  to  gain  a  very  correct 
knowledge  of  everything  that  comes  under  this  head- 
ing. .  This  is  a  ready  work  for  the  country  physician, 
who  must  of  necessity  have  a  more  practical  acquain- 
tance with  pharmaceutical  processes. — Medical 
Brief. 


One    12mo    volume   of   37O  pages.         Handsomely   Bound    in   Dark-Blue    Cloth. 

Price,   post-paid,  in  the  United    States  and    Canada,  $1.40,   net; 

in  Great  Britain,  6s.  6d.;  in  France,  9  fr.  25. 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


BASHORE'S  IMPROVED  CLINICAL  CHART. 

For  the  SEPARATE  PLOTTING  of  TEMPERATURE,  PULSE,  and  RESPIRATION. 

Designed  for  the  Convenient,   Accurate,   and  Permanent  Daily   Recording  of  Cases  in 
Hospital  and  Private  Practice. 


By   HARYKY  B.    BASHORB 


COPYRIGHTED,  1888,  BY  F.  A.  DAVIS. 

SO  Charts,  In  Tablet  Forma..  Size,  a  32  12  indies. 


Price,  in  the  United  States  and  Canada,  Post-paid,  5O  Cents, 
Net ;  Great  Britain,  2s.  6d. ;  France,  3  fr.  6O. 

The  above  diagram  is  a  little  more  than  one-fifth  (1-5)  the  actual  size  of  the  chart  and  shows  the 
method  of  plotting,  the  upper  curve  being  the  Temperature,  the  middle  the  Pulse,  and  the  lower  the 
Respiration.  By  this  method  a  full  record  of  each  can  easily  be  kept  with  but  one  color  ink. 

It  is  so  arranged  that  all  practitioners  will  find  it  an  invaluable  aid  in  the  treatment  of  their  patients-. 

On  the  back  of  each  chart  will  be  found  ample  space  conveniently  arranged  for  recording  "Clinical 
History  and  Symptoms"  and  "Treatment." 

By  its  use  the  physician  will  secure  such  a  complete  record  of  his  cases  as  will  enable  him  to  review 
them  at  any  time.  Thus  he  will  always  have  at  hand  a  source  of  individual  improvement  and  benefit  in 
the  practice  of  his  profession,  the  value  of  which  can  hardly  be  overestimated. 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


-4HBOO 


The  Physician  Himself 


AND  THINGS  THAT  CONCERN 

HIS  REPUTATION  AND  SUCCESS. 

BY 

D.    W.    CATHELL,    M.D., 

BALTIMORE,  MD. 

Being   the   NINTH  EDITION  (Enlarged  and    Thoroughly   Revised)    of  the   "PHYSICIAN 

HIMSELF,  AND  WHAT  HE  SHOULD  ADD  TO  HIS  SCIENTIFIC  ACQUIREMENTS 

IN  ORDER  TO  SECURE  SUCCESS." 


In  One  Handsome  Octavo  Volume  of  298  Pages,  Bound  in  Eztra  Cloth. 

Price,  Poet-paid,  in  United  States  and  Canada,  $2.OO,  Net;  Great 

Britain,  8s.  6d. ;  France,  12  fr.  4O. 


This  remarkable  book  has  passed  through  eight  (8)  editions  in  less 
than  live  years,  has  met  with  the  unanimous  and  hearty  approval  of  the 
Profession,  and  is  practically  indispensable  to  every  young  graduate 
who  aims  at  success  in  his  chosen  profession.  It  has  just  undergone  a 
thorough  revision  by  the  author,  who  has  added  much  new  matter  cover- 
ing many  points  and  elucidating  many  excellent  ideas  not  included  in 
former  editions.  This  unique  book,  the  only  complete  one  of  the  kind 
ever  written,  will  prove  of  inestimable  pleasure  and  value  to  the  practi- 
tioner of  many  years'  standing,  as  well  as  to  the  young  physician  who 
needs  just  such  a  work  to  point  the  way  to  success. 

We  give  below  a  few  of  the  many  unsolicited  letters  received  by 
the  author,  and  extracts  from  reviews  in  the  Medical  Journals  of  the 
former  editions  : 


'•  'The  Physician  Himself  is  an  opportune  and 
most  useful  book,  which  cannot  fail  to  exert  a  good 
influence  on  the  morale  and  the  business  success  of 
the  Medical  profession." — Front  Prof.  Roberts 
rarf.holo-M,  Philadelphia,  Pa. 

"I  have  read  'The  Physician  Himself  with 
pleasure — delight.  It  is  brimful  of  medical  and 
social  philosophy  ;  every  doctor  in  the  land  can 
study  it  with  pleasure  and  profit.  1  wish  I  could 
have  read  such  a  work  thirty  years  ago." — From 
Prof.  John  S.  Lynch,  Baltimore,  Md. 

"'The  Physician  Himself  interested  me  so 
much  that  I  actually  read  it  through  at  one  sitting. 
It  is  brimful  of  the  very  best  advice  possible  for 
medical  men.  I,  for  one,  shall  try  to  profit  by  it." — 
From  Prof.  William  Goodell,  Philadelphia. 

"  I  would  be  glad  if,  in  the  true  interest  of  the 
profession  in  'Old  England,'  some  able  practitioner 
here  would  prepare  a  work  for  us  on  the  same  line  as 
'The  Physician  Himself.'"— From  Dr.  Jukes  de 
Styrap,  Shrewsbury,  England. 

"  I  am  most  favorably  impressed  with  the 
wisdom  and  force  of  the  points  made  in 'The  Phy- 
sician Himself,'  and  believe  the  work  in  the  hands 


Prof.  D.  Hayes 


of  a  young  graduate  will  greatly  enhance  his  chances 
for  professional  success." — From  } 
Agnew,  Philadelphia,  Pa 

"This  book  is  evidently  the  production  of  an 
unspoiled  mind  and  the  fruit  of  a  ripe  career.  I 
admire  its  pure  tone  and  feel  the  value  of  its  practi- 
cal points.  How  I  wish  I  could  have  read  such  a 
guide  at  the  outset  of  my  career!" — Front  Prof. 
James  Nevins  Hyde,  Chicago,  III. 

"  It  contains  a  great  deal  of  good  sense,  well 
expressed." — From  Prof  .  Oliver  Wendell  Holmes, 
Harvard  University. 


"  'The  Physician  Himself  is  usefu!  alike  to  the 
tyro  and  the  sage — the  neophyte  and  the  veteran.  It 
is  a  headlight  in  the  splendor  of  whose  beams  a 
multitude  of  our  profession  shall  find  their  way  to 
success."—  From  Prof.  J.  M.  Bodine,  Dean  Uni- 
versity of  Louisville. 

"  It  is  replete  with  good  sense  and  sound  phi- 
losophy. No  man  can  read  it  without  realizing  that 
its  author  is  a  Christian,  a  gentleman,  and  a  shrewd 
observer." — From  Prof.  Edward  Warren  (Bey), 
Chevalier  of  the  Legion  of  Honor,  etc.,  Paris, 
France. 

"I  have  read  'The  Physician  Himself,'  care- 
fully. I  find  it  an  admirable  work,  and  shall  advise 
our  Janitor  to  keep  a  stock  on  hand  in  the  book  de- 
partment of  Bellevue." — From  Prof.  William  T. 
Lusk,  New  York. 

"  It  must  impress  all  its  readers  with  the  belief 
that  it  was  written  by  an  able  and  honest  member  of 
the  profession  and  for  the  good  of  the  profession." — 
From  Prof.  W.  H.  Byford,  Chicago,  III. 

"  It  is  marked  with  good  common  sense,  and 
replete  with  excellent  maxims  and  suggestions  for 
the  guidance  of  medical  men." — From  The  British 
Medical  Journal,  London. 

"  We  strongly  advise  every  actual  and  intend- 
ing practitioner  of  medicine  or  surgery  to  have 
'  The  Physician  Himself,'  and  the  more  it  influences 
his  future  conduct  the  better  he  will  be." — From 
The  Canada  Medical  and  Surgical  Journal, 
Montreal. 

"  We  would  advise  every  doctor  to  well  wotgh 
the  advise  given  in  this  book,  and  govern  his  con- 
duct accordingly." — From  The  Virginia  Medical 
Monthly. 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


AN  IMPORTANT  PUBLICATION  OF  GREAT  VALUE  TO  THE  MEDICAL 
AND  LEGAL  PROFESSIONS. 


SPINAL  CONCUSSION: 

Surgically  Considered  as  a  Cause  of  Spinal  Injury,  and  Neurologi- 

oally  Restricted  to  a  Certain  Symptom  Group,  for 

•which  is  Suggested  the  Designation 

ERICHSEN'S  DISEASE,  AS  OHE  FORM  OF  THE  TRAUMATIC  NEUROSES, 


S.  V.    CLEVENGER,   M.D., 

CONSULTING  PHYSICIAN  REESE  AND  ALEXIAN  HOSPITALS;    LATE  PATHOLOGIST  COUNTY  INSANE  ASYLUM, 
CHICAGO;  MEMBER  OF  NUMEROUS  AMERICAN  SCIENTIFIC  AND  MEDICAL  SOCIETIES;  COLLABORATOR 
AMERICAN  NATURALIST,  ALIENIST  AND  NEUROLOGIST,  JOURNAL  OF  NEUROLOGY  AND 
PSYCHIATRY,  JOURNAL  OF  NERVOUS  AND  MENTAL  DISEASES;  AUTHOR  OF  "COM- 
PARATIVE PHYSIOLOGY  AND  PSYCHOLOGY,"  "ARTISTIC  ANATOMY,"  ETC. 


For  more  than  twenty  years  this  subject  has  occasioned  bitter  con- 
tention in  law  courts,  between  physicians  as  well  as  attorneys,  and  in 
that  time  no  work  has  appeared  that  reviewed  the  entire  field  judicially 
until  Dr.  Clevenger's  book  was  written.  It  is  the  outcome  of  five  years' 
special  study  and  experience  in  legal  circles,  clinics,  hospital  and  private 
practice,  in  addition  to  twenty  years'  labor  as  a  scientific  student,  writer, 
and  teacher. 

The  literature  of  Spinal  Concussion  has  been  increasing  of  late  years 
to  an  unwieldy  shape  for  the  general  student,  and  Dr.  Clevenger  lias  in  this 
work  arranged  and  reviewed  all  that  has  been  done  by  observers  since 
the  days  of  Eriehsen  and  those  who  preceded  him.  The -different  and 
sometimes  antagonistic  views  of  many  authors  are  fully  given  from  the 
writings  of  Eriehsen,  Page,  Oppenheim,  Erb,  Westphal,  Abercrombie, 
Sir  Astley  Cooper,  Boyer,  Charcot,  Leyden,  Rigler,  Spitzka,  Putnam, 
Knapp,  Dana,  and  many  other  European  and  American  students  of  the 
subject.  The  small,  but  important,  work  of  Oppenheim,  of  the  Berlin 
Universit3T,  is  fully  translated,  and  constitutes  a  chapter  of  Dr.  Cleven- 
ger's book,  and  reference  is  made  wherever  discussions  occurred  in 
American  medico-legal  societies. 

There  are  abundant  illustrations,  particularly  for  Electro-diagnosis, 
and  to  enable  a  clear  comprehension  of  the  anatomical  and  pathological 
relations. 

The  Chapters  are :  I.  Historical  Introduction ;  II.  Eriehsen  on 
Spinal  Concussion  ;  III.  Page  on  Injuries  of  the  Spine  and  Spinal  Cord: 
IV.  Recent  Discussions  of  Spinal  Concussion;  V.  Oppenheim  on  Trau- 
matic Neuroses;  VI.  Illustrative  Cases  from  Original  and  all  other 
Sources;  VII.  Traumatic  Insanity;  VIII.  The  Spinal  Column;  IX. 
Symptoms;  X.  Diagnosis;  XI.  Pathology;  XII.  Treatment;  XIII. 
Medico^legal  Considerations. 

Other  special  features  consist  in  a  description  of  modern  methods 
of  diagnosis  by  Electricity,  a  discussion  of  the  controversy  concerning 
hysteria,  and  the  author's  original  pathological  view  that  the  lesion  is 
one  involving  the  spinal  sympathetic  nervous  system.  In  this  latter 
respect  entirely  new  ground  is  taken,  and  the  diversity  of  opinion  con- 
cerning the  functional  and  organic  nature  of  the  disease  is  afforded  a 
basis  for  reconciliation. 

Every  Physician  and  Lawyer  should  own  this  work. 

In  one  handsome  Royal  Octavo  Volume  of  nearly  400  pages,  with 
Thirty  Wood-Engravings.  Net  price,  in  United  States  and  Canada, 
$2.50,  post-paid  ;  in  Great  Britain,  Us.  3d. ;  in  France,  15  fr. 


CF.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa..  U.S.A.) 


JUST  READY-A  NEW  AND  IMPORTANT  WORK. 


ESSAY 


MEDICAL  PNEDMATOLOGY I AEROTHERAPY: 

A  PRACTICAL  INVESTIGATION  OF  THE  CLINICAL  AND  THERAPEUTIC  VALUE 

OF  THE  GASES  IN  MEDICAL  AND  SURGICAL  PRACTICE,  WITH  ESPECIAL 

REFERENCE  TO  THE  VALUE  AND  AVAILABILITY  OF 

OXYGEN,  NITROGEN,  HYDROGEN,  AND  NITROGEN  MONOXIDE. 

BY  d.   N.   DEMARQUAY, 

Surgeon  to  the  Municipal  Hospital,  Paris,  and  of  the  Council  of  State ;  Member  of  the  Imperial  Society 

of  Surgery ;  Correspondent  of  the  Academies  of  Belgium,  Turin,  Munich,  etc.  ;  Officer 

of  the  Legion  of  Honor  ;  Chevalier  of  the  Orders  of  Isabella-the- 

Catholic  and  of  the  Conception,  of  Portugal,  etc. 

TRANSLATED,  WITH  NOTES,  ADDITIONS,  AND  OMISSIONS, 

BY    SAMUEL   S.   WALLIAN,    A.M.,    M.D., 

Member  of  the  American  Medical  Association  ;  Ex-President  of  the  Medical  Association  of  Northern  New 
York ;  Member  of  the  New  York  County  Medical  Society,  etc. 


In  one  Handsome  Octavo  Volume  of  316  Pages,  Printed  on  Fine  Paper,  in  the  Best 
Style  of  the  Printer's  Art,  and  Illustrated  with  21  "Wood-Cuts. 

United  States.        Canada  (duty  paid).        Great  Britain.  France. 

NET  PRICE,  CIX>TH,  Post-paid,        S2.OO  S2.2O  SB.  6d.  12  fr.  4O 

^-RUSSIA,      "  3.OO  3.30  13s.  18  fr.  6O 


For  some  years  past  there  has  been  a  growing  demand  for  something  more  satisfac- 
tory and  more  practical  in  the  way  of  literature  on  the  subject  of  what  has,  by  commom 
consent,  come  to  be  termed  "  Oxygen  Therapeutics."  On  all  sides  professional  men  of 
standing  and  ability  are  turning  their  attention  to  the  use  of  the  gaseous  elements  about 
us  as  remedies  in  disease,  as  well  as  sustainers  in  health.  In  prosecuting  their  inquiries, 
the  first  hindrance  has  been  the  want  of  any  reliable,  or  in'  any  degree  satisfactory, 
literature  on  the  subject. 

Purged  of  the  much  quackery  heretofore  associated  with  it,  Aerotherapy  is  now 
recognized  as  a  legitimate  department  of  medical  practice.  Although  little  noise  is  made 
about  it,  the  use  of  Oxygen  Gas  as  a  remedy  has  increased  in  this  country  within  a  few 
years  to  such  an  extent  mat  in  New  York  City  alone  the  consumption  for  medical  pur- 
poses now  amounts  to  more  than  300.000  gallons  per  annum. 

This  work,  translated  in  the  main  from  the  French  of  Professor  Demarquay,  contains 
also  a  very  full  account  of  recent  English,  German,  and  American  experiences,  prepared 
by  Dr.  Samuel  S.  Wallian,  of  New  York,  whose  experience  in  this  field  antedates  that  of 
any  other  American  writer  on  the  subject. 

Plain  Talks  on  Avoided  Subjects. 

HENRY  N.  GUERNSEY,  M.D., 

Formerly  Professor  of  Materia  Medica  and  Institutes  in  the  Hahnemann  Medical  College  of  Philadelphia; 

Author  of  Guernsey's  "  Obstetrics,"  including  the  Disorders  Peculiar  to  Women  and 

Young  Children  ;  Lectures  on  Materia  Medica,  etc. 


IN  ONE  NEAT  16mo  VOLUME.      BOUND  IN  EXTRA  CLOTH.     Price,  Post-paid,  in 
United  States  and  Canada,  81. OO;  Great  Britain,  4s.  6d. ;  France,  6  fr.  2O. 


This  is  a  little  volume  designed  to  convey  information  upon  one  of  the  most  important  subjects  con- 
nected with  our  physical  and  spiritual  well-being,  and  is  adapted  to  both  sexes  and  all  ages  and  conditions 
of  society  ;  in  fact,  so  broad  is  its  scope  that  no  human  being  can  well  afford  to  be  without  it,  and  so  com- 
prehensive in  its  teachings  that,  no  matter  how  well  informed  one  may  be,  something  can  yet  be  learned  from 
this,  and  yet  it  is  so  plain  that  any  one  who  can  read  at  all  can  fully  understand  its  meaning. 

The  Author,  Dr.  H.  N.  Guernsey,  has  had  an  unusually  long  and  extensive  practice,  and  his  teachings  in 
this  volume  are  the  results  of  his  observation  and  actual  experience  with  all  conditions  of  human  life. 

His  work  is  warmly  indorsed  by  many  leading  men  in  all  branches  of  professional  life,  as  well  as  by 
many  whose  business  connections  have  caused  them  to  be  close  observers. 

The  following  Table  of  Contents  shows  the  scope  of  the  book: — 

CONTENTS.  CHAPTER  I.— INTRODUCTORY.  II.— THE  INFANT.  III.— CHILDHOOD.  IV.— ADOLES- 
CENCE OF  THE  MALE.  V. — ADOLESCENCE  OF  THE  FEMALE.  VI. — MARRIAGE:  THE  HUSBAND.  VII. — 
^'HE  WIFE.  VIII. — HUSBAND  AND  WIFE.  IX. — To  THE  UNFORTUNATE.  X. — ORIGIN  OF  THE  SEX. 

(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.)  7 


Lessons  in  Gynecology. 

By  WILLIAM  GrOODELL,  A.M.,  M.D.,  Etc., 

PKOFKSSOR  OF  CLINICAL  GYNECOLOGY  IN  THE  UNIVERSITY  OF  PENNSYLVANIA. 

With  112  Illustrations.      Third  Edition,  Thoroughly  Revised  and  Greatly   Enlarged. 
XONE  VOLUME,  LARGE  OCTAVO,   578  PAGES. 


This  exceedingly  valuable  work,  from  one  of  the  most  eminent  specialists  and  teachers  in  gynecology 
in  the  United  States,  is  now  offered  to  the  profession  in  a  much  more  complete  condition  than  either  of  the 
previous  editions.  It  embraces  all  the  more  important  diseases  and  the  principal  operations  in  the  field  of 
gynecology,  and  brings  to  bear  upon  them  all  the  extensive  practical  experience  and  wide  reading  of  the 
author.  It  is  an  indispensable  guide  to  every  practitioner  who  has  to  do  with  the  diseases  peculiar  to 
women. 

FIG.  44. 


NATURAL  POSITION  OP  THE  WOMB  WHEN  THE  BLADDER  is  FULL. 
AFTER  BRIESKY. 


These  lessons  are  so  well  known  that  it  is  en- 
tirely unnecessary  to  do  more  than  to  call  attention 
to  the  fact  of  the  appearance  of  the  third  edition.  : 
It  is  too  good  a  book  to  have  been  allowed  to  remain  ! 
out  of  print,  and  it  has  unquestionably  been  missed. 
The  author  has  revised  the  work  with  special  care, 
adding  to  each  lesson  such  fresh  matter  as  the  prog- 
ress in  the  art  rendered  necessary,  and  he  has  en- 
larged it  by  the  insertion  of  six  new  lessons.  This 
edition  will,  without  question,  be  as  eagerly  sought 
for  as  were  its  predecessors. — American  Journal 
of  Obstetrics. 

The  former  editions   of  this  treatise   were   well 
received  by  the  profession,  and  there  is  no  doubt 
that  the  new  matter  added  to  the  present  issue  makes  * 
it  more  useful  than  its   predecessors. — New    York 
Medical  Record. 

His  literary  style  is  peculiarly  charming.    There 


is  a  directness  and  simplicity  about  it  which  is  easier 
to  admire  than  to  copy.  His  chain  of  plain  words 
and  almost  blunt  expressions,  his  familiar  compari- 
son and  homely  illustrations,  make  his  writings,  like 
his  lectures,  unusually  entertaining.  The  substance 
of  "his  teachings  we  regard  as  equally  excellent.— 
Phila.  Medical  and  Surgical  Reporter 

Extended  mention  of  the  contents  of  the  book  is 
unnecessary;  suffice  it  to  say  that  every  important 
disease  found  in  the  female  sex  is  taken  up  and  dis- 
cussed in  a  common-sense  kind  of  a  way  We  wish 
every  physician  in  America  could  read  and  carry 
out  the  suggestions  of  the  chapter  on  "the  sexual  re- 
lations as  causes  of  uterine  disorders — conjugal 
onanism  and  kindred  sins."  The  department  treat-  \ 
ing  of  nervous  counterfeits  of  uterine  diseases  is 
a  most  valuable  one.  —  Kansas  City  Medical 
Index. 


Price,  in  United  States  and  Canada,  Cloth,  $5,00;  Full  Sheep,  $6.00.    Discount,  20  per 

cent.,  making  it,  net,  Cloth,  $100;  Sheep,  $4.80.    Postage,  27  Cents  extra.    Great 

Britain,  Cloth,  18s. ;  Sheep,  £1.2s.,  post-paid,  net.    France,  30  fr.  80. 

8  (F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


AMERICAN    RESORTS, 

WITH  NOTES  UPON  THEIR  CLIMATE. 


Member  of  the  American  Association  for  the  Advancement  of   Science,   the  American  Public  Health  Association,   the 

Pennsylvania  Historical  Society,  the  Franklin  Institute,  and  the  Academy  of  Natural  Sciences.  Philadelphia; 

the  Society  of  Alaskan  Natural  History  and  Ethnology,  Sitka,  Alaska,  etc. 

WITH  A  TRANSLATION  FROM  THE  GERMAN,  BY  MR.  S.  KAUFFMANN, 

Of  those  chapters  of  '•'  Die  Klimate  der  Erde"  written  by  Dr.  A.  Woeikof,  of  St.  Petersburg,  Russia,  that 
relate  to  North  and  South  America  and  the  islands  and  oceans  contiguous  thereto. 


In  One  Octavo  Volume.      Handsomely   Bound  in   Cloth.      Nearly  30O   Pages.      Price, 
Post-paid,  in  U.  S.  and  Canada,  SS2.OO,  net.    Great  Britain,  8s.  6d.    France,  12  fr.  4O. 


This  is  a  unique  and  valuable  work,  and  useful  to  physicians  in  all  parts  of  the  country.  It  is  just  such 
a  volume  as  the  MedicaLProfession  have  stood  in  need  of  for  many  years.  We  mention  a  few  of  the  merits 
it  possesses:  First.  List  of  all  the  Health  Resorts  of  the  country,  arranged  according  to  their  climate. 
Second.  Contains  just  the  information  needed  by  tourists,  invalids,  and  those  who  visit  summer  or  winter 
resorts.  Third.  The  latest  and  best  large  railroad  map  for  reference.  Fourth.  It  indicates  the  climate 
each  one  should  select  for  health.  Fifth.  The  author  has  traveled  extensively,  and  most  of  his  suggestions 
are  practical  in  reference  to  localities. 


Taken  altogether,  this  is  by  far  the  most  complete  ex- 
position of  the  subject  of  resorts  that  has  yet  been  put 
forth,  and  it  is  one  that  every  physician  must  needs  possess 
intelligent  information  upon.  We  predict  a  large  demand 
for  this  useful  and  attractive  book.— Buffalo  Med.  and 
Surg.  Jmtr. 

The  special  chapter  on  the  therapeutics  of  climate  .  . 
is  excellent  for  its  precautionary  suggestions  in  the  selec- 
tion of  climates  and  local  conditions,  with  reference  to 
known  pathological  indications  and  constitutional  predis- 
positions.— The  Sanitarian. 

It  is  arranged  in  such  a  manner  that  it  will  be  of  great 
service  to  medical  men  whose  duty  it  often  becomes  to  rec- 
ommend a  health  resort.— N.  W.  Med.  Jour. 

A  well-arranged  map  of  the  United  States  serves  as  the 
frontispiece  of  the  book ;  and  an  almost  perfect  index  is 
appended,  while  between  the  two  is  an  amount  of  informa- 
tion as  to  places  for  the  health-seeker  that  cannot  be  gotten 
elsewhere.  We  most  cordially  recommend  the  book  to 
travelers  and  to  the  doctor.—  Virginia  Med.  Monthly. 

This  is  a  work  that  has  long  been  needed,  as  there  is 
has  not  had  occasion  to  look  up 
«,  elevation,  drvness,  humidity, 

eic  .  etc..  of  the  various  health  resorts,  and  has  had  great 
•difficulty  in  finding  reliable  information.  It  certainly 


scarcely  a  physician  who  hj 
the  authorities  on  climate, 


Clh, 


ought,  as  it  deserves,  to  receive  a  hearty  welcome  from  the 
profession. — Medical  Advance. 

The  book  before  us  is  a  very  comprehensive  volume, 
giving  all  necessary  information  concerning  climate,  tem- 
perature, humidity,  sunshine,  and  indeed  everything  neces- 
sary to  be  stated  for  the  benefit  of  the  physician  or  invalid 
seeking  a  health  resort  in  the  United  States.— Southern 

This  work  is  extremely  valuable,  owing  to  the  liberal 
and  accurate  manner  in  which  it  gives  information  regard- 
ing the  various  resorts  on  the  American  continent,  without 
being  prejudice_d  in  the  least  in  favor  of  any  particular  one, 
but  giving  all  in  a  fair  manner.  .  .  .  All  physicians 
need  just  such  a  work,  for  the  doctor  is  always  asked  to 
give  information  on  the  subject  to  his  patients.  Therefore, 
it  should  find  a  place  in  every  physician's  library.— The 
Med.  Brief. 

The  author  of  this  admirable  work  has  long  made  a 
study  of  American  climate,  from  the  stand-point  of  a  phy- 
sician, with  a  view  to  ascertaining  the  most  suitable  locali- 
ties for  the  residence  of  invalids,  believing  proper  climate 
to  be  an  almost  indispensable  factor  in  the  treatment,  pre- 
vention, and  cure  of  many  forms  of  disease.  .  .  .  The 
book  evidences  careful  research  and  furnishes  much  useful 
information  not  to  be  found  elsewhere. — Pacific  Med.  Jjiir. 


JUST    PUBLISHED' 


RECORD-BOOK  OF  MEDICAL  EXAMINATIONS 

For  Life  Insurance. 

Toy 


In  examining  for  Life  Insurance,  questions  are  easily  overlooked  and  the  answers  to 
them  omitted  ;  and,  as  these  questions  are  indispensable,  they  must  be  answered  before  the 
case  can  be  acted  upon,  and  the  examiner  is  often  put  to  much  inconvenience  to  obtain 
this  information. 

The  need  has  long  been  felt  among  examiners  for  a  reference-book  in  which  could  be 
noted  the  principal  points  of  an  examination,  and  thereby  obviate  the  necessity  of  a 
second  visit  to  the  applicant  when  further  information  is  required. 

After  a  careful  study  of  all  the  forms  of  examination  blanks  now  used  by  Insurance 
Companies,  Dr.  J.  M.  Keating  has  compiled  such  a  record-book  which  we  are  sure  will  fill 
this  long-felt  want. 

This  record-book  is  small,  neat,  and  complete,  and  embraces  all  the  principal  points 
that  are  required  by  the  different  companies.  It  is  made  in  two  sizes,  viz.  :  No.  1,  cover- 
ing one  hundred  (100)  examinations,  and  No.  2,  covering  two  hundred  (200)  examina- 
tions. The  size  of  the  book  is  7  x3|  inches,  and  can  be  conveniently  carried  in  the 
pocket. 


PRICES,    I»OST-I»AID. 

U.  S.  and  Canada.        Great  Britain.  France 

No.  1,  For  100  Examinations,  in  Cloth,         -         &  .50                      »s.  6d.  3  fr.  6O 
No.  2,  For  2OO  Examinations,    in   Full 

Leather,  witk  Side  Flap,          ....         i.oo                      4s.  6d.  6  fr.  2O 

(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S  A.)  9 


OF    THE 

Heart  and  Circulation 

IN  INFANCY  AND  ADOLESCENCE. 

Witli  an  Appendix  entitled  "  Clinical  Studies  on  the 
Pulse  in  Childhood." 


JOHN  M.  KEATING,  M.D., 

©bstetrician  to  the  Philadelphia  Hospital,  and  Lecturer  on  Diseases  of  Women  and  Children;  Surgeon  to 

the  Maternity  Hospital  ;  Physician  to  St.  Joseph's  Hospital;  Fellow  of  the 

College  of  Physicians  of  Philadelphia,  etc., 

— AND — 

WILLIAM  A.  EDWARDS,  M.D., 

Instructor  in  Clinical  Medicine  and  Physician  to  the  Medical  Dispensary  in  the  University  of  Pennsylvania  ^ 

Physician  to  St.  Joseph's  Hospital ;  Fellow  of  the  College  of  Physicians  ;  formerly 

Assistant  Pathologist  to  the  Philadelphia  Hospital,  etc. 


ILLUSTRATED  BY  PHOTOGRAPHS  AND  WOOD-ENGRAVINGS. 

About  225  Pages.    8vo.    Bound  in  Cloth.    Price,  post-paid,  in  U.  S. 
and  Canada,  $1.5O,  net;  Great  Britain,  6s.  6d. ;  France,  9  fr.  35. 


There  are  many  excellent  text-books  on  children's  diseases,  but  they  have  failed  to  give  a  satisfactory 
account  of  the  diseases  of  the  heart  ;  and,  indeed,  as  far  as  known,  this  work  of  Keating  and  Edwards'  n  nv 
presented  to  the  profession  is  the  only  systematic  attempt  that  has  been  made  to  collect  in  book  form  the 
abundant  material  which  is  scattered  throughout  medical  literature  in  the  form  of  journal  articles,  clinical 
lectures,  theses,  and  reports  of  societies, 

The  authors  have  endeavored,  in  their  difficult  task,  to  collect  these  valuable  materials  and  place  them 
within  easy  reach  of  those  who  are  interested  in  this  important  subject.  That  they  have  succeeded  will,  we 
believe,  be  conceded  by  all  who  obtain  and  make  use  of  their  very  valuable  contribution  to  this  hitherto- 
neglected  field  of  medical  literature. 

An  appendix,  entitled  "  Clinical  Studies  on  the  Pulse  in  Childhood,"  follows  the  index  in  the  book,  and 
will,  we  are  sure,  be  found  of  much  real  value  to  every  practitioner  of  medicine.  The  work  is  made  available 
for  ready  reference  by  a  well-arranged  index.  We  append  the  table  of  contents  showing  the  scope  of  the 
book :— 


CHAPTER  VII. — General  Diagnosis,  Prognosis,  and 
Treatment  of  Valvular  Disease. 

CHAPTER  VI11.—  Endocarditis— Atheroma—  Aneu- 
rism. 

CHAPTER  IX. — Cardiac  Neuroses — Angina  Pectoris- 
— Exophthalmic  Goitre. 

CHAPTER  X. — Diseases  of  the  Blood  :  Plethora, 
Anaemia,  Chlorosis,  Pernicious  Anaemia.  Leu- 
kaemia—Hodgkin's  Disease — Hssmophilia,Throm- 
bosis,  and  Embolism. 

INDEX. 

APPENDIX.— CLINICAL  STUDIES  ON  THE  PULSE 
IN  CHILDHOOD. 


CHAPTER  I. — The  Methods  of  Study — Instruments — 
Foetal  Circulation — Congenital  Diseases  of  the 
Heart — Malformations — Cyanosis. 

CHAPTER  II. — Acute  and  Chronic  Endocarditis — 
Ulcerative  endocarditis. 

CHAPTER  III. — Acute  and  Chronic  Pericarditis. 

CHAPTER  IV.— The  treatment  of  Endo-  and  Peri- 
carditis— Paracentesis  Pericardii — Hydropericar- 
dium — Haemopericardium — Pneumopericardium. 

CHAPTER  V. — Myocarditis — Tumors,  New  Growths, 
and  Parasites 

CHAPTER  VI.— Valvular  Disease:  Mitral,  Aortic, 
Pulmonary,  and  Tricuspid. 


Drs.  Keating  and  Edwards  have  produced  a  work  that 
•will  give  material  aid  to  every  doctor  in  his  practice  among 
children.  The  style  of  the  book  is  graphic  and  pleasing, 
the  diagnostic  points  are  explicit  and  exact,  and  the  thera- 
peutical resources  include  the  novelties  of  medicine  as  well 
as  the  old  and  tried  agents.— Pittshnruli  M<->J.  BfoSetD. 

A  very  attractive  and  valuable  work  has  been  given  to 
the  medical  profession  by  Drs.  Keating  and  Edwards,  in 
their  treatise  on  the  diseases  of  the  heart  and  circulation 
in  infancy  and  adolescence,  and  they  deserve  the  greatest 
credit  for  the  admirable  manner  in  which  they  have  col- 
lected, reviewed,  and  made  use  of  the  immense  amount  of 
material  on  this  important  subject.— A rchives  of  Pedintrirx. 

The  plan  of  the  work  is  the  correct  one,  viz.,  the  sup- 
plementing of  the  observations  of  the  better  class  of  prac- 
titioners by  the  experience  of  those  who  have  given  the 
subject  systematic  attention. — Medical  -Age. 


It  is  not  a  mere  compilation,  but  a  systematic  treatise, 
and  bears  evidence  of  considerable  labor  and  observation  on- 
the  part  of  the  authors.  Two  fine  photographs  of  dissect 
tions  exhibit  mitral  stenosis  and  mitral  regurgitation ; 
there  are  also  a  number  of  wood-cuts. — Cleveland  Medical 
Gazette. 

As  the  works  upon  diseases  of  children  give  little  or  no 
attention  to  diseases  of  tbe  heart,  this  work  of  Drs.  Keat- 
ing and  Edwards  will  supply  a  want.  We  think  that 
there  will  be  no  physician,  who  takes  an  interest  in  the 
affections  of  young  folks,  who  will  not  wish  to  consult  it. 
—  Ciiirhinfifi  M':<1.  K'nra. 

The  work  takes  up,  in  an  able  and  scientific  manner, 
diseases  of  the  heart  in  children.  This  is  a  part  of  the 
field  of  medical  science  which  has  not  been  cultivated  to 
the  extent  that  the  importance  of  the  subject  deserves.— 
Canada  Lancet. 


10 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


PERPETUAL  CLINICAL  INDEX 

MATERIA    MEDICA,   CHEMISTRY,    AND   PHARMACY  CHARTS. 
By  A.  H.  KELLER,  Ph.G.,  M.D. 

Consisting    of    (1)    the  "Perpetual  Clinical   Index,"  an   oblong    volume,    9x6    inches, 
neatly  bound  in  extra  Cloth  ;  (3)  a  Chart  of  "Materia  Medica,"  32x44  inches, 
mounted  on  muslin,  with  rollers  ;  (3)  a  Chart  of  »  Chemistry  and  Phar- 
macy," 32  x44  inches,  mounted  on  muslin,  with  rollers. 

United  States.        Canada  (duty  paid).       Great  Britain.  France. 

Net  Price  for  the  Complete  Work,       $5,00  $5,50  £l.ls.         30  fr.  30 


Bead  the  Following  Description  and  Explanation  of  the 

In  presenting  the  objects  and  advantages  of  these  Charts  and  "  Perpetual  Clinical  Index"  it  becomes 
necessary  to  state  that  the  Author's  many  years'  experience  as  a  physician  and  Pharmacist  enables  him 
to  produce,  in  terse  language,  a  volume  of  facts  that  must  be  of  inestimable  value  to  the  busy  physician  and 
pharmacist,  or  to  any  student  of  either  profession.  He  has  endeavored  to  describe  all  that  have  borne  inves- 
tigation up  to  date. 

The  system  will  prove  to  be  of  great  value  in  this,  that  so  little  labor  will  be  required  to  add  new 
investigation  as  fast  as  may  be  gathered  from  new  books,  journals,  etc.  The  classification  is  alphabetical 
and  numerical  in  arrangement,  and  serves  so  to  unite  the  various  essentials  of  Botany,  Chemistry,  and 
Materia  Medica,  that  the  very  thought  of  the  one  will  readily  associate  the  principal  properties  and  uses,  as 
well  as  its  origin. 

The  "MATERIA  MEDICA"  CHART,  in  the  first  place,  aids  at  a  glance:  ist,  Botanical  or 
U.  S.  P.  Name;  2d,  The  Common  Name ;  ^d,  Natural  Order  ;  4th,  Where  Indigenous ;  sth,  Principal  Con- 
stituent; 6th,  Part  Used — herbs,  leaves,  flowers,  roots,  barks,  etc.  ;  yth,  Medicinal  Properties — mainly  con- 
sidered ;  8th,  The  Dose — medium  and  large. 

On  this  Chart  there  are  475  first  names ;  Section  A.  is  numbered  from  i  to  59,  each  section  commencing 
with  the  capital  letter,  and  having  its  own  numbers  on  both  left-hand  and  right-hand  columns,  to  prevent 
mistakes  in  lining  out,  all  in  quite  large  type.  In  the  centre  of  the  Chart,  occupying  about  6  inches  in 
width,  is  a  term  index  of  common  names.  In  the  second  column  of  Chart,  like  this  : 

ACONITE  LEAVES,        .        .      • 4  A. 

Then  by  reference  to  4  A  in  first  column,  you  there  find  the  Botanical  or  U.  S.  P.  N«.me.     On  this  Chart  is 
also  found  a  brief  definition  of  the  terms  used,  under  the  heading  "  Medicinal  Properties." 

The  "CHEMISTRY"  CHART  takes  in  regular  order  the  U.S.  Pharmacopoeia  Chemicals,  with 
the  addition  of  many  new  ones,  and  following  the  name,  the  Chemical  Formula,  the  Molecular  Weight,  and 
next  the  Origin.  This  is  a  brief  but  accurate  description  of  the  essential  points  in  the  manufacture  :  The 
Uose,  medium  and  large;  next,  Specific  Gravity;  then,  whether  Salt  or  Alkaloid;  next,  Solubilities,  by 
abbreviation,  in  Water,  Alcohol,  and  Glycerine,  and  blank  columns  for  solubilities,  as  desired. 

Alkaloids  and  Concentrations  are  tabulated  with  reference  numbers  for  the  Perpetual  Clinical  Index,  giving 
Medicinal  Properties,  Minute  Dose^and  Large  Dose  For  example,  ALKALOIDS  AND  CONCENTRATIONS  : 

A.  MEDICINAL  PROPERTIES.  MINUTE  DOSE,      i       LARGE  DOSE. 

(a)  Aconitine.  Narcotic  and  Apyretic.  1-500  gr.  1-16  gr. 

Following  this,  Preparations  of  the  Pharmacopoeia,  each  tabulated.     For  example  : 

TINCTURAL. 


TlNCTURA. 

DRUG. 

AMOUNT. 

ALCOHOL. 

DOSE. 

*  Aconiti. 

$  Aconite. 
I  Tartaric  Acid,  60  f  P.    j 

S1A  oz.  to  24  gr. 

100 

i  to  3  drops. 

*  60  Fineness  of  Powder  as  per  U.  S.  P. 

t  P.  Macerate  24  hours.     Percolate,  adding  Menstruum  to  complete  (1)  pint  tincture. 


They  are  all  thus  abbreviated,  with  a  ready  reference  head-note. 

Next,  Thermometers,  Metric  Table  of  Weights,  Helps  to  the  Study  of  Chemistry,  Examples  in  Work- 
ing Atomic  Molecular  Formulae  Next,  Explanation  of  Terms  Used  in  Columns  of  Solubilities,  List  of 
Most  Important  Elements  Now  in  Use,  and  Definitions  or  Terms  Frequently  Used  in  Chemistry  and 
Pharmacy. 

The  "PERPETUAL,  CLINICAL  INDEX"  is  a  book  6  by  9  inches,  and  one-half  inch  thick. 
It  contains  135  pages,  divided  as  follows  (opposite  pages  blank)  : 

The  Index  to  Chemistry  Chart  occupies  two  pages;  Explanations,  Abbreviations,  etc.,  forty  pages,  with 
diseases,  and  with  an  average  of  ten  references  to- each  disease,  leaving  room  for  about  forty  more  remedies 
for  each  disease.  The  numbers  refer  to  the  remedies  used  in  the  diseases  by  the  most  celebrated  physicians 
and  surgeons,  and  the  abbreviations  to  the  manner  in  which  they  are  used.  Eight  pages,  numbered  and 
bracketed,  for  other  diseases  not  enumerated.  The  Materia  Medica,  Explanations,  Abbreviations,  and 
Remedies  suggested  for,  occupy  twenty-six  pages.  For  Abbreviated  Prescriptions,  seventeen  blank  pages. 
Then  the  Index  to  Alkaloids  and  Concentrations.  These,  already  enumerated,  with  their  reference,  number 
six  blank  tabulated  pages,  for  noting  any  new  Alkaloids  and  Concentrations.  Then  the  Chemistry  Index, 
giving  the  same  number  as  on  Chart,  with  Name,  Doses,  Specific  Gravity,  Salt  or  Alkaloid  in  the  same 
line,  as  for  example : 

NAME.  DOSES.       j      SPECIFIC  GRAVITY.       j     SALT  OR  ALKALOID.  MEMORANDA. 

~:  !  !'  i 

This  Alemorarlda  place  is  for  Physicians'  or  Pharmacists'  reference  notes ;  and  with  the  addition  of 
several  tabulated  blank  pages,  in  which  to  add  any  new  chemical,  with  doses,  etc.  The  remaining  sixteen 
pages  for  Materia  Medica  Index,  leaving  blanks  following  each  other  for  new  names  and  reference  numbers. 

To  show  the  ready  and  permanent  use  of  the  "Perpetual  Clinical  Index"  of  the  "Chemistry"  and 
"Pharmacy"  Charts  or  Index  in  the  book,  suppose  the  Physician  reads  in  a  book  or  journal  that  Caffeine 
Citras  is  useful  in  the  disease  Chorea,  and  he  wishes  to  keep  a  permanent  record  of  that,  he  refers  to  the 
Chart,  and  if  it  does  not  already  appear  there,  it  can  be  placed  opposite  and  numbered,  and  thereafter  used 
for  reference.  But  we  find  its  permanent  number  is  No.  99,  so  he  will  write  down  in  the  line  left  blank  for 
future  use  in  his  book,  in  line  already  used,  running  parallel  with  other  reference  numbers  in  Chorea,  the 
No.  99,  and  immediately  under  he  can  use  the  abbreviation  in  the  manner  in  which  it  is  given.  Though 
years  may  have  passed,  he  can  in  a  moment,  by  referring  there,  see  that  No.  99  is  good  for  Chorea.  If  fail- 
ing to  remember  what  No.  99  is,  he  glances  at  the  Chart  or  Index.  He  sees  that  No.  99  is  Caffeine  Citras, 
and  he  there  learns  its  origin  and  dose  and  solubility,  and  in  a  moment  an  intelligent  prescription  can  be 
constructed. 

(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.AJ  11 


New  Edition  of  an  Important  and  Timely  Work  Just  Published. 


Electricity  in  the  Diseases  of  ^fomen 


"With  Special  Reference  to  the  Application  of  Strong  Currents. 

G.  BETTON  MASSEY,  M.D., 

Hospi 
Neurological  Ass'n,  of  the  Philadelphia  Neurological  Society,  of  the  Franklin  Institute,  etc. 


By 

Physician  to  the  Gynecological  Department  of  Howard  Hospital  ;  Late  Electro-Therapeutist  to  the  Phila- 
delphia  Orthopaedic   Hospital  and   Infirmary   for  Nervous    Diseases  ;    Member   of  the  American 


ZEoLitioia.- 


ZES-e-srised.    smd. 


WITH  NEW  AND  ORIGINAL  WOOD-ENGRAVINGS.     HANDSOMELY  BOUND  IN  CLOTH.     OVER  200  PAGES. 

12mo.        Price,   in  United  States  and  Canada,   $1.50,  net,   post-paid. 

In  Great  Britain,  6s.  6d.    In  France,  9  fr.  35. 


This  work  is  presented  to  the  profession  as  the  most  complete  treatise  yet  issued  om 
the  electrical  treatment  of  diseases  of  women,  and  is  destined  to  fill  the  increasing  demand 
for  clear  and  practical  instruction  in  the  handling  and  use  of  strong  currents  after  the 
recent  methods  first  advocated  by  Apostoli.  The  whole  subject  is  treated  from  the  present 
stand-point  of  electric  science  with  new  and  original  illustrations,  the  thorough  studies  of 
the  author  and  his  wide  clinical  experience  rendering  him  an  authority  upon  electricity 
itself  and  its  therapeutic  applications.  The  author  has  enhanced  the  practical  value  of 
the  work  by  including  the  exact  details  of  treatment  and  results  in  a  number  of  cases 
taken  from  his  private  and  hospital  practice. 


FIG.  15.— AUTHOR'S  FIBROID  SPEAR. 


FIG.  18.— BALL  ELECTRODE  FOR  ADMINISTERING  FRANKLINIC  SPARKS. 


CHAPTER  I,  Introductory  ;  II,  Apparatus  required  in  gynecological  applications  of  the  galvanic  current ; 
HI,  Experiments  illustrating  the  physical  qualities  of  galvanic  currents ;  IV,  Action  of  concentrated  gal- 
vanic currents  on  organized  tissues  ;  V,  Intra-uterine galvano-chemical  cauterization;  VI,  Operative  details 
of  pelvic  electro-puncture;  VII,  The  faradic  current  in  gynecology  ;  VIII,  The  franklinic  current  in  gyne- 
cology';  IX,  Non-caustic  vaginal,  urethral,  and  rectal  applications  ;  X,  General  percutaneous  applications  in 
the  treatment  of  nervous  women  ;  XI,  The  electrical  treatment  of  fibroid  tumors  of  the  uterus  ;  XII,  The 
electrical  treatment  of  uterine  hemorrhage;  XIII,  The  electrical  treatment  of  subinvolution ;  XIV,  The 
electrical  treatment  of  chronic  endometritis  and  chronic  metritis ;  XV,  The  electrical  treatment  of  chronic 
diseases  of  the  uterus  and  appendages;  XVI,  Electrical  treatment  of  pelvic  pain;  XVII,  The  electrical 
treatment  of  uterine  displacements;  XVIII,  The  electrical  treatment  of  extra-uterine  pregnancy;  XIX, 
The  electrical  treatment  of  certain  miscellaneous  conditions  ;  XX,  The  centra-indications  and  limitations  to 
the  use  of  strong  currents. 

An  Appendix  and  a  Copious  Index,  including  the  definitions  of  terms  used  in  the  work,  concludes 
the  book. 


The  author  gives  us  what  he  has  seen,  and  of  which 

he  is  assured  by  scientific  study  is  correct We 

are  certain  that  this  little  work  will  prove  helpful  to  all 
physicians  who  desire  to  use  electricity  in  the  management 
of  the  diseases  of  women. — The  American  Lancet. 

To  say  that  the  author  is  rather  conservative  in  his 
ideas  of  the  curative  powers  of  electricity  is  only  another 
way  of  saying  that  he  understands  his  subject  thoroughly. 
The  mild  enthusiasm  of  our  author  is  unassailable,  because 
it  is  founded  on  science  and  reared  with  experience.—  The 
Medical  Analectic. 

The  work  is  well  written,  exceedingly  practical,  and 
can  be  trusted.  We  commend  it  to  the  profession." — Mary- 
land Medical  Journal. 

The  book  is  one  which  should  be  possessed  by  every 
physician  who  treats  diseases  of  women  by  electricity.— 
The  Brooklyn  Medical  Journal. 

The  departments  of  electro-physics,  pathology,  and 
electro-therapeutics  are  thoroughly  and  admirably  con- 


sidered, and  by  means  of  good  wood-cuts  the  beginner  has 
before  his  eye  the  exact  method  of  work  required.— The 
Medical  Register. 

"  The  author  of  this  little  volume  of  210  pages  ought 
to  have  added  to  its  title,  "  and  a  mo'st  happy  dissertation 
upon  the  methods  of  using  this  medicinal  agent;  "  for  in 
the  first  100  pages  he  has  contrived  to  describe  the  techni 
of  electrization  in  as  clear  and  happy  a  manner  as  no 
author  has  ever  succeeded  in  doing,  and  for  this  part  of  the 
book  alone  it  is  almost  priceless  to  the  beginner  in  the 

treatment  with  this  agent The  little  book  ia 

worthy  the  perusal  of  every  one  at  all  interested  in  the 
subject  of  electricity  in  medicine. — Tfie  Omaha  Clinic. 

The  treatment  of  fibroid  tumor  of  the  uterus  will, 
perhaps,  interest  the  profession  more  generally  than  any 
other  question.  This  subject  has  been  accorded  ample 
space.  The  method  of  treatment  in  many  cases  has  been 
recited  in  detail,  the  results  in  every  instance  reported  be- 
ing beneficial,  and  in  many  curative.— Pacific  Med.  Jour. 


r> 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.} 


PRACTICAL  SURGERY. 

By  J.  EWING  MEARS,  M.D., 

Lecturer  on  Practical  Surgery  and  Demonstrator  of  Surgery  in  Jefferson   Medical  College;    Professor  of 
Anatomy  and  Clinical  Surgery  in  the  Pennsylvania  College  of  Dental  Surgery,  etc. 


With  490  Illustrations,  Second  edition,  revised  and  enlarged,   794  pp.   12mo, 


PRICE,  IN  UNITED  STATES  AND  CANADA  :  CLOTH,  $3.00.     DISCOUNT,  20  PER  CENT.,  MAKING  IT,  NET, 
$2.40;  POSTAGE,  20  CENTS  EXTRA.     GREAT  BRITAIN,   13s.     FRANCE,  18  fr.  75. 


MEARS'  PRACTICAL  SURGERY  includes  chapters  on  Surgical  Dress- 
ings, Bandaging,  Fractures,  Dislocations,  Ligature  of  Arteries,  Amputa- 
tions, Excisions  of  Bones  and  Joints.  This 
work  gives-  a  complete  account  of  the 
methods  of  antiseptic  surgery.  The  dif- 
ferent agents  used  in  antiseptic  dressing, 
their  methods  of  preparation,  and  their 
application  in  the  treatment  of  wounds  are 
fully  described.  With  this  work  as  a  guide 
it  is  possible  for  every  surgeon  to  practice 
antiseptic  surgery.  The  great  advances 
made  in  the  science  and  art  of  surgery  are 
largely  due  to  the  introduction  of  anti- 
septic methods  of  wound  treatment,  and  it 
is  incumbent  upon  every  progressive  sur- 
geon to  employ  them. 

An    examination    of    this   work   will 
show  that  it  is  thoroughly  systematic  in 

its  plan,  so  that  it  is  not  only  useful  to  the  practitioner,  who  may  be 
called  upon  to  perform  operations,  but  of  great  value  to  the  student  in 
his  work  in  the  surgical  room,  where  he  is  required  to  apply  bandages 
and  fracture  dressings,  and  to  perform  operations  upon  the  cadaver.  The 
experience  of  the  author,  derived  from  many  years'  service  as  a  teacher 
(private  and  public)  and  practitioner,  has  enabled  him  to  present  the 
topics  discussed  in  such  a  manner  as  to  fully  meet  the  needs  of  both  prac- 
titioners and  students. 


is   full  of  common  sense,  and  may  be  safely 


taken  as  a  guide  in  the  matters  of  which  it  treats 
It  would  be  hard  to  point  out  all  the  excellences  of 


tioner  who  follows  it  intelligently  cannot  easily  go 


astray. — Journal  American  Medical  Asso' 

We  cannot  speak  too  highly  of  the  volume  under 

this  book.    We  can  heartily  recommend  it  to  students    H    review.— Canada.  Med.  and  Surg .  Jour. 
and  to  practitioners  of  surgery.—  American  Jour-    ji        The  space  devoted  to  fractures  and  dislocations 


nal  of  the  Medical  Sciences. 

We  do  not  know  of  any  other  work  which  would 
be  of  greater  value  to  the  student  in  connection  with 
his  lectures  in  this  department. — Buffalo  Medical 


— by  far  the  most  difficult  and  responsible  part  of 
surgery — is  ample,  and  we  notice  many  new  illustra- 
tions explanatory  of  the  text. — North  Carolina 
Medical  Journal. 


*nd  Surgical  journal.  It  is  one  of  the  most  valuable  of  the  works  of  its 

The  work  is   excellent.      The  student   or  practi-         kind.— New  Orleans  Med.  and  Surg.  Jour. 


(F.  A,  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.)  13 


AN  ENTIRELY  NEW  PHYSICIAN'S  VISITING  LIST. 


MEDICAL  BULLETIN  VISITING  LIST 

-  OR  - 

-  PHYSICIAN'S  QALL  RECORD. 


ARRANGED  UPON  AN  ORIGINAL  AND  CONVENIENT  MONTHLY  AND  WEEKLY  PLAN 
FOR  THE  DAILY  RECORDING  OF  PROFESSIONAL  VISITS. 


Frequent  Rewriting  of  Names  Unnecessary. 

THIS  YISITING  LIST  is  arranged  upon  a  plan  best  adapted  to  the  most 
convenient  use  of  all  physicians,  and  embraces  a  new  feature  in  recording 
daily  visits  not  found  in  any  other  list,  consisting  of  STUB  OR  HALF  LEAVES 
IN  THE  FORM  OF  INSERTS,  a  glance  at  which  will  suffice  to  show  that  as  the 
first  week's  record  of  visits  is  completed  the  next  week's  record  may  be 
made  by  simply  turning  over  the  stub-leaf,  without  the  necessity  of  re- 
writing the  patients'  names.  This  is  done  until  the  month  is  completed, 
and  the  physician  has  kept  his  record  just  as  complete  in  every  detail  of 
VISIT,  CHARGE,  CREDIT,  etc.,  as  he  could  have  done  had  he  used  any  of  the 
old-style  visiting  lists,  and  has  also  SAVED  himself  three-fourths  of  the 
time  and  labor  formerly  required  in  transferring  names  EVERY  week. 
There  are  no  intricate  rulings ;  everything  is  easity  and  quickly  under- 
stood ;  not  the  least  amount  of  time  can  be  lost  in  comprehending  the 
plan,  for  it  is  acquired  at  a  glance. 

The  Three  Different  Styles  Made. 

The  UTo.  1  Style  of  this  List  provides  ample  space  for  the  DAILY 
record  of  seventy  (70)  different  names  each  month  for  an  entire  year 
(two  full  pages,  thirty-five  [35]  names  to  a  page,  being  allowed  to  each 
month),  so  that  its  size  is  sufficient  for  an  ordinary  practice ;  but  for 
physicians  who  prefer  a  List' that  will  accommodate  a  larger  practice  we 
have  made  a  UTo.  2  Style,  which  provides  ample  space  for  the  daily 
record  of  ONE  HUNDRED  AND  FIVE  DIFFERENT  NAMES  (105)  each  month  for 
an  entire  year  (three  full  pages  being  allowed  to  each  month),  and  for 
physicians  who  may  prefer  a  Pocket  Record  Book  of  less  thickness  than 
either  of  these  styles  we  have  made  a  Wo.  3  Style,  in  which  "  The 
Blanks  for  the  Recording  of  Visits  In  "  have  been  made  into  removable 
sections.  These  sections  are  very  thin,  and  are  made  up  so  as  to  answer 
in  full  the  demand  of  the  largest  practice,  each  section  providing  ample 
space  for  the  DAILY  RECORD  OF 'TWO  HUNDRED  AND  TEN  (210)  DIFFERENT 
NAMES  for  one  month;  or  one  hundred  and  five  (105)  different  names 
daily  each  month  for  two  months ;  or  seventy  (TO)  different  names  daily 
each  month  for  three  months ;  or  thirty-five  (35)  different  names  daily 
each  month  for  six  months.  Four  sets  of  these  sections  go  with  each 
copy  of  No.  3.  Style. 

Special  Features  Not  Found  in  Any  Other  List. 

In  this  No.  3  STYLE  the  PRINTED  MATTER,  and  such  matter  as  the 
BLANK  FORMS  FOR  ADDRESSES  OF  PATIENTS,  Obstetric  Record,  Vaccination 
Record,  Cash  Account,  Births  "and  Deaths  Records,  etc.,  are  fastened 
permanently  in  the  back  of  the  book,  thus  reducing  its  thickness.  The 
addition  of  one  of  these  removable  sections  does  not  increase  the  size 
quite  an  eighth  of  an  inch.  This  brings  the  book  into  such  a  small  com- 
pass that  no  one  can  object  to  it  on  account  of  its  thickness,  as  its  bulk 

14 


is  V'ERY  MUCH  LESS  than  that  of  any  visiting  list  ever  published.  Every 
physician  will  at  once  understand  that  as  soon  as  a  section  is  full  it  can 
be  taken  out,  filed  away,  and  another  inserted  without  the  least  incon- 
venience or  trouble. 

This  Visiting  List  contains  a  Calendar  for  the  last  six  months 
of  last  year,  all  of  this,  and  next  year;  Table  of  Signs  to  be  used 
in  Keeping  Accounts;  Dr.  Ely's  Obstetrical  Table;  Table  of  Cal- 
culating the  Number  of  Doses  in  a  given  R,  etc.,  etc.;  for  converting 
Apothecaries' Weights  and  Measures  into  Grammes ;  Metrical  Avoirdu- 
pois and  Apothecaries' Weights ;  Number  of  Drops  in  a  Fluidrachm  ; 
-Graduated  Doses  for  Children  ;  Graduated  Table  for  Administering 
Laudanum  ;  Periods  of  Eruption  of  the  Teeth  ;  The  Average  Frequency 
of  the  Pulse  at  Different  Ages  in  Health;  Formula  and  Doses  of  Hypo- 
dermic Medication;  Use  of  the  Hypodermic  Syringe;  Formulae  and 
Doses  of  Medicine  for  Inhalation;  Formulae  for  Suppositories  for  the 
Rectum ;  The  Use  of  the  Thermometer  in  Disease ;  Poisons  and  their 
Antidotes ;  Treatment  of  Asphyxia ;  Anti-Emetic  Remedies ;  Nasal 
Douches ;  Eye-Washes. 

Most  Convenient  Time-  and  Labor-  Saving  List  Issued. 

It  is  evident  to  eve^  one  that  this  is,  beyond  question,  the  best  and 
most  convenient  time- and  labor-saving  Physicians' Record  Book  ever 
published.  Ph3rsicians  of  many  years'  standing  and  with  large  practices 
pronounce  this  the  Best  List  they  have  ever  seen.  It  is  handsomely 
bound  in  fine,  strong  leather,  with  flap,  including  a  pocket  for  loose 
memoranda,  etc.,  and  is  furnished  with  a  Dixon  lead-pencil  of  excellent 
quality  and  finish.  It  is  compact  and  convenient  for  carrying  in  the 
pocket.  Size,  4  x  6|  inches. 

IN    THREE    STYI^ES-KET    PRICES,    POST-PAID. 

U.  S.  and  Canada.    Great  Britain.      France. 

No.  i.     Regular  Size,  for  70  patients  daily  each  month  for  one  year,        SI. 25  5s.  3.          7  fr.  75 

"No.  2.     Large  Size,  for  105  patients  daily  each  month  for  one  year,  1.5O  6s.  6.          9  fr.  35 

No.  3.     In  which  "The  Blanks  for  Recording  Visits  in"  are  in  re- 
movable sections,  as  described  above,         ...        -  1.75  7s.  3.       12  fr.  2O 


EXTRACTS    FROM    REVIEWS.- 


"  While  each  page  records  only  a  week's  visits, 
"yet  by  an  ingenious  device  of  half  leaves  the  names 
-of  the  patients  require  to  be  written  but  once  a 
month,  and  a  glance  at  an  opening  of  the  book 
shows  the  entire  visits  paid  to  any  individual  in  a 
month.  It  will  be  found  a  great  convenience." — 
Jioston  Medical  and  Surgical  Journal. 

"Everything  about  it  is  easily  and  quickly 
understood." — Canadian  Practitioner. 

"Of  the  many  visiting  lists  before  the  profes- 
sion, each  has  some  special  feature  to  recommend 
it.  This  list  is  very  ingeniously  arranged,  as  by  a 
series  of  narrow  leaves  following  a  wider  one,  the 
name  of  the  patient  is  written  but  once  during  the 
month,  while  the  account  can  run  for  thirty-one 
days,  space  being  arranged  for  a  weekly  debit 
and  credit  summary  and  for  special  memoranda. 
The  usual  pages  for  cash  account,  obstetrical 
record,  addresses,  etc.,  are  included.  A  large 
amount  of  miscellaneous  information  is  presented 
in  a  condensed  form."  —  Occidental  Medical 
Times. 

"It  is  a  monthly  instead  of  a  weekly  record, 
thus  obviating  the  transferring  of  names  oftener 
than  once  a  month.  There  is  a  Dr.  and  Cr.  column 
following  each  week's  record,  enabling  the  doctor 
to  carry  a  patient's  account  for  an  indefinite  time, 
•or  until  he  is  discharged,  with  little  trouble." — 
Indiana  Medical  Journal.  " 


"Accounts  can  begin  and  end  at  any  date. 
Each  name  can  be  entered  for  each  day  of  every 
month  on  the  same  line.  To  accomplish  this,  four 
leaves,  little  more  than  one-third  as  wide  as  the 
usual  leaf  of  the  book,  follow  each  page.  Oppo- 
site is  a  full  page  for  the  recording  of  special 
memoranda.  The  usual  accompaniments  of  this 
class  of  books  are  made  out  with  care  and  fitness." 
—  The  American  Lancet. 

"This  is  a  novel  list,  and  an  unusually  con- 
venient one." — Journal  of  the  Amer.Med.Assoc. 

"This  new  candidate  for  the  favor  of  physi- 
cians possesses  some  unique  and  useful  points. 
The  necessity  of  rewriting  names  every  week  is 
obviated  by  a  simple  contrivance  in  the  make-up 
of  its  pages,  thus  saving  much  valuable  time, 
besides  reducing  the  bulk  of  the  book." — Buffalo 
Medical  and  Surgicai  Journal. 

"This  list  is  an  entirely  new  departure,  and 
on  a  plan  that  renders  posting  rapid  and  easy.  It 
is  just  what  we  have  often  wished  for,  and  really 
fills  a  long-felt  want."—  The  Medical  Waif. 

"It  certainly  contains  the  largest  amount  of 
practical  knowledge  for  the  medical  practitioner 
in  the  smallest  possible  volume,  besides  enabling 
the  poorest  accountant  to  keep  a  correct  record, 
and  render  a  correct  bill  at  a  moment's  notice." — 
Medical  Chips. 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


HAND-BOOK  OF  ECLAMPSIA; 

OK, 

Notes  and  Cases  of  Puerperal  Convulsions. 


E.  MICHENER,  M.D.,  J.  H.  STUBBS,  M.D.,  R.  B.  EWING,  M.D. 

B.THOMPSON,  M.D.,  S.  STEBBINS,  M.D. 


Price,  in  United  States  and  Canada,  Bound  in  Cloth,  I6mo,  Net,  75  Cents;  in  Great 
Britain,  3  Shillings ;  in  Prance,  4  fr.  20. 

In  our  medical  colleges  the  teachers  of  Obstetrics  dwell  upon  the  use  of  blood-letting  (phlebotomy)  ia 
cases  of  puerperal  convulsions,  and  to  this  method  Dr.  Michener  and  his  fellows  give  their  unqualified 
support — not  to  take  a  prescribed  number  of  ounces,  but  to  bleed  for  effect,  and/Vow  a  large  orifice.  This 
is  plainly  and  admirably  set  forth  in  his  book.  To  bleed  requires  a  cutting  instrument, — not  necessarily  a 
lancet, — for  Dr.  M.  states  how  in  one  case  a  pocket-knife  was  used  and  the  desired  effect  produced. 

Let  the  young  physician  gather  courage  from  this  little  book,  and  let  the  more  experienced  give  testi- 
mony to  confirm  its  teaching. 


have  always    thought  that  this    treatment  was 
1      '  '     s  generally; 
ig  we  would 


3rsed,  approved, "and  practiced  by  physicians  generally  ; 
and  to  such  as  doubt  the  efficacy  of  blood-lettins 


)mmend  this  little  volume. — Southern  Clinic. 

The    authors    are   seriously   striving  to  restore    the 


'•  lost  art"  of  blood-letting,  and  we  must  commend   the 
modesty  of  their  endeavor. — North  Carolina  Med.  Jour. 

The  cases  were  ably  analyzed,  and  this  plea  for  vene- 
section should  receive  the  most  attentive  consideration  from 
obstetricians. — Medical  and  Surgical  Reporter. 


JTJST 


A  MANUAL  OF  INSTRUCTION 


FOR  GIVING 


PROK. 


NISSKN, 


Director  of  the  Swedish  Health  Institute,  Washington,  D.C.  ;  Late  Instructor  in  Physical  Culture  and. 

Gymnastics  at  the  Johns  Hopkins  University,  Baltimore,  Md.  ;  Author  of 

"  Health  by  Exercise  without  Apparatus." 


ILLUSTRATED   WITH  29   ORIGINAL    WOOD-ENGRAVINGS. 


In  One  12mo  Volume  of  128  Pages.     Neatly  Bound  in  Cloth.     Price,, 

post-paid,  in  United  States  and  Canada,  Net,  $1.OO;  in 

Great  Britain,  4s.  3d. ;  in  France,  6  fr.  2O. 


This  is  the  only  publication  in  the  English  language  treating  this  very  important, 
subject  in  a  practical  manner.  Full  instructions  are  given  regarding  the  mode  of 
applying 

The  Swedish  Movement  and  Massage  Treatment 

in  various  diseases  and  conditions  of  the  human  system  with  the  greatest  degree  of 
effectiveness.  Professor  Nissen  is  the  best  authority  in  the  United  States  upon  this  prac- 
tical phase  of  this  subject,  and  his  book  is  indispensable  to  every  physician  who  wishes  to- 
know  how  to  use  these  valuable  handmaids  of  medicine. 


This  manual  is  valuable  to  the  practitioner,  as  it 
contains  a  terse  description  of  a  subject  but  too  little  under- 
stood in  this  country The  book  is  got  up  very 

creditably.— N.  Y.  Med.  Jour. 

The  present  volume  is  a  modest  account  of  the  appli- 
cation of  the  Swedish  Movement  and  Massage  Treatment, 
in  which  the  technique  of  the  various  procedures  are  clearly 
stated  as  well  _  as  illustrated  in  a  very  excellent  manner. 
— North  American  Practitioner. 

This  little  manual  seems  to  be  written  by  an  expert, 
and  to  those  who  desire  to  know  the  details  connected  with 


the  Swedish  Movement  and  Massage  we  commend  the- 
"book . — Practice. ' 

This  attractive  little  book  presents  the  subject  in  a  very 
practical  shape,  and  makes  it  possible  for  every  physician  to 
understand  at  least  how  it  is  applied,  if  it  does  not  give  him 
dexterity  in  the  art  of  its  application.  He  can  certainty 
acquire  dexterity  by  following  the  directions  so  plainly  ad- 
viied  in  this  book. — Chicago  Mf.d.  Times. 

It  is  so  practical  and  clear  in  its  demonstrations  that 
if  you  wish  a  work  of  this  nature  you  cannot  do  better  than- 
peruse  this  one.— Medical  Brief. 


H) 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


JUST  READY— THE  LATEST  AND  BEST  PHYSICIAN'S  ACCOUNT 
BOOK  EVER  PUBLISHED. 


PHYSICIAN'S- 


ALL-REQC1I5ITE  TIME* 

A-  LABOR-  SAVINS 


Account- 


BEING  A  LEDGER  AND  ACCOUNT-BOOK  FOR  PHYSICIANS'  USE,  MEETING  ALL 
THE  REQUIREMENTS  OF  THE  LAW  AND  COURTS. 


DESIGNED   BY 


Of 


PROBABLY  no  class  of  people  lose  more  money  through  carelessly  kept 
accounts  and  overlooked  or  neglected  bills  than  physicians.  Often 
detained  at  the  bedside  of  the  sick  until  late  at  night,  or  deprived  of 
even  a  modicum  of  rest,  it  is  with  great  difficulty  that  he  spares  the 
time  or  puts  himself  in  condition  to  give  the  same  care  to  his  own 
financial  interests  that  a  merchant,  a  lawyer,  or  even  a  farmer  devotes. 
It  is  then  plainl}7  apparent  that  a  system  of  bookkeeping  and  accounts 
that,  without  sacrificing  accuracy,  but,  on  the  other  hand,  ensuring  it,  at 
the  same  time  relieves  the  keeping  of  a  physician's  book  of  half  their 
complexity  and  two-thirds  the  labor,  is  a  convenience  which  will  be 
eagerly  welcomed  by  thousands  of  overworked  physicians.  Such  a  sys- 
tem lias  at  last  been  devised,  and  we  take  pleasure  in  offering  it  to  the 
profession  in  the  form  of  THE  PHYSICIAN'S  ALL-REQUISITE  TIME-  AND 
LABOR-  SAVING  ACCOUNT-BOOK. 

There  is  no  exaggeration  in  stating  that  this  Account-Book  and 
Ledger  reduces  the  labor  of  keeping  your  accounts  more  than  one-halfr 
and  at  the  same  time  secures  the  greatest  degree  of  accuracy.  We  may 
mention  a  few  of  the  superior  advantages  of  THE  PHYSICIAN'S  ALL- 
REQUISITE  TIME-  AND  LABOR-  SAVING  ACCOUNT-BOOK,  as  follow: — 


First — "Will  meet  all  the  requirements  of 
the  law  and  courts. 

Second — Self-explanatory  ;  no  cipher  code. 

Third— Its  completeness  without  sacrificing 
anything. 

Fourth — No  posting;  one  entry  only. 

'Fifth — Universal ;  can  be  commenced  at  any 
time  of  year,  and  can  be  continued  in- 
definitely until  every  account  is  filled. 

Sixth — Absolutely  no  waste  of  space. 

Seventh — One  person  must  needs  be  sick 
every  day  of  the  year  to  fill  his  account, 
or  might  be  ten  years  about  it  and  re- 
quire no  more  than  the  space  for  one 
account  in  this  ledger. 

Eighth — Double  the  number  and  irfany  times 
more  than  the  number  of  accounts  in 


any  similar  book;  the  300-page  book 
contains  space  for  900  accounts,  and  the 
600-page  book  contains  space  for  1800 
accounts. 

Ninth — There  are  no  smaller  spaces. 

Tenth — Compact  without  sacrificing  com- 
pleteness; every  account  complete  on 
same  page — a  decided  advantage  and 
recommendation. 

Eleventh — Uniform  size  of  leaves. 

Twelfth — The  statement  of  the  most  com- 
plicated account  is  at  once  before  you 
at  any  time  of  month  or  year — in  other 
words,  the  account  itself  as  it  stands  is 
its  simplest  statement. 

Thirteenth — No  transferring  of  accounts, 
balances,  etc. 


To  all  physicians  desiring  a  quick,  accurate,  and  comprehensive 
method  of  keeping  their  accounts,  we  can  safely  sa}r  that  no  /book  as 
suitable  as  this  one  has  ever  been  devised. 


Great 
Britain. 


NET  PRICES,  SHIPPING  EXPENSES  PREPAID. 

No.  1.  3OO  Pages,  for  90O  Accounts  per  Year,  Canada 

Size  10x12,  Bound  in  ?i  Russia,  Raised  In  U-  S-         (duty  paid). 

Back-Bands,  Cloth  Sides,         .          .         .  85.0O            85.5O           SO.  18s. 
No.  2.  GOO  Pages,  for  18OO  Accounts  per  Year, 

Size  10x12,  Bound  in  %  Russia,  Raised 

Back-Bands,  Cloth  Sides,         .         .         .  8.0O                8.8O               1.13s. 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


France. 
3O  fr.  3O 


49  fr.  4O 


17 


PHYSICIANS'  INTERPRETER 

IN  FOUR  LANGUAGBS. 

(ENGLISH,  FRENCH,  GERMAN,  AND  ITALIAN.) 


Specially  Arranged  for  Diagnosis  by  m.  von  \. 


The  object  of  this  little  work  is  to  meet  a  need  often  keenly  felt  by 
the  busy  physician,  namely,  the  need  of  some  quick  and  reliable  method 
of  communicating  intelligibly  with  patients  of  those  nationalities  and 
languages  unfamiliar  to  the  practitioner.  The  plan  of  the  book  is  a  sys- 
tematic arrangement  of  questions  upon  the  various  branches  of  Practical 
Medicine,  and  each  question  is  so  worded  that  the  only  answer  required 
of  the  patient  is  merely  YES  or  No.  The  questions  are  all  numbered, 
and  a  complete  Index  renders  them  always  available  for  quick  reference. 
The  book  is  written  by  one  who  is  well  versed  in  English,  French,  Ger- 
man, and  Italian,  being  an  excellent  teacher  in  all  those  languages,  and 
who  has  also  had  considerable  hospital  experience. 

Bound  in  Full  Russia  Leather,  for  Carrying  in  the  Pocket.  (Size,  5x2£ 

Inches.)     2O6  Pages.     Price,  post-paid,  in  United  States  and 

Canada,  $1.OO,  net;  Great  Britain,  4s.  6d. ;  France,  6  fr.  &O. 


To  convey  some  idea  of  the  scope  of  the  questions  contained  in  the 
Physicians'  Interpreter,  we  append  the  Index  : — 


NOS. 

General  health 1-50 

Special  diet 31-  47 

Age  of  patient 52-  62 

Necessity  of  patients  undergoing  an  opera- 
tion   63-  70 

Office  hours 7i-  77 

Days  of  the  week 78-  84 

Patient's  history:  hereditary  affections  in  his 
family;  his  occupation;    diseases   from 

his  childhood  up 85-130 

Months  of  the  year. 106-117 

Seasons  of  the  year 118-121 

Symptoms  of  typhoid  fever. . .  . .  131-158 

Symptoms  of  Bright's  disease 159-168 

Symptoms  of  lung  diseases 169-194  and  311-312 

Vertigo • 195-201 

The  eyes 201-232 

Paralysis  and  rheumatism 236-260 


Stomach  complaints  and  chills. 


?6 1-269 


Falls  and  fainting  spells 271—277 

How  patient's  illness  began,  and  when  pa- 
tient was  first  taken  sick 278-279 

Names  for  various  parts  of  the  body 283-299 

The  liver 300-301 

The  memory 304-305 

Bites,  stings,  pricks 314-316 

Eruptions 317-318 

Previous  treatment 3 19 

Symptoms  of  lead-poisoning 320-3*4 

Hemorrhages 325-3*8 

Burns  and  sprains 33°~33* 

The  throat 332-335 

The  ears 336-339 

General    directions    concerning     medicines, 
baths,     bandaging,    gargling,     painting 

swelling,  etc 34°-373 

Numbers .pages  202-204 


The  work  is  well  done,  and  calculated  to  be  of  great 
service  to  those  who  wish  to  acquire  familiarity  with  the 
phrases  used  in  questioning  patients.  More  than  this,  we 
believe  it  would  be  a  great  help  in  acquiring  a  vocabulary 
to  be  used  in  reading  medical  books,  and  that  it  would  fur- 
nish an  excellent  basis  for  beginning  a  study  of  any  one  of 
the  languages  which  it  includes. — Medical  and  Surgical 
Reporter. 

Many  other  books  of  the  same  sort,  with  more  ex- 
tensive vocabularies,  have  been  published,  but,  from  their 
size,  and  from  their  being  usually  devoted  to  equivalents 
in  English  and  one  other  language  only,  they  have  not  had 
the  advantage  which  is  pre-eminent  in  this — convenience. 
It  is  handsomely  printed,  and  bound  in  flexible  red  leather 
in  the  form  of  a  diary.  It  would  scarcely  make  itself  felt 
in  one's  hip-pocket,  and  would  insure  its  bearer  against  any 
ordinary  conversational  difficulty  in  dealing  with  foreign- 
speaking  people,  who  are  constantly  coming  into  our  city 
hospitals.— New  York  Medical  Journal. 

In  our  larger  cities,  and  in  the  whole  Northwest,  the 
physician  is  constantly  meeting  with  immigrant  patients, 
to  whom  it  is  difficult  for  him  to  make  himself  understood, 
«r  to  know  what  they  say  in  return.  This  difficulty  will 


little  work.—  The  Phy- 


be  greatly  obviated  by  use  of  tin 
sician  and  Surgeon. 

The  phrases  are  well  selected,  and  one  might  practice 
long  without  requiring  more  of  these  languages  than  this 
little  book  furnishes.— Phi/a.  Medical  Tiiutf. 

How  ofttn  the  physician  is  called  to  attend  those  with 
whom  the  English  language  is  unfamiliar,  and  many  phy- 
sicians are  thus  deprived  of  the  means,  save  through  an 
interpreter,  of  arriving  at  a  correct  knowledge  on  which  to 
base  a  diagnosis.  An  interpreter  is  not  always  at  hand, 
but  with  this  pocket  interpreter  in  your  hand  you  are  able 
to  ask  all  the  questions  necessary,  and  receive  the  answer 
in  such  manner  that  you  will  be  able  to  fully  comprehend. 
— The  Medical  Brief. 

This  little  volume  is  one  of  the  most  ingenious  aids 
to  the  physician  which  we  have  seen.  We  heartily  com- 
mend the'book  to  any  one  who,  being  without  a  knowledge 
of  the  foreign  languages,  is  obliged  to  treat  those  who  d» 
not  know  our  own  language.—^.  Louis  Courier  of  JMH> 

It  will  rapidly  supersede,  for  the  practical  use  of  the 
doctor  who  cannot  take  the  time  to  learn  another  language 
all  other  suggestive  works.— Chicago  Medical  Times. 


18 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


An  Important  Aid  to  Students  in  the  Study  of  Anatomy. 


THREE  CHARTS  or 


The  Nervo- Vascular  System. 

PART  I.— THE  NERVES. 

PART  II.— THE  ARTERIES. 

PART  III.— THE  VEINS. 

ARRANGED  BY  W.  HENRY  PRICE,  A.M.,  M.D.,  AND  S.  POTTS  EAGLETON. 
ENDORSED  BY  LEADING  ANATOMISTS. 


PRICE,  IN  THE  UNITED  STATES  AND  CANADA,  50  CENTS,  NET,  COMPLETE; 
GREAT  BRITAIN,  2s.  6d.     FRANCE,  3  fr.  60. 


"THE  NERVO-VASCULAB  SYSTEM  OF  CHARTS"  far  Excels  Every  Other  System 
in  their  Completeness,  Compactness,  and  Accuracy. 


I.  The  Nerves. — Gives  in  a  clear  form  not  only  the  Cranial 
and  Spinal  Nerves,  showing  the  formation  of  the  different  Plexuses 
and  their  branches,  but  also  the  complete  distribution  of  the 
k  OIPATHETIC  NERVES,  thereby  making  it  the  most  complete  and 
concise  chart  of  the  Nervous  System  yet  published. 
Part  II.  The  Arteries. — Gives  a  unique  grouping  of  the  Arterial 
System,  showing  the  divisions  and  subdivisions  of  all  the  vessels, 
beginning  from  the  heart  and  tracing  their  CONTINUOUS  distribution 
to  the  periphery,  and  showing  at  a  glance  the  terminal  branches 
of  each  artery. 

Part  III.  The  Veins. — Shows  how  the  blood  from  the  periphery 
of  the  body  is  gradually  collected  by  the  larger  veins,  and  these 
coalescing  forming  still  larger  vessels,  until  they  finally  trace 
themselves  into  the  Right  Auricle  of  the  heart. 

It  is  therefore  readily  seen  that  "  The  Nervo- Vascular  System  of 
Charts"  offers  the  following  superior  advantages: — 

1.  It  is  the  only  arrangement  which  combines  the  Three  Systems, 
and  yet  each  is  perfect  and  distinct  in  itself. 

2.  It  is  the  only  instance  of  the  Cranial,  Spinal,  and  Sympathetic 
Nervous  Systems  being  represented  on  one  chart. 

3.  From  its  neat  size  and  clear  type,  and  being  printed  only  upon 
one  side,  it  may  be  tacked  up  in  any  convenient  place,  and  is  always 
read}r  for  freshening  up  the  memory  and  reviewing  for  examination. 

4.  The  nominal  price  for  which  these  charts  are  sold  places  them 
within  the  reach  of  all. 


For  the  student  of  anatomy  there  can  possibly  be  no    ' 
more  concise  way  of  acquiring  a  knowledge  of  the  nerves,    ; 
veins,  and  arteries  of  the  human  system.    It  presents  at  a 
glance  their  trunks  and  branches  in  the  great  divisions  of 
the  body.    It  will  save  a  world  of  tedious  reading,  and  will    '• 
impress  itself  on  the  mind  as  no  ordinary  vade  mecum,    j 
«veu.  could.     Its  price  is  nominal  and  its  value  inestima- 
ble.    No  student  should  be  without  it.— Pacific  Record  of 
Mrili-inn  and  Surgery. 

We  take  pleasure  in  calling  attention  to  these  charts, 
as  they  are  so  arranged  that  a  study  of  them  will  serve  to    ; 
impress  them  more  indellibly  on  your  mind  than  can  be 
gained   in   any  other  way.    They   are  also  valuable  for 
reference.—  Medical  Brief. 

These  are  three  admirably  arranged  charts  for  the 
•se  of  students,  to  assist  in  memorizing  their  anatomical 
studies.— Bu/nlo  Jftd.  and  Surg.  Jour. 

This  is  a  series  of  charts  of  the  nerves,  arteries,  and    i 


veins  of  the  human  body,  giving  names,  origins,  distribu- 
tions, and  functions,  very  convenient  as  memorizers  and 
reminders.  A  similar  series,  prepared  by  the  late  J.  H. 
Armsby,  of  Albany,  N.Y.,  and  framed,  long  found  a  place 
in  the  study  of  the  writer,  and  on  more  than  one  occasion 
was  the  means  of  saving  precious  moments  that  must 
otherwise  have  been  devoted  to  tumbling  the  pages  of  ana- 
tomical works. — Med.  Age. 

These  three  charts  will  be  of  great  assistance  to 
medical  students.  They  can  be  hung  on  the  wall  and  read 
across  any  ordinary  room.  The  price  is  only  fifty  cents  for 
the  set. — Practice. 

These  charts  have  been  carefully  arranged,  and  will 
prove  to  be  very  convenient  for  ready  reference.  They 

are  three  in  number,  each  constituting  a  part 

It  is  a  high  recommendation  that  these  charts  have  beem 
examined  and  approved  by  John  B.  Beaver,  M.D.,  Demon- 
strator of  Anatomy  in  the  University  of  Pennsylvania.— 
Pacific  Med.  and  Surg.  Jour,  and  Western  Lancet. 


(F.  A.  DAVIS,  Medical  Publisher  Philadelphia,  Pa.,  U.S.A.) 


19 


EVERY    SANITARIAN   SHOUJLD    HAVE    ROME'S    "TEXT-BOOK    OF    HYGIENE" 
AS  A  WORK  OF  REFERENCE. 


SEOOIsTID 


TEXT-BOOK  OF  HYGIENE: 

A  COMPREHENSIVE  TREATISE  ON  THE  PRINCIPLES  AND  PRACTICE  OF  PREVENTIVE  MEDICINE 
FROM  AN  AMERICAN  STAND-POINT. 

By    GEORGB    H.    ROHK,    M.D., 

Pwfessor  of  Obstetrics  and  Hygiene  in  the  College  of  Physicians  and  Surgeons,  Baltimore ;  Director  of  the  Maryland 

Maternite ;  Member  of  the  American  Public  Health  Association  ;  Foreign  Associate  of  the  Societe  Franchise 

d'Hygiene,  of  the  Societe  des  Chevaliers-Sauveteurs  des  Alpes  Maritimes,  etc. 


Net  Price,  in  the  United  States,  $2.5O;   in  Canada  (duty  paid),  82.75;   in 
Great  Britain,  lls.  3d. ;  France,  16  fr.  8O. 


SECOND  EDITION — THOROUGHLY  REVISED  AND  LARGELY  REWRITTEN,  WITH  MANY  ILLUSTRATIONS 
AND  VALUABLE  TABLES.  Robe's  Hygiene  is  the  Standard  Text-Book  in  many  Medical  Colleges  in  the 
United  States  and  Canada.  It  is  a  sound  guide  to  the  most  modern  and  approved  practice  in  Applied 
Hygiene.  This  New  Edition  will  be  issued  early  in  the  Spring  of  1890,  in  one  handsome 
Octavo  volume  of  about  400  pages,  bound  in  Extra  Cloth.  Read  what  competent  critics  have  said  of  the 
first  edition  of  Robe's  "Text-Book  of  Hygiene":— 


A  storehouse  of  facts. — British  Medical  Journal. 

Of  invaluable  assistance  to  the  student.— Sanitary  News. 

This  interesting  and  valuable  book.— Pacific  Medical 
mnd  Surgical  Journal. 

Based  upon  sound  principles  and  good  practice. — Phila- 
delphia Medical  Times. 

Full  of  important  matter,  told  in  a  very  interesting 
•tanner. — Science. 

In  harmony  with  the  most  recent  advances  in  pathology. 
—Medical  Times  and  Gazette,  London. 


Nothing  better  for  the  teacher,  practitioner,  or  student, 
—Mississippi  Valley  Medical  Monthly. 

Contains  a  mass  of  information  of  the  utmost  impor- 
tance.— Independent  Practitioner. 

Just  the  work  needed  by  the  medical  student  and  tht 
busy,  active,  sanitary  officer. — Southern  Practitioner. 

This  very  useful  work. — American  Jour.  Med.  Sciences. 

Comprehensive  in  scope,  well  condensed,  clear  in  style, 
and  abundantly  supplied  with  references. — Journal  Amer- 
ican Medical  Association. 


JUST    ISSUED 

PHYSICIANS'  AND  STUDENTS'   READY-REFERENCE   SERIES 


The  Neuroses  of  the  Genito-Urinary  System 


I3NC 
WITH  STERILITY  AND   IMPOTENCE. 

BY 

DR.     R.     UI/TZNIANN, 

PROFESSOR  OF  GENITO-URINARY  DISEASES  IN  THE  UNIVERSITY  OF  VIENNA. 
TRANSLATED,  WITH  THE  AUTHOR'S  PERMISSION,  BY 

GARDNER  W.  ALLEN,  M.D., 

SURGEON   IN   THE  GENITO-URINARY   DEPARTMENT   BOSTON   DISPENSARY. 


Illustrated.    12mo.   Handsomely  Bound  in  Dark-Blue  Cloth.   Net  Price,  in  the  United 
States  and  Canada,  81.0O,  Post-paid  ;  Great  Britain,  4s.  6d.  :  France,  6  fr.  2O. 


This  great  work  upon  a  subject  which,  notwithstanding  the  great  strides  that  hav» 
been  made  in  its  investigation  and  the  deep  interest  it  possesses  for  all,  is  nevertheless 
still  but  imperfectly  understood,  has  been  translated  in  a  most  perfect  manner,  and  pre- 
serves most  fully  the  inherent  excellence  and  fascinating  style  of  its  renowned  and 
lamented  author.  Full  and  complete,  yet  terse  and  concise,  it  handles  the  subject  with 
such  a  vigor  of  touch,  such  a  clearness  of  detail  and  description,  and  such  a  directness  to 
the  result,  that  no  medical  man  who  once  takes  it  up  will  be  content  to  lay  it  down  until 
its  perusal  is  complete, — nor  will  one  reading  be  enough. 

Professor  Ultzmann  was  recognized  as  one  of  the  greatest  authorities  in  his  chosen 
specialty,  and  it  is  a  little  singular  that  so  few  of  his  writings  have  been  translated  into 
English.  Those  wfyo  have  been  so  fortunate  as  to  benefit  by  his  instruction  at  the  Vienna 
Polyclmic  can  testify  to  the  soundness  of  his  pathological  teachings  and  the  success  of  his 
methods  of  treatment.  He  approached  the  subject  from  a  somewhat  different  point  of 
view  from  most  surgeons,  and  this  gives  a  peculiar  value  to  the  work.  It  is  believed, 
moreover,  that  there  is  no  convenient  hand-book  in  English  treating  in  a  broad  manner 
the  Genito-urinary  Neuroses. 

SYNOPSIS  OF  CONTENTS.  FIRST  PART.— I.  Chemical  Changes  in  the  Urine  in 
Oases  of  Neuroses.  II.  The  Neuroses  of  the  Urinary  and  of  the  Sexual  Organs,  classi- 
fiVd  as  :  1,  Sensory  Neuroses  ;  2,  Motor  Neuroses  ;  3,  Secretory  Neuroses.  SECOND  PART. — 
Sterility  and  Impotence. 

THE  TREATMENT  IN  ALL  CASES  is  DESCRIBED  CLEARLY  AND  MINUTELY. 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


HAY  FEVER 


ITS  SUCCESSFUL   TREATMENT   BY   SUPERFICIAL   ORGANIC 
ALTERATION  OF  THE  NASAL  MUCOUS  MEMBRANE. 


CHARLES  K.  SAJOUS,  M.O., 

Lecturer  on  Rhinology  and  Laryngology  in  Jefferson  Medical  College :  Vice-President  of  the  American  Laryngological 

Association :  Officer  of  the  Academy  of  France  and  of  Public  Instruction  of  Venezuela ;  Corresponding 

Member  of  the  Royal  Society  of  Belgium,  of  the  Medical  Society  of  Warsaw  (Poland), 

and  of  the  Society  of  Hygiene  of  France  ;  Member  of" the  American 

Philosophical  Society,  etc.,  etc. 


WITH    13    ENGRAVINGS    ON    WOOD.       13nao.      BOUND    IN    CL.OTH.      BEVELE» 

EDGES.     PKICE,    IN    UNITED   STATES    AND   CANADA,    NET,  Sl.OO; 

GREAT   BRITAIN,   4s.    3d.;    FRANCE,    6  fr.  2O. 


The  object  of  this  little  work  is  to  place  in  the  hands  of  the  general 
practitioner  the  means  to  treat  successfully  a  disease  which,  until  lately, 
was  considered  as  incurable ;  its  history,  causes,  pathology,  and  treat- 
ment are  carefully  described,  and  the  latter  is  so  arranged  as  to  be 
practicable  by  any  physician. 


Dr.  Sajous'  volume  must  command  the  attention  of 
those  called  upon  to  treat  this  heretofore  intractable  com- 
plaint.— Medical  and  Surgical  Reporter. 

Few  have  had  the  success  in  this  disease  which  has 
so  much  baffled  the  average  practitioner  as  Dr.  Sajous,  con-   j 
•equently  his  statements  are  almost  authoritative.    The 
book  must  be  read  to  be  appreciated.— American  Medical    \ 
Digest. 

Dr.  Sajous  has  admirably  presented  the  subject,  and,  • 
AS  this  method  of  treatment  is  now  generally  recognized  ' 
*c  efficient,  we  can  recommend  this  book  to  all  physicians  I 


who  are  called  upon  to  treat  this  troublesome  disorder.— 
The  Buffalo  Medical  and  Surgical  Journal. 

The  symptoms,  etiology,  pathology,  and  treatment  of 
Hay  Fever  are  fully  and  ably  discussed.  The  reader  will 
not  regret  the  expenditure  of  the  small  purchase  price  of 
this  work  if  he  has  cases  of  the  kind  to  treat.— California 
Medical  Journal. 

We  are  pleased  with  the  author's  views,  and  heartily 
commend  his  book  to  the  consideration  of  the  profession 
— The  Southern  Clinic. 


PHYSICIANS'   AND  STUDENTS'   READY   REFERENCE   SERIES. 


ILTo. 


OBSTETRIC  SYNOPSIS 

By  JOHN  S.  STEWART,  M.D., 

Demonstrator  of  Obstetrics  and  Chief  Assistant  in  the  Gynaecological  Clinic  of  the  Medico-Chirurgical 

College  of  Philadelphia. 


WITH   AN   INTRODUCTORY   NOTE   BY 


WILLIAM  S.  STEWART,  A.M.,  M.D., 

Professor  of  Obstetrics  and  Gynaecology  in  the  Medico-Chirurgical  College  of  Philadelphia. 


42  ILLUSTRATIONS.    202  PAGES.    12 mo.    HANDSOMELY  BOUND  IN  DARK-BLUE  CLOTH. 

Price,  Post-paid,  in  the  United  States  and  Canada,  Net,  $1.OO; 
Great  Britain,  4s.  3d. ;  France,  6  fr.  2O. 


By  students  this  work  will  be  found  particularly  useful.  It  is  based 
upon  the  teachings  of  such  well-known  authors  as  Playfair,  Parvin, 
Lush,  Galabin,  and  Cazeaux  and  Tarnier,  and,  besides  containing  much 
new  and  important  matter  of  great  value  to  both  student  and  practi- 
tioner, embraces  in  an  Appendix  the  Obstetrical  Nomenclature  sug- 
gested by  Professor  Simpson,  of  Edinburgh,  and  adopted  by  the 
Obstetric  Section  of  the  Ninth  International  Medical  Congress  held  in 
Washington,  D.C.,  September,  1887. 


It  is  well  written,  excellently  illustrated,  and  fully  up  [ 
to  date  in  every  respect.    Here  we  find  all  the  essentials  of  j 
Obstetrics  in    a  nutshell,   Anatomy,  Embryology,  Physi-   I 
•logy.  Pregnancy,  Labor,  Puerperal  State,  and  Obstetric 
Operations  all  being  carefully  and  accurately  described.— 
Buffalo  Medical  and  Surgical  Journal. 

It  ie  clear  and  concise.    The  chapter  on  the  develop- 
ment of  the  «vum  is  especially  satisfactory.   The  judicious 


use  of  bold-faced  type  for  headings,  and  italics  for  impor- 
tant statements,  gives  the  book  a  pleasing  typographical 
appearance. — Medical  Record. 

This  volume  is  done  with  a  masterly  hand.  The 
scheme  is  an  excellent  one.  .  .  .  The  whole  is  freely 
and  most  admirably  illustrated  with  well-drawn,  new 
engravings,  and  the  book  is  of  a  very  couvenieat  size.— 
St.  Louis  Medical  and  Surgical  Journal. 


(F.  A.  DAVIS,   Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


DIPHTHERIA: 

CROUP,  TRACHEOTOMY,  **>  INTUBATION 

FROM  THE  FRENCH  OF  A.  SANNE. 

TRANSLATED  AND  ENLARGED  BY 

Z.    GILL,    Nl.D.,    UL.D. 


United  States.     Canada  (duty paid).     Great  Britain.        France. 

Net  Price,  Post-paid,  Cloth,    -       -$100.  $140.  £  0.18s.        24fr.6Q 

Leather,    -        5.00.  5.50.  1.  Is.        30  fr.  30 


The  above  work,  recently  issued,  is  a  translation  from  the  French  of  SANNE'S  great 
work  on  "  Diphtheria,"  by  H.  Z.  GILL,  late  Professor  of  Surgery  in  Cleveland,  Ohio. 

SANNE'S  work  is  quoted,  directly  or  indirectly,  by  every  writer  since  its  publication, 
as  the  highest  authority,  statistically,  theoretically,  and  practically.  The  translator, 
having  given  special  study  to  the  subject  for  many  years,  has  added  over  fifty  pages,  in- 
cluding the  Surgical  Anatomy,  Intubation,  and  the  recent  progress  in  the  branches 
treated  down  to  the  present  date;  making  it,  beyond  question,  the  most  complete  work 
extant  on  the  subject  of  Diphtheria  in  the  English  language. 

Facing  the  title-page  is  found  a  very  fine  Colored  Lithograph  Plate  of  the  parts  con- 
cerned in  Tracheotomy.  Next  follows  an  illustration  of  a  cast  of  the  entire  Trachea,  and 
bronchi  to  the  third  or  fourth  division,  in  one  piece,  taken  from  a  photograph  of  a  case 
in  which  the  cast  was  expelled  during  life  from  a  patient  sixteen  years  old.  This  is  the 
most  complete  cast  of  any  one  recorded. 

Over  fifty  other  illustrations  of  the  surgical  anatomy  of  instruments,  etc.,  add  to  the 
practical  value  of  the  work. 

Diphtheria  having  become  such  a  prevalent,  wide-spread,  and  fatal  disease,  no 
general  practitioner  can  afford  to  be  without  this  work.  It  will  aid  in  preventive  meas- 
ures, stimulate  promptness  in  the  application  of,  and  efficiency  in,  treatment,  and 
moderate  the  extravagant  views  which  have  been  entertained  regarding  certain  specifics 
in  the  disease  Diphtheria. 

A  full  Index  accompanies  the  enlarged  volume,  also  a  List  of  Authors,  making 
altogether  a  very  handsome  illustrated  volume  of  over  680  pages. 


In  this  book  we  have  a  complete  review  and  j 
compendium  of  all  worth  preserving  that  has  hitherto 
been  said  or  written  concerning  diphtheria  and  the 
kindred  subjects  treated  of  by  our  author,  collated, 
arranged,  and  commented  on  by  both  author  and 
translator.  The  subject  of  intubation,  so  recently 
revived  in  this  country,  receives  a  very  careful  and 
impartial  discussion  at  the  hands  of  the  translator, 
and  a  most  valuable  chapter  on  the  prophylaxis  of 
diphtheria  and  croup  closes  the  volume. 


Sanne's  work  is  quoted,  directly  or  indirectly,, 
by  many  writers  since  its  publication,  as  the  highest 
authority,  statistically,  theoretically,  and  practi- 
cally. The  translator,  having  given  special  study 
to  the  subject  for  many  years,  has  added  over  fifty 
pages,  including  the  surgical  anatomy,  intubation, 
and  the  recent  progress  in  the  branches  treated, 
down  to  the  present  date ;  making  it,  beyond  ques- 
tion, the  most  complete  work  extant  on  the  subject 
of  diphtheria  in  the  English  language.  Diphtheria 
having  become  such  a  prevalent,  wide-spread,  and 
fatal  disease,  no  general  practitioner  can  afford  to 


His  notes  are  frequent  and  full,  displaying  deep 
knowledge  of  the  subject-matter.      Altogether  the 

book   is   one  that    is  valuable  and  timely,  and  one    i  be   without    this   work.     It    will   aid    in   preventive 

that  should  be  in  the  hands  of  every  general  practi-    j  measures,  stimulate  promptness  in  application  of,  and 

tioner. — St.  Louis  Med.  and  Surgical  Journal.         |  efficiency  in,  treatment. — Southern  Practitioner. 

PRACTICAL  AND  SCIENTIFIC  PHYSIOGNOMY  i 


TO    E2.EJQLID 

By  MARY  OLMSTED  STANTON. 


Copiously   Illustrated.  Two  Large  Octavo  Volumes. 

United  States.       Canada  (duty  paid).       Great  Britain.  France. 

Price,  per  Volume,  Cloth,  885.OO  $5.5O  JEl.ls.  3O  fr.  3» 

«  "  Sheen,  6.OO  6. GO  1.6s.  36  fr.  4O 

Half-Russia,  7.0O  7.7O  1.9s.  43  fr.  3O 

$1.00  DISCOUNT  FOB  CASH.    Sold  only  by  Subscription,  or  sent  direct  on  receipt  of  price,  shipping  expenses  prepaid. 


The  author,  Mrs.  Mary  O.  Stanton,  has  given  over  twenty  years  to  the  preparation  of  this  work.  Her 
style  is  easy,  and,  by  her  happy  method  of  illustration  of  every  point,  the  book  reads  like  a  novel,  and 
memorizes  itself.  To  physicians  the  diagnostic  information  conveyed  is  invaluable.  To  the  general 
reader  each  page  opens  a  new  train  of  ideas.  (This  book  has  no  reference  whatever  to  Phrenology.) 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


ANNOUNCEMENT. 


A    TREATISE 

Materia  Medica,  Pharmacology,  $  Therapeutics. 

* 

BY 

dOHN  U.  SHOEMAKER,  A.M.,   M.D., 

Professor  of  Materia  Medica,  Pharmacology,  and  Therapeutics  in  the  Medico-Chirurgical  College  of  Phila- 
delphia, and  Member  American  Medical  Association, 

AND 

dOHN    AULDE,    M.D., 

Demonstrator  of  Clinical  Medicine  and  of  Physical  Diagnosis  in  the  Medico-Chirurgical  College  of  Phila- 
delphia, and  Member  American  Medical  Association. 


IN   TWO  HANDSOME   ROYAL   OCTAVO   VOLUMES. 

NET  PRICES,  per  Volume,  in  United  States:  Cloth,  S2.5O;  Sheep,  $3.25.     In  Canada 

(duty  paid)  :  Cloth,  82.75  ;  Sheep,  S3. 55.     In  Great  Britain:  Cloth,  11s.  3d.  ; 

Sheep,  14s.  6d*     In  France:  Cloth,  16  fr.  20  ;  Sheep,  2O  fr.  20. 


THE  Publisher  takes  pleasure  in  announcing  that  VOLUME  I  of  this  eagerly -looked-for 
work  is  Now  READY,  and  that  the  utmost  diligence  will  be  exercised  in  filling  with 
she  greatest  rapidity,  and  in  regular  order  of  receipt,  the  numerous  orders  now  awaiting 
its  publication. 

The  general  plan  of  the  work  embraces  three  parts,  each  of  which  is  practically  inde- 
pendent of  the  other,  as  will  be  understood  from  the  accompanying  analysis,  and  of  which 
Parts  I  and  II  are  contained  in  the  volume  now  announced ;  this,  however,  is  not  the  only 
advantage  accruing  from  the  preparation  of  the  work  in  two  volumes.  Each  volume  will 
thus  be  much  smaller  and  more  convenient  to  handle,  while  some  may  wish  to  secure  a 
particular  portion  of  the  work,  and  to  them  the  cost  is  lessened. 

Several  blank  sheets  of  closely -ruled  letter-paper  are  inserted  at  convenient  places  in 
the  work,  thus  rendering  it  available  for  the  student  and  physician  to  add  valuable  notes- 
concerning  new  remedies  and  other  important  matters. 

PART  I  embraces  three  subdivisions,  as  follow : — 

first.  A  brief  synopsis  upon  the  subject  of  pharmacy,  in  which  is  given  a  clear  and 
concise  description  of  the  operations  and  preparations  taken  into  account  by  the  physician 
when  prescribing  medicines,  together  with  some  practical  suggestions  regarding  the  most 
desirable  methods  for  securing  efficiency  and  palatability. 

Second.  A.  Classification  of  Medicines  is  presented  under  the  head  of  "  General  Phar- 
macology and  Therapeutics,"  with  a  view  to  indicate  more  especially  the  methods  by 
which  the  economy  is  affected.  Thus,  there  are  Internal  and  External  Remedies,  and, 
besides,  a  class  termed  Chemical  Agents,  including  Antidotes,  Disinfectants,  and  Anti- 
septics, and  an  explanatory  note  is  appended  to  each  group,  as  in  the  case  of  Alterative-. 
Antipyretics,  Antispasmodics,  Purgatives,  etc. 

Third.  A  Summary  has  been  prepared  upon  Therapeutics,  covering  methods  of 
Administration,  Absorption  and  Elimination,  Incompatibility,  Prescription-writing,  and 
Dietary  for  the  Sick,  this  section  of  the  work  embracing  nearly  one  hundred  and  fifty 
pages. 

PART  II  is  devoted  to  "Remedies  and  Remedial  Agents  Not  Properly  Classed  with 
Drugs,"  and  includes  elaborate  articles  upon  the  following  topics :  Electro-Therapy, 
Hydro-Therapy,  Masso-Therapy,  Heat  and  Cold,  Oxygen,  Mineral-Waters,  and,  in  addi- 
tion thereto,  other  subjects,  perhaps  of  less  significance  to  the  practitioner,  such  as  Clima- 
tology, Hypnotism- and  Suggestion,  Metallo-Therapy,  Transfusion,  and  Baunscheidtisnms. 
have  received  a  due  share  of  attention.  This  section  of  the  work  embraces  over  two  hun- 
dred pages,  and  will  be  found  especially  valuable  to  the  student  and  recent  graduate,  a* 
these  articles  are  fully  abreast  of  the  times. 

VOLUME  II,  which  is  Part  III  of  the  work,  is  wholly  taken  up  with  the  consideration 
of  drugs,  each  remedy  being  studied  from  three  points  of  view,  viz.,  the  Preparations,  or 
Materia  Medica;  the  Physiology  and  Toxicology,  or  Pharmacology,  and,  lastly,  its 
Therapy.  IT  WILL  BE  READY  ABOUT  MAY  1,  1890. 

The  typography  of  the  work  will  be  found  clean,  sharp,  and  easily  read  without 
injury  to  the  visual  organs,  and  the  bold-face  type  interspersed  throughout  the  text  makes 
the  different  subjects  discussed  quick  of  reference.  The  paper  and  binding  will  also  be  up 
to  the  standard,  and  nothing  will  be  left  undone  to  make  the  work  first-class  in  every 
particular, 

(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S  A.)  23 


:JUST   PUBLISHED.: 


THE  PHYSIOLOGY 

OF  THE 

DOMESTIC  ANIMALS. 

A  TEXT-BOOK  FOR  VETERINARY  AND  MEDICAL 
STUDENTS  AND  PRACTITIONERS. 

—BY— 

ROBERT  MEADE  SMITH,  A.M.,  M.D., 

Professor  of  Comparative  Physiology  in  University  of  Pennsylvania  ;  Fellow  of  the  College  of  Physicia»8 

and  Academy  of  the  Natural  Sciences,  Philadelphia  ;  of  the  American  Physiological 

Society  ;  of  the  American  Society  of  Naturalists  ;  Associe  Etraager 

de  la  Societe  Francaise  U'  Hygiene,  etc. 


FIG.  117. —PAROTID  AND  SITBMAXILLARY  FISTULA  IN  THE  HORSE,  AFTER  COLIN. 

(Thankoffer  and  Tormay.) 
K,  K',  rubber  bulbs  for  collecting  saliva;  cs,  cannula  in  the  parotid  duct. 


In  One  Handsome  Royal  Octavo  Volume  of  over  95O  Pages,  Pro- 
fusely Illustrated   with  more  than   4OO   Fine   "Wood- 
Engravings  and  many  Colored  Plates. 

United  States.        Canada  (duty  paid).        Great  Britain.  France. 

NET  PRICES,  CLOTH, $5.00  $5.50  £1.  30  fr.  30. 

SHEEP, 6.00  6.60  1.6.  36  fr.  20. 


nPHIS  new  and  important  work,  the  most  thoroughly  complete  in  the  English  language 
on  this  subject,  has  just  been  issued.  In  it  the  physiology  of  the  domestic  animals 
is  treated  in  a  most  comprehensive  manner,  especial  prominence  being  given  to  the  sub- 
ject of  foods  and  fodders,  and  the  character  of  the  diet  for  the  herbivora  under  different 
conditions,  with  a  full  consideration  of  their  digestive  peculiarities.  Without  being  over- 
burdened with  details,  it  forms  a  complete  text-book  of  physiology,  adapted  to  the  use  of 
students  and  practitioners  of  both  veterinary  and  human  medicine.  This  work  has  already 
been  adopted  as  the  Text-Book  on  Physiology  in  the  Veterinary  Colleges  of  the  United 
States,  Great  Britain,  and  Canada. 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


ABSTRACTS  FROA 


PHYSIOLOQY. 


The  work  throughout  is  well  balanced. 
Broad,  though  not  encyclopaedic,  concise 
without  sacrificing  clearness,  it  combines 
the  essentials  of  a  successful  text-book.  It 
is  eminently  modern,  and,  although  first  in 
the  field,  is  of  such  grade  of  excellence  that 
successors  must  reach  a  high  standard  be- 
fore they  become  competitors. — Annals  of 
Surgery. 

Dr.  Smith  has  conferred  a  great  benefit 
upon  the  veterinary  profession  by  his  con- 
tribution to  their  use  of  a  work  of  immense 
value,  and  has  provided  the  American  vet- 
erinary student  with  the  only  means  by 
which  he  can  become  properly  familiar  with 
the  physiology  of  our  domestic  animals. 
Veterinary  practitioners  and  graduates  will 
read  it  with  pleasure.  Veterinary  students 
will  readily  acquire  needed  knowledge  from 
its  pages,  and  veterinary  schools  which 
would  oe  well  equipped  for  the  work  they 
aim  to  perform  cannot  ignore  it  as  their 
text-book  in  physiology. — American  Veteri- 
nary Review. 

Dr.  Smith's  presentment  of  his  subject 
is  as  brief  as  the  status  of  the  science  per- 
mits, and  to  this  much-desired  conciseness 
he  has  added  an  equally  welcome  clearness 
of  statement.  The  illustrations  in  the  work 
are  exceedingly  good,  and  must  prove  a 
valuable  aid  to  me  full  understanding  of 
the  text. — Journal  of  Comparative  Medicine 
and  Surgery. 

We  have  examined  the  work  in  a  great 
many  particulars,  and  find  the  views  so 
correct,  where  we  have  had  the  means  of 
comparison  of  statements  with  those  of  some 
recognized  authority,  that  we  will  be  com- 
pelled hereafter  to  look  to  this  work  as  the 
text-book  on  physiology  of  animals.  The 
book  will  prove  of  incalculable  benefit  to 
veterinarians  wherever  they  may  be  found ; 
and  to  the  country  physician,  who  is  often 
called  upon  -  to  attend  to  sick  animals  as 
well  as  human  beings,  we  would  say,  lose 
no  time  in  getting  this  work  and  let  him 
familiarize  himself  with  the  facts  it  con- 
tains.—  Virginia  Medical  Monthly. 

Altogether,  Professor  Smith's  "  Physi- 
ology of  the  Domestic  Animals"  is  a  happy 
production,  and  will  be  hailed  with  delight 
in  both  the  human  medical  and  veterinary 
medical  worlds.  It  should  find  its  place 
besides  in  all  agricultural  libraries. — PAUL 
PAQUIN,  M.D.,  VA,  in  the  Weekly  Medical 
Review. 

It,  may  be  said  that  it  supplies  to  the 
veterinary  student  the  place  in  physiology 
that  Chauveau's  incomparable  work — "  The 
Comparative  Anatomy  of  the  Domesticated 
Animals" — occupies  in  anatomy.  Higher 
praise  than  this  it  is  not  possible  to  bestow. 
And  since  it  is  true  that  the  same  laws  of 
physiology  which  are  applicable  to  the  vital 
process  of  the  domestic  animals  are  also  ap- 
plicable to  man,  a  perusal  of  this  carefully 
written  book  will  repay  the  medical  student 
or  practitioner.— Canadian  Practitioner. 


The  work  before  us  fills  the  hiatus  of 
which  complaint  has  so  often  been  made, 
and  gives  in  the  compass  of  less  than  a 
thousand  pages  a  very  full  and  complete 
account  of  the  functions  of  the  body  in  both 
carnivora  and  herbivora.  The  author  has 
judiciously  made  the  nutritive  functions  thn 
strong  point  of  the  work,  and  has  devoted 
special  attention  to  the  subject  of  foods  and 
digestion.  In  looking  through  the  other 
sections  of  the  work,  it  appears  to  us  thai  a 
just  proportion  of  space  is  assigned  to  ea.rh. 
in  view  of  their  relative  importance  to  tin- 
practitioner.  Thus,  while  the  subject  of  re- 
production is  dismissed  in  a  few  pages,  a 
chapter  of  considerable  length  is  devoted 
to  locomotion,  and  especially  to  the  gaits  of 
the  horse. — London  Lancet. 

This  is  almost  the  only  work  of  the  kind 
in  the  English  language,  and  it  so  fully 
covers  every  detail  of  general  and  special 
physiology  that  there  is  no  room  for  any 
rival.  The  excellence  of  typographical 
work,  and  the  wealth,  beauty,  and  clear- 
ness of  the  illustrations,  correspond  with 
the  thoroughness  and  clearness  of  the 
treatise. — Albany  Medical  Annals. 

It  is  not  often  that  the  medical  profes- 
sion has  the  opportunity  of  reading  a  new 
book  upon  a  new  subject,  and  doubtless 
English-speaking  physicians  will  feel  grai< •- 
ful  to  Professor  Smith  for  his  admirable 
ainl  pioneer  work  in  a  branch  of  medical 
science  upon  which  a  great  amount  of  ignor- 
ance prevails.  .  .  .  The  last  portion  of 
the  work  is  devoted  to  the  reproductive 
functions,  and  contains  much  valuable  in- 
formation upon  a  portion  of  animal  physi- 
ology concerning  which  many  are  ignorant. 
The  book  is  a  valuable  one  in  every  way, 
and  will  be  consulted  largely  by  veterinary 
and  medical  students  and  practitioners. — 
Buffalo  Medical  and  Surgical  Journal. 
The  appearance  of  this  work  is  mo 
portune.  It  will  be  much  appreciated,  a- 
tending  to  secure  the  thorough  comprehen- 
sion of  function  in  the  domesticated  ani- 
mals, and,  in  consequence,  their  general 
well-being — a  matter  of  world- wide  impor- 
tance. With  a  thorough  sense  of  gratifica- 
tion we  have  perused  its  pages :  throughout 
we  find  clear  expression,  clear  reasoning, 
and  that  patient  accumulation  of  facts  so 

li  valuable    in    a   text-book   for  students. — 

|    British  Medical  Journal. 

For  notice  this  time,  I  take  up  the  vol- 
J!  ume   on   the  "  Physiology  of  the  Domestic 
:|  Animals."  by  Dr.  R.  Meade  Smith,  a  volume 
of  938  pages,  closely  printed,  and  dealing 
with  its  subject  in  a  manner  sufficiently  ex- 
haustive to  insure  its  place  as  a  text-book 
for   fifteen    years    at   the   very   least.      Its 
learning  is  only  equaled  by  'its   industry, 
;  and    its   industry  by    the   consistency  and 
;  skill  with  which  its  varied  parts  are  brought 
:  together   into   harmonious,    lucid,  an«l    in- 
'  tellectual    unity. — DR.    BENJAMIN    WARD 
RICHARDSON,  in  the  London 


(F.   A.   DAVIS,    Medical  Publisher,   Philadelphia,   Pa.,   U.S.A.) 


International  poeket  Medical 

ARRANGED   THERAPEUTICALLY. 

BY  G.  SUMMER  WlTMERSTlNE,   M.S.,   M.D., 

Associate  Editor  of  the  "Annual  of  the  Universal  Medical  Sciences  ;"  Visiting  Physician  of  the  Home  for 
the  Aged,  Germantown,  Philadelphia;  Late  House-Surgeon  Charity  Hospital,  New  York. 

More  than  1800  Formulae  from  Several  Hundred  Well-Known  Authorities. 

With  an  APPENDIX  containing  a  Posological  Table,  the  newer  remedies  included  ;  Important  Incompati- 
bles  ;  Tables  on  Dentition  and  the  Pulse  ;  Table  of  Drops  in  a  Fluidrachm  and  Doses  of  Laudanum  graduated 
for  age  ;  Formulae  and  Doses  of  Hypodermic  Medication,  including  the  newer  remedies;  Uses  of  the  Hypo- 
dermic Syringe;  Formulae  and  Doses  for  Inhalations,  Nasal  Douches,  Gargles,  and  Eye-washes  ;  Formulae 
for  Suppositories;  Use  of  the  Thermometer  in  Disease;  Poisons,  Antidotes,  and  Treatment;  Directions  for 
Post-Mortein  and  Medico-Legal  Examinations;  Treatment  of  Asphyxia, -Sun-stroke,  etc.;  Anti-emetic 
Remedies  and  Disinfectants;  Obstetrical  Table;  Directions  for  Ligation  of  Arteries  ;  Urinary  Analysis; 
Table  of  Eruptive  Fevers  :  Motor  Points  for  Electrical  Treatment,  etc.,  etc. 


This  work,  the  best  and  most  complete  of  its  kind,  contains  about  275  printed  pages,  besides 
extra  blank  leaves.  Elegantly  printed,  with  red  lines,  edges,  and  borders  ;  with  illustrations.  Round 
in  leather,  with  side  flap.  It  contains  more  than  180O  Formulae,  exclusive  of  the  large  amount  of 
other  very  valuable  matter. 

Price,  Post-paid,  in  the  United  States  and  Canada,  $2.OO,  net ; 
Great  Britain,  8s.  6d. ;  France,  12  fr.  4O. 

WHY  EVERY  MEDICAL  MAN  SHOULD  POSSESS  A  COPY  OF 
THE  INTERNATIONAL  POCKET  MEDICAL  FORMULARY. 

1.  Because  it  is  a  handy  book  of  reference,  replete  with  the  choicest  formulae  (over  1800  in  number)  of 
more  than  six  hundred  of  the  most  prominent  classical  writers  and  modern  practitioners. 

2.  Because  the  remedies  given  are  not  only  those  whose  efficiency  has  stood  the  test  of  time,  but  also  the 

newest  and  latest  discoveries  in  pharmacy  and  medical  science,  as  prescribed  and  used  by  the  best- 
known  American  and  foreign  modern  authorities. 

3.  Because  it  contains  the  latest,  largest  (66  formulae)  and  most  complete  collection  of  hypodermic  formulas 

(including  the  latest  new  remedies)   ever  published,  with  doses  and  directions  for  their  use  in  over 
fifty  different  diseases  and  diseased  conditions. 

4.  Because  its  appendix  is  brimful  of  information,  invaluable  in  office  work,  emergency  cases,  and  the 

daily  routine  of  practice. 

5.  Because  it  is  a  reliable  friend  to  consult  when,  in  a  perplexing  or  obstinate  case,  the  usual  line  of  treat- 

ment is  of  no  avail.     (A  hint  or  a  help  from  the  best  authorities,  as  to  choice  of  remedies,  correct 
dosage,  and  the  eligible,  elegant,  and  most  palatable  mode  of  exhibition  of  the  same.) 

6.  Because  it  is  compact,  elegantly  printed  and  bound,  well  illustrated,  and  of  convenient  size  and  shape 

for  the  pocket. 

7.  Because  the  alphabetical  arrangement  of  the  diseases  and  a  thumb-letter  index  render  reference  rapid 

and  easy. 


8*   Because  blank  leaves,  judiciously  distributed  throughout  the  book,  afford 
favorite  formula;. 


place  to  record  and  index 


9.  Because,  as  a  student,  he  needs  it  for  study,  collateral  reading,  and  for  recording  the  favorite  prescriptions 

of  his  professors,  in  lecture  and  clinic ;  as  a  recent  graduate,  he  needs  it  as  a  reference  hand-book  for 
daily  use  in  prescribing  (gargles,  nasal  douches,  inhalations,  eye-washes,  suppositories,  incompatibles, 
poisons,  etc.) ;  as  an  old  practitioner,  he  needs  it  to  refresh  his  memory  on  old  remedies  and  combi- 
nations, and  for  information  concerning  newer  remedies  and  more  modern  approved  plans  of  treatment. 

10.  Because  no  live,  progressive  medical  man  can  afford  to  be  without  it. 


It  is  sometimes  important  that  such  prescriptions  as 
have  been  well  established  in  their  usefulness  be  preserved 
for  reference,  and  this  little  volume  serves  such  a  purpose 
better  than  any  other  we  have  seen.— Columbus  Medical 
Journal. 

Without  doubt  this  book  is  the  best  one  of  its  class 
that  we  have  ever  seen.  .,.  .  .  The  printing,  binding. 
and  general  appearance  of  the  volume  are  beyond  praise.—- 
University  Medical  Magazine. 

It  may  be  possible  'to  get  more  crystallized  knowledge 
in  an  equally  small  space,  but  it  does  not  seem  probable.— 
Medical  Classi.cn. 

A  very  handy  and  valuable  book  of  formulae  for  the 
physician's  pocket. — St.  Louis  Medical  and  Surg.  Journal. 

This  little  pocket-book  contains  an  immense  number 
of  prescriptions  taken  from  high  authorities  in  this  and 
other  countries. — Northwestern  Lancet. 

This  one  is  the  most  complete  as  well  as  the  most 
conveniently  arranged  of  any  that  have  come  under  our 
attention.  The  diseases  are  enumerated  in  alphabetical 
order,  and  for  each  the  latest  and  most  approved  remedies 
from  the  ablest  authorities  are  prescribed.  The  book  is  in- 
dexed entirely  through  after  the'  order  of  the  first  pages  of 
a  ledger,  the  index  letter  being  printed  on  morocco  leather 
and  thereby  made  very  durable.— Pacific  Medical  Journal. 

It  is  a 'book  desirable  for  the  old  practitioner  and  for 
his  younger  brothers  as  well.—  St.  Joseph  Medical  Herald. 


As  long  as  "combinations"  are  sought  sm-h  :i  book 
will  be  of  value,  especially  to  those  who  cannot  spare  the 
time  required  to  learn  enough  of  incompatibilities  before 
commencing  practice  to  avoid  writing  incompatible  and 
dangerous  prescriptions.  The  constant  use  of  such  a  book 
by  such  prescribers  would  save  the  pharmacist  much 
anxiety.—  T he.  Drugg-islx1  Circular. 

In  judicious  selection,  in  accurate  nomenclature,  in 
arrangement,  and  in  style  it  leaves  nothing  to  be  desired. 
The  editor  and  the  publisher  are  to  be  congratulated  on  tin- 
production  of  the  very  best  book  of  its  clsuBS.—Ptttthttrg/i 
Mi'dicii!  I{i'ri''ir. 

One  must  see  it  to  realize  how  much  information  can 
be  got  into  a  work  of  so  little  bulk.— Canadn  Medical 
Record. 

To  the  young  physician  just  starting  out  in  practice 
this  little  book  will  prove  an  acceptable  companion 

The  want  of  to-day  is  crystallized  knowledge.  This 
neat  little  volume  contains  in  it  the  most  accessible  form. 
It  is  bound  in  morocco  in  pocket  form,  with  alphabetical 
divisions  of  diseases,  so  that  it  is  possible  to  turn  instantly 
to  the  remedy,  whatever  may  be  the  disorder  or  wherever 

the  patient  mav  be  situated To  the  physi.-ian 

it  is  invaluable*,  and  others  should  not  be  without  it.  We 
heartily  commend  the  work  to  our  readers.— Jfi»««*»M 
Medical  Journal. 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S. A 


JUST    ISSUED 

PHYSICIANS'    AND    STUDENTS'    READY-REFERENCE    SERIES. 

— INTO.  a. — 

Synopsis  of  Human  Anatomy 

Being   a  Complete    Compend  of  Anatomy,  including1  the 
Anatomy  of  the  Viscera,  and  Numerous  Tables. 


JAMES   K.  YOUNG,  M.D., 

Instructor  in  Orthopaedic  Surgery  and  Assistant    Demonstrator  of  Surgery,  University  of  Pennsylvania; 
Attending  Orthopaedic  Surgeon,  Out-Patient  Department,  University  Hospital,  etc. 


ILLUSTRATED  WITH  76  WOOD-ENGRAVINGS.     390  PAGES. 

12 mo.     HANDSOMELY  BOUND    IN   DARK-BLUE  CLOTH. 

Price,  Post-paid,  in  the  United  States  and  Canp,da,  $1.4O,  net; 
Great  Britain,  6s.  6d. ;  France,  9  fr.  25. 


While  the  author  has  prepared  this  work  especially  for  students,  sufficient  de- 
scriptive matter  has  been  added  to  render  it  extremely  valuable  to  the  busy  practitioner, 
particularly  the  sections  on  the  Viscera,  Special  Senses, 
and  Surgical  Anatomy. 

The  work  includes  a  complete  account  of  Osteology, 
Articulations  and  Ligaments.  Muscles.  Fascias,  Vascular 
and  Nervous  Systems,  Alimentary,  Vocal,  and  Respiratory 
and  Genito-Urinary  Apparatuses,  the  Organs  of  Special 
Sense,  and  Surgical  Anatomy. 

In  addition  to  a  most  carefully  and  accurately  prepared 
wherever  possible,  the  value  of  the  work  has  been 
enhanced  by  tables  to  facilitate  and  minimize  the  labor  of 
students  in  acquiring  a  thorough  knowledge  of  this  impor- 
tant subject.  The  section  on  the  teeth  has  also  been 
especially  prepared  to  meet  the  requirements  of  students 
of  Dentistry. 

In  its  preparation.  Gray's  Anatomy  [last  edition], 
edited  by  Keen,  being  the  anatomical  work  most  used,  has 
been  taken  as  the  standard. 


Anatomy  is  a  theme  that  allows  such  concen- 
tration better  than  most  medical  subjects,  and,  as 
the  accuracy  of  this  little  book  is  beyond  question, 
its  value  is  assured.  As  a  companion  to  the  dis- 
secting-table,  and  a  convenient  reference  for  the 
practitioner,  it  has  a  definite  field  of  usefulness. — 
Pittsburgh  Medical  Review. 

This  is  a  very  carefully  prepared  compend  of 
anatomy,  and  will"  be  useful  to  students  for  college 
or  hospital  examination.  There  are  some  excellent 
tables  in  the  work,  particularly  the  one  showing  the 
origin,  course,  distribution,  and  functions  of  the 
cranial  nerves. — Medical  Record. 

Dr.  Young  has  compiled  a  very  useful  book. 
We  are  not  inclined  to  approve  of  compends  as  a 
general  rule,  but  it  certainly  serves  a  good  purpose 
to  have  the  subject  of  anatomy  presented  in  a  com- 
pact, reliable  way,  and  in  a  book  easily  carried  to 
the  dissecting-room.  This  the  author  has  done. 
The  book  is  well  printed,  and  the  illustrations  well 
selected.  If  a  student  can  indulge  in  more  than  one 
work  on  anatomy, — for,  of  course,  he  must  have  a 
general  treatise  on  the  subject, — he  can  hardly  do 
better  than  to  purchase  this  compend  It  will  save 
the  larger  work,  and  can  always  be  with  him  during 
the  hours  of  dissection. — Buffalo  Medical  and 
Sn  rgica,  I  Jo  urnal. 


Excellent  tables  have  been  arranged,  which 
tersely  and  clearly  present  important  anatomical 
facts,  and  the  book  will  be  found  very  convenient 
for  ready  reference. — Columbus  Medical  Journal. 

The  book  is  much  more  satisfactory  than  the 
"remembrances"  in  vogue,  and  yet  is  not  too  cum- 
bersome to  be  carried  around  and  read  at  odd 
moments — a  property  which  the  student  will  readily 
appreciate.—  Weekly  Medical  Review. 

If  a  synopsis  of  human  anatomy  may  serve  a 
purpose,  and  we  believe  it  does,  it  is  very  important 
that  the  synopsis  should  be  a  good  one.  In  this 
respect  the  above  work  may  be  recommended  as  :i 
reliable  guide.  Dr.  Young  has  shown  excellent 
judgment  in  his  selection  of  illustrations,  in  the 
numerous  tables,  and  in  the  classification  of  the 
various  subjects. —  Therapeutic  Gazette. 

Every  unnecessary  word  has  been  excluded,  out 
of  regard  to  the  very  limited  time  at  the  medical 
student's  disposal.  It  is  also  good  as  a  reference 
book,  as  it  presents  the  facts  about  which  he  wisihes 
to  refresh  his  memory  in  the  briefest  manner 
consistent  with  clearness. — Neiv  York  Medical 
yournal 

It  is  certainly  concise  and  accurate,  and  should 
be  in  the  hands  of  every  student  and  practitioner. — 
The  Medical  Brief. 


(F.  A.  DAVIS.  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


•27 


ANNUAL- 

<.'!'    THP; 

Universal  Medical 

A    YEARLY  REPORT   OF    THE  PROGRESS   OF    THE   GENERAL    SANITARY 
SCIENCES  THROUGHOUT  THE  WORLD. 

Edited   by   CHARLES   E.    SAJOUS,    M.  D., 

LECTURER    ON    LARYNGOLOGY  AND   RHINOLOGY    IN   JEFFERSON    MEDICAL   COLLEGE,  PHILADELPHIA,  KTC. 

AND 

SEVENTY   ASSOCIATE   EDITORS, 

Assisted  by  over  TWO  HUNDRED  Corresponding  Editors  and  Collaborators. 

In  Five  Royal  Octavo  Volumes  of  about  500  pages  each,  bound  in  Cloth  and  Holf-Rn** 
Magnificently  Illustrated  with  Chromo -Lithographs,  Engravings, 
Maps,  Charts,  and  Diagram*. 


1st.  To  assist  the  busy  practitioner  in  his  efforts  to  keep  abreast  of  the  rapid  strides 
of  all  the  branches  of  his  profession. 

3d.  To  avoid  for  him  the  loss  of  time  involved  in  searching  for  that  which  is  n.-\v  in 
the  profuse  and  constantly  increasing  medical  literature  of  our  day. 

3d.  To  enable  him  to  obtain  the  greatest  possible  benefit  of  the  limited  titim  lie  is 
able  to  devote  to  reading,  by  furnishing  him  with  new  matter  ONLY. 

4th.  To  keep  him  informed  of  the  work  done  by  ALL  nations,  including  many  other- 
wise seldom  if  ever  heard  from. 

5th.  To  furnish  him  with  a  review  of  all  the  new  matter  contained  in  the  periodicals 
to  which  he  cannot  (through  their  immense  number)  subscribe. 

6th.  To  cull  for  the  specialist  all  that  is  of  a  progressive  nature  in  the  general  and 
special  publications  of  all  nations,  and  obtain  for  him  special  reports  from  countries  in 
which  such  publications  do  not  exist,  and 

Lastly,  to  enable  any  physician  to  posses^.  ;u  a  moderate  oost,  ;i  eomplof- 

CONTEMPORARY  HISTORY  OF  UNIVERSAL  MEDICINE,  - 

edited  by  many  of  America's  ablest  teachers,  and  superior  in  every  detail,  of  print,  paper, 
binding,  etc.,  etc.,  a  befitting  continuation  of  such  great  works  as  "  Pepper's  System  of 
Medicine/'  "Ashhurst's  International  Encyclopaedia  of  Surgery,"  "  Buck's  Reference 
Hand-Book  of  the  Medical  Sciences,"  etc.,  etc. 

EDITORIAL  STAFF  of  the  ANNUAL  of  the  UNIVERSAL  MEDICAL  SCIENCES.  ' 

ISSUE    OF    1888. 
-  Chief  Editor,  DR.  CHARL.ES  E.  SAJOUS,  Philadelphia  -- 

-A-SSOOI-A-TZE 


Volume  I.  —  Obstetrics,  Gynaecology,  Pediatrics,  Anatomy,  Physiology,  Pathoi-o;/?/. 
Histology,  and  Embryology. 

Prof.  Wm.  L.  Richardson,  Boston.  Prof.  William  Goodell  and  Dr.  W.  C.     Prof.  H.  Newell  Martin  and  Dr.  W.  H. 
Prof.  Thwphilus  Parvin,  Philada.  Goodell.  Philadelphia.  Howell.  Baltimore. 

Prof.  Louis  Starr,  Philadelphia.  Prof.  E.  C.  Dudley,  Chicago.  Dr.  Chas.  S.  Minot.  Boston. 

Prof.  J.  Lewis  Smith,  New  York  Citv.  Prof.  W.  H.  Parish,  Philadelphia.  Dr.  E.  O.  Shakespeare,  Philadelphia. 

Prof.  Paul  F.  Munde  and  Dr.  E.  H.  *  Prof.  William  S.  Forbes,  Philadelphia.  >  Dr.  W.  X.  Sudduth.  Philadelphia. 
Grandin,  New  York  City. 

Volume  H.  —  Diseases  of  the  Respiratory,  Circulatory,  Digestive,  and  JWrro?/.s  ,S'yx//'///.s: 
Fevers,  Exanthemata,  etc.,  etc. 


Prof.  A.  L.  Loomis,  New  York  City. 
Prof.  Jas.  T.  Whittaker,  Cincinnati. 
Prof.  W.  H.  Thomson,  New  York  City. 
Prof.  W.  W.  Johnston,  Washington. 
Prof  Jos.  Leidy,  Philadelphia. 


Prof.  E.  C.  Seguin,  New  York  City.  ;  Prof.  Jas.  Tvson,  Philadelphia. 

Prof.  E.  C.  Spitzka,  New  York  City.  \  Prof.  N.  S.  Davis,  Chicago. 

ProfChas.K.  Mills  and  Dr.  J.H.Lloyd,  ;  Prof.  John  Guit^ras,  Charleston,  S.  C. 

Philadelphia.  I  Dr.  Jas.  C.  Wilson,  Philadelphia. 
Prof.  Francis  Delafteld,  N.  Y.  City. 


Volume  III. — General  Surgery,  Vemereol  Diseases,  Anaesthetics,  Surf/iff// 

Dietetics,  etc.,  etc. 
Prof.  D.  Hayes  Agnew,  Philadelphia. 


Prof.  Hunter  McGuire,  Richmond 
Prof.  Lewis  A.  Stimson,  New  York. 
Prof.  P.  8.  Conner,  Cincinnati. 
Prof.  J.  EwingMears,  Philadelphia. 


Prof.  F.  R.  Sturgis,  New  York  City.  Prof.  T.  G.  Morton  and  Dr.  Win.  Hunt, 

Prof.  N.  Senn,  Milwaukee.  Philadelphia. 

Prof.  J.  E.  Garretson,  Philadelphia.  Dr.  MorrisJLongstreth,  Philadelphia 

Prof.  Christopher  Johnston,  Baltimore. 

Dr.  Cha3.  B.  Kelsey,  New  York  City. 


Dr.  Chas.  Wirgman,  Philadelphia. 
Dr.  C.  C.  Davidson,  Philadelphia. 
Prof.  E.  L.  Keyee,  New  York  City. 

Volume  IV. — Ophthalmology,  Otology,  Laryngology,  Jthinology,  Dermatology,  Dentisfa 
Hygiene,  Disposal  of  the  Dead,  etc.,  etc. 

Prof.  William  Thomson,  Philadelphia.  I  Prof.  C.  N.  Peirce,  Philadelphia.  Dr.  Chas.  S.  Turubull,  Philadelphia. 

Prof.  J.  Solis  Cohen,  Philadelphia.  Prof.  John  B.  Hamilton,  Washington.  Dr.  Edw.  C.  Kirk,  Philadelphia. 

Prof.  D.  Bryson  Delavan,  New  York.        Prof.  H.  M.  Lyman,  Chicago.  Dr.  John  G.  Lee,  Philadelphia. 

Prof.  A.  Van  Harlingen,  Philadelphia.  !  Prof.  S.  H.  Guilford,  Philadelphia.  Dr.  Cha*.  E.  Sajous,  Philadelphia, 
ffi 


List  of  Collaborators  to  Dental  Department. 

Prof.  James  Truinan.  Philadelphia.  Prof.  E.  H.  Angle,  Minneapolis,  Minn.     Dr.  J.  D.  Patterson,  Kansas  City.  Mo. 

Prof.  J.  A.  Marshall,  Chicago,  111.  Prof.  J.  E.  Cravens,  Indianapolis,  Ind.     Dr.  J.  B.  Hodgkin,  Washington,  D.  C. 

Prof.  A.  W.  Harlan,  Chicago,  111.  Prof.  R.  Stubbleneld,  Nashville,  Tenn.     Dr.  R.  R.  Andrews,  Cambridge,  Mass. 

1'rof.  G.  V.  Black,  Chicago.  111.  Prof.  W.  C.  Barrett,  Buffalo,  N.  Y.  Dr.  Albion  M.  Dudley,  Salem.  Mass. 

Prof.  C.  11.  Stowell.  Ann  Arbor.  Mich.  '  Prof.  A.  H.  Thompson,  Topeka,  Kan.        Dr.  Geo.  S.  Allen,  New  York  City. 

Prof.  L.  C.  Ingersoll.  Ke.ikuk.  Iowa.  Dr.  James  W.  White,  Philadelphia.  Dr.  G.  S.  Dean,  San  Francisco,  Cal. 

Prof.  F.  J.  S.  Gorgas.  Baltimore,  Md.  Dr.  L.  Ashley  Faught,  Philadelphia.  i  Dr.  M.  H.  Fletcher,  Cincinnati,  Ohio. 

Prof.  H.  A.  Smith,  Cincinnati.  Ohio.  Dr.  Robert  S.  Ivy,  Philadelphia.  \  Dr.  A.  Morsman,  Omaha,  Neb. 

Prof.  C.  P.  Pengra,  Boston.  Mass.  Dr.  W.  Storer  How,  Philadelphia.  Dr.  G.  W.  Melotte,  Ithaca,  N.  Y. 

Volume  V.  —  General  and  Experimental  Therapeutics,  Medical  Chemistry,  Medical 
Jurisprudence,  Demography,  Climatology,  etc.,  etc. 

Prof.  William  Pepper,  Philadelphia.'  ,  Prof.  George  H.  Rohe,  Baltimore.  Dr.  W.  P.  Mantou,  Detroit.  Miofe. 

Prof.  F.  W.  Draper,  Boston.  Dr.  Albert  L.  Gihon,  U.  S.  N.  Dr.  Hobart  A.  Hare,  Philadelphia. 

Prof.  J.  W.  Holland,  Philadelphia.  Dr.  R.  J.  Dunglison,.  Philadelphia.  '  Dr.  C.  S.  Witherstine,  Philadelphia. 

Prof.  A.  L.  Ranney.  New  York  City. 


(Including  the  "SATELLITE"  for  one  year). 

United  State-.     Canada  (duty  paid).  Great  Britain.  France. 

Cloth,  5  Vols.,  Royal  Octavo,      -      -      $15.00           $16.50  £3.6s.  93  fr.  95 

Half-Rusaia,  5  Vols.,  Royal  Octavo,  -        20.00             22.00  16s.  124  fr.  35 


EXTRACTS    FROM    REVIEWS. 

We  venture  to  say  that  all  who  saw  the  ANNUAL  as  it  appeared  in  1888  were  on  the 

>ut  for  its  reappearance  this  (1889)  year ;  but  there  are  many  whose  knowledge  of  this 
magnificent  undertaking  will  date  with  this  present  issue,  and  to  those  a  mere  examina- 
tion of  the  work  will  suffice  to  sho"w  that  it  fills  a  legitimate  place  in  the  evolution  of 
knowledge,  for  it  does  what  no  single  individual  is  capable  of  doing. 

These  volumes  make  readily  available  to  the  busy  practitioner  the  best  fruits  of 
iiR-dical  progress  for  the  year,  selected  by  able  editors  from  the  current  literature  of  the 
world:,  such  a  work  cannot  be  overlooked  by  anyone  who  would  keep  abreast  of  the 
i  :mes.  With  so  much  that  is  worthy  of  notice  incorporated  in  one  work,  and  each  depart- 
ment written  up  with  a  minuteness  and  thoroughness  appreciated  particularly  by  the 
-!>"<-ialist,  it  would  avail  nothing  to  cite  particular  instances  of  progress.  Let  it  be  suffi- 
cient to  say.  however,  that  while  formerly  there  was  a  possible  excuse  for  not  having  the 
latwst  information  on  matters  pertaining  to  the  medical  sciences,  there  can  no  longer  be 
>uch  an  excuse  while  the  ANNUAL  is  published. — Journal  of  the  American  Medictol 
Association. 

We  have  before  us  the  second  issue  of  this  ANNUAL,  and  it  is  not  speaking  too 
strongly  when  we  say  that  the  series  of  five  volumes  of  which  it  consists  forms  a  most 
important  and  valuable  addition  to  medical  literature. 

Great  discretion  and  knowledge  of  the  subjects  treated  of  are  required  at  the  hands 
of  those  who  have  taken  charge  of  the  various  sections,  and  the  manner  in  which  the 
gentlemen  who  were  chosen  to  fill  the  important  posts  of  sub-editors  have  acquitted 
themselves  fully  justifies  the  choice  made.  We  know  of  no  branch  of  the  profession  to 
which  this  ANNUAL  could  fail  to  be  useful.  Dr.  Sajous  deserves  the  thanks  of  the  whole 
profession  for  his  successful  attempt  to  facilitate  the  advance  of  medical  literature  and 
practice. — London  Lancet. 

This  very  valuable  yearly  report  of  the  progress  of  medicine  and  its  collateral 
sciences  throughout  the  world  is  a  work  of  very  great  magnitude  and  high  importance. 
IT  is  edited  by  Dr.  C.  E.  Sajous,  assisted,  it  is  stated,  by  seventy  associate  editors,  whose 
names  are  given,  making  up  a  learned  and  most  weighty  list.  Their  joint  labors  have 
combined  to  produce  a  series  of  volumes  in  which  toe  current  progress  throughout  the 
world,  in  respect  to  all  the  branches  of  medical  science,  is  very  adequately  represented. 
The  general  arrangements  of  the  book  are  ingenious  and  complete,  having  regard  to 
thoroughness  and  to  facility  of  bibliographical  reference. — British  Medical  Journal. 


ANNUAL,   1890. 

The  editor  and  publishers  of  the  ANNUAL  OF  THE  UNIVERSAL 
MEDICAL  SCIENCES  take  this  opportunity  to  thank  its  numerous  friends 
juid  patrons  for  the  liberal  support  accorded  it  in  the  past,  and  to 
announce  its  publication,  as  usual,  in  1890.  Recording,  as  it  does,  the 
progress  of  the  world  in  medicine  and  surgery,  its  motto  continues  to 
be,  as  in  the  past,  •'  Improvement,"  and  its  friends  may  rest  assured  that 
no  effort  will  be*  spared,  not  only  to  maintain,  but  to  surpass,  the  high 
standard  of  excellence  already  attained. 

The  Subscription  Price  will  be  the  same  as  last  year's  issue  and 
the  issue  of  1888. 

(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.)  29 


ISSUE   OK   1889 


The  Annual  of  the  Universal  Medical  Sciences. 

In   Five  Royal  Octavo  Volumes   of  over  5OO  pages  each,  bound  in  Clotli  and 

Half-Russia,  Magnificently  Illustrated  with  Chromo-Lithographs, 

Kngravings,  Maps,  Charts,  and  Diagrams. 

THE  SUBSCRIPTION  PRICE  (including  the  "Satellite"  for  one  year). 

United  States.     Canada  (duty  paid).     Great  Britain.  France. 

Cloth,  5  Vols.,  Royal  Octavo,      -       -     $15.00  $16.50  £3.6s.        93  fr.  95 

Half-Russia,  5  Vols.,  Royal  Octavo,    -       20.00  22.00  16s.       124  fr.  35 

This  work  is  bound  in  above  styles  only,  and  sold  by  Subscription. 


PUBLISHED  IN  CONNECTION  WITH  THE  ANNUAL  AND  FOR  SUBSCRIBERS  ONLY. 

THE    SATELLITE 


OF*    THK    UBJIVKK-SAr,    MEDICAL 

A  Monthly  Review  of  the  most  important  articles  upon  the  practical  branches  of  medicine  appearing  in 
the  medical  press  at  large,  edited  by  the  Chief  Editor  of  the  ANNUAL  and  an  able  staff. 


Editorial  Staff  of  the  Annual  of  the  Universal  Medical  Sciences,  issue  of  1889. 

Chief  Editor,  Dr.  CHAS.  E.  SAJOUS,  Philadelphia. 


jft.S5SOCljRi.TE; 

Volume  I.  —  Diseases  of  the  Lungs,  Diseases  of  the  Heart,  Diseases  of  the  Gastro- 
Hepatic  System,  Diseases  of  the  Intestines,  Intestinal  Entozoa,  Diseases  of 
the  Kidneys  and  Bladder,  Fevers,  Fevers  in  Children,  Diphtheria,  Rheu- 
matism and  Gout,  Diabetes,  Volume  Index. 

Prof.  Jas.  T.  Whittaker,  Cincinnati. 
Prof.  A.  L.  Loomis,  New  York  City. 
Prof.  E.  T.  Bruen,  Philadelphia. 


Prof.  W.  W.  Johnston,  Washington. 
Dr.  L.  Emmett  Holt,  New  York. 
Prof.  Jos.  Leidy,  Philadelphia. 


Dr.  Jas.  C.  Wilson,  Philadelphia. 
Prof.  Louis  Starr,  Philadelphia. 
Prof.  J.  Lewis  Smith,  New  York. 
Prof.  N.  S.  Davis,  Chicago. 
Prof.  Jas.  Tyson,  Philadelphia. 


Volume  II. — Diseases  of  the  Brain  and  Cord,   Peripheral   Nervous  System,   Mental 
Diseases,  Inebriety,  Diseases  of  the  Uterus,  Diseases  of  the  Ovaries,  Diseases 
of  the  External  Genitals  in  Women,  Diseases  of  Pregnancy,  Obstetrics,  Dis- 
eases of  the  Newborn,  Dietetics  of  Infancy,  Growth,  Volume  Index. 
Prof.  E.  C.  Seguin,  New  York  City.  Prof.  W.  H.  Parish,  Philadelphia. 

Prof.  Henry  Hun,  Albany.  ?ro:[-  Theophilus  Parvin,  Philadelphia, 

elphia. 


Dr.  E.  N.  Brush,  Philadel 

Dr.  W.  R.  Birdsall,  New  Vork. 

Prof.  Paul  F.  Munde,  New  York  City. 

Prof.  Wm.  Goodell,  Philadelphia. 

Dr.  W.  C.  Goodell,  Philadelphia. 


Prof.  Wm.  L.  Richardson,  Boston. 
Dr.  A.  F.  Currier,  New  York. 
Prof.  Louis  Starr,  Philadelphia. 
Dr.  Chas.  S.  Minot,  Boston. 


Volume  III.  —  Surgery  of  Brain,  Surgery  of  Abdomen,  Genito-Urinary  Surgery,  Dis- 
eases of  Rectum  and  Anus,  Amputation  and  Resection  and  Plastic  Surgery, 
Surgical  Diseases  of  Circulation,  Fracture  and  Dislocation,  Military  Surgery, 
Tumors,  Orthopaedic  Surgery,  Oral  Surgery,  Surgical  Tuberculosis,  etc.,  Sur- 
gical Diseases,  Results  of  Railway  Injuries,  Anaesthetics,  Surgical  Dressings, 
Volume  Index. 


Prof.  N.  Senn,  Milwaukee. 
Prof.  E.  L.  Keyes,  New  York  City. 
Prof.  J.  Ewing  Mears,  Philadelphia. 
Dr.  Chas.  B.  Kelsey,  New  York  City. 


Prof.  D.  Hayes  Agnew,  Philadelphia. 
Dr.  Morris  Longstreth,  Philadelphia. 
Dr.  Thos.  G.  Morton,  Philadelphia. 
Prof.  J.  E.  Garretson,  Philadelphia. 
Prof.  J.  W.  White,  Philadelphia. 
Prof.  C.  Johnston,  Baltimore. 
Prof.  E.  C.  Seguin,  New  York  City. 


Prof.  P.  S.  Conner,  Cincinnati. 

Dr.  John  H.  Packard,  Philadelphia. 

Prof.  Lewis  A.  Stimson,  New  York  City. 

Dr.  J.  M.  Barton,  Philadelphia.  | 

Volume  IV.  —  Skin  Diseases,  Ophthalmology,  Otology.  Rhinology,  Diseases  of  Pharynx, 
etc.,  Intubation,  Diseases  of  Larynx  and  (Esophagus"  Diseases  of  Thyroid 
Gland,  Legal  Medicine,  Examination  for  Insurance,  Diseases  of  the  Blood, 
Urinalysis,  Volume  Index. 


Prof.  A.  Van  Harlingen,  Philadelphia. 
Dr.  Chas.  A.  Oliver  and  Dr.  Geo.  M. 

Gould,  Philadelphia. 
Dr.  Charles  S.  Turnbull,  Philadelphia. 
Prof.  J.  Solis  Cohen,  Philadelphia. 
Prof.  John  Guiteras,  Charleston,  S.  C. 


Dr.  Chas.  E.  Sajous,  Philadelphia. 
Prof.  D.  Bryson  Delavan,  New  York. 
Prof.  R.  Fletcher  Ingals,  Chicago. 
Prof.  F.  W.  Draper,  Boston. 
Prof.  Jas.  Tyson,  Philadelphia. 


Volume  V.  —  General  Therapeutics,  Experimental  Therapeutics,  Poisons,  Electric 
Therapeutics,  Climatology,  Dermography,  Technology,,  Bacteriology,  Embry- 
ology, Physiology,  Anatomy,  General  Index. 


Dr.  J.  P.  Crozer  Griffith,  Philadelphia. 
Dr.  Hobart  A.  Hare,  Philadelphia. 
Prof  Geo.  H.  Rohe,  Baltimore. 
Prof.  John  B.  Hamilton,  Washington. 
Dr.  Harold  C.  Ernst,  Boston. 
Prof.  H.  Newell  Martin,  Baltimore. 
Dr.  R.  J.  Dunglison,  Philadelphia. 


Dr.  C.  Sumner  \Vither*tine,  Philadelphia. 

Prof.  J.  W.  Holland,  Philadelphia. 

Prof.  A.  L.  Ranney.  New  York. 

Dr.  Albert  H.  Gihon,  U.  S.  N. 

Dr.  W.  P.  Manion,  Detroit. 

Dr   W    X    Sudduth,  Philadelphia. 

Prof.  Wm.  T.  Forbes,  Philadelphia. 


(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


THE  LATEST  BOOH  OF  REFERENCE  ON  NERVOUS  DISEASES. 


Lectures  on  Nervous  Diseases, 

FROM  THE  STAND-POINT  OF  CEREBRAL  AND  SPINAL  LOCALIZATION,  AND 

THE  LATER  METHODS  EMPLOYED  IN  THE  DIAGNOSIS  AND 

TREATMENT  OF  THESE  AFFECTIONS. 

BY   AMBROSE    L.    RANNEY,  A.M.,   M.D., 

Pri  "cssor  of  the  Anatomy  and  Physiology  of  the  Nervous  System  in  the  New  York  Post-Graduate  Medicai 

School  and  Hospital  ;  Professor  of  Nervous  and  Mental  Diseases  in  the  Medical  Department  of  the 

University  of  Vermont,  etc.  ;  Author  of  "The  Applied  Anatomy  of  the  Nervous  System," 

"  Practical  Medical  Anatomy,"  etc.,  etc. 


With  Original  Diagrams  and  Sketches  in  Color  by  the  Author,  carefully  selected  Wood- 
Engravings,  and  Reproduced  Photographs  of  Typical  Cases. 

ONE    HANDSOME    ROYAL  OCTAVO    VOLUME   OF    780    PAGES. 

United  States.         Canada  (duty  paid).           Great  Britain.  France. 

CLOTH,             -                                      S5.5O                       S6.O5                        JB1.3s.  34  fr.  7O 

SHEEP,       -            -                                  6.5O                          7.15                            1.6s.  4O  f r.  45 

HALF-RUSSIA,         -                            7.0O                          7.7O                            1.9s.  43  fr.  3O 

SOLID    OiETIjY    BY    STJBSCIRIIPTIOICT. 


It  is  now  generally  conceded  that  the  nervous  system  controls  all  of  the  physical 
functions  to  a  greater  or  less  extent,  and  also  that  most  of  the  symptoms  encountered  at 
the  bedside  can  be  explained  and  interpreted  from  the  stand-point  01  nervous  physiology. 

The  unprecedented  sale  of  this  work  during  the  short  period  which  has  elapsed  since 
its  publication  has  already  compelled  the  publishers  to  print  a  second  edition,  which  is 
already  nearly  exhausted. 

appeared  in  medical  literature,  is  presented  in  com- 
pact form,  and  thus  made  easily  accessible.     In  ou 


We  are  glad  to  note  that  Dr.  Ranney  has  pub- 
lished in  c^ok  form  his  admirable  lectures  on  nervous 
diseases.  His  book  contains  over  seven  hundred 
large  pages,  and  is  profusely  illustrated  with  origi- 
nal diagrams  and  sketches  in  colors,  and  with  many 
carefully  selected  wood-cuts  and  reproduced  photo- 
graphs of  typical  cases.  A  large  amount  of  valua 


opinion,  Dr.  Ranney's  book  ought  to  meet  with  a 
cordial  reception  at  the  hands  of  the  medical  pro- 
fession, for,  even  though  the  author's  views  may  be 
sometimes  open  to  question,  it  cannot  be  disputed 
that  his  work  bears  evidence  of  scientific  method  and 


ble  in  for  mat  ion,  not  a  little  of  which  has  but  recently   .]    honest  opinion. — American  Journal  of  Insanity 

LECTURES 

ON   THE 

Diseases  of  the  Nose  and  Throat. 

DELIVERED  AT  THE  JEFFERSON  MEDICAL  COLLEGE,  PHILADELPHIA, 
BY   CHARLES    E.  SAdOUS,   M.D., 

Lecturer  on  Rhinology  and  Laryngology  in  Jefferson  Medical  College;  Vice-President  of  the  American  Laryngological 

Assqpiation :  Officer  of  the  Academy  of  France  and  of  Public  Instruction  of  Venezuela :  Corresponding  Member 

of  the  Royal  Society  of  Belgium,  of  the  Medical  Society  of  Warsaw  (Poland),  and  of  the  Society  of 

Hygiene  of  France  ;  Member  of  the  American  Philosophical  Society,  etc.,  etc. 


ILLUSTRATED  WITH  1OO  CHBOMO-LITHOGBAPHS,  FROM  OIL  PAINTINGS  BY 
THE  AUTHOR,  AND  93  ENGRAVINGS  ON  WOOD. 

ONE  HANDSOME  ROYAL  OCTAVO  VOLUME.         SOLD  ONLY  BY  SUBSCRIPTION. 

United  States.        Canada  (duty  paid).      Great  Britain.  France. 

Cloth,  Royal  Octavo,      ...        $4.OO  #4.4O  *O.18s.  24  fr.  6O 

Halt-Russia,  Royal  Octavo,      -  5.OO  5.5O  1.   Is.  3O  fr.  3O 


ince  the  publisher  brought  this  valuable  work  before  the  profession,  it  has  become : 
1st,  the  text-book  of  a  large  number  of  colleges ;  %d,  the  reference-book  of  the  U.  S.  Army, 
Navy,  and  the  Marine  Service ;  and,  3d,  an  important  and  valued  addition  to  the  libraries, 
of  over  7000  physician?. 

This  book  has  not  only  the  inherent  merit  of  presenting  a  clear  expose  of  the  subject, 
but  it  is  written  with  a  view  to  enable  the  general  practitioner  to  treat  his  cases  himself. 
To  facilitate  diagnosis,  colored  plates  are  introduced,  showing  the  appearance  of  the  differ- 
ent parts  in  the  diseased  state  as  they  appear  in  nature  by  artificial  light.  No  error  can 
thus  be  made,  as  each  affection  of  the  nose  and  throat  has  its  representative  in  the  100 
rhromo-lithographs  presented.  In  the  matter  of  treatment,  the  indications  are  so  complete 
that  even  the  slightest  procedures,  folding  of  cotton  for  the  forceps,  the  use  of  the  jirobe, 
etc.,  are  clearly  explained. 


It  is  intended  to  furnish  the  general  practitioner 
lot  only  with  ?  guide  for  the  treatment  of  diseases  of 
the  nose  and  throat,  but  also  to  place  before  him  a 


they  would  appear  to  him  were  they  seen  in  the 
living  subject.  As  a  guide  to  the  treatment  of  the 
nose  and  throat,  we  can  cordially  recommend  this 


representation  of  the  normal  and  diseased  parts  as        work. — Boston  Medical  and  Surgical  Journal. 

(F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.)  31 


FHE  MEDICAL  BULLETIN 

MONTHLY— ONE  DOLLAR  A  YEAR. 


Bright,  Original,  and   Readable. 

ARTICLES  by  the  best  PRACTICAL 
writers  procurable. 

pVERY  article  as  BRIEF  as  is  consist-  'THERAPEUTIC  NOTES  by  the  leaders 

^    ent    with    the    preservation    of    its  of  the  medical  profession  THEOUGH- 


value.  OUT  THE  WOKLD. 

'"THESE,  and  many  other  UNIQUE  FEATURES, 
L    help  to  keep  THE  MEDICAL  BULLETIN  in 
its  present  position  as 

The  LEADING    LOW    PRICE   MEDICAL  MONTHLY  of  the  WORLD. 


SUBSCRIBE;     NOW  ! 


TERMS,    $1.00    A     YEAR    IN    ADVANCE 

In  United  States,  Canada,  and  Mexico. 
FOREIGN  SUBSCRIPTION  TERMS,  POSTAGE  PAID: 

England,  5  Shillings.  France,  6  Francs.  Germany,  5  Marks. 

Australia,  5  Shilling's.        Japan,  1  Yen.  Holland,  3  Florins. 


r.  A.  DAV15,  PUDLKSHER,  PHILADELPHIA,  PA.,  CJ.5.A. 

BRANCH  OFFICES: 

45  Kast  12th  St.,  New  York  City,  U.S.A.        1  Kimball  House,  Atlanta,  Ga.,  U.S.A. 
£4   Lakeside   Building,  22O  S.Clark  St.,        427  Sutter  St.,  San  Francisco,  Cal.,  U.S.A. 
Cor.  Adams,  Chicago,  111.,  U.S.A.  139-143  Oxford  St.,  London,  TV.,  England. 

FOREIGN    AGENCIES: 

PARIS— L,e  Soudier.  VIENNA— Josef  Safar,  VIII  Schlosselgasse,  34. 

TOKIO,  JAPAN— Z.  P.  Marnya  &  Co. 


IN   PRESS       SECOND  EDITION. 


Ointments  and  Oleates  in  Diseases  of  the  Skin. 


dOHN  U.  SHOEMAKER,  A.M.,   M.D., 

ica,  Pharmacology,  Therapeutics,  and  Clinical  Medicine,  and  Clini 
of  the  Skin  in  the  Medico-Chirurgical  College  of  Philadelphia,  etc. 


Professor  of  Materia  Medica,  Pharmacology,  Therapeutics,  and  Clinical  Medicine,  and  Clinical  Professor  of  Diseases 
in  the 


16mo.    NEATLY  BOUND  IN  CLOTH.    PRICE,  IN  UNITED  STATES  AND  CANADA, 
NET,  $1.OO,  POST-PAID  ;  GREAT  BRITAIN,  4s.  3d. ;  FRANCE,  6  fr.  2O. 


The  accompanying  Table  of  Contents  will  give  a  general  idea  of  the  work  : 

fTC-siNT1 1 '  t-»rT<rrrrc={  PART  I. — HISTORY  AND  ORIGIN.  PART  II. — PROCESS  OF  MANUFACTURE.  PART 
111. — PHYSIOLOGICAL  ACTION  OF  THE  OLEATES.  PART  IV. — THERAPEUTIC  EFFECT  OF  THE  OLEATES. 
PART  V. — OINTMENTS  :  Local  Medication  of  Skin  Diseases. — Antiquity  of  Ointments. — Different  Indi- 
cations for  Ointments,  Powders,  Lotions,  etc. — Information  about  Ointments:  Scanty,  Scattered,  and 
Insufficient  — Fats  and  Oils:  Animal  and  Vegetable. — Their  Chemical  Composition. — Comparative 
Permeability  of  Oils  into  Skin  ;  of  Animal,  of  Vegetable.  Incorporation  of  Medicinal  Substances  into 
Fats:  (i)  Mode  of  Preparation,  (2)  Vegetable  Powders  and  .Extracts,  (3)  Alkaloids,  (4)  Mineral  Sub- 
stances, (5)  Petroleum  Fats  ;  Chemical  Composition;  Uses  and  Disadvantages. — List  of  Officinal  Oint- 
ments.— Indications. — Substances  often  Prescribed  Extemporaneously  in  Ointment  Form. — Indications. 
A  FULL  INDEX  RENDERS  THE  BOOK  CONVENIENT  FOR  QUICK  REFERENCE. 


CRITICISMS  OF  FIRST   EDITION. 


The  profession  in  both  countries  is  deeply  in- 
debted to  Dr.  Shoemaker  for  his  excellent  work  in 
this  department  of  medicine. —  William  Whitla, 
M.D.  (Q.U.I.). 

It  is  the  most  complete  exposition  of  their  action 
which  has  yet  appeared.  They  are  very  valuable 
accessions  to  the  materia  medica,  and  should  be 
familiar  to  every  practitioner. — Medical  and  Sur- 
f i \  al  Reporter. 


To  those  of  our  readers  who  wish  to  learn  the 
therapeutic  effects  of  a  class  of  preparations  which 
are  destined  to  grow  in  favor  as  their  merits  be- 
come more  generally  known,  we  commend  this 
book. — Journal  of  Cutaneous  and  Venereal 
Diseases. 

No  physician  pretending  to  treat  skin  diseases 
should  be  without  a  copy  of  this  very  instructive 
little  book. — Canada  Medical  Record. 


32  (F.  A.  DAVIS,  Medical  Publisher,  Philadelphia,  Pa.,  U.S.A.) 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

BIOLOGY  LIBRARY 

TEL  NO.  642-2532 

This  book  is  due  on  the  last  date  stamped  below,  or 

on  thejjlate  to  which  renewed. 
Renewed  bool^are  subject  to  immediate  recall. 

-6 


LD2lA-6m-l,'75 
(S3364SlO)476-A-32 


General  Library 

University  of  California 

Berkeley 


U.C.BERKELEY  LIBRARIES 


